T. Norah Ali Al moneef
1
30.1 Radioactivity
Radioactive Decay:
the spontaneous disintegration of a nucleus into a slightly lighter
nucleus, accompanied by emission of particles, electromagnetic
radiation, or both.
Radioactivity is a natural and spontaneous process by which the
unstable atoms of an element emit or radiate excess energy in the
form of particles or waves. These emissions are collectively called
ionizing radiations. Depending on how the nucleus loses this
excess energy either a lower energy atom of the same form will
result, or a completely different nucleus and atom can be formed.
T. Norah Ali Al moneef
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Atomic Structure
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Complete Symbols
• Contain the symbol of the element,
the mass number and the atomic
number.
Mass
Superscript →
number
Subscript →
Atomic
number
X
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A
X
Z
A
= number of protons + number of neutrons
Z
= number of protons
A – Z = number of neutrons
Number of neutrons = Mass Number – Atomic Number
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Subatomic Particles in Some Atoms
16
8
O
8 p+
8 n0
8 e-
31
65
P
15
15 p+
16 n0
15 eT. Norah Ali Al moneef
Zn
30
30 p+
0
35 n
30 e6


Find each of these:
a) number of protons
b) number of neutrons
c) number of electrons
d) Atomic number
e) Mass Number
80
Br
35
If an element has an atomic number of 34 and a mass number
of 78, what is the:
a) number of protons
b) number of neutrons
c) number of electrons
d) complete symbol
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
If an element has 78 electrons and 117 neutrons what is the
a) Atomic number
b) Mass number
c) number of protons
d) complete symbol

If an element has 91 protons and 140 neutrons what is the
a) Atomic number
b) Mass number
c) number of electrons
d) complete symbol
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Isotopes
• Atoms of the same element can have different
numbers of neutrons.
• Thus, different mass numbers.
• These are called isotopes.
•Chemically identical
Isotopes: elements with the same number of protons,
but a different number of neutrons.
12
6
C
13
6
C
14
6
C
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Isotopes
• Frederick Soddy (1877-1956)
proposed the idea of isotopes in
1912
• Isotopes are atoms of the same element
having different masses, due to varying
numbers of neutrons.
• Soddy won the Nobel Prize in
Chemistry in 1921 for his work with
isotopes and radioactive materials.
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There are many types of uranium:
235
238
A
A
Z
Z
Number of protons
Number of protons
Number of neutrons
Number of neutrons
U
92
U
92
T. Norah Ali Al moneef
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There are many types of uranium:
235
238
U
92
U
92
A
235
A
238
Z
92
Z
92
Number of protons
92
Number of protons
92
Number of neutrons
143
Number of neutrons
146
Isotopes of any particular element contain the same
number of protons, but different
numbers of neutrons. 12
T. Norah Ali Al moneef
Most of the isotopes which occur naturally are stable.
A few naturally occurring isotopes and all of the manmade isotopes are unstable.
Unstable isotopes can become stable by releasing
different types of particles.
This process is called radioactive decay and the
elements which undergo this process are called
radioisotopes/radio nuclides.
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CHARACTERISTICS OF RADIOACTIVE DECAY
• It is a natural process in our universe
• It is spontaneous – we cannot predict when an atom will undergo decay
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Alpha radiation - 
Description:
2 neutrons, 2 protons (helium nuclei)
Electric Charge:
+2
Relative Atomic Mass:
4
Penetration power:
Stopped by paper or a few cm of air
Helium nuclei
Ionisation effect:
Strongly ionising
Effects of Magnetic/Electric Field:
Weakly deflected
Alpha, Beta, and Gamma
• Historically, the products of radioactivity were called
alpha, beta, and gamma when it was found that they
could be analyzed into three distinct species by either
a magnetic field or an electric field:
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Radioactive Decay
It is not uncommon for some nuclides of an element to be
unstable, or radioactive.We refer to these as radionuclides.
There are several ways radionuclides can decay into a
different nuclide.
Unstable nuclei decay releasing energy and radiation.
Three types of radiation
alpha (α) particles - 42He nuclei(+2 charge
beta (β) particles - electrons(- charge)
positrons (+ charge)
gamma (γ) particles - high frequency electromagnetic radiation.
Increasing penetration
(uncharged)
Radioactive decay results in the emission of either:
• an alpha particle (),
• a beta particle (b),
• or a gamma ray(g).
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• Alpha Emission:
– Alpha Particle: Two protons and two neutrons
bound together and emitted from the nucleus
during some kinds of radioactive decay.
– Helium nuclei with charge of 2+
– Symbol: 42He
• Net effect is loss of 4 in mass number and loss of 2 in
atomic number.
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Alpha Decay
An alpha particle is identical to that of a helium nucleus.
It contains two protons and two neutrons.
A
Z
X
A-4
Z-2
4
Y + 2 He
unstable atom
alpha particle
more stable atom
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Alpha Decay
A
Z
226
88
222
86
222
86
X
Ra
Rn
Rn
A-4
Z-2
222
86
Y +
4
2
He
Rn +
4
2
He
A
Z
4
2
Y + He
218
84
Po +
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2
He
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Alpha Decay
Daughter
Nucleus
Np-237
Th-234
Ra-228
Rn-222
Parent Nucleus
Am-241
U-238
Th-232
Ra-226
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 

Alpha Particle
(Helium Nucleus)
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Beta Radioactivity
• Beta particles are just electrons
from the nucleus, the term "beta
particle" being an historical term
used in the early description of
radioactivity. The high energy
electrons have greater range of
penetration than alpha particles,
but still much less than gamma
rays.
The emission of the electron's
antiparticle, the positron, is
also called beta decay.
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Beta Decay
A beta particle is a fast moving electron which is
emitted from the nucleus of an atom undergoing
radioactive decay.
Beta decay occurs when a neutron changes into a
proton and an electron.
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Daughter
Nucleus
Osmium-187
Calcium-40
Beta Decay


Antineutrino
Parent Nucleus
Rhenium-187
Potassium-40
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

b

Beta Particle
(electron)
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b-particle production
The common modes of decay
Th 
234
90
131
53
234
91
Pa  e  
0
1
I Xe  e  
131
54
0
1
(a)The net effect of b-particle production is to
change a neutron to a proton.
(b)The nuclides lie above the zone of stability.
(c) The ratios of neutron/proton are too high.
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Beta radiation - b
Description:
High energy electron
Electric Charge:
-1
Relative Atomic Mass:
1/1860th
high energy electron
Penetration power:
Stopped by few mm of aluminium
Ionisation effect:
Weakly ionising
Effects of Magnetic/Electric Field:
Strongly deflected
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Gamma radiation - g
Description:
High energy electromagnetic radiation
Electric Charge:
0
Relative Atomic Mass:
0
Penetration power:
Electromagnetic radiation
Reduced by several cm’s of lead or
several metres of concrete
Ionisation effect:
Very weakly ionising
Effects of Magnetic/Electric Field:
NO deflection
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γ-radiation
• γ radiation is high frequency electromagnetic
radiation. When they are emitted from the
nucleus the nuclear structure stays the same, it
simply represents a loss of energy
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1. Proton
2. Neutron
3. Electron
4. Positron
5. Gamma ray
1H or 1p
1
1
1n
0
0
0
1 e or 1 b
0 e or 0 b
1
1
0g
0
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The penetration power of the three
types of radiation.

b
g
Thin mica
Skin or paper
stops ALPHA
Thin aluminium
stops BETA
Thick lead
reduces GAMMA
The effects of a field on radiation
Beta radiation has a –1
charge and a small mass so
is strongly deflected
Gamma radiation
has no mass or
charge so it is
not deflected.
The effect of a magnetic or electric
field on radiation depends upon the
nature of the radiation.
Alpha radiation has
a +2 charge but a
RAM of 4 so is
only weakly
deflected.
Radioactive Emissions
Emission
Alpha
Beta

b
Gamma g
What?
Penetration
2 protons
2 neutrons
few cm in air. Stopped by
paper
electron
1 metre in air. Stopped by
thin aluminium
electromagnetic
wave
few metres of concrete will
reduce their energy.
Difficult to stop
1. Proton
2. Neutron
3. Electron
4. Positron
5. Gamma ray
1H or 1p
1
1
1n
0
0
0
1 e or 1 b
0
0
1 e or 1 b
0g
0
•
Physical
Half-Life
Useful parameter related to the decay constant;
defined as the time required for the number of
radioactive atoms in a sample to decrease by one
half
• Physical half-life and decay constant are inversely
related and unique for each radionuclide
 If the particle’s lifetime is very short, the particles decay away
very quickly.
 When we get to subatomic particles, the lifetimes are typically
only a small fraction of a second!
 If the lifetime is long (like 238U) it will hang around for a very
long time!
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Radioactive Decay
• The number of atoms in a sample that decay depends on
the total number of atoms in the sample!!
• This fact yields a rate of decay called an exponential decay
The Decay Constant, λ
• The rate of decay is called the decay constant. It determines the
half-life of a radioactive element.
• The decay constant is unique for each radioactive element.
• Number of atoms decaying per unit time is
proportional to the number of unstable atoms
• The decay constant of radioactive decay is equal to
the reciprocal value of the half life time
• Constant of proportionality is the decay constant ()
dN/dt =-  N
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Radioactive Half-Life
The time it takes for one-half
of a radioactive sample to
decay
Look at factors of 2
One half-life (1/2)
Two half-lives (1/4)
Three half-lives (1/8)
For Example: A material has decreased by ¼ of its original amount it
has gone through two half-lives
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Half-Life
• Number of atoms decaying per unit time is
proportional to the number of unstable atoms
• Constant of proportionality is the decay constant ()
∆N/ ∆ t =-  N
dN/dt =-  N0
N
ln t = -  t
N0
Nt = N0e-t
(this is a decrease, since sign is - )
where:
Nt = number of radioactive atoms at time t
N0 = initial number of radioactive atoms
e = base of natural logarithm = 2.71828…
t = time
Note when t = 0, N = N0
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Physical Half-Life
• Useful parameter related to the decay constant;
defined as the time required for the number of
radioactive atoms in a sample to decrease by one
half
 = ln 2/T1/2 = 0.693/T1/2
• Physical half-life and decay constant are inversely
related and unique for each radionuclide
• The half-life of such a process is:
0.693
= t1/2

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Half-life is the time it required for half the atoms of a
radioactive nuclide to decay. It can be measured in
seconds, minutes, days, or years.
decay curve
initial
1
half-life
8 mg
4 mg
2
2 mg
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1 mg
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Half-Life Problem
Ra-223 has a half-life of 12 days. If today, you
had 100 grams of this isotope, how much
would remain after 36 days?
1.
How many half-life periods has it undergone in 36 days?
36 days
= 3 half life periods
12 days/half-life
100 g
50g
25g
12.5 g
T. Norah Ali Al moneef
12.5 g
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Physical Half Life
• Longer the half life, the longer the isotope will
continue to emit radiation
• Half Life REMAINS the same, no matter how
many atoms present
• The Half Life and Decay Constant of a material
are related!
Physical Half-Life
• 238U (Uranium) : 4.47 x 109 years
• 226Ra (Radium) : 1600 years
• 99mTc (technetium) : 6.4 hours
• 140Xe (Xenon) : 13.6 seconds
• 212Po (Polonium) : 299 x 10-9 secs
• Wait a minute…….. A negatively charge particle from the nucleus?
• A neutron decomposes into a proton and an electron. The proton stays in
the nucleus and the electron is released.
234
90
0
th 234
pa

91
1 e
• Beta Particles can pass through paper, but are stopped by metals
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• Physical Half-Life
Time (in minutes, hours, days, or years) required for
the activity of a radioactive material to decrease by
one half due to radioactive decay
• Biological Half-Life
Time required for the body to eliminate half of the
radioactive material (depends on the chemical form)
• Effective Half-Life
The net effect of the combination of the physical and
biological half-lives in removing the radioactive
material from the body
• 1 HL = 50%
2 HL = 25%
3 HL = 12.5%
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Half-life, effective
The period during which the quantity of a radionuclide in a biological system is reduced by half by
interaction of radioactive decay and excretion due to biological processes.
Tbiol: biological half-life
Tphys:physical half-life
1. Tphysical the time taken for half of the atoms in a radioactive material to undergo
decay.
2. T biological the time required for half of a quantity of radioactive material absorbed by a
living tissue or organism to be naturally eliminated (biological half-life) or removed by
both elimination and decay (effective half-life)
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The half life of radium Ra is 1.6x103 yr. If the sample contains
3.00x1016 nuclei find the decay constant
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The half life of I-123 is 13 hr. How much of a 64 mg sample
of I-123 is left after 26 hours?
t1/2
26 hours
=
13 hrs
=
2 x t1/2
Amount initial =
64mg
Amount remaining = 64 mg x ½ x ½
= 16 mg
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The half-life of a radioactive substance is 2.5 minutes. What fraction
of the original radioactive substance remains after 10 minutes?
(1) ½
(2) 1/8
(3) ¼
Nt = N0e-t
(4) 1/16
Nt /N0= e-t
= e-0.693x10/2.5
=1/16
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What is the half-life of an isotope if it decays to 12.5% of its radioactivity in
18 minutes?
(a) 9 minutes
(b) 8 minutes
N
(c) 12 minutes
e T
N
(d) 6 minutes
N
(e) 0.17 minutes
e T

0.69318
1/ 2
0
0.69318
0
1/ 2
N
0.69318
100
 e T 1/ 2
12.5
100 0.693  18
ln

12.5
T 1/ 2
T
1/ 2

0.693  18
 6 min utes
100
ln
12.5
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The half life of radium Ra is 1.6x103 yr. If the sample contains
3.00x1016 nuclei. Find the number of nuclei after 4.8x103 yr.
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30.9 radioactive decays
In all nuclear processes , the following quantities must be conserved
1- energy (including mass energy)
2- momentum ( both linear and angular)
3- electric charge the number of elementary positive and negative
charges must be equal before and after NT
4- number of nucleons , - A is the same before and after NT
• Einstein - mass IS energy
• E = mc2
• m is the mass difference between the parent nuclei
and the daughters. The equation gives the energy
released. Mass is converted into energy!
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BASIC TYPES OF RADIOACTIVE DECAY
Alpha () decay
•
•
•
•
•
•
• Occurs when atomic nuclei have too many protons and neutrons
(i.e., Are heavy) (A > 150) and is often followed by gamma
and characteristic x-ray emission
Consist of 2 protons and 2 neutrons
Mass of an alpha particle is ~8000 me
Charge = +2 charge
Are highly ionizing
Have low penetrating abilities (only cm in air and mm in water)
Easily shielded; common types of shielding are paper, cardboard, air,
clothing; will not penetrate skin
• Changes both the mass and identity of the nucleus of the parent radionuclide
• This means that the decay results in the formation of a new element as the
daughter product
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Alpha Decay
A
Z
X
A4
Z2
Y
4
2
He
alpha particles are very heavy and very energetic compared to other
common types of radiation. These characteristics allow alpha particles to
interact readily with materials they encounter, including air, causing many
ionizations in a very short distance.
α-particles are relatively large particles, thus they have lots of collisions with atoms of
the materials through which they pass. During these collisions the α-particles energy can
cause ionisation of the materials. α- particles cause lots of ionisation
Are deflected by electric and magnetic fields (i.e. are charged
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Alpha Radiation
Only a hazard when inside your body
(internal hazard)
can’t penetrate skin
internal hazard
stopped by paper
found in soil, radon and
other radioactive materials
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Converting protons and neutrons
• There are certain combinations of protons and neutrons that
are more stable than others
• If the number of protons :neutrons is not correct the nucleus is
unstable.
• The solution is to release certain types of radioactivity. Note:
proton (11p), neutron (10n)
1 n  1 p + 0 e
– emission)
(b
0
1
–1
1 p  1 n + 0 e
(b+ emission)
1
0
1
1 p + 0 e  1 n
(EC – electron capture)
1
–1
0
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What makes unstable nuclei unstable?
. Each nuclear energy level can- contain four
particles: two protons (s=½) and two
neutrons (s=½).
energy
0
r
The potential experienced by nucleons is a 3D potential well.
The ground-state configuration of the carbon-16 nucleus :
12
6
If a nucleus is allowed to decrease its energy by transforming
“excessive” protons (neutrons) into neutrons (protons), it will do
it!
The processes responsible for these transformations are
driven by weak interaction (the fourth fundamental
interaction):
protons neutrons
Some important transformation processes driven by weak interaction:
n  e   p  
p   n  e  
p   e   n 
C
Why N  Z for light nuclei
13
8
O
13
7
energy
N
energy
t1/2  8.9ms
protons
14
6
C
neutrons
protons
14
7
energy
N
neutrons
energy
t1/2  5730 y
protons
neutrons
protons
If
the
electrostatic
repulsion of protons can
be neglected (this is the
case of light nuclei: recall
that
the
positive
electrostatic energy Z2),
the nucleus tends to keep
approximately
equal
numbers of protons and
neutrons.
neutrons
Even in this case, the
nucleus can still lower
its total energy: the
rest energy of neutron
is slightly more than
the rest energy of a
proton
and
an
electron.
β- radiation
• β – particles are high speed electrons ejected from the
nuclei of radioactive atoms
• It occurs when a neutron in the nucleus splits to become a
proton and an electron. The proton remains in the nucleus
and the electron (β- particle) is emitted at high speeds
• Β – particles are more penetrating than α – particles (since they
are smaller particles they have less collisions and so penetrate
further).
• The fact that they have less collisions means that they cause less
ionisation.
• They are deflected by electric and magnetic fields (i.e. they are
charged particles)
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• When a β particle is emitted the mass no. stays the
same (since the mass of an electron is very small) and
the atomic no. increases by one (as an extra proton is
created with the β particle.
Beta Particles: Electrons or positrons having small mass and variable energy.
Electrons form when a neutron transforms into a proton and an electron or:
neutron decay (b-, lowers the N/Z ratio
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Beta Radiation Hazards
skin, eye and internal hazard
stopped by plastic
found in natural food, air and water
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Beta decay ( b
•
•
•
•
•
•
)
is a stream of negatively charged electrons.
has a very light mass of an electron
has a -1 charge
can be stopped by a piece of aluminum
has a speed that is 90% of the speed of light.
can ionize air and other particles.
- release of anti-neutrino
A
Z
X
A
Z1
Y

0
1
e
(no charge, no mass) )

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0 
0
70
•Beta-minus (b-) decay characteristically occurs with radionuclide's that have an
excess number of neutrons compared with the number of protons (i.e., high
N/Z ratio)
•Any excess energy in the nucleus after beta decay is emitted as gamma rays,
internal conversion electrons or other associated radiations
218
84
234
90
Po
Th
210
81 Tl
218
85
234
91
210
82
Rn
Pa
Pb
+
+
+
0
-1
b
0b
-1
0
-1
b
- release of neutrino (
)
•Beta-plus (b+) decay characteristically occurs with radionuclides that are “neutron
poor” (i.e., low N/Z ratio)
proton decay (b+, raises the N/Z ratio):
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A
Z
X
A
Z1
Y

0
+1
e
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
0 
0
76
Beta Particles: Electrons or positrons having small mass and variable energy.
Electrons form when a neutron transforms into a proton and an electron or:
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NEGATIVE BETA (ß-) DECAY
Occurs when atoms have too many neutrons (i.e., Are
“neutron-rich”) and decay by emitting a negative beta particle (ß)
During
negative beta decay, excess neutrons are converted into protons, electrons, and
antineutrinos. The protons remain in the nucleus but the new electrons are emitted as
negative beta particles (ß-) or negatrons.
 Less ionizing than alphas due to decreased mass of negatrons
 Changes the identity of the nucleus but not the mass
 The z number is increased due to onversion of neutrons into protons
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17
POSITRON (ß+) EMISSION
Occurs when the nucleus of the atom has too many protons
(i.e., is proton-rich). It is also known as positive beta decay.
Results in a positive electron emitted from the nucleus of the
proton rich atom. This positive electron is known as a positron. An
additional particle, a neutrino, is also emitted from the nucleus.
Neutrinos are very small particles with no electric charge.
They have little or no mass and participate in weak interactions.
Positrons have same mass as electrons
Positrons have charge +1
Positrons are less ionizing than alphas
Positrons are more penetrating than alpha decay
but less than gamma
The best shielding is lead with thickness of 1 inch or more
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Electron Capture
electron capture: (inner-orbital electron is captured by the
nucleus)
• Electron capture is one form of radioactivity. A parent nucleus may capture
one of its orbital electrons and emit a neutrino. This is a process which
competes with positron emission and has the same effect on the atomic
number. Most commonly, it is a K-shell electron which is captured, and this is
referred to as K-capture.
Addition of an electron to a proton in the nucleus
– As a result, a proton is transformed into a neutron.
1
1
p
+
0
−1
e

1
0
n
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electron capture
(raises the N/Z ratio):
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b decay - three types
1) b- decay
3
1
b
H 
 23 He  e   e
- converts one neutron into a proton and electron
- no change in mass number, but different element
- release of anti-neutrino (no charge, no mass)
2) b+ decay
b
C  115 B  e  e
11
6
- converts one proton into a neutron and electron
- no change in mass number, but different element
- release of neutrino
3) Electron capture
7
4
EC
Be  e  
 37 B  e
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Gamma Radioactivity
• Gamma radioactivity is composed of electromagnetic
rays. It is distinguished from x-rays only by the fact that it
comes from the nucleus. Most gamma rays are higher in
energy than x-rays and therefore are very penetrating.
Gamma rays are not charged particles like  and b particles.
A
Z
X*
A
Z
X

0 g
0
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• Gamma ray release
•
Gamma ray – high energy photon
– Examples
• Net effect is no change in mass number or atomic
number.
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GAMMMA (g) -ray
Is a form of pure electromagnetic radiation emitted from nuclei that have excess
energy. It is sometimes called gamma photon radiation.
Are photons emitted from unstable nuclei to rid themselves of excess energy.
Gamma photons are subatomic packets of pure energy. They are higher in energy
of ~ 1 x 10-12 J). with high frequency and more penetrating than the photons
that make up visible light.
When atoms decay by emitting  or b particles to form a new atom, the nuclei of
the new atom formed may still have too much energy to be completely stable.
GAMMMA RAYS AND X RAYS
Have the same properties except for their origin Gammas come from
within the nuclei of atoms X-rays come from outside the nuclei
Both are electromagnetic energy in the form of emitte photons
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27
2
5
Have the same properties except for their origin
Gammas come from within the nuclei of atoms X-rays
come from outside the nuclei
Both are electromagnetic energy in the form of
emitted photons
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27
g decay
3
2
g
He* 
 23 He  g
- conversion of strong to coulombic E
- no change of A or Z (element)
- release of photon
- usually occurs in conjunction with other decay
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Penetration of Matter
• Though the most massive and most energetic of radioactive
emissions, the alpha particle is the shortest in range because of
its strong interaction with matter. The electromagnetic gamma
ray is extremely penetrating, even penetrating considerable
thicknesses of concrete. The electron of beta radioactivity
strongly interacts with matter and has a short range.
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T. Norah Ali Al moneef
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Protons
Classification of Decays
b
e
EC
-decay:
•
•
•
•
emission of Helium nucleus
Z  Z-2
N  N-2
A  A-4
e--decay (or b-decay)
•
•
•
•
emission of e- and 
Z  Z+1
N  N-1
A = const
e+-decay

Neutrons
• emission of e+ and 
• Z  Z-1
• N  N+1
• A = const
Electron Capture (EC)
• absorbtion of e- and emiss 
• Z  Z-1
• N  N+1
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• A = const
Four types of radioactive decay
1) alpha () decay - 4He nucleus (2p + 2n) ejected
2) beta (b) decay - change of nucleus charge, conserves mass
3) gamma (g) decay - photon emission, no change in A or Z
4) spontaneous fission - for Z=92 and above, generates two smaller nuclei
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An Example….
Parent
U238
→
8 alpha + 6 beta =
92 protons
146 neutrons
?
An Example….
Parent
U238 → 8 alpha
8 {lose 2 protons} +
+
6 beta
6 (add 1 proton)
{lose 2 neutrons}
- 16 protons
- 16 neutrons
+ 6 protons
An Example….
Parent
U238 → 8 alpha
8 {lose 2 protons} +
{lose 2 neutrons}
- 16 protons
- 16 neutrons
- 32 atomic mass
+
6 beta
6 (add 1 proton)
+ 6 protons = - 10 protons
- 10 atomic number
An Example….
Parent
U238 → 8 alpha
8 {lose 2 protons} +
{lose 2 neutrons}
- 16 protons
- 16 neutrons
- 32 atomic mass
U238 – 32 = “X” 206
+
6 beta
6 (add 1 proton)
+ 6 protons = - 10 protons
- 10 atomic number
An Example….
Parent
U238 → 8 alpha
8 {lose 2 protons} +
{lose 2 neutrons}
- 16 protons
- 16 neutrons
- 32 atomic mass
U238 – 32 = “X” 206
92 protons – 10 protons = 82 protons
+
6 beta
6 (add 1 proton)
+ 6 protons = - 10 protons
- 10 atomic number
An Example….
Parent
U238 → 8 alpha
8 {lose 2 protons} +
{lose 2 neutrons}
- 16 protons
- 16 neutrons
- 32 atomic mass
U238 – 32 = “X” 206
92 protons – 10 protons = 82 protons
“X” 206 with 82 protons
+
6 beta
6 (add 1 proton)
+ 6 protons = - 10 protons
- 10 atomic number
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Which type of radioactive emission has a positive charge and weak penetrating
power?
(1) alpha particle
(3) gamma ray
(2) beta particle
(4) neutron
When a neutron is transformed into a proton what else is emitted
a) alpha
b) position
c) 1H
d) electron
e) none of these
What is the missing particle?
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A. Radioactive Decay
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Which of the following statements about alpha particles (α) is
correct?
A. They are massless particles.
B. They are electromagnetic wave.
C. They are traveling at the speed of light.
D. They will be deflected by electric and magnetic field.
There are two radioactive sources A and B, both of them have the
same number of active nuclei at the beginning. After 10 days, the
number of active nuclei in B is more than A. Which of the following
statements is correct?
A. The mass of A is larger than B. B. The mass of B is larger than A.
C. The half-life of B is longer than A. D. The half-life of A is longer than
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