INTRODUCTION TO 

RADIOACTIVITY AND 

RADIATION

1/18/2011 
BASIC CONCEPTS
The Atom

• It is the basic building block of matter• It consists of two components:

Electron(s)Nucleus
Electron

• Point particle (lepton), it is not made up o

smaller particles

• Has mass• Has an electrical charge -1 (1.6 x 10-19

coulombs)
Electron

• The energy levels of electrons in an atom 

referred to as shells.

L shellM shell

y

e

K shell

Energ

e

e

e

e

Nucleus
Electron

• Only a specific number of electrons is all

each shell (energy level).

• Electrons (like all particles) “want” to occ

lowest possible energy level.

p gy

• The number of electrons in the valence s

(highest occupied shell) determines the cproperties of the atom.

• When an electron moves (undergoes a t

to a lower energy level, it must release e
Electron

• When an electron fills a vacancy in an inner shell 

to a lower energy level), the released energy mighthe form of a characteristic x-ray.

ee

Ch t i t

e

e

Nucleus

Characterist
X-ray

• An x-ray is electromagnetic radiation (emr

emitted when an electron loses energy.

• X-rays are part of the electromagnetic spe

which includes radio waves, infra-red radi

visible light ultra violet radiation and gammvisible light, ultra-violet radiation and gamm

• X-rays (and gamma rays) have a high eno

energy to ionize atoms (remove electrons atoms) and are therefore considered a typionizing radiation.
X-ray

• X-rays can be treated as if they are particl

(called photons) or they can be treated as 

• Most of the time it is best to think of x-rays 

photons rather than waves.

• A photon is a packet of electromagnetic en• Photons have no mass or charge.• Unless they interact, they travel in straight 

the speed of light.
X-ray

There are two types of x-rays:1. Characteristic x-rays.

Produced by atomic electrons as they fall from (energy level) to a lower shell, e.g., L shell to K Monoenergetic. The energy depends on atomiMonoenergetic. The energy depends on atomi

2. Bremsstrahlung.

Produced by “free” electrons as they change dand slow down, e.g., electrons striking an x-ray target.Have a range of energies. Sometimes called cx-rays.
The Nucleus

• The nucleus forms the central dense core 

atom (ca. 10-12 cm diameter). It consists o

particles referred to as nucleons. There atypes of nucleons: protons and neutrons.

A n cle s contains at least one proton

• A nucleus contains at least one proton. 

• Most nuclei also contain one or more neut

p

p

n

n

n

p
Quarks

• Protons and neutrons are composed of qu• There are six different types of quarks.

u upd down

t top (truth)b bottom (beauty)c charms strange

• Quarks have an electrical charge, e.g., up 

have a charge of +2/3 while down quarks charge of -1/3
The Nucleus

Proton• Positive charge (+1)• Three quarks: u (+2/3)

u (+2/3) 

d

( )

d (-1/3)

Neutron• No charge (neutral)• Three quarks: u (+2/3)

d (-1/3)d (-1/3)

d
Nuclide

• A nuclide is an atom or a group of atoms t

a specific combination of neutrons and pro(e.g., six protons and six neutrons).
Describing a Nuclide

A nuclide can be described by specifying:1. The number of protons. The number of p

referred to as the atomic number and is g

symbol Z.

The number of protons is the same as the number of electrons.The atomic number specifies the element=1 (hydrogen), Z = 2 (helium), Z =3 (lithiu
Describing a Nuclide

A nuclide can be described by specifying:1. The number of protons (the atomic numb2. The number of neutrons. The number of n

is referred to as the neutron number and the symbol N.The neutron number has nothing to do wielement. If an atom has two protons, it is It might have 0, 1, 2, 3 or more neutrons. 
Describing a Nuclide

A nuclide can be described by specifying:1. The number of protons (the atomic numb2. The number of neutrons (the neutron num3. The total number of protons and neutrons

total number of nucleons is referred to as atomic mass number and is given the sym

A = Z + N 
Symbolizing a Nuclide

A nuclide can be symbolized as follows:

M

AZ

Atomic mass number

Symbol for chemical el

Atomic number

For simplicity, it is more common to ignore thnumber and follow the symbol for the elemethe atomic mass number:

M -

A
Symbolizing a Nuclide

Examples:

C

12

6

6 protons and 6 neutrons, refecarbon twelve, also symbolize

C

13

6

6 protons and 7 neutrons, refecarbon thirteen, also symboliz

C

14

6

6 protons and 8 neutrons, refecarbon fourteen, also symboliz
Two Types of Nuclides

1. Stable nuclides.2. Radionuclides.

C-12 ?C-13C-14
Two Types of Nuclides

1. Stable nuclides.2. Radionuclides.

C-12 stable nuclideC-13C-14 ?
Two Types of Nuclides

1. Stable nuclides.2. Radionuclides.

C-12 stable nuclideC-13 ?C-14 radionuclide
Two Types of Nuclides

1. Stable nuclides.2. Radionuclides.

C-12 stable nuclideC-13 stable nuclideC-14 radionuclide
Three Types of Nuclides

1. Isotopes. Different nuclides with the sam

number of protons, i.e., different nuclides same element. U-235, U-238

2. Isotones. Different nuclides with the sam

number of neutrons. C-14, N-15

3. Isobars. Different nuclides with the same 

mass number. Sr-90, Y-90
Mass

• Basic unit: kilogram• Special unit: atomic mass unit (u or amu

1 amu /1/12 mass of C-12

• Mass of a proton. 1.0073 amu• Mass of a neutron. 1.0087 amu • Mass of an electron. 0.000549 amu • Mass of H-1 (proton + electron). 1.0078 a
Mass

• Mass of C-12 is 12.000 amu even though 

sum of the masses of its individual comp(6 protons and 6 neutrons ) is greater tha12.000 amu.

• The explanation is that mass is lost when 

components are brought together to form The mass is lost in the form of released e
Energy

• Energy can be described as the ability to • Two kinds of energy: potential energ

kinetic energy

• Kinetic energy is the energy of motion (1/

• Basic unit: joule (J)• Special unit: electron volt (eV)

1 eV = 1.6 x 10-19 J
Relationship Between Mass and Ene

• Mass can be converted into energy and e

can be converted into mass.

E = m c

2

E is energy in joulesE is energy in joulesm is mass in kilogramsc is the speed of light (meters per seco

• E = 931.5 m

E is the energy in MeVm is the mass in amu
Relationship Between Mass and Ene

• The mass of atomic constituents can be e

as energy.

• Mass of proton . 931.5 MeV• Mass of neutron . 931.5 MeV• Mass of electron = 931.5 MeV/amu x 0.00

= 0.511 MeV= 511 keV
Binding Energy

• The binding energy of a nuclide is the ene

released when the nuclide is formed from constituent parts, i.e., protons, neutrons aelectrons.

• It is the energy equivalent of the mass def

It is the energy equivalent of the mass def

• The mass defect is the difference between 

mass of the nuclide and the mass of the constituent parts.
Binding Energy

• For example, the mass defect of C-12 is th

of 6 protons, 6 electrons and 6 neutrons mmass of C-12:

= 6(1.0078 amu) + 6(1.0087 amu) - 

= 0.099 amu

• As such, the total binding energy is:

= 0.099 amu x 931.5 MeV/amu= 92.2 MeV
Binding Energy per Nucleon

• The binding energy per nucleon is the tota

energy of the nuclide divided by the numbnucleons (the atomic mass number).

• As an example, the binding energy per nu

C-12 is approximatel

y 7.7 MeV 

(92.2 MeV 

pp y (

• The production of nuclides whose binding 

per nucleon is greater than that of the rearesults in the release of energy. The followgraph indicates that energy is released by fusion of nuclides of low atomic mass numthe fission of nuclides with high atomic manumbers. 
Binding Energy per Nucleon
Binding Energy of a Particle

• The binding energy of a particle (e.g., elec

neutron, proton) is the energy that is requremove the particle from the atom.

• It depends on the type of particle (e.g., ele

vs neutron) and the atom (e g H

-2 vs P

vs. neutron) and the atom (e.g., 

H

2 vs. P

• It is not energy that is possessed by the p• For example, the neutron binding energy i

is the energy released when a neutron is absorbed by C-12 to form C-13. The same is required to remove a neutron from C-13
THE CHART OF THE 

NUCLIDES
Chemistry

• Chemists are interested in electrons beca

number of electrons and their distribution electron shells determines the chemical pof the atom.

• The Periodic Table organizes the various 

according to the number and distribution electrons.

• The Periodic Table therefore illustrates th

chemical properties of the elements. 
Physics

• Physicists are interested in the nucleus b

the number and distribution of protons anneutrons determines the radioactive propthe different nuclides.

• The Chart of the Nuclides organizes the v

nuclides according to the number and disof their protons and neutrons.

• The Chart of the Nuclides therefore illust

radioactive properties of the nuclides. 
Chart of the Nuclides

• Over the years there have been a numbe

different versions of the chart. Today, the version that is likely to be encountered is developed by Emilio Segre. In fact, it useknown as the Segre Chart.

• This chart is a checkerboard. The rows in

the atomic number (number of protons). Tcolumns indicate the neutron number. Earepresents a different nuclide.

• The following illustrates the lower left han

of the chart.
7

65

Z 4

Chart of the Nuclides

321

0 1 2 3 4 5 6 7 

N 
7

65

Z 4

Chart of the Nuclides

321

0 1 2 3 4 5 6 7 

N 

?
7

65

Z 4

Chart of the Nuclides

321

0 1 2 3 4 5 6 7 

N 

H-1 ?
7

65

Z 4

Chart of the Nuclides

321

0 1 2 3 4 5 6 7 

N 

H-1 H-2 ?
7

65

Z 4

Chart of the Nuclides

321

0 1 2 3 4 5 6 7 

N 

?

H-1 H-2 H-3
7

65

Z 4

Chart of the Nuclides

321

0 1 2 3 4 5 6 7 

N 

?

H-1 H-2 H-3

He-2
7

65

Z 4

Chart of the Nuclides

321

0 1 2 3 4 5 6 7 

N 

?

H-1 H-2 H-3

He-2 He-3
7

65

Z 4

?

Chart of the Nuclides

321

0 1 2 3 4 5 6 7 

N 

H-1 H-2 H-3

He-2 He-3 He-4
7 Chart of the Nuclides

65

Z

4

C-12

321

0 1 2 3 4 5 6 7 

N 

H-1 H-2 H-3

He-2 He-3 He-4
Chart of the Nuclides

• The most basic thing that the chart does 

distinguish the stable nuclides from the radionuclides by the use of color.

• The stable nuclides are colored gray - o

some part of the block is colored gray.

• Other colors are used to indicate other 

characteristics of the nuclides, but they cignored. 
7

65

Z 4

C-12

B-10

C-13N-14 

Be-9

B-11

321

0 1 2 3 4 5 6 7 

N 

H-1 H-2

He-3 He-4

Li-6 Li-7
Chart of the Nuclides

• The stable nuclides are arranged so that th

a gray line called the Line of Stability

Z

N
7

65

Z 4

C-12

B-10

C-13N-14 

Be-9

B-11

nes

321

0 1 2 3 4 5 6 7 

N 

H-1 H-2

He-3 He-4

Li-6 Li-7

Isotopes

Isoton
CHARACTERISTICS OF 

STABLE NUCLIDESSTABLE NUCLIDES
Common Characteristics of Stable N

1. Atomic Number Must be 

# 83

There are radionuclides for every element those elements with 83 or fewer protons hstable nuclides. 

Protons in the nucleus repel each other by electromagnetic force. This destabilizes tnucleus. Neutrons help overcome this repbecause they attract each other and they the protons in the nucleus by the strong fo
Common Characteristics of Stable N

1. Atomic Number Must be 

# 83

Protons on opposite sides of a large nucleeach other because the electromagnetic fexerted over large distances. 

H th t f l tHowever, the s

trong 

force only opera

tes o

short distances within the nucleus. As a result, the number of neutrons needestability increases faster than the atomic nthe greater the atomic number, the greateneutron to proton ratio must be for stability
Common Characteristics of Stable N

1. Atomic Number Must be 

# 83

It is expected that as yet undiscovered veatomic number elements will possess stabnuclides and form an “island of stability.”

Z

N

83 Hypo

island 
Common Characteristics of Stable N

2. Stable Nuclides with Small Atomic Num

tend to have Equal Numbers of Protons Neutronse.g., H-2, He-4, Li-6, B-10, C-12, N-14, O-

Stable Nuclides with High Atomic Numberhave More Neutrons than Protonse.g., Pb-206, 82 protons and 124 neutron
Common Characteristics of Stable N

3. Stable Nuclides tend to have an Even 

of Protons and/or an Even Number of There are 266 known stable nuclides. 

159 Even Z Even N

Even

Z Even

N

53 Even Z Odd N50 Odd Z Even N

4 Odd Z Odd N
Common Characteristics of Stable N

3. Stable Nuclides Tend to have an Even 

of Protons and an Even Number of NeThe neutrons in the nucleus pair up - onin one direction and the other spinning in 

opposite direction. If there is an even number of neutrons, thpair up.Similarly, the protons in the nucleus pair each other.
Common Characteristics of Stable Nuc

4. Magic Numbers

Certain numbers of neutrons and protons particularly stable. These “magic numbersame for neutrons and protons. All the m

n mbers are e en The aren

umbers are

e

ven. They are:

2, 8, 20, 28, 50, 82, 126.

On the chart of the nuclides, the magic nare bounded with extra heavy lines. 
7

65

Z 4

C-12

B-10

C-13N-14 

Be-9

B-11

Chart of the Nuclides

321

0 1 2 3 4 5 6 7 

N 

H-1 H-2

He-3 He-4

Li-6 Li-7
Common Characteristics of Stable Nuc

4. Magic Numbers

Like the electrons of an atom, the neutronucleus exist in different energy levels. Tenergy levels are referred to as shells.

The magic numbers are the numbers of nrequired to fill the neutron shells and the protons required to fill the proton shells.When the shells are filled, the nucleus hadegree of stability - analogous to the atostability associated with filled electron sh
RADIOACTIVE DECAY
Radioactive Decay

• Radionuclides undergo a process referre

decay (also referred to as transformation transition).

• During decay, a radionuclide changes its 

of protons and its number of neutrons to of protons and its number of neutrons to

stable combination - it becomes a differenuclide.

• In the process, some mass is converted 

energy. This energy is carried off by the of the decay. The products of the decay energy are referred to as radiation.
Radioactive Decay

• Decay represents movement towards th

stability on the chart of the nuclides.

Alp

Positron (

$

+) decay

or

Electron capture (EC or

,

)

Z

N

Beta (

$) decay

Electron capture (EC or

,

)
Radioactive Decay

• Other less common processes accompl

same things, e.g.:

Spo

fis

Z

N

Neutron emission (n)
Radioactive Decay

• Sources of radionuclides:

Accelerator 

d d

Natural

radionu

tran

produce

Z

N

Fission products (produced by nuclear fission e.g., in reactorsand activation products producby neutron capture

pro

duce

d

radionuclides

p
MAJOR TYPES OF DECAY:

BETA DECAY

ALPHA DECAY

POSITRON DECAY

ELECTRON CAPTURE
BETA DECAY
Beta Decay

• A beta particle is an electron “born” in the • Beta emission is characteristic of nuclides 

the line of stability - they have too many neutrons to be stable.

• In beta decay a neutron is converted into 

(a down quark is converted into an up qua

• In beta decay an antineutrino is also prod

(L). 
Beta Decay

• A neutrino, like an electron, is a point part

has no charge. Any mass that it might havextremely small. Although a neutrino or antineutrino can possess considerable enthis is not a concern because they are un

y 

transfer this energy to the matter they travthrough.

• For the purpose of radiation protection, ne

and antineutrinos can be ignored.
Beta Decay

• In beta decay, a parent radionuclide deca

decay product (daughter), a beta particle, antineutrino:

ZPA Z+1DA + $ + Z Z+1 $

• The energy released in the decay process 

distributed between these decay products
Beta Decay

ZPA Z+1DA + $ + 

• In pure beta decay (no gamma emission), 

energy given to the decay products takes of kinetic energy. 

• This energy can be distributed between th

products in an infinite variety of ways.

• As an average, the beta particle gets 1/3 o

energy and the antineutrino gets 2/3 of thenergy. The recoil decay product gets sufflittle energy that it is usually ignored.
p

n

n

p n p

Parent Radionuclide
Beta

p

p p

n

n

p

Decay product

Antineutrino
Beta Decay

ZPA Z+1DA + $ + 

• When the beta particle energy of a radion

referred to, it is usually done by specifying maximum kinetic energy that the beta par

could have (i.e., the antineutrino gets no e

• Sometimes the average energy is specifie

average beta energy is approximately 1/3 maximum.

• Keep in mind that a “high energy beta em

emits many very low energy beta particles
Beta Decay

• A typical beta spectrum:

Number

Beta Energy

of Beta 

Particles

Maximu

ene

Average 

beta energy
Beta Decay

Example:

15P32 16S32 + $ + L 

• Phosphorous-32 (15 protons and 17 neutr

d i t th t bl lid lf 32 (1decays into the stable nuclide sulfur-32 (1

protons and 16 neutrons).

• P-32 is a high energy beta emitter (1.71 M

maximum). 
Beta Decay

• On the chart of the nuclides, beta decay r

moving diagonally one up to the left - a loone neutron and an increase of one proto

S-32

16

P-32

14.26 d

$ 1.710no (

Z

1615

N 16 17
Beta Decay

• It is also common to depict radioactive de

decrease in energy as follows:

P-32

$ 1.71 MeV

Energy
ALPHA DECAY
Alpha Decay

• An alpha particle is a helium-4 nucleus (tw

protons and two neutrons). It is sometimesymbolized as follows

"2

4

• Alpha decay is characteristic of nuclides w

atomic numbers greater than 83. For exanuclides of high Z elements such as poloradium, uranium, thorium and plutonium, be alpha emitters. They have too many pto be stable.
Alpha Decay

• There are exceptions. A few alpha emitter

atomic numbers less than 83 (e.g., Gd-14there are many beta emitters with atomic numbers greater than 83 (e.g., Ra-228, P

AZP Z-2 D A-4 + "

• The kinetic energy released in the decay p

is distributed between the decay product aalpha particle. There is no neutrino.
Alpha Decay

• In pure alpha decay (no gamma emission)

energy given to the products of the decay takes the form of kinetic energy. In this caenergy can only be distributed in one way the alpha particle and the decay product.

• As a result, alpha particles are monoenerg

(unlike beta particles which have a range oenergies up to some specific maximum). Fexample, all alpha particles emitted by Po-have a kinetic energy of 6 MeV. Only a smfraction of the beta particles emitted by P-an energy of 1.7 MeV.
Alpha Decay

Parent Radionuclide
Alpha Partic

Alpha Decay

Decay Product 
Alpha Decay

• A typical alpha spectrum:

Number 

of Alpha 

Particles

Alpha Energy

• Alpha energies typically range from 4 to 8 

The shorter the half-life, the higher the en
Alpha Decay

Example:

94Pu 239 92U 235 + "

• The decay products produced in alpha de

The decay products produced in alpha de

usually radionuclides as well (e.g., U-235
Alpha Decay

• On the chart of the nuclides, alpha decay 

in moving diagonally two down to the left of two neutrons and two protons.

" 5 157

Pu-239

94 24110 a

" 5.157no (

Z

92

N

93

U-235
Alpha Decay

• It is common to depict alpha decay as a d

in energy as follows:

U-235" 5.157 MeV

Energy
GAMMA RAY EMISSION
Gamma Ray Emission

• Gamma rays are electromagnetic radiatio

from the nucleus when it moves to a lowelevel (x-rays are emitted by electrons whemove to a lower energy level).

F t b itt d d i d 

•

For a gamma ray 

to 

be emitt

e

d

during 

dec

decay product nucleus must be left in an estate. When the decay product nucleus dexcites, a gamma ray can be emitted. Thdepicted as a two step process.
Gamma Ray Emission

Example:

88Ra 226 86Rn (excited) + 

"

222

86

222 R

It is easier to depict this two-step proces

226 222

88Ra 86Rn + 

" + 

(

222

• Even though the gamma ray actually com

the decay product nucleus (Rn-222), it is ato the parent nuclide (Ra-226). This is donbecause the gamma ray is produced at thmoment that the parent decays.
Gamma Ray Emission

• An energy diagram can also be used to d

emission of the gamma ray:

Ra-

" 4.59 MeV

Rn-222

4.59 MeV

Energy Rn-222 (exc

( 0.186 MeV
Gamma Ray Emission

• Ra-226 only emits a gamma ray in a fract

decays.

Ra-

" 4.59 MeV

Rn-222

4.59 MeV

Energy

" 4.78 MeV

( 0.186 MeV
Gamma Ray Emission

Parent Radionuclide
Alpha Partic

Gamma Ray Emission

Decay Product 

(Excited)
Alpha Partic

Gamma Ray Emission

Decay Product 

Gamma Ra
POSITRON DECAY 

AND

ELECTRON CAPTURE
Positron Decay and Electron Captur

• Positron decay and electron capture are d

modes that are characteristic of nuclides aline of stability - they have too many protstable.

• In each case a proton is converted into a 

In each case, 

a proton is converted into

a 

the decay product is the same for both mo

• Some nuclides only decay by positron em

some nuclides only decay by electron capsome nuclides decay both ways (positron in a certain percentage of the decays and capture the rest of the time).
POSITRON DECAY
Positron Decay

• A positron is an antimatter electron “born” 

nucleus. It has the same mass as an elecit has a positive charge.

• Positron emission is characteristic of nucl

above the line of stability - they have too above the line of stability - they have too 

protons to be stable.

• In positron emission a proton is converted 

neutron (an up quark is converted into a dquark).

• A neutrino is also produced (L). 
Positron Decay

• In positron decay, a parent radionuclide d

into a decay product (daughter), a positroneutrino:

ZPA Z-1 DA + $+ + 

• Positrons usually have more energy than 

particles - their positive charge causes thbe repelled by the positive charge of the nin which they were born. In other words, treceive an extra “kick” when they leave thnucleus.
Positron Decay

• Every time a positron is produced, two 51

photons (annihilation radiation) will also bproduced). These photons are rarely mendecay data tables or other sources of infosuch as the chart of the nuclides.

• When the positron has given up all, or alm

of its kinetic energy, it will combine with an electron – the electron and positron are atto each other because of their opposite ch
Positron Decay

• The electron and positron annihilate each 

their mass is completely converted into electromagnetic energy.

• The annihilation of the electron produces 

k V h t d th ihil ti f th keV photon and the annihilation of the pos

produces a 511 keV photon. The two 511 photons head off in opposite directions (1degrees apart).
Positron Decay

• It is common to depict positron decay as 

decrease in energy as follows:

Na

Ne-22

$+ 0.545 MeV

Energy 1275

0

(
Positron Decay

• On the chart of the nuclides, positron dec

results in moving diagonally one down to - a loss of one proton and a gain of one n

2.60 a

Na-22

11

Ne-22

$+ 0.545

( 1275 Z

1110

N 11 12
p

n

n

Positron Decay

p p

n

p

Parent Radionuclide
p

n

n

Positron

Positron Decay

p n p

Decay Product

Neutrino
p

p

n

n

p

Positro

Positron Decay

n

p p

Decay Product

Neutrino
Positron Decay

Positron ($+)

Electron (e-)

- an innocent bystan
Positron Decay

Positron has given up all its kinetic energy.

Positron ($+)

Electron (e-)

- an innocent bystan
Positron Decay

Because of their opposite charges, the positelectron are attracted to each other.

Positron ($+)

Electron (e-)
Positron Decay

Positron and electron annihilate each other.

511 keV ph

511 keV photon

511 keV ph
ELECTRON CAPTURE
Electron Capture

• In electron capture (EC or ,) the nucleus 

an orbiting electron. 

• Electron capture is characteristic of nuclid

above the line of stability - they have too 

protons to be stableprotons to be stable.

• In electron capture a proton is converted i

neutron (an up quark is converted into a dquark).

• A monoenergetic neutrino is also produce
Electron Capture

• The captured electron comes from one of 

inner shells (e.g., K capture).

ZPA Z-1 DA + L 

Example

I 53

125

52Te 125 + L 
Electron Capture

• On the chart of the nuclides, electron cap

results in moving diagonally one down to - a loss of one proton and a gain of one n

59.5 d

I-125

53

Te-125

EC( 35.49 Z

5352

N 72 73
Electron Capture

• It is common to depict electron capture as 

decrease in energy as follows (in this casgamma ray is also emitted):

I-1

Te-125

EC

Energy 35.49

0

(
SPONTANEOUS FISSION
Spontaneous Fission

• A number of nuclides with large atomic ma

numbers undergo spontaneous fission (sfexample, many nuclides of plutonium can undergo spontaneous fission.

• Their primary mode of decay is usually alp

emission and they tend to have an even nof protons.

• Fission is a very effective method to rapid

change the number of neutrons and protoa more stable combination.
Spontaneous Fission

• In fission, the parent radionuclide usually 

two fission products.

• The split is not uniform. One of the fission 

usuall

y has an atomic mass number of 80 

(e.g., Sr-90) while the other typically has amass number of 130 – 160 (e.g., Cs-137)

• The fission products have considerable ki

energy.

• Several neutrons are also emitted (usually 
Spontaneous Fission

Z

P

A FP 80-120 + FP + (

130-160

Example 

(one of man

y possible wa

ys that C

(y y

can fission):

Cf 98 252 Tc 112 + Cs + 

137

43 55
MULTIPLE MODES OF DECAY
Multiple Modes of Decay

• Some nuclides decay by more than one m• For example, Cu-64 can undergo beta de

electron capture or positron emission. Approximately 40% of the time, it undergo

d 40% f th ti it d l tdecay, 40% o

f the time it un

dergoes elec

t

capture and 20% of the time it undergoes emission.
Multiple Modes of Decay

• Potassium-40 can decay by one of two m

" 5.157no 

(

20

Ca-40

96.94

K-40

1.28 E9 a

Z

EC, B18

N

19

Ar-40

99.6
Multiple Modes of Decay

• It is common to depict decay as a decreas

energy as follows:

K-40

EC

(10.72%)

1461

Ar-40

(

$

(89.28%)
CHART OF THE NUCLIDES

ADDITIONAL INFORMATION

- ADDITIONAL INFORMATION 
Gray indic

stable nuc

Percent a(by mass

Chart of the Nuclides

F indicates neutron cross sections in barns

Half-life 

P-32 emits particle with MeV maxim

P-32 does gamma ra

Isotopic mass in amu 
Chart of the Nuclides

Black box indicates naturally occurring rad

Grey bboth pe

abunda

Two major decay 

abundahalf-life very loradionufound i

modes: beta emission and electron capture

Minor (very weak) decay mode: positron emission
Black box 

indicates naturally occurring radionuclide -historical name is 

Chart of the Nuclides Indic

emisbetamaxenerMeV othemax

“Radium B”

Indicates that at least three gamma rays are emitted351.9 keV, 295.2 keV and 242.0 keV

maxenerMeV
Chart of the Nuclides

Isomeric Transition

Gamma ray at 140.5 keV

Blue uppeblock half-

Gree

Metastable state (Tc-99m) Ground state 

Weak (infrequent) beta decay

Greelowereferneutsecti
Q Values
Q Values

The Q value is the total energy change (usuMeV) for a reaction or decay event. It is the energy equivalence of the mass of treactants (or parent radionuclide) minus thareaction products (or decay product).

p ( yp )

A positive Q value indicates that the reaction exothermic. All radioactive decay processes positive Q value.A negative Q value indicates that the reactioendothermic and that energy must come frothe reactants (usually as kinetic energy). 
Q Values

When mass is lost during radioactive decayis lost in a reaction, the energy released is tvalue. It is calculated by Einstein’s equation E = m

lb d

can also be expressed as:

Q (MeV) = m (amu) x 931.5 (MeV/amu

Where m is the mass difference between thradionuclide (or reactants) and the decay pr
Q Values

In practice, Q is calculated in one of two wa

1. Using the actual masses in amu2. Using ) (delta) values in MeV
Q Values – calculations using mass

Alpha Decay: Q = 931.5 (M

p – M

d – M

"

)

Beta Decay: Q = 931.5 (M

p – M

d

)

Positron Decay: Q = 931.5 (M

p – M

d – 2M

El t C t Q 931 5 (M

M

) BE

Elec

tron 

Cap

ture: 

Q = 931.5 (M

p

–

M

d

)

– BE

M

p is the atomic mass of the parent (amu)

M

d is the atomic mass of the decay produc

M

e is the mass of an electron (0.000549 am

M

" is the mass of an alpha (4.0026 amu)

M

e is the binding energy of the electron (M
Q Values – calculations using 

) valu

The delta value is the difference between a atomic weight/mass (M) and its atomic mass (A) expressed in MeV. The delta values for different nuclides are looked up in tables.

) 931 5 (M A)

= 931.5 (M

– A)

The delta values provide a more convenient calculate the Q values than using actual ma
Q Values – calculations using 

) valu

Alpha Decay: Q = 

)

p

–

)

d

–

)

"

Beta Decay: Q = 

)

p

–

)

d

Positron Decay: Q = 

)

p

–

)

d – 1.022

El t C t Q

)

) BE

Elec

tron 

Cap

ture: 

Q = 

)

p

–

)

d

– BE

e

)

p is the delta value of the parent (MeV)

)

d is the delta value of the decay product (

)

" is the delta value of an alpha/He-4 (2.42 

BE

e is the binding energy of the electron (M
The Q Value and Alpha Decay

When two particles of mass m and M (e.g., an alpha and the recoil nucleus of the decay product) share a energy (Q), the kinetic energy of the two particles is

m

M
Q Values – example using mass

When a boron-10 nucleus absorbs a thermal neutrobecomes B-11 in an excited state. The excited B-11 can split to produce a Li-7 nucleus and an alpha paIn 4% of these reactions, the Li-7 is left in the grouna result, the Li-7 and alpha particle share the maximenergy possible:

n + B-10 Li-7 + 

"

However, 96% of the time the Li-7 is left in an exciteThis leaves the Li-7 and alpha particle less kinetic eshare.

n + B-10 Li-7* + 

"
n + B-10 Li-7 + "

Mass of neutron = 1.00866 amuMass of B-10 = 10.01294 amu

Mass of ne tron and B 10 11 0216 amQ Values – example using mass The energy to be shared between the two particles value. It is the energy associated with the decrease occurs in the reaction and is calculated as follows:Mass of neutron and B-10 = 11.0216 amu

Mass of Li-7 = 7.01600 amuMass of alpha particle = 4.0026 amuMass of Li-7 and alpha = 11.0186 amuDecrease in mass = 0.003 amuQ value = 0.003 x 931.49 MeV/amu = + 2.79 MeV 
Q Values – example using mass

The 4% of the time that the lithium is left in the grounkinetic energies of the lithium and alpha particles are

n + B-10 Li-7 + 

"

If the neutron that initiated the reaction had kinetic eenergy would have to be included in the Q value.
Q Values – example using 

) values

Positron Decay

Na-22 

 Ne-22 + 

$+ + 

L

Q = 

)

p

–

)

d – 1.022

) is the delta value of the parent (MeV

)

p is the delta value of the parent

(MeV

)

)

d is the delta value of the decay product (

Q = 

)

p

-

)

d - 1.0

= - 5.182 - (-8.025) - 1.0= 1.821 MeV

Since the Q value is positive, this process is exothermic and can occur spontaneously. 
Q Values – example using 

) values

When Na-22 undergoes positron decay, a 1gamma ray is emitted. As such it is impossibof the Q value energy to be given to the posneutrino).

Na-22 1.821 Me

1.275 MeV

0 MeV

$

+ 0.545 MeV

(

Ne-22Ne-22
Effective Atomic Number
Effective Atomic Number

In some situations, the “effective atomic numa compound (e.g., H

2O) is of importance. Th

following equation has been widely employecalculate the effective atomic number.

ZEff is the effective atomic number of the comA

n is the fraction of the total electrons in a ma

contributed by element n Zn is the atomic number of element n
Effective Atomic Number

Water, air and human tissue have effective anumbers on the order of 7.5 to 8.