Remember the easy stuff!!
nucleus
Electrons
We don’t care about the electrons right now…

What particles make up the nucleus?
Both protons and neutrons are called NUCLEONS protons neutrons

Recall some stuff about the nucleus:
Notation:
Mass number
238
92
U element
Atomic number
Isotopes: nuclei with the same number of protons, but not necessarily the same number of neutrons

Isotopes
• Isotopes have the same number of protons, different number of neutrons
• Another way to show an isotope is to have the mass number follow the name of the element (Carbon-14)

12 C and 13 C differ in their
(a) number of neutrons.
(b) number of protons.
(c) number of electrons in orbit around the nucleus.
(d) chemical behavior.
(e) all of the above.

What is the charge on a proton? The neutron?
What is the nature of the force between the nucleons?
How does the nucleus hold itself together??!!

The Nucleus is a delicate balance between
[1] The attractive nuclear strong force between all of the nucleons, and
[2] The repulsive electromagnetic force between all of the protons

It turns out that our delicate balance of forces tends to break down when nuclei get large:
The electromagnetic forces eventually overcome the nuclear ones and the nucleus spontaneously breaks apart

This “instability” is called radioactivity :
All nuclei having atomic number larger than
83 (bismuth) are radioactive.

Radioactivity
• Radioactivity is the process in which an unstable atomic nucleus emits charged particles and energy
• Any atom containing an unstable nucleus is called a radioactive isotope or radioisotope for short

•As more protons are added (the nucleus gets heavier) the proton-proton repulsion gets larger.
•The heavier the nucleus, the more neutrons are required for stability.
•The belt of stability deviates from a 1:1 neutron to proton ratio for high atomic mass.

Ratio of neutrons to protons in nucleus determines if nuclei are stable
Too many neutrons
Too few neutrons nuclei with
>than 83 protons all unstable

sometimes an unstable nucleus goes through a series of nuclear reactions before it gains stability.
This sequence is called a radioactive series

High energy photon (light)

Lead block
Uranium
Florescent
Screen
Gold Foil

Ernest Rutherford’s Other Experiment:

• No study on radiation is complete without giving credit to the Curies (Marie, Pierre and Irene)-
• Their discoveries include radium, polonium and positron.
• Marie-died from
Overexposure
To radiation
Pierre Curie
(1859-1906)
Marie Curie
(1867-1934)

Types of Nuclear Radiation



What is an alpha-particle?
It has two protons and two neutrons
4
2
He

What is alpha-decay?
It is when a nucleus emits an alpha particle
4
2
He
Alpha Decay = Alpha Particle Emission

Nuclear Equations -represent nuclear decay to become stable - they must balance.
The total number of p + and n 0 before a nuclear reaction must be the same as the total number of nucleons after reaction.

Remember: This is the mass number, which is the number of protons plus neutrons
Alpha Particles (  )-
They have a mass of 4 and charge of +2
Radium Radon
Ra 226
88
+
Rn 222
86
88 protons
138 neutrons
86 protons
136 neutrons
•The alpha-particle () is a Helium nucleus.
•It’s the same as the element Helium, with the electrons stripped off !
•The alpha particles go in the air collide with air molecules and become Helium – not dangerous.
n p p n
 ( 4 He)
2 protons
2 neutrons

Example: Write the nuclear equation for the alpha decay of uranium 238:
238
92
U
234
90
X
+
4
2
He
Now look at the chart to find this one:
THORIUM

Nuclear Equation Practice:
Alpha Decay
How would alpha decay equations be written for these atoms:
• 238
92
U 
• 209
84
Po 



Beta Decay
Electron!
14
6
C
14
7
N
+ electron (beta)

200link
A neutron turns into a proton and an electron.
The beta particle is the electron, written as
0
-1
or
0
-1


Beta Particles (  )are electrons, “no” mass and charge of –1.
The decay of Carbon 14
Carbon
C 14
6
Nitrogen
N
7
14
+ e -
6 protons
8 neutrons
7 protons
7 neutrons
-1
0 Electron
(beta-particle)
We see that one of the neutrons from the C 14 nucleus
“converted” into a proton, and an electron was ejected.
The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus.
In symbolic notation, the following process occurred: n  p + e

Write out the nuclear equations in each case and identify the daughter nuclei:
Alpha decay of 222 Rn:
86
Beta decay of 3 H:
1
Beta decay of 90 Sr
38

Beta Decay

Nuclear Reaction Equation Practice:
Beta Decay
• A beta particle is written 0
-1 e or 0
-1

• During beta decay, the mass remains the same and the atomic number increases by one
• 214
82
Pb 
• 218
84
Po 

38
90 Sr is a radioactive isotope that decays by beta-decay. Its daughter nucleus is
(a)
36
86 Kr.
(b)
37
88 Rb.
(c)
37
89 Rb.
(d)
39
89 Y.
(e)
39
90 Y.


rays

Gamma decay occurs because the nucleus is at too high an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon known as a gamma particle. Here's a diagram of gamma decay with helium-3:
Gamma decay is only energy emission, not particle emission.

Gamma particles ( g )
In much the same way that electrons in atoms can be in an excited state , so can a nucleus.
Neon
Ne 20
Neon
Ne 20 +
10 protons
10 neutrons
(in excited state)
10 protons
10 neutrons
(lowest energy state)
A gamma is a high energy light particle .
gamma
It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum. It has neither
Charge nor mass. They are highly penetrating.

Gamma decay

Gamma decay
• During gamma decay, the atomic number and mass remain the same, but the energy of the nucleus decreases
• Gamma rays can be stopped by several centimeters of lead or by several meters of concrete

not

The unit of radiation exposure is called the
REM (Radiation Equivalent in Man)
This is a direct measure of the number of damaged cells.
The average dose for one year is about
0.3 Rem
Sudden dose of 1000 rems causes death in 30 days!!

Exposure to ionizing radiation: alpha beta gamma
All of these are
IONIZING RADIATION
Ionizing radiation causes cell damage that can lead to DNA damage that can lead to CANCER.

Radiation Doses
• Normal
– 1 XRay (medical)
– CAT Scan
0.04 rem = 40 mrem
3 rem
– Portland  New York 1 mrem (4 hr flight)
(0.001 rem)
– Cosmic Rays
– Food ( 40 K, Ra)
30 – 50 mrem/year
~40 mrem/year

Bad News
(acute radiation exposures)
• 1 rem  More cancer ~ 100 extra cases per 10 6 people
(+0.0001 chance)
• 25-50 rem  Lose white blood cells (+ above)
• 50-200 rem
• 450 rem
 Sick, low white blood cell count, Get Leukemia in 10-30 years, Genetic mutations in progeny.
 50% death in 30 days (with “heroic” medical intervention)
• 1000 rem
• 5000 rem
 Death, 100%
 Can’t shoot back

Detecting Radiation

Penetrating Radiation
The penetrating power of radiation is really a function of mass.
g
-radiation (zero mass) penetrates much further than

-radiation, which penetrates much further than

-radiation.
l http://library.thinkquest.org/3471/radiation_effects_body.htm

“Background” Radiation
• Background radiation is nuclear radiation that occurs naturally in the environment
– Radioisotopes in the air, water, rocks, plants, and animals all contribute to background radiation
– Cosmic rays (streams of charged particles) from outer space that collide with the Earth’s atmosphere also contribute
– Background radiation levels are low enough to be safe

RATES OF NUCLEAR DECAY
• A half-life decay is the time required for one half of a sample of radioactive sample of a radioisotope to
– Unlike chemical reactions, nuclear decay rates are constant regardless of temperature, pressure or surface area

A very important concept in nuclear chemistry and its applications is the idea of
HALF-LIFE
Half-Life: the TIME it takes for half of a given amount of a specific isotope to decay
This depends on the relative stability of the the isotope in question: semi-stable nuclei last longer than very unstable ones.

1 Kg
Example: 14 C (half-life
6,000 years).
How much is left after 6,000 years?
12,000 years?
18,000 years?
24,000 years?
30,000 years?
36,000 years?

1 Kg
Example: 14 C (half-life
6,000 years).
There must be an easier way!
How much is left after 6,000 years?
12,000 years?
We divided by
2 six times
18,000 years?
24,000 years?
30,000 years?
36,000 years?

We can do the process in reverse to see how much time it took a substance to decay:
Radioactive Dating:

Let’s meet some of the unstable isotopes in our neighborhood:
• Radon -222
– Forms as part of the Uranium Series
– Decomposition of Uranium in many rocks-granite
– Migrates into basement cracks
– Dense and collects in lower part of house
– Readily inhaled
– Its decomposition product is polonium, if it decays in the lung it emits an alpha particle
– The polonium solid decays resulting in lung disease

Radium 226
• 1 st radioactive element associated with biological damage
• Some are phosphorescent (glow)
• Believed to cause the reaction that caused leukemia that killed Marie Currie
Uranium-238
• Used to estimate age of earth
• We use its half life to estimated how long it has been since the rock solidified.

Potassium 40
• Light element (one of the few)
• Emits positron to form Ar-40
• Most of argon in atmosphere is Ar-40

Artificial Radioactive isotopes-
Transmutation
• Artificial radioactive
Isotopes are produced by bombarding a target element with nuclei of other elements
• Carried out in cyclotron
• Many new and useful
Isotopes have been created.

Practical uses of Radioisotopes
H-3 Tritium Archaeological dating
Am-241 Americium-241 Smoke detectors
Co-60 Cobalt-60 Cancer treatment
Cr-51 Chromium-51 Determination of
U-235blood volume
Uranium-235 Nuclear reactors and weapons
U-238 Uranium-238 Archaeological dating

Artificial Radioactive isotopes may be used as tracer materials.
Example: We might like to know how phosphorus in fertilizers is used by plants. By incorporating a small amount of radioactive Phosphorus in the fertilizer, chemists can measure the time it takes for plants to utilize the
Phosphorus. They also can track where the P goes.

Dating Archeological samples
Example:
U-238 decays slowly through the uranium disintegration series to lead-206. The half-life of this conversion is 4.5 X 10 9 years. To determine the age of a rock, we need to determine the amount of uranium present when the rock solidified, N o and the amount of uranium in the rock today, N f

• The amount of U-238 present in the rock today can be measured. However, we can’t calculate the original. The solution lies in the fact that each atom of uranium ends up as an atom of lead. Therefore, if we take a rock sample and determine the number of atoms of U-238 and the number of atoms of Pb-206, we can say that
• N o
• N t
= atoms U-238 + atoms Pb-206
= atoms 238-U
• **Errors will exist, the original rock may have contained some Pb-206 and some of the original U-238 may not end up as Pb-206

FISSION AND FUSION
•
•
is the
of an atomic nucleus into two smaller parts
is a process in which the nuclei of two atoms nucleus
to form a larger

Fission
• A chain reaction a nucleus is a chain of fission reactions triggered by neutrons released during the fission of
• About 20% of the electricity in the US comes from fission reactions

• A tremendous amount of energy is produced during a fission reaction

Fission
• Advantages to using fission reactions is the lack of air pollution.
• Disadvantages include the risk of exposure and radioactive waste

Nuclear Power Plant
FG21_020.JPG

Atomic Bomb

Fusion
• Fusion reactions can release huge amounts of energy
• Fusion reactions occur in the sun and stars

Nuclear Fission-the process that yields two nuclei of almost equivalent mass.
• It does not occur spontaneously
• It is a chain reaction
• It is usually used to generate electricity.
Heat is generated in fission reactions.

• Nuclear Fusion- The combination of two nuclei into a larger atom is called nuclear fusion.
• The reactions within the sun are fusion reactions that combine Hydrogen nuclei to form a helium atom
• It takes simple, nonradioactive materials and produces helium, so it should be a clean and inexpensive source of energy.
• Several designs for fusion reactors are being tested. Some success, it will be some time before this cheap, nonpolluting energy source will become a reality.

• Fusion of tritium and deuterium requires about
40,000,000K:
2
1
H + 3
1
H  4
2
He + 1
0 n
• These temperatures can be achieved in a nuclear bomb or a tokamak.
• A tokamak is a magnetic bottle: strong magnetic fields contained a high temperature plasma so the plasma does not come into contact with the walls. (No known material can survive the temperatures for fusion.)
• To date, about 3,000,000 K has been achieved in a tokamak.

Fat Man
Produced this cloud after its detonation at
Nagasaki on August
15 th , 1945, killing at least
80,000 civilians instantly.
140,000 civilians perished in Hiroshima when Little Boy was dropped just two weeks earlier.
No attack involving nuclear weapons has occurred since.

In 1961, when the USSR tested the Hydrogen Bomb “Tsar
Bomba”, it was 4000 times more powerful than Little Boy. Its energy yield was ten times greater then exploded during all of the munitions all of World War 2.
The USSR concluded that Tsar could not be safely deployed against Western European
New York, Chicago, and Los Angeles metropolitan areas; the use of Tsar was