answers to tutorial
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Tutorial: Basic Information on Ionising Radiation
1. What is meant by radioactivity?
Ans: Is a spontaneous disintegration in the nucleus of an unstable atom to
form a nuclide of different Z by emission of radiation from the nucleus
2. What are the old and S.I. units for measuring an activity of a radionuclide?, andhow are they correlated ?
Ans: Old Unit: Curie (Ci) S.I. Unit: Becquerel (Bq)
I Ci = 3.7 x 1010
Bq
3. Determine the atomic mass (A), atomic number (Z), no. of protons (#P), neutrons
(#N) of the radionuclides in the following table. Based on the completedinformation in the box, complete the symbol for each species.
NUCLIDES Z #P #N A
13C
6
6 6 7 13
?Cl
?
17 17 18 35
?Fe
?
26 26 30 56
?H
?
1 1 2 3
?Te
?
52 52 76 128
?Sn
?
50 50 70 120
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4. Calculate the activity of Co-60 in kCi and TBq after 5 years, if the current activityis 100 kCi. Given the T = 5.27 years.
A(t) = A0 e-l t
=
l = ln 2/ T = 0.693 / 5.27
= 0.1317
l t = 0.1317 x 5 = 0.6584A(t) = 100 x e
-0.6584
A(t) = 100 x 0.517679
A(t) = 51.77 kCi
Since 1 Ci = 10-3
kCi = 3.7 x 1010
Bq = 3.7 x 10-2
TBq
A(t) = 51.77 kCi x 3.7 x 10-2
TBq / 10-3
kCi
A(t) = 1,920 TBq
5. Complete the following radioactivity decay schemes
a. 60Co 60Ni +0e
27 28 -1
b.137
Cs137
Ba +0e
55 56 -1
c.90
Sr90
Y +0
e90
Zr +0
e38 39 -1 40 -1
d.85
Kr85
Rb +0e
36 36 -1
e.226
Ra222
Rn +4He
88 86 2
6. What is meant by half-life? Give one example.
Ans: Is the time required for an activity of a radionuclide to reduce by half.
T1/2 of Cs-137 is 30 years C-14 (5736y) H-3(12.33y) Co-60(5.27y) Ir-192(73.83d) U-238(4.47x10-9
y) Th-232(14x10-9
y)
7. A company bought a gamma projector using Iridium-192 having activity of 50 Ci.The source need to be changed once the activity reached 5 Ci.
a. Determine the time (in days) this change will take place. Given T =
73.83 days,
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A(t) = A0 e-l t
Ao = 50 Ci
A(t) = 5 Ci
T = 73.83 d
t = ? d
T Aot = - ln - = 73.83/ 0.693 x (ln (50/5)) = 106.54 x ln 10 = 245.31d
0.693 A(t)
b. Suppose you want to change the source once in 5 years, what would be theactivity of the source to procure?
A(t) = A0 e
-l t
=> Ao = A(t) el t
Ao = ? Ci
A(t) = 5 Ci
T = 73.83 d
t = 5 y = 5x 365 d = 1825 d
Ao = 5 x e0.693 x 1825 / 73.83
= 5 x e17.13
= 5 x 27,508,345.79 Ci = 137.5 x 106
Ci = 137.5 MCi
8. What are the old and S.I. units for absorbed dose, equivalent dose and effectivedose?, and how are they correlated ?
Parameters Old Unit S.I. Unit Correlation
Absorbed dose (D) rem Gray (Gy) 100 rem = 1Gy
Equivalent dose (H) rad Sievert (Sv) 100 rad = 1Sv
Effective dose (E) rad Sievert (Sv) 100 rad = 1Sv
9. Calculate the dose equivalent and effective dose of a radiation worker whose lungand skin have been subjected to a total 20 Gy of alpha radiation from a uranium
source.
Ans: Absorbed Dose (D) = 20 Gy
WR (alpha) = 20
WT (lung) = 0.12
WT (skin) = 0.01
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H = D x WR =20 x20 = 400 Sv
E (lung) = H x WT (lung) = 400 x 0.12 = 4.80Sv
E (skin) = H x WT (skin) = 400 x 0.01 = 0.04 Sv
10. What are the sources of natural and man-made ionizing radiation? What is theaverage annual dose of ionizing radiation received by members of the public?
Ans: Sources of radiation
Natural radiation in the environment (Cosmic, terrestrial ) Medical exposure
Occupational exposure Artificial radioactivity in the environment
products Medical X ray (0.1 mSv per chest x ray), nuclear medicine (diagnostic
and therapeutic) [0.3 mSv/y] Nuclear weapon test - radioactive fall-out (.006 mSv/y)
Nuclear power (0.008 mSv/y to the public), industries (process control,QC)
Consumer products: smoke detectors, luminous watches, gas mantles,TV. [very low]
(Source: UNSCEAR, 2.7 mSv total)
48 %9%
11 %
0%
17 %15%
Radon
Internal
Medical
Others
Gamma
C osmic