Inside the center of the atom, far below the electrons, lies the atom’s tiny and extremely dense core. For the entire
year, we have focused on the chemistry associated with an atom’s electrons. We completely ignored the nucleus,
taking the positive core for granted as it holds the electrons in place through electrostatic attractions between the
charged particles (protons attracted to the electrons). The history of science, over the past 1000 years, has focused
on technology, medicine, and a long time ago – alchemy. The goal of all alchemists was to turn other species into
gold – to have Midas’ touch so to speak. This is not possible through chemical processes, as that only involves the
movement of the electrons. No species can be turned into gold by losing or gaining electrons. Gold is gold because
of the numbers of protons and neutrons. However, we now know that it is possible to transmutate (change) one
element into another through nuclear reactions – which is NOT the same as a chemical reaction. The goal is no
longer to change species into gold (personally I would shoot for platinum  ), as there are far more important and
valuable products of nuclear reactions.
Society as a whole has many concerns about the applications of nuclear chemistry in their own lives. Many of their
concerns stem from mis-information. The promise of an abundant energy source and treatment for diseases comes
hand in hand with the threat of nuclear waste contamination, nuclear melt-downs, and nuclear war/terrorism.
Can we, as fallible humans, harness the power of the nucleus without destroying ourselves or others? Do we have
the moral strength to use our powers only for good? Or are the risks just too great?
The changes that occur in the nucleus are completely different from all that we have studied to this point. In
chemical reactions, electrons are shared, lost or gained, in order to form new compounds. In these processes, the
nuclei just sit there are watch the show, passively sitting by and never changing their identities. In nuclear
reactions, the roles of the subatomic particles are reversed. The electrons do not participate in the reactions, instead
they stay in their orbitals while the protons and neutrons undergo changes. In fact, during these changes, in nearly
every case, the change results in the formation of a different element! Nuclear reactions are accompanied by
energy changes that are a million times greater than those in chemical reactions. Energy changes that are so great
that changes in mass are detectable. Also, nuclear reaction yields and rates are not affected by the same factors (e.g.
pressure, temperature, and catalysts) that influence chemical reactions.
First, it is important to understand nuclear stability. Why are some nuclei stable where others are not? When
nuclei are unstable, they are termed radioactive. All matter is composed of atoms and many atoms are unstable. In
fact, over half of the elements in the periodic table including uranium, are in a constant process of rearranging
themselves. This is not something that humanity can control.
When the nucleus of an atom attempts to become more stable, it releases energy, known as radiation. Once this
happens the original atom changes into a new atom. In some instances, a new element is formed and in other cases,
a new form of the original element, called an isotope, appears. The spontaneous change in the nucleus of an
unstable atom that results in the emission of radiation is called radioactivity and this process of change is often
referred to as the decay of atoms.
A stable nucleus will remain intact indefinitely. An unstable nucleus will not, and a great majority of nuclei from
atoms on the periodic table are unstable! The unstable nucleus exhibits radioactivity: the nucleus will
spontaneously disintegrate (fall apart) or decay by emitting radiation. Each type of unstable nucleus has a
characteristic rate of decay. Some decay very quickly, e.g. in a fraction of a second, others can take billions of years.
1
Why Radioactivity:
Radioactivity comes out of the nucleus of atoms. The nucleus is radioactive because it is unstable. Like electrons in
an excited state dropping back down to ground state and releasing a photon, nuclei need an outlet for their excited
state. This outlet is radiation or nuclear reactions. Nuclear reactions, radioactivity, are spontaneous decays, there
is no way to tell when it will occur, but eventually they will decay. These radioactive decays occur in any atom
with more than 83 protons. Also, in any atom with an exceptionally small or large proton to neutron ratio will be
radioactive.
Recall that the atom is an electrically neutral, spherical species that contains a positively charged nucleus
surrounded by one or more negatively charged electrons. The electrons move rapidly around the nucleus and are
held there in space by attraction with the positively charged nucleus. The nucleus takes up 1 ten-trillionth of the
volume but makes up 99.97% of the atom’s mass and is therefore incredibly dense. The atom’s total diameter is
about 10,000 times the diameter of the nucleus!
The nucleus is composed of neutrons and protons. The protons are positively charged and the neutrons have no
charge at all, they just contribute to the overall mass of the atom. The magnitude of the charge of a proton is equal
to that of an electron, but the electron is negatively charged. An atom is neutral because the number of protons
ALWAYS equals the number of electrons.
Protons and neutrons are collectively termed nucleons. Most elements exist in nature as a mixture of isotopes,
which are species that are the same atom (they have the same number of protons and electrons if neutral!) but
different numbers of neutrons. A complimentary term to the isotope is the nuclide, which represents the isotopes
of an element. It refers to the variety of nuclei with a particular composition of nucleons (the differing numbers of
protons and neutrons). Each isotope is a nuclide. This means that 16O – which has 8 protons and 8 neutrons is a
nuclide, and 17O – which has 8 protons and 9 neutrons, is a nuclide of oxygen.
Recall that we can write the element or a particular isotope from the periodic table using a variety of notations.
Atomic Notation: 3 Types
A = Atomic Mass = protons + neutrons
Z = Atomic Number = protons
X = Atomic Symbol = the elements letter designation
Type 1
Type 2
Type 3
A
Z
A
X
12
6
X
12
X–A
C
C
C -12
This type came first and gives the most information
This type came second as the first type is redundant. You do
not need to tell me carbon has an atomic number of 6, all
carbons atomic numbers are 6.
This type came last and is the easiest to type, and still relays all
the info you need. This symbol is spoken, “carbon twelve.”
The same type of notation can and will be applied to the subatomic particles in the nucleus. Thus, a neutron that
has a mass of 1 (due to the neutron itself) and a charge of zero will be written as 01 n . A proton, that has a mass of 1
(due to the proton itself) and a charge of +1 will be written as 11 p . And an electron, that has a mass of zero (due to
the electron itself) and a charge of -1 will be written as
1
0n
(neutron)
0
-1 e .
1
1p
(proton)
2
0
-1 e (electron)
It is important to be very familiar with this notation, as we will use it in nuclear reactions. It is important to
remember how to determine the numbers of protons, neutrons, and electrons in particular nuclides (or isotopes) in
order to understand what type of nuclear reaction is taking place.
Concept Test:
Determine the number of protons and neutrons in
35
17 Cl
Write the atomic notation for the nuclide of chlorine that has 20 neutrons:
In 1896, Antoine-Henri Bacquerel discovered that uranium minerals emitted a penetrating radiation that produced
images on photographic plates, even though the plates were covered with paper to prevent them from developing
in the presence of light – but somehow, the radiation penetrated the paper and developed the plate! Several years
later, Marie Curie began a search for other mineral that emitted radiation.
Marie Curie found that thorium minerals emit radiation. She also showed that the intensity of radiation depended
on the concentration of the radioactive element in the mineral, not on the nature of the compound. Marie Curie
and her husband, Pierre, through their examination of uranium minerals, discovered two other radioactive
elements, one was named Polonium (after her native Poland), and the other was named Radium.
During the next few years, Bacquerel, the Curies, and Rutherford began to study the nature of radioactive
emissions. Rutherford observed that elements other than radium were formed as radium decayed. In 1902, they
proposed that radioactive emission results as an element changes from one element into another, completely
different element. To many, at this time, this sounded like the revival of alchemy. And it was met with ridicule.
Now, however, we know this to be true! Under most circumstances when a nuclide (isotope) of a one element
decays, it changes into a nuclide (isotope) of a different element.
Their work led to an understanding of the three most common types of radioactive emission.
3 Main Types of Radioactive Particles:
alpha particles – (symbolized as a helium nucleus 24 He ) are dense, positively charged particles identical to
helium nuclei. They consist of two protons and two neutrons, identical to the nucleus of a helium atom. A
sheet of paper or a person's surface layer of skin will stop them. Alpha particles are only considered
hazardous to a person's health if they are ingested or inhaled and thus come into contact with sensitive
cells such as in the lungs, liver and bones. A source of alpha particles is radon gas, a colorless and odorless
gas formed from the radioactive decay of radium which in turn is one of the products of the uranium decay
chain. It is not radon itself that is a health concern, but the radioactive products into which it decays.
Radon, being a gas, is simply the vehicle by which members of the uranium decay chain can enter the
lungs. Outside the body, radon is not a concern since the alpha particles it emits cannot penetrate the skin.
beta particles – (symbolized as β, β-1, or -01 β) are negatively charged particles identified as high speed
electrons which are emitted from the nuclei of many fission products. They can travel a few feet in air but
can usually be stopped by clothing or a few centimeters of wood. They are considered hazardous mainly if
ingested or inhaled, but can cause radiation damage to the skin if the exposure is large enough.
3
gamma particles – (symbolized as γ or sometimes 00 γ) are high energy photons (electromagnetic radiation)
– about 105 times as energetic as visible light. They penetrate matter easily and are best stopped by water
or thick layers of lead or concrete. Gamma radiation is hazardous to people inside and outside of the body.
The three types of particles that are emitted behave very differently in the presence of an electric field. Alpha
particles are positively charged and thus bend towards the negative plate. Beta particles are negatively charged
and thus bend towards the positive plate. Gamma particles have no charge and are thus not affected by the
charged plates. The degree of “bending” is related to the mass of the particle. Alpha particles are heavier than beta
particles and thus are less easily moved in space.
The use of a magnetic field to direct
beta particles is what allows your TV
to work.
Your TV has a
phosphorescent
screen
that
is
bombarded with precisely directed
beta particles. If you look very closely
at your TV when it is turned on you
can see small blocks of color.
Every second your TV shoots 60 beta
particles a second at each one of those
little blocks. It starts shooting in one
corner and works it way across the
screen then drops down to the next
row. It hits every block in every row
then begins again. It fills the screen 60
times a second with colored blocks.
These blocks, in conjunction with each
other, present an image to your eye.
When a particular nuclide decays, it forms a nuclide (the product) that is of lower energy and the energy that is
lost, is emitted radiation. Remember that nature always wants to form a lower energy species – and as such,
nuclear decay is no different.
Nuclides can decay in several ways, but they all share some things in common. First, the reactant species/nuclide
is called the parent species while the product is called the daughter. Second, the full atomic notation of the
nuclides is used in writing the nuclear reactions. Writing the equations in this manner allows us to indicate the
type of nuclear reaction the nuclide participated in.
4
When a nuclide changes from one isotope to another or from one element to another, the atomic masses will
change (for species that change isotopes), and if the species changes from one element to another, both the atomic
mass and the atomic number will change. In order to balance the equation, we must account for all species that are
gained or lost in the change.
Let’s examine the types of nuclear reactions that we will see:
Alpha Decay: Since an alpha particle represents a helium nucleus, we will be losing two protons and two neutrons
from our parent nuclide. A general reaction is seen below, followed by an actual example of alpha decay. Again,
we must make sure that we account for all species!
atomic mass
atomic number X
226
88 Ra

atomic mass- 4
atomic number - 2 X
222
86 Rn

 24 He
 24 He
Notice that when you add the atomic masses of the daughter 222-Rn with 4-He you get the same atomic mass that
appears in the parent 226-Ra (222+4 = 226). And when you add the atomic numbers of the daughter 222-Rn with 4He you get the same atomic number that appears in the parent 226-Ra (86+2 = 88). Since alpha decay involved the
loss of a helium nucleus, you are losing protons. The product in an alpha decay will be a different element – it will
be the element that is 2 atomic numbers away! Also, the mass difference will be 4 amu different between the parent
and the daughter species.
Beta Decay: A beta particle represents the loss of an electron. It might seem odd that an electron is leaving the
nucleus, but that is exactly what happens in beta decay. How is this possible? A neutron is located in the nucleus.
A neutron is a neutral particle. Why is a neutron neutral? It is neutral because a neutron is the combination of a
proton and an electron:
1
1p
+
0
-1 e
→
1
0n
for decay
1
0n
→
1
1p
+
0
-1 e
Remember that a beta particle is an electron, so the more common representation of the neutron looks like this:
1
0n
→
1
1p
+
0
-1
β
In essence, for beta decay, the electron is ejected from the nucleus, leaving behind the proton. Since the neutron no
longer exists as a neutron, but now as a proton, the overall mass of the species does not change (remember that the
mass is due to number of protons and neutrons, and while we lost a “neutron”, we kept it as a proton, so no net
change in mass!). BUT, by losing the neutral particle, we gained a positive particle, which means that the total
number of protons in the nucleus has changed – and it changed by one.
63
28 Ni
→
63
29 Cu
+
0
-1
β
Beta decay will result in a species that has the same atomic mass, but contains one
MORE proton than itself, thus its daughter will be found one atomic number higher than itself.
Note: when a neutron decays a neutral particle called a neutrino (: the little neutral one) is also emitted. It is
emitted in other nuclear reactions as well. They will not be discussed further except to mention that experiments in
Japan have shown that they do have mass and they may account for a significant portion of the “missing” matter in
the universe (remember that matter cannot be created or destroyed . . .) For simplicity’s sake, they will not be
included in any of the nuclear reactions.
5
Positron decay: A positron is the antiparticle to the beta particle. A key idea of modern physics is that every
fundamental particle has a corresponding antiparticle, or a particle with the same mass but opposite charge. The
positron has the same mass as a beta particle but opposite charge, therefore it has a +1 charge. It is symbolized as
0
1 β. Sometimes positron decay is referred to as positive beta decay. In 1932, Carl D. Anderson found positrons
created by cosmic-ray collisions in a cloud chamber, in which moving electrons (or positrons) leave behind trails as
they move through the gas. The electric charge-to-mass ratio of a particle can be measured by observing the curling
of its cloud-chamber track in a magnetic field. Originally, positrons, because of the direction that their paths curled,
were mistaken for electrons traveling in the opposite direction.
Positron decay occurs through a process whereby a proton in the nucleus is converted into a neutron and a
positron is expelled. This process is called pair production, which involves energy turning into matter as a high
energy photon becomes an electron and a positron simultaneously. The electron and proton bind and form a
neutron, while the positron is expelled.
Because the proton becomes a neutron and stays in the nucleus, the overall mass will not change, but the charge
will. In essence, the atom just “lost” a proton. Therefore the new species will have the same mass but will have
one fewer proton, so its atomic number will decrease by 1.
11
11
0
6 C → 5 B + 1 β
Positron emission will result in the daughter having the same atomic mass, but
will be one atomic number LOWER than the parent species
Electron capture: Electron capture occurs when the nucleus of an atom draws in an electron from an orbital of the
lowest energy level, the 1s orbital. As the electron comes into the nucleus, it will be attracted to and bind with a
proton. This will neutralize the proton’s positive charge and create a neutron. This is an electron that is taken
INTO the nucleus, not an electron that leaves, as such, it should not be confused with the beta particle mentioned
previously. In order to distinguish between the two “types” of electrons, the symbol for this extranuclear electron
that enters the nucleus is : -01 e. The loss of this inner electron from the first shell is a vacancy. This vacancy will
6
be quickly filled by an electron that resided in a higher energy level. When the electron from the higher n value
falls to the lower energy level, a photon is released in the x-ray region of the EM spectrum.
55
26
Fe +
0
-1
55
25
e →
Mn + h (x-ray)
Electron capture causes the loss of a proton as it becomes a neutron. As such,
the atomic mass will stay constant but the atomic number will DECREASE
by one. The daughter will be the species one atomic number LOWER
than the parent species.
Electron capture results in the same product that would result from positron decay but the processes are entirely
different and should not be confused!
Gamma Emission: Gamma emission involves the radiation of high energy or gamma (γ) photons being emitted
from an excited nucleus. Recall that an atom in an excited electronic state will promote electrons to higher energy
levels. Those electrons cannot stay in the higher level indefinitely, the atom releases the energy absorbed, the
electron falls, and the energy is released as a photon (h) which is of a specific energy – usually in the UV or visible
region, but also the IR. A nucleus that is excited will need to release that energy also, and it does so by releasing a
photon in the gamma region. The gamma photon is of MUCH higher energy (shorter wavelength) than a UV or
visible photon. Many nuclear processes leave the nucleus in an excited state, so gamma emission accompanies
most other types of decay. Because gamma rays have no mass or charge, gamma emission will not change the
atomic number or the atomic mass of the species. Gamma rays will also result when a particle and its antiparticle
meet and annihilate one another.
238
92
U →
234
90
Th 
4
2
He 
0
0
γ
For example, when uranium-238 undergoes alpha decay, a gamma ray is also emitted.
7
Other Types of Nuclear Reactions:
 Neutron Emission – a neutron is emitted from the nucleus cause the mass to drop by 1.
Nuclear Equations:
Nuclear equations are similar to chemical equations in that the total mass must be conserved. The difference is the
components in the nucleus change. For instance, in the first example with C-14 the mass did not change but the
number of protons did giving a total mass on each side of 14 and a total number of protons as 6. 6 = 7 + -1
Examples:
14
6
14
6
1
0
n
235
92
C147 N  10
C  11 H147 N  10 n
U
236
93
U Ba  Kr 3 n
141
56
92
36
1
0
Electromagnetic Radiation – EM Radiation:
Electromagnetic radiation is most simply defined as light, and as you know, not all light is visible to the human
eye. Electromagnetic radiation is broken up in to regions based on the frequency of the light, the full range of
radiation is called the electromagnetic spectrum, EMS.
The major regions are radio, micro, infrared, visible, ultra violet, x-rays and gamma rays.
8
Usage of Different Wavelengths of light:
Radio waves are used to transmit radio and television signals. Radio waves have wavelengths that range from less
than a centimeter to tens or even hundreds of meters. FM radio waves are shorter than AM radio waves. For
example, an FM radio station at 100 on the radio dial (100 megahertz) would have a wavelength of about three
meters. An AM station at 750 on the dial (750 kilohertz) uses a wavelength of about 400 meters. Radio waves can
also be used to create images. Radio waves with wavelengths of a few centimeters can be transmitted from a
satellite or airplane antenna. The reflected waves can be used to form an image of the ground in complete darkness
or through clouds.
Microwave wavelengths range from approximately one millimeter (the thickness of a pencil lead) to thirty
centimeters (about twelve inches). In a microwave oven, the radio waves generated are tuned to frequencies that
can be absorbed by the food. The food absorbs the energy and gets warmer. The dish holding the food doesn't
absorb a significant amount of energy and stays much cooler. Microwaves are emitted from the Earth, from objects
such as cars and planes, and from the atmosphere. These microwaves can be detected to give information, such as
the temperature of the object that emitted the microwaves.
Infrared is the region of the electromagnetic spectrum that extends from the visible region to about one millimeter
(in wavelength). Infrared waves include thermal radiation. For example, burning charcoal may not give off light,
but it does emit infrared radiation which is felt as heat. Infrared radiation can be measured using electronic
detectors and has applications in medicine and in finding heat leaks from houses. Infrared images obtained by
sensors in satellites and airplanes can yield important information on the health of crops and can help us see forest
fires even when they are enveloped in an opaque curtain of smoke.
The rainbow of colors we know as visible light is the portion of the electromagnetic spectrum with wavelengths
between 400 and 700 billionths of a meter (400 to 700 nanometers). It is the part of the electromagnetic spectrum
that we see, and coincides with the wavelength of greatest intensity of sunlight. Visible waves have great utility for
the remote sensing of vegetation and for the identification of different objects by their visible colors.
9
Ultraviolet radiation has a range of wavelengths from 400 billionths of a meter to about 10 billionths of a meter.
Sunlight contains ultraviolet waves which can burn your skin. Most of these are blocked by ozone in the Earth's
upper atmosphere. A small dose of ultraviolet radiation is beneficial to humans, but larger doses cause skin cancer
and cataracts. Ultraviolet wavelengths are used extensively in astronomical observatories. Some remote sensing
observations of the Earth are also concerned with the measurement of ozone.
X-rays are high energy waves which have great penetrating power and are used extensively in medical
applications and in inspecting welds. X-ray images of our Sun can yield important clues to solar flares and other
changes on our Sun that can affect space weather. The wavelength range is from about ten billionths of a meter to
about 10 trillionths of a meter.
Gamma rays have wavelengths of less than about ten trillionths of a meter. They are more penetrating than X-rays.
Gamma rays are generated by radioactive atoms and in nuclear explosions, and are used in many medical
applications. Images of our universe taken in gamma rays have yielded important information on the life and death
of stars, and other violent processes in the universe
Given all the reactions that we examined, there are several ways that an unstable nuclide might decay, but can we
predict how it will decay? Can we predict if a nuclide will decay at all? Our knowledge of the nucleus is still very
limited compared to our knowledge of the atom as a whole. But there are some patterns that do emerge.
The Stability Band: The neutron to proton ratio (N/Z)
Remember that the number of neutrons (N) is determined by taking the atomic mass (A) and subtracting the
number of protons:
#no = atomic mass – atomic number
or #no = A-Z
A key factor that determines the stability of a particular nuclide is its ratio of neutrons to its number of protons, or
the N/Z ratio. For lighter nuclides, where the N/Z ratio  1, this provides stability. For heavier nuclides to be
stable, the number of neutrons must exceed the number of protons. As you increase the positive charges in the
nucleus (meaning the number of protons) you need more neutral “buffers” which are the neutrons in order to
increase its stability. Stability can be thought of as the amount of time that the nuclide will exist as that isotope and
not undergo some sort of decay. However, if the N/Z ratio is too high or too low, the nuclide will be unstable and
will decay. There are some generalities that can be made.
The minimum N/Z value for stability is 1. Two exceptions are 11 H and
4
2
3
2
He. For lighter stable nuclides,
12
16
20
6 C, 8 O, 10 Ne
N/Z  1: He,
The N/Z ratio which indicates stable nuclides increases gradually as Z increases. The ratio will be larger
than 1 but not much greater than 1.5. Bismuth-209 is the heaviest stable nuclide, which has an N/Z value
of 1.52.
All nuclides with Z > 83 are unstable, regardless of their N/Z ratio. Therefore the largest members of
Groups 1A, 2A, 6A, 7A, and 8A are radioactive, as are all actinides and the elements in the 4 th transition
series (Period 7).
Why are neutrons necessary? What does it mean for the neutron to be this “buffer” inside the nucleus? Given that
the protons are positively charged and the neutrons have no charge, what exactly holds the nucleus together?
Nuclear scientists answer this question and explain the importance of this N/Z ratio in terms of two opposing
forces. Electrostatic repulsive forces between the positively charged protons (remember +/+ do not want to be
anywhere near one another!!) would rip the nucleus apart if it were not for something called the strong force. The
strong force is an attractive force that exists between the neutrons and protons (termed nucleons) in a nucleus. This
force is about 100 times stronger than the proton-proton repulsive forces but it only operates over very short
10
distances. It is the competition between the repulsive forces and attractive forces that ultimately determines
nuclear stability.
Interestingly, the oddness or the evenness of the N and Z value is related to some important patterns of nuclear
stability. Two interesting points appear when stable nuclides are examined:
Elements with an even number of protons (even Z) usually have a larger number of stable nuclides
(isotopes) than elements with odd numbers of protons.
11
Over half of the known stable nuclides (isotopes) have BOTH even N and Z values. Only 7 isotopes with
odd N and odd Z are either stable: 21 H, 63 Li, 105 B, 147 N – or they decay so slowly that their amounts have
changed very little since the Earth was formed
50
138
176
23 V, 57 La, 71
Lu.
One model of nuclear structure that attempts to explain these findings theorizes that the protons and neutrons lie
in shells, nucleon shells, or energy levels where the protons and neutrons reside, and that the stability results from
the pairing of the nucleons. This arrangement leads to the stability of even numbers of species, such that all species
are paired. Just like noble gases (elements 2, 10, 18, 36, 54, and 86) are extremely stable because of their filled
energy levels (s2p6) for electrons, nuclides with N or Z values of 2, 8, 20, 28, 50, 82, and 126 are also exceptionally
stable. These are so called “magic numbers” and are thought to possibly correspond to the number of protons or
neutrons that would exist in a filled nucleon shell. A few examples are given below:
50
22
Ti N  28
88
38
Sr N  50
4
2
He N  2
16
8
O
40
20
Ca N  20
208
82
N8
Pb N  126
Predicting the Mode of Decay:
Remember that nature always moves towards a more stable product. As such, an unstable nucleus must undergo
some sort of change in order to become stable. An unstable nucleus will decay in a manner that brings its ratio of
N/Z into the band of stability. Generally speaking, nuclides will decay as follows:
Neutron rich nuclides: Isotopes/nuclides that have too many neutrons are unstable. These species have a
large N/Z ratio. In order to achieve stability, these species will undergo beta decay, which converts a
neutron into a proton. Thus, the overall number of neutrons decreases, the number of protons increase,
and the N/Z value is lowered or reduced as well.
Neutron-poor nuclides: Isotopes/nuclides that have too few neutrons are unstable. These species have a
small N/Z ratio. In order to achieve stability, these species undergo positron decay or electron capture.
Both of these processes convert a proton into a neutron. Thus, the number of neutrons is increased and the
number of protons decreased, thus the N/Z value is increased as well.
Heavy nuclides: Isotopes/nuclides with atomic numbers (Z) > 83 are too heavy and do not lie in the band
of stability. These species must reduce their mass – thus their number of protons and neutrons – thus they
undergo alpha decay. This will reduce their atomic mass by 4 and the atomic number by 2 (remember an
alpha particle is represented by helium).
12
A parent nuclide may undergo several decays, in succession, before reaching a stable form. This is called
undergoing a decay series, where each decay step happens, one after the other until the nuclide is stable.
Sometimes this is also referred to as a disintegration series. Typically a decay series is depicted using a grid-like
display to show the species as it changes from one unstable species to another, until finally becoming stable.
Or, the decay might be shown in a simple manner as shown below.
13
Finally, the decay could be shown by writing out the balanced nuclear reactions that the species undergoes in a
step by step manner (only the first four steps in the decay are shown below):
238
92
U

234
90
Th 
4
2
He
234
90
Th 
234
91
Pa 
0
-1

Pa 
234
92

230
90
234
91
234
92
U
U 
Th 
0
-1
4
2

He
Remember that alpha decay changes the mass of the nuclide and the number of protons (N and Z both change),
while beta decay turns neutrons into protons so the mass number stays the same, but the number of protons
increases. (thus N decreases by 1, but Z increases by 1 so the mass stays constant)
Rate of Radioactive Decay:
We know that systems will change to reach the minimum energy state. As such, radioactive decay is all about
turning an unstable nuclide into a stable one. However, there is no mention of how long this process will take.
Radioactive nuclei will decay at a characteristic rate, regardless of the chemical species in which they occur. This
means that regardless of the source of the unstable nuclide, it will decay at the same rate. The decay rate, or
activity, of a radioactive sample is the change in the number of nuclei divided by the change in time. Because the
number of nuclei are decreasing, and rates are inherently positive, we must take the negative of the change in order
to keep the rate positive!
Decay rate = -  nuclei
 time
The SI unit for radioactivity is the becquerel (Bq) and is defined as one disintegration per second. 1Bq = 1d/s. A
more common unit for radiation is the curie (Ci). 1 Ci = the number of nuclei disintegrating each second in 1 gram
of radium-226. Because the curie is so large, millicuries (mCi) or microcuries (Ci) are often used. Several other
units of radiation are given below:
Units of Radiation:
Becquerel: 1 nuclear disintegration per second
Roentgen: 2.1 x 109 ion pairs per cm3 of dry air
Roentgen: 1.8 x 1012 ion pairs per 1 g of tissue
rad: The absorption of 0.01 Joules of energy per kilogram of material, radiation absorbed dose.
gray(Gy): The absorption of 1 Joules of energy per kilogram of material. The official SI Unit.
rem:
 (roentgen equivalent man) specific to human beings.
 this unit is found by multiplying the amount of radiation in rads by the QF.
 rem = rad x QF
 the QF (Quality Factor) is determined by which radiation you are exposed to:
 QF = 1
 and 
 QF = 10

 QF = 20

Curie(Ci):
 37 billion radioactive decays in one second.
 equivalent to the number of decays in one gram of radium in one second.
An activity is meaningful only when one considers a large number of nuclei in a macroscopic sample. For example,
suppose that you have 1 x 1015 radioactive nuclei of a particular type and it decays at a rate of 10% per hour. What
this means is that that average of all the decays results in 10% of the entire sample of radioactive nuclei will
disintegrate in that hour. Thus, after 1 hour, 10% of the original number of nuclei, thus 1 x 1014 nuclei will decay.
This leaves behind, 9 x 1014 nuclei that have not yet decayed. During the next hour, 10% of the remaining 9 x 10 14
nuclei will decay, which is 9 x 1013 nuclei. This process will continue to occur as the nuclei continue to decay.
Radioactive decay is a first order process, it will depend on the number of nuclei present.
14
Half-Life:
Decay rates are commonly expressed in terms of the fraction of nuclei that decay over a given time period. The
half-life (t1/2) is the time required for one half of a number of an isotope to decay into a new isotope. Half-lives
differ greatly from isotope to isotope, they can range from picoseconds to billions of years. The number of nuclei
that are left after the set time is ½ the original number that were present.
For example, 14C has a half-life of 5,730 years. What that means, is that if you had a 50.0 gram sample of 14C, after
5,730 years you would have 25.0 grams left. Then, after another 5,730 years you would have 12.5 grams left and so
on.
There are several mathematical equations that can be used to calculate amounts or the half-life of species:
ln 
 N0
 Nt

  kt

 Nt
 N t1 /2


  kt 1 / 2


ln 
t1/2 = ln 2
k
Thus, the half-life is not dependent on the amount of nuclei that are present! A 50.0 gram sample of 14C will have
the same half-life as a 150.0 gram sample of 14C!
Concept Test:
How long would it take for 500 grams for protactinium-234 to decay to 10 grams?
The half life of Pa-234 is 72 seconds.
15
Given the following table of information, we can see that our time is very reasonable!
Mass
500
250
125
62.5
31.25
15.6
7.8
Time
0
72
144
216
288
360
432
The answer should be longer than 360 sec but shorter than 432 sec – and it is!
The nuclear processes that we have been considering so far have involved radioactive decay, where a nucleus emits
or absorbs (electrons capture) a few small particles or photons. Eventually, through the decay processes, the
product is a lighter nucleus. Two other processes cause changes in/with the nucleus as well. They are fission and
fusion. In nuclear fission, a heavy nucleus splits into two light nuclei. In nuclear fusion, lighter nuclei combine
(think fuse together) and form a heavier product. Both fission and fusion release enormous quantities of energy.
The Mass Defect:
Throughout the 20th century, it has become known that mass and energy are interconvertible. The traditional mass
and energy conservation laws that we discussed in term 1 have been combined to state that the total quantity of
mass-energy in the universe is constant. Therefore, when any reacting system releases or absorbs energy, there
must be an accompanying loss or gain of mass.
This relationship really did not concern us (was negligible) when we were examining chemical reactions. The
energy changes involved in breaking or forming chemical bonds are so small that the mass changes are therefore
negligible as well. For example, when 1 mole of water breaks up into its atoms, heat must be put into the system:
H2O (g) → 2H (g) + O (g)
H = +934 kJ
Mass is equivalent or related to energy through Einstein’s equation E = mc 2 where m is the mass and c is the speed
of light. We can use this equation to examine changes in reactions. Remember that H values are changes – the
difference in energy between the products and the reactants (H = npHfp - nrHfr). So the equation becomes:
E = mc2
or
m = E/c2
Using Einstein’s equation, we can examine the change in mass that occurs during the chemical reaction:
m =
9.34 x 105 J/mol
(2.9979 x 108m/sec)2
m = 1.04 x 10-11 kilograms/mole = 1.04 x 10-8 grams/mole
16
The change in mass, while a number that can be calculated, is 10 ng – which is a change that is too small to measure
with any balance that we have today. (m = mass products – mass reactants). Such small mass changes that occur
when chemical bonds break or chemical bonds form allows us to say that mass IS conserved in chemical reactions.
Nuclear processes are accompanied by a much larger measurable mass change. This mass change is related to the
enormous energy required to bind the nucleus together or to break it apart. For example, what happens if we try
and rip apart the nucleus of a carbon atom into its protons and neutrons? A carbon-12 isotope has 6 protons and 6
neutrons. A proton is essentially a hydrogen atom (remember that the mass of an electron is negligible). So let’s
combine 6 H atoms with 6 neutrons and see what we get:
Mass of 6 1H atoms = 6(1.007825 amu)
Mass of 6 neutrons = 6(1.008665 amu)
H atoms = 6.046950 amu
+Neutrons = 6.051990 amu
total mass = 12.098940 amu
BUT!! The mass of one 12C atom is exactly 12 amu!
The difference between the calculated (predicted or theoretical mass) and the actual mass is
0.098940 amu
Note that the mass of the real nucleus is LESS than the calculated or the combined mass of its nucleons (protons
and neutrons). The mass decrease occurs when the nucleons are united into the nucleus and is called the mass
defect. The size of this mass 9.8940 x 10 -2 g/mole IS measurable on any laboratory balance.
If we know the m (the mass defect) we can, using Einstein’s equation, calculate the energy equivalent associated
with the defect. For 12C, after converting the mass to kilograms, we can calculate E!
E = mc2
E = (9.8940 x 10-5 kg/mol)(2.9989 x 108m/sec)2
E = 8.8921 x 1012 kgm2/sec2mol = 8.8921 x 1012 J/mol
E = 8.8921 x 109 kJ/mole
This quantity of energy, the energy associated with the loss of mass, is called the nuclear binding energy for 12C. In
general, the nuclear binding energy can be calculated for any nucleus, and it is the quantity of energy required to
break up the nucleus into its component protons and neutrons (nucleons). Such that:
1 mole Nucleus + Nuclear Binding Energy → nucleons (protons and neutrons separated)
Binding energies are typically expressed in electron volts, specifically the megaelectron volt (MeV).
1 amu = 931.5 x 106 ev = 931.5 MeV
We can compare the stabilities of nuclides by determining the binding energy per nucleon. The equation is:
Binding Energy
Total # nucleons
17
Fission or Fusion: The Means of Increasing the Binding Energy per Nucleon
Binding energies for different species vary greatly. And it is known that the greater the binding energy per
nucleon, the more stable the species, meaning the harder it is to rip the nucleus apart. Nuclides with atomic masses
less than 10 (less than 10 total nucleons) have rather small binding energies, with the exception of helium, which
has an unexpectedly large binding energy, which is a reason why it is emitted intact as an alpha particle from
nuclei. When species have more than 12 nucleons, binding energies vary between 7.6 to 8.8 MeV.
The binding energy in the table above peaks for elements that have a total number of nucleons around 60. In other
words, as the binding energy increases up to this point, the stability of the nuclides increases as well. Then the
binding energy begins to decrease after masses = 60, so the nuclides become less stable. This point, mass number =
60 is important. It represents the place where the atom can be “most” stable. Other nuclides would like to get to
this place on the plot. Species with lower numbers of nucleons need to INCREASE their total number of nucleons
while species with too many nucleons need to “lose” some. Two nuclear processes can help a nuclide become more
stable.
Fission: A heavier nucleus can split into lighter ones. This means that a species with too many nucleons
will now split into to nuclei that have less nucleons. The product nuclei will have a greater binding energy
per nucleon and thus be more stable. Energy will be released as the product is more stable (at a lower
energy state) than the reactant. Nuclear power plants use fission as do atomic bombs
Fusion: A lighter nucleus needs to gain more nucleons. It can do so by combining with other nuclei.
Again the product is more stable than the reactant, so it is at a lower energy state and that energy is
released. The sun and stars generate energy through fusion as do hydrogen bombs. Current research is
focusing on the fusion of hydrogen nuclei to form a stable helium nucleus as a useful source of energy.
Of the many beneficial applications of nuclear reactions the greatest is the potential for limitless amounts of energy.
In the mid-1930’s, Enrico Fermi bombarded uranium with neutrons. What they observed, were, what they
believed, were smaller particles. Subsequent experiments proved these results. In fact, when uranium is
bombarded with neutrons, it breaks apart into 92Kr and 141 Ba and releases a lot of energy.
18
The uranium-235 nucleus can split in many different ways, but what is most important is that it happens quickly
(10-14 seconds) and it releases extraordinary amounts of energy. In fact, ½ pound of coal releases 2 x 10 4 J when it is
burned while ½ pound of uranium releases 2.1 x 10 13 J of energy – that is a billion times more!
One of the other products of a fission reaction is the release of neutrons. These neutrons will be moving, pretty
fast, and they will begin colliding with the species that are present, which will cause more splitting and more
neutrons to be produced . . . and you can see where this is going! This is called a chain reaction, where splitting
and collisions propagates more splitting.
The occurrence of a chain reaction depends on the amount of substance. This is termed critical mass. There must
be enough of a species present or the neutrons will “miss” the species and fly out of the sample. Think about firing
a gun at a group of animals. If you are 50 feet away and there is 1 animal, you have to be a pretty good shot –
right? What if you are 50 feet away from 100 animals. Chances are, just firing in the general direction of the group
will land you a hit. The same applies to the neutrons. A direct hit is likely if there is enough stuff there! The
minimum amount of nuclide necessary for a chain reaction to occur is called the critical mass. If the mass of the
sample is lower than the critical mass, then the neutrons will leave the sample and a chain reaction will not occur.
19
Uncontrolled Fission: The Atomic Bomb
When the fissionable species is present in abundance, meaning they exceed this critical mass, the ensuing chain
reaction brings about an explosion. In order to “by some time” subcritical masses of fissionable material are kept
separate and then brought together by some explosions which then allows the chain reaction to take over.
Controlled Fission: The Nuclear Reactor
It is not too difficult to understand some people’s fears with regard to nuclear energy compared to nuclear bombs.
After all, they are the same process, just used or handled differently. What if the power plant goes haywire – out of
control – what if it explodes like the atomic bomb. What prevents the fission inside the nuclear reactor from
experiencing the uncontrolled chain reaction?
Nuclear Reactors:
Nuclear reactors are not the most popular source of power in this country. There are many people who wish that
these power plants would be shut down. They have good reasons and bad reasons for wanting them to be shut
down. One good reason is that we do not have a truly viable method for getting rid of the reactor fuel once it has
been used. This material is called spent fuel. One bad reason is the fear of the plant becoming unstable and
causing a nuclear explosion. The fuel used in a nuclear reactor is not concentrated enough for an explosion, like
that in an atomic bomb, to occur. This is simply not possible. So, put the thought of mushroom clouds or melt
downs ending in China out of your mind!
You may be asking yourself, with all the controversy why build them at all? Well, we are an electric society. All
methods for producing electricity will be developed in some capacity. A tidal power plant was built in the US
many years ago, at great taxpayer expense, unfortunately it failed miserably. The flow of the water in tides is just
too slow to produce electricity.
Speaking of electricity, how is it generated? To produce voltage, you need 3 things. A magnetic field, a current
carrying conductor (a wire) and relative motion between the two. By relative motion between the two it is meant
that either the wire or the magnetic field must move so that the magnetic lines of flex cut across the wire. So, if a
wire is waved it back and forth between a magnet, a voltage will be generated. Seems simple enough, so why build
a nuclear reactor or build a dam if all that is need is to move wire? Well the wire used in electric power plants is
actually a very long wire wrapped thousands of times around an axle, then large magnets are placed around the
wire. With this amount of wire the axle can weigh quite a lot. By a lot I mean hundreds of tons. Look below, these
are BIG!
20
That is a man standing on the generator. The other picture is of a row of generators like those found in most dams.
The problem is how do you turn this axle? Humans have come up with a few means. First a turbine is attached to
the axle. A turbine is really a large fan, but instead of these fan blades blowing air, water or steam or wind is used
to push the blades. Since the turbine is attached to the axle wrapped in wire the wire turns in the magnetic field,
abracadabra electricity is being generated. When water is used, this is called a hydroelectric plant, or dam. When
wind is used, this is called a windmill. But these methods can only be used if there is water or wind available. The
most common method used to turn the generator is with a steam turbine.
Where does the steam come from? Boiled water. It is as simple as that, if you can boil water you can generate
electricity. In order to boil the water you must have a heat source, for example, fire. The typical heat sources are
coal, natural gas or oil, and garbage is now being used as well. It is unclear who lives down wind of the garbage
burning electrical power plant but I am sure they are not thrilled with their power source! There is another
method, nuclear power.
There are two types of nuclear reactions that can be used to generate power. Nuclear fusion and fission. The sun
uses nuclear fusion, which is the combining of two smaller nuclei to make one large nuclei. It might not seem like
much energy would be given off by this reaction, but sit outside on a the first sunny day of spring with in a bathing
suit and tell me the sun does not have a lot of power. This is the method we would like to use, the problem is there
is too much energy given off. The fusion reaction gives off so much heat it melts every container known to man.
Humans are currently attempting to create a magnetic field which will hold the fusion reaction but this research is
moving ahead very slowly. The best part of this reaction is the waste product is helium, certainly not a threat to the
environment as it is a noble gas.
Fission is the nuclear reaction of choice for nuclear power plants. In this reaction a neutron hits and enters a large
nucleus. This nucleus is split into two smaller nuclei, a few neutrons and releases a lot of heat. Not as much heat
as in fusion but plenty enough to boil water. The main problem with this reaction is that the two smaller nuclei
produced in the splitting are very radioactive. And their half lives are very long, ranging from thousand to
millions of years. It is very difficult to build a container which will hold something for a million years. Other ideas
of disposal have been considered such as shooting the waste into space or into the sun, but this is not really a
practical solution.
21
Regardless of politics, these power plants exist. Here are the basics on how a nuclear reactor works and why the
odds are stacked against a leak of any radioactive material reaching the environment.
The fuel used in nuclear power plants is U-235. This in itself is a problem as uranium is not a common element,
and the most common isotope of uranium is U-238. Unfortunately U-238 does not fission every time a neutron hits
it, normally it simply absorbs the neutron and becomes U-239. So, U-235 must be purified out of large sample of all
the uranium isotopes. This is very costly. An aircraft carrier, such as the USS Abraham Lincoln costs 2 billion
dollars, the nuclear reactor cores’ U-235 fuel that is used to run the Lincoln is 1 billion of that total cost.
The U-235 and all the radioactive products of the fission reaction are contained in fuel assemblies. The fuel
assemblies are basically bars or rods composed of very strong very corrosion resistant metal. All the radioactivity
of a nuclear reactor is trapped in these assemblies. There would have to be a serious problem for the fuel assembly
to break and release radioactive material.
A nuclear power plant is divided up in to loops. These loops prevent water that has touched the reactor fuel
assembles from reaching the environment. This water, called primary coolant, is not actually radioactive, but it is
isolated in case there is a problem. The primary coolant is contained in the primary loop. Again, this loop is
wholly separated from the next loop of water called the secondary loop. The secondary loop contains the water
that is actually boiled to steam and is used to turn the steam turbine. Remember that the entire purpose of the
reactor is to turn the generator. The next loop is the condensing loop. It cools the spent steam from the turbine
back to into liquid water which is looped back to be boiled again. The final cooling loop begins at a lake or river.
This lake or river water cools the condensing loop so it can cool the spent steam.
For a reactor to release radioactive material to the environment the fuel assemblies would have to break, at the
same time that the primary loop ruptures into the secondary loop which must itself leak into the condensing loop
whereupon it must burst into the cooling loop. This is just not going to happen unless someone bombs the plant.
Regardless, if any of these systems where to break and leak into any of the other systems the reactor would
instantly and automatically shut down.
Primary Coolant:
 normally composed of water
 very high pressure, 2000 lb.
22


very high temperature, 500F
water performs 2 functions, heat exchanger and as a moderator to slow neutrons to aid in fission of U-235
Primary Loop:
1. begins cycle at pump
2. flows to reactor core and is heated by U-235 chain reaction
3. is piped to steam generator through U-tubes and heats secondary water
Secondary Loop:
1. begins at the pump under the condenser
2. flows to bottom of steam generator
3. hits U-tubes and is heated to steam
4. is piped to steam turbine where it strikes the turbine blades and is spins the turbine
5. exits the turbine and enters the condenser
6. hits condenser U-tubes and is condensed to water
Basic Diagram of a Nuclear Reactor:
Radioactive Dating:
Radioactive dating uses half-lives to determine how long something has been around. All objects take in
radioactive materials over the course of their lives. When they die they stop taking in these radioactive materials.
The radioactive materials decay over time. If you know how much of a particular radioactive material is in a live
organism you have the No value. You can use a detector to determine the amount of this radioactive material in the
dead organism, which give you N. If you know the half-life you can calculate how long the organism has been
dead.
23
C-14 dating is most famous isotopes used for dating but it has limitations. The accuracy of half-life dating is very
poor after the isotope has undergone 5 half-life cycles. So, C-14 with a half-life of 5730 years is not very accurate
after 40,000 years. Potassium-40 is used to date farther back in history. K-40 has a half-life of 1.28 x 109 years this
allows scientist to date much older objects, meteors, dinosaurs, crater, etc. A table of useful isotopic decays follows.
Useful Isotopic Decay
System
Material
Half-life/years
Age range/years
C-14
organic remains
5730
200 - 50,000
U-238 to Pb-206 ratio
Minerals
4510 million
10-4500 million
U-235 to Pb-207 ratio
Minerals
704 million
10-4500 million
Rb-87 to Sr-87 ratio
Minerals
48,800 million
60-4500 million
K-40 to Ar-40 ratio
Minerals
1250 million
0.1-3000 million
Sm-147 to Nd-143 ratio
Minerals
110,000 million
1000-4500 million
Transuranium Elements:
Humans have created new elements by bombarding atoms with other particles such as, alpha particles, neutrons,
or even with other nuclei. Most of these can be found past uranium on the periodic table and therefore are named
transuranium elements. Uranium is the element with the most protons that occurs in nature. As of today there are
not a lot of uses for transuranium elements. Here is a short list of their uses today: in smoke detectors, nuclear
power and nuclear bombs. Most of these isotopes do not last long, having half-lives in the seconds.
Acute Dose-Response Effects in Humans:
Dose (mrem)
Effect
Immediate prostration, coma, followed by death within 1 or 2 days from severe central nervous
10,000,000
system damage.
Immediate nausea, vomiting, diarrhea. Death within 1 or 2 weeks from blistering of small
1,000,000
intestine. Complications from depressed bone marrow activity.
No overt effects. Some depression of white cell count. Statistical increase in
100,000
probability of radiogenic leukemia and life shortening (1 to 5 days/rem).
Effects are difficult to measure. In early embryo, developmental defects are possible. Subtle
10,000
abnormalities of brain structure and perhaps also function may
occur above 10 rem.
No measurable effects except a statistical increase of tumor incidence before
1,000
age of 10 in infants exposed in-utero.
Inverse Square Law of Radiation:
This equation calculates the intensity of radiation for a given distance from the source of the radiation and is called
the inverse square law of radiation. The equation used to calculate the effects of gravity is in the same format,
simply replace I, intensity with G, gravity.
I = intensity of radiation
d= distance from the intensity
2
Ix d y
 2
Iy dx
Shielding will also reduce the intensity. The calculation for shielding
works on 10th thickness. This is the amount of shielding to reduce the
intensity of the radiation to 1/10th of what it was. This is specific for the
type of radiation and the shielding used. For example, the 10th thickness
for gamma is 2 inches of lead. The 10 th thickness for neutrons in 10 inches
of concrete or water.
24
 and  radiation are really not a threat
outside the body. The dead layer of
skin that covers your body is enough to
shield you from them.
 and 
radiation are really only harmful if the
radiation is generated from within the
body. A radioactive isotope can be
eaten, drank or breathed in. When this
occurs the isotope can decay. The tissue
in the body has no protective layer and
is
easily
ionized,
killing
the
surrounding cells. Or worse, mutating
them.
Radiation Detection
We detect radiation by using its high energy to cause a reaction to occur. Detection is necessary as radiation has
the potential to harm us. Radiation that harms living organisms is called ionizing radiation. If radiation is strong
enough to cause atoms and molecules in the body to be ionized bad things can happen to the organism. Cells die,
or worse cells live in a mutated state, which is one cause of cancer.
The detector is normally gas filled and when ionizing radiation enters this area, the interior gas is ionized. Thus,
the neutral gas is now charged. A large electrical probe runs through the middle of the detector and when these
ions are formed in the detector, they will now be attracted to this probe in the middle of the detector as opposite
charges attract. The center probe is positively charged so the newly released electrons are drawn to the probe, then
travel through the detectors circuits where they are counted. They travel back to the chamber holding the gas and
return to the ionized gas from which they came. More ions mean more ionizations which means more electrons
and ultimately, more radiation. The Geiger counter is such a device also known as an ion-chamber detector.
Another method used to detect radiation is a scintillation counter. When radiation hits a material in the detector
the material gives off a photon, which is read by a photon detector and counted. These detectors use a sodium
iodine crystal, which when it is exposed to high energy radiation, will release light, which is detected by the photo
25
detector. Hand held scintillation counters are still in use by the Navy. Others do use the scintillation detectors but
ironically they have grown while the gas filled detectors have shrunk. With the exception of the Navy, all other
scintillation counters are now large cabinet-sized pieces of equipment and the gas filled counters are very small.
Medical Applications
Radioactive tracers are used to make a part of the body temporarily opaque to radioactivity to check for a problem,
like a leak in your digestive system, or to check if an organ has increased in size. The isotopes absorb the radiation
and do not allow it to reach the x-ray film or detector.
X-rays can diagnose bone breaks and the CAT scan or CT (computed tomography scanning,) which is many x-rays
taken with a computer used to generate an image, can diagnose internal injuries.
Radiation therapy for cancer victims is another important use of radiation. Directing gamma radiation at tumor
can kill the tumor. This is sometimes the only hope for those persons with a tumor in an inoperable location, i.e.
the brain.
As a side note, MRI, magnetic resonance imaging, is a big improvement over x-rays in diagnosing problems in soft
tissue, muscles, organs, tendons and the like. X-rays don’t show soft tissue well MRI does, the damage tissue is
affected differently than healthy tissue, all based on charges, but on the computer screen it shows up as a different
color.
Scientific Applications
Atom Tracking:
Using isotopes allows chemists to track the flow of a molecule or atom through a biological process. For example a
scientist can use heavy water, water which has its normal hydrogen, H-1 replaced with H-2 called deuterium. It is
twice as heavy as a normal hydrogen but it chemically behaves the same as normal hydrogen. The water will react
normally and the hydrogen will be tracked through series of chemical reactions. The deuterium acts as a tag. The
substance which has taken up this heavy hydrogen has a different spectrum or appearance when analyzed by
certain instruments.
A Further Look at the Limits of Nuclear Stability
One of the basic questions of nuclear science remains unanswered: What combinations of neutrons and protons
does nature allow to form a nucleus?
It is possible that there are isotopes of aluminum with twice the mass of a normal aluminum nucleus, but no one
has produced such isotopes. We cannot predict what the mass limit might be, yet.
The Rare Isotope Accelerator, RIA scientific program will allow dramatic steps toward understanding nuclear
binding and the limits of nuclear stability. Working with a variety of very fast ions from powerful accelerators,
scientists have already made several thousand different nuclei that can be shown on a chart of nuclei.
The figure shows three different kinds of nuclei. The combinations of neutrons and protons that make up the
stable nuclei, those found on the earth are shown by the black squares. The unstable known nuclei that have been
produced at one time or another in the laboratory are shown in yellow. The larger region of unknown but
predicted nuclei is shown in green. RIA will allow scientists to explore this region.
26
The unexplored green region, terra incognita, of the chart of nuclides is very large with literally thousands of
unknown nuclei. The limit on the neutron-rich side is called the neutron drip line. The addition of another neutron
would lead to its immediate re-emission—it’s like trying to add a drop of water to a bucket filled to the rim.
Experiments with RIA will extend our present knowledge of heavy isotopes and the neutron drip-line far beyond
the present limit, our present limit is oxygen, not too far down this long road of research. Challenging experiments
are planned that will detect and identify individual rare nuclei as they fly from the production target.
Additional Information:
What is PET?
The name "PET" comes from Positron Emission Tomography. It is a new scanning technique in medical research.
PET allows us, for the first time, to measure in detail the functioning of distinct areas of the human brain while the
patient is comfortable, conscious and alert. We can now study the chemical process involved in the working of
healthy or diseased human brains in a way previously impossible. Before the advent of the PET scanner, we could
only infer what went on within the brain from post-mortems (dissections after death) or animal studies.
PET represents a new step forward in the way scientists and doctors look at the brain and how it functions. An Xray or a CT scan shows only structural details within the brain. The PET scanner gives us a picture of the brain at
work.
27
Positron: Antimatter equivalent of the electron
A positron is an anti-electron. Positrons are given off during the decay of the nuclei of specific radioisotopes. A
type of radioactive fluorine produced at TRIUMF for the PET program is a positron emitter. When matter collides
with its corresponding antimatter, both are annihilated. When a positron meets an electron, the collision produces
two gamma rays having the same energy, but going in opposite directions. The gamma rays leave the patient’s
body and are detected by the PET scanner. The information is then fed into a computer to be converted into a
complex picture of the patient’s working brain.
How does it work?
A conventional "X-ray" is taken by firing X-rays through a person and onto a film. This "shadow" image shows
some structures in the body, such as cartilage and bone. A CT scanner uses fine streams of X-rays. By firing them
through the body from several directions, the CT scanner is able to build up a composite picture of anatomical
details within a "slice" through the person. Magnetic Resonance Imaging (MRI) does much the same thing, but
using magnetic and radiowave fields. In contrast, the PET scanner utilizes radiation emitted from the patient to
develop images. Each patient is given a minute amount of a radioactive pharmaceutical that closely resembles a
natural substance used by the body. One example of such a pharmaceutical produced at TRIUMF is 2-fluoro-2deoxy-D-glucose (FDG), which is similar to a naturally occurring sugar, glucose, with the addition of a radioactive
fluorine atom. Gamma radiation produced from the positron-emitting fluorine is detected by the PET scanner and
shows in fine detail the metabolism of glucose in the brain.
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What does a PET scan show?
The brain function being studied during a PET scan determines which radiopharmaceutical is used. Oxygen-15 can
be used to label oxygen gas for the study of oxygen metabolism, carbon monoxide for the study of blood volume,
or water for the study of blood flow in the brain. Similarly, fluorine-18 is attached to a glucose molecule to produce
FDG for use in the observation of the brain’s sugar metabolism. Many more PET radiopharmaceuticals exist, and
research is under way to develop still more to assist in the exploration of the working human brain. For example,
dopa, a chemical active in brain cells, is labeled with positron-emitting fluorine or carbon and applied in research
on the communication between certain brain cells which are diseased, as in dystonia, Parkinson’s disease, or
schizophrenia.
PET radioisotopes produced at TRIUMF
Labeling agent
Half-life
carbon-11
20.3 minutes
oxygen-15
2.03 minutes
fluorine-18
109.8 minutes
bromine-75
98.0 minutes
How much radiation does a patient get?
PET scans using radioactive fluorine in FDG would result in patients receiving exposures comparable to (or less
than) those from other medical procedures, such as the taking of X-rays. Other scanning agents - for instance, 6-Fdopa or radioactive water - normally cause even less
exposure.
PET: Research tool of the future
The PET program at TRIUMF and UBC is in a unique
position among world medical research centers in
having many of the expensive major facilities required to
mount a powerful PET program. These include the
cyclotrons and radiochemistry laboratories at the
TRIUMF project that are the source of the PET scanning
agents. The laboratories are linked to the UBC Health
Sciences Centre Hospital by the world’s longest "pea
shooter", a 2.4 km pneumatic pipeline used for the
delivery of PET scanning agents in the shortest possible
time. These facilities have a capacity that has not been
equaled by any other university/health sciences center
in the world.
http://www.triumf.ca/welcome/petscan.html
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More information on the PETTVI scanner