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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