Basic concept of radiation, radioactivity, radiation dose

Training Course on Radiation Protection for Radiation
Workers and RCOs of BAEC, Medical Facilities & Industries
24 - 28 October 2021
Training Institute
Atomic Energy Research Establishment, Savar, Dhaka
Institute of Nuclear Science and Technology
Atomic Energy Research Establishment
Ganakbari, Savar, Dhaka
E-mail: dpaulbaec@yahoo.com
BASIC CONCEPT OF RADIATION, RADIOACTIVITY,
RADIATION DOSE AND THEIR UNITS

Atomic Structure
proton neutron electron

3
Classification of Atom
The complete classification of any atom is given by
where A is the mass number, Z is the atomic number and X
stands for the chemical symbol of the element.
Atomic number (z) = Number of proton(s)
Mass number (A) = Number of protons and neutrons
Example: for Cobalt we write
X
A
Z
60
60
60
27 

 Co
Co
Co

4
Isotope
; Z=8; N=5
; Z=8; N=6
; Z=8; N=7
; Z=8; N=8
; Z=8; N=9
O
13
8
O
14
8
O
15
8
O
16
8
O
17
8
For Example:
Isotopes of Oxygen: ; Z=6; N=5
; Z=6; N=6
; Z=6; N=7
; Z=6; N=8
; Z=6; N=9
C
11
6
C
12
6
C
13
6
C
14
6
C
15
6
Isotopes of Carbon:
All atoms having the same number of protons but different number
of neutrons are called isotopes of the same element.
Consequently, their mass numbers are different.

5
Radioactivity
Radioactivity was discovered in 1896 by A. H. Becquerel.
A few naturally occurring substances consists of unstable
atoms. They undergo spontaneous transformations into
more stable product atoms.
Such substances are said to be radioactive and the
transformation process is known as radioactive decay.
Radioactivity is the change of one type of atom into
another with the emission of radiation (in the form of
charged particles and gamma rays).
All meaningful measurements require unit.

Radiation
Radiation is the emission or transmission of energy in the
form of waves or particles through space or through a
material medium.
The two general classifications of radiation are ionizing and
nonionizing.
Ionizing radiation is capable of ionizing an atom.
Nonionizing radiation lacks the ability to create ions.
 Non-ionizing radiation : ultraviolet light,
radiowaves, microwaves etc.
 Ionizing radiation : X-ray, gamma ray etc.

Ionization
-1
+1
Radiation path
ejected electron
Ionized atom

NON-IONIZINGRADIATION IONIZINGRADIATION
THE ELECTROMAGNETIC SPECTRUM
RADIOFREQUENCY MICROWAVES INFRARED UV
VISIBLELIGHT
X-RAYS
GAMMA
COSMIC
RADIATION
LOWER FREQUENCY HIGHER FREQUENCY
LONGER WAVELENGTH SHORTER WAVELENGTH
LESS ENERGY MOREENERGY
Radiation

Alpha Radiation
Alpha particle charge +2
Alpha particles are positively charged
particles. They are easily stopped by
paper or skin and are only hazardous if
alpha-emitting materials are breathed
into the body.
Alpha radiation is not considered an external exposure problem.
Radium
Ra226
88 protons
138 neutrons
Radon
Rn222
86 protons
136 neutrons
+
2 protons
2 neutrons
a
He4

10
88Ra226 (T1/2 = 1602 yr)
a2 = 4.78 MeV (94%)
a1 = 4.59 MeV (6%)
 = 0.19 MeV
86Rn222
Example of an Alpha Decay: Radium-226

Beta Radiation (-ve Beta Decay)
Beta particle charge -1
 Beta particle may be considered
to be equivalent to an electron.
 Its penetration in any absorber
will be much greater than that of an
alpha particle.
 Beta radiation is considered a
slight external hazard.
 Beta radiation refers to - particles.
Example of Beta Decay – Phosphorus-32 (T½=14.3 d)
15P32
16S32 + - + Energy

Gamma radiation
Gamma radiation
Gamma rays are electromagnetic radiations with short
wavelengths and thus high energy.
They are very penetrating and heavy shielding
materials like lead and concrete are needed to stop
them.

13
27Co60 (T1/2 = 5.3 yr)
2 = 1.332 MeV
- = 0.31 MeV
1 = 1.173 MeV
28Ni60
Example of Gamma Emission – beta decay of Cobalt-60

Neutron Radiation
americium-241 neutron
beryllium
alpha particle
 Neutrons are uncharged particles and are capable of
considerable penetration in matter.
 They make the nucleus of an atom unstable.
 They do not produce ionization directly, but their interaction
with atoms can give rise to a, ,  which produce
ionization.
Example of neutron source is Americium-Beryllium
4Be9 + 2He4
6C12 + 0n1

15
Beta Plus Radiation
 Beta plus radiation (+) consists of particles which are similar
to beta particles except that they are positively charged.
 + particles are often referred to as positrons.
 The + decay is a process where by a proton in nucleus
spontaneously transform into a neutron resulting in the
emission of a positive beta particles and a neutrino.
Sodium
Na22
11 protons
11 neutrons
Neon
Ne22
10 protons
12 neutrons
+ β+
(beta (+) particle)

16
11Na22 (T1/2 = 2.6 yr)
+ = 1.81 MeV (0.54 + 1.27)
(0.05%)
+ = 0.54 MeV
 = 1.27 MeV
10Ne22
Example of a Positive Beta Decay-Sodium-22

X-ray production (1)
characteristic
X-rays
If the normal electron arrangement is altered through
ionization of an inner electron, the electron begin a
series of transition to vacancies in the lower shell.
It is useful as a tool for identifying unknown elements.

X-ray production (2)
bremsstrahlung
When fast-moving electrons are slowed in materials
they emit radiation called bremsstrahlung or braking
radiation.
Bremsstrahlung or X-radiation is identical in its properties
to gamma radiation.
Bremsstrahlung
sources should
be regarded as
gamma sources
from the point of
view of radiation
protection.

X-ray tube
anode
cathode
X-rays are just bremsstrahlung.
Most of the energy carried by the electrons is transformed
into heat and only about 1% is transformed into X-rays.

Units of Radioactivity (Activity)
 The amount of a radionuclide
 Old unit: Curie (Ci),  SI unit: Becquerel (Bq)
Curie (Ci): The radioactivity of one gram of radium was
called one curie. Subsequently, the curie was defined as:
1 Ci = 3.7 x 1010 dps
Becquerel (Bq): The SI unit of radioactivity is called
Becquerel (Bq) which is defined as one disintegration per
second.
1 Bq = 1 disintegration per second
Activity concentration:
Becquerel per cubic metre
Becquerel per litre
Becquerel per Kg

Multiples & prefixes (Activity)
Multiple Prefix Abbreviation
1 - Bq
1,000,000 Mega (M) MBq
1,000,000,000 Giga (G) GBq
1,000,000,000,000 Tera (T) TBq

22
Units Associated with Radiation Protection
 Based on the effect of X- and Gamma radiation on air, the
first widely used radiation unit was the Roentgen.
Roentgen – the former system of exposure unit where
1 R = 2.58 x 10-4 C/Kg of air
 This unit had several limitations and two further units, the
Rad and Rem, were introduced.
 More recently, these two units have been replaced in the
SI system by the Gray and the Sievert, respectively.

23
Absorbed Dose - energy deposition in any medium
by any type of ionizing radiation.
Gray - SI unit of absorbed dose.
1 joule of energy absorbed from any ionizing
radiation on 1 kg of any material.
1 Gy = 1 J/kg.
Rad - former unit of absorbed dose.
1 rad = 0.01 J/kg or
1 rad = 100 ergs/g

24


Fractions & prefixes (Dose)
Fraction Prefix Abbreviation
1 - Sv
1/1000 milli (m) mSv
1/1,000,000 micro () Sv

Dose-rate
Dose - rate = Dose/Time
Example :
 Sv/hour
 mSv/hour

Quantity Old unit SI unit Conversion
Activity curie (Ci) becquerel (Bq) 1 Ci=3.7 x 1010Bq
Absorbed rad gray (Gy) 1 rad = 0.01 Gy
Dose
Equivalent rem sievert (Sv) 1 rem = 0.01 Sv
Dose
Non-SI Units

28
Radiation Weighting Factor
Radiation Weighting Factor (WR) – measure of the ability
of a particular type of radiation to cause biological damage.
For example, 0.05 Gy of fast neutrons can do as much
biological damage as 1 Gy of gamma radiation.

Table-1: Radiation Weighting Factors for Various Radiation
Radiation WR
X-rays, gamma rays, beta (electron) and positrons 1
Protons 5
Neutrons
Thermal or < 10 keV 5
> 10 keV to 100 keV 10
> 100 keV to 2 MeV 20
> 2 MeV to 20 MeV 10
> 20 MeV 5
Alpha particles, fission fragments, heavy nuclei 20

Problem
The dose rates outside the shielding of a cyclotron are found to
be 5 µGy/h gamma, 2 µGy/h thermal neutrons, and 1 µGy/h fast
neutrons greater than 2 MeV. What is the equivalent dose rate of
the combined radiations according to the ICRP values for WR?
D X WR = H
Gamma rays 5 µGy/h X 1 = 5 µSv/h
Thermal neutrons 2 µGy/h X 5 = 10 µSv/h
Fast neutrons 1 µGy/h X 10 = 10 µSv/h
Equivalent dose, H = 25 µSv/h

Tissue Weighting Factor
Tissue or Organ Tissue Weighting Factor (WT)
Gonads 0.20
Bone marrow (red) 0.12
Colon 0.12
Lung 0.12
Stomach 0.12
Bladder 0.05
Breast 0.05
Liver 0.05
Oesophagus 0.05
Thyroid 0.05
Skin 0.01
Bone surface 0.01
Remainder 0.05
Total 1.00
Tissue Weighting Factor (WT) – a factor reflecting the
radiosensitivity of a particular tissue or organ.
The values are averages across a population of all ages & both sexes.

32
Thank You For Your Kind Attention !
"Not all of us can do great things. But we
can do small things with great love."
...Mother Teresa

Basic concept of radiation, radioactivity, radiation dose

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