1. Different units are used to measure various properties of ionizing radiation, including the curie, becquerel, roentgen, rad, gray, rem, and sievert. 2. The roentgen measures exposure to gamma or X-rays, while the rad measures absorbed dose, accounting for different materials. The gray is now the SI unit for absorbed dose, replacing the rad. 3. The rem accounts for the different biological effects of various types of ionizing radiation based on their quality factor, and is used to measure equivalent dose. The sievert, replacing the rem, measures stochastic health risks from radiation exposure.

1. RADIATION UNITS
MODERATOR :- Mr. TEERTHRAJ SIR
PRESENTER :- DR.VIJAY.P.RATURI
KGMU , RADIATION ONCOLOGY DEPTT.

2. RADIOACTIVITY & DISINTEGRATION
EXCESS ENERGY IN FORM OF E.M RADIATION
ANOTHER NUCLEUS + CHARGED PARTICLE
DAUGHTER
ONE NUCLEUS
PARENT
DISINTEGRATION

3. Co Ni + e
60
27
60
28
0
-1
GAMMA RAY EMISSION
PHOTON

5. NEED OF MEASURING SYSTEM
• MAGNITUDE OF BIOLOGICAL EFFECT
IN RADIOTHERAPY & RADIODIAGNOSIS.
• DIRECT MEASUREMENT IMPRACTICABLE

6. CRITERIA FOR MEASURING SYSTEM
• REPRODUCIBLE
• REPEATABLE
• SENSITIVE
• OBJECTIVE
• LINEAR

7. • IONIZATION OF AIR, IS NOW
INTERNATIONALLY ACCEPTED BASIS OF
STANDARD X-RAY DOSIMETRY
• IONIZATION IS MAJOR PRODUCT OF ENERGY
ABSORPTION PROCESS
• DEPENDS UPON ENERGY OF RADIATION &
ON ATOMIC NUMBER OF MATERIAL

8. UNITS OF RADIOACTIVITY
Curie
Becquerel
UNITS OF RADIATION DOSES
1) Units of Exposure
Roentgen
2) Units of Absorption
Physical dose – Rad/ Gray
Biological dose – rem/seivert
RADIATION UNITS

10. DECAY CONSTANT
• No of atom disintegrating / time ( dN/dt)
is proportional to No of radioactive atoms
(N)
dN
dt
N - N
• Rate of disintegration dN/dt is called
activity

11. • Unit of activity is curie (Ci)
• 1 Curie = 3.7 x 10 disintegration/sec ( or Bq)
• SI unit is Becquerel
• 1 Bq = 1 radioactive decay per second
= 2.703 x 10 Ci
UNITS OF RADIOACTIVITY
-11
10

12. THE ROENTGEN
• AMOUNT OF X, OR GAMMA RADIATION
SUCH THAT ASSOCIATED CORPUSCULAR
EMISSION PER 0.001293 GM( 1CC) OF AIR
PRODUCES IN AIR IONS CARRYING 1 ELECTRO
STATIC UNIT OF CHARGE OF EITHER SIGN.

13. • Roentgen is unit of X or GAMMA ray & can’t
be used for other ionizing radiation like BETA
ray or NEUTRON.
• For these, an additional unit the RAD was
introduced in 1956
• In 1962 , it was decide
roentgen -- unit of exposure.
rad unit -- unit of absorbed dose.
• 1 R = 2.58 * 10 c/kg of air
-4

14. THE RAD
• Absorbed dose is what we want to measure
Defined by I.C.R.U, D= Ed
m
Ed ( energy imparted by ionizing radiation
to the matter )
m ( mass of matter)
• 1 rad = 100 erg per gram

15. THE GRAY
• In JUNE 1975 , International committee on
weights & measures adopted the gray (sym
G) as S.I unit of absorbed dose ( named after
Dr.L.H.Gray)
1 gray = 1 joule /kg = 100 rad

16. CONVERSION FACTORS FOR ROENTGEN TO RAD
Absorbed energy/gram = energy in the beam*
mass absorption coefficient
= E ( mass abs coefficient)
After some calculation we get
Absorbed energy /gram = f R rads
factor f , for converting roentgen into rads.
factors varies with the material & with radiation
energy .

17. •0.87
•0.94
•0.96
•0.96
WATER
•0.91
•0.94
•0.95
•0.955
MUSCLE
•4.23
•1.46
•0.91
•0.92
BONE
ROENTGEN TO RAD CONVERSION FACTOR ( f )
FOR WATER ,MUSCLE & BONE
100KV
200KV
1 MEV
4 MEV
ENERGY

18. RADS ( PER ROENTGEN)
MUSCLE
92
94
95.6
95.7
BONE
414
191
92.1
92
VOLTAGE OF RADIO-
ACTIVE SOURCE
100KV
200KV
4 MV
C0 60
ABSORBED DOSES IN MUSCLE & BONE

19. Radiation increases the risk of cancer
and other stochastic effects at any
dose.
The ICRP maintains a model of these
risks as a function of absorbed dose
and other factors. That model
calculates an effective radiation dose,
measured units of rem, which is more
representative of the stochastic risk.

20. THE REM
• Dose of any ionizing radiation which will produce
the same biological effect as 1 rad of Co 60
gamma ray ( for which the Q.F is 1)
• Dosimetric quantity relevant to radiation
protection is dose equivalent (H)
• Rem is designed to represent stochastic biological
effect of ionizing radition
H = D * Q ( D – Absorbed dose
Q – Quality factor )

21. ICRP officially adopted the rem as the unit
of equivalent dose in 1962 to measure the
way different types of radiation distribute
energy in tissue
Dose equivalent in rem = (dose in rad * QF)
+ ( dose in rad * QF) + …
QUALITY FACTOR(QF) :- value based on
range of RBE related to LET of radiation .
Radiation 2
Radiation 1

22. QUALITY FACTOR
X RAY , GAMMA RAY
ELECTRON
THERMAL SLOW
NEUTRON
FAST NEUTRON ,
PROTONS
1
3
10
L.E.T

23. • The S.I unit of dose equivalent is
Sievert (Sv)
1 Sv = 1 joule /kg
• It is a measure of the health effect of
low levels of ionizing radiation on
the human body.

24. Quantities that are measured in
sieverts are intended to represent the
stochastic health risk, which for
radiation dose assessment is defined as
the probability of cancer induction and
genetic damage.

27. The ICRP calculation provides two weighting factors
to enable the calculation of protection quantities.
1. The radiation factor WR, which is specific for
radiation type R - This is used in calculating the
equivalent dose HT which can be for the whole body
or for individual organs.
2. The tissue weighting factor WT, which is specific
for tissue type T being irradiated. This is used with
WR to calculate the contributory organ doses to
arrive at an effective dose E.
.

28. When a whole body is irradiated uniformly
only the radiation weighting factor WR is
used, and the effective dose equals the
whole body equivalent dose.
If the irradiation of a body is partial or non-
uniform the tissue factor WT is used to
calculate dose to each organ or tissue.

29. RADIATION WEIGHtING FACTOR (WR)
"The 2007 Recommendations of the International Commission on Radiological Protection". Annals of the
ICRP. ICRP publication 103 37 (2–4). 2007. ISBN 978-0-7020-3048-2. Retrieved 17 May 2012.

30. TISSUE WEIGHTING FACTOR (WT)
"1990 Recommendations of the International Commission on Radiological Protection". Annals of the
ICRP.
ICRP publication 60 21 (1-3). 1991. ISBN 978-0-08-041144-6. Retrieved 17 May 2012.

32. • Acronym for Kinetic Energy released per unit
mass
• K = sum of kinetic energy all charged particle
liberated by ionizing radiation per unit
weight of matter
dE
dm
• It is different from absorbed dose as some of
the kinetic energy escapes from the
absorbing volume
KERMA
K = Unit – j/kg
(gray)

33. THANK YOU…