1. A radioactive source emits 4200 beta particles in a time of 2 minutes.
Calculate the activity of the source.
A = N / t
A = 4200 / (2 x 60)
A = 35 Bq
2. Find the absorbed dose if 2 mJ of energy from radiation is absorbed by
(a) 40 kg of lead
D = E / m = 2 x 10-3 / 40 = 5 x 10-5 Gy
(b) 8 kg of steel
D = E / m = 2 x 10-3 / 8 = 2.5 x 10-4 Gy
3. How much energy would have to be absorbed by 0.3 kg of aluminium to give an absorbed dose of 6 mGy?
D = E / m
6 x 10-3 = E / 0.3
E = 1.8 x 10-3 J
4. A shielding material of mass 25 kg absorbs 400 J of energy from radiation in 16 days.
Calculate the absorbed dose and the absorbed dose rate.
D = E / m = 400 / 25 = 16 Gy
Ḋ = D / t = 16 / 16 = 1 Gy/day
5. What would be the values for absorbed dose and absorbed dose rate in the following circumstances?
(a) 200 kg receives 200 kJ of energy every 100 hours.
D = E / m = 200,000 / 200 = 1000 Gy
Ḋ = D / t = 1000 / 100 = 10 Gy hr-1
(b) 6 kg absorber accepts 24 MJ in one year.
D = E / m = 24 x 106 / 6 = 4 x 106 Gy = 4 MGy
Ḋ = D / t = 4 x 106 / 1 = 4 MGy/year
6. An absorbed dose of 200 µGy is caused by thermal neutrons (WR = 3).
What is the equivalent dose?
H = D WR = 200 x 10-6 x 3 = 600 µSv
7. A physics teacher is irradiated by alpha particles when using a 185 kBq source .
(a) Calculate the equivalent dose received if the teacher has a mass of 6O kg and the total energy absorbed is 9 x 10-7 J.
D = E / m = 9 x 10-7 / 60 = 1.5 x 10-8 Gy
H = D WR = 1.5 x 10-8 x 20 = 30 x 10-8 Sv
(b) Calculate what the equivalent dose would be if all the ionisation took place in the teacher's hand which has a mass of 0.5 kg?
D = E / m = 9 x 10-7 / 0.5 = 1.8 x 10-6 Gy
H = D WR = 1.8 x 10-6 x 20 = 3.6 x 10-5 Sv
8. A nuclear fuel process worker receives the following: 2O µGy from fast neutrons, 1O µGy from thermal neutrons and 25 µGy from gamma radiation.
Calculate the total equivalent dose?
H1 = D Q = 20 x 10-6 x 10 = 200 µSv
H2 = D Q = 10 x 10-6 x 3 = 30 µSv
H3 = D Q = 25 x 10-6 x 1 = 25 µSv
Total H = 255 µSv
9. A research physicist receives a total of 100 µGy of gamma radiation and 10 µGy of thermal neutron radiation during an experiment lasting 10 hours.
Calculate the total equivalent dose rate.
H1 = D Q = 100 x 10-6 x 1 = 100 µSv
H2 = D Q = 10 x 10-6 x 3 = 30 µSv
Total H = 130 µSv
Ḣ = H / t = 130 x 10-6 / 10 = 13 µSv hr-1
10. A reactor worker receives a total of 8 mSv after working for forty weeks at 20 hours a week in the radiation zone.
What was the equivalent dose rate?
Ḣ = H / t = 8 x 10-3 / (40 x 20) = 1 x 10-5 = 10 µSv hr-1
11. Two metres from a point source of radiation the equivalent dose rate is 800 µSv h-1 .
Calculate what the equivalent dose rate would be at
(a) 4 metres and
I1 d1 2 = I2 d2 2
800 x 22 = I2 x 42
I2 = 200 µSv h-1
(b) 10 metres from the source?
I1 d1 2 = I2 d2 2
800 x 22 = I2 x 102
I2 = 32 µSv h-1
12. For the same source, at what distance would the equivalent dose rate be 5O µSv h-l ?
I1 d1 2 = I2 d2 2
800 x 22 = 50 x d2 2
d2 = 8 m
13. A radioactive source produces a count rate of 1024 c/s. After 6 mm of lead shielding is used the count rate falls to 128 c/s.
What is the half-value thickness of the source?
1024 -> 512 -> 256 -> 128
6 mm / 3 = 2 mm