Question

What is the dose rate in mrem/h corresponding to a continuous 1.25 MeV gamma ray flux of 4.7×103 cm–2 ∙ s–1 ? How many hours per week a radiation worker should be allowed spending in this environment to stay below company limit of 2 rem/year? What is this time if worker is to reach NRC limit of 5 rem/year?

Answer 1

The dose rate is calculated as

Dose rate = Gamma ray flux X Energy X Energy X absorption coeffecient of soft tissues

Gamma ray flux = 4.7 X 10³ cm²s^-1

energy = 1.25 Mev = 1.25 X 10^6 ev = 1.25 X 10⁶ X 1.6 X 10^-19 Joules

Absorption coeffecient = 3.299 X 10^-2

Dose rate = 4.7 X 10³ X 1.25 X 10⁶ X 1.6 X 10^-19 X 3.299 X 10^-2

Dose rate = 31.01 X 10^-12 J / g s

1J /g = 10^5 rad

1 year = 365 X 24 X 60 X 60 seconds = 3.153 X 10^7 seconds

Dose rate = 31.01 X 10^-12 X 10^5 X 3.153 X 10^7 = 97.77 mrem / year

dose rate per hour = 97.77 mrem / 8760 = 0.011 mrem / hour

b) the limit of radiation dose = 2rem / year

the hours in a year = 365 X 24 = 8760 hours

the number or rem / hour = 2 / 8760 = 2.28 X 10^-4 rem / hour = 0.228mrem / hour

so the number of hours it can work = 0.228 / 0.011 = 20.73 hours / per week

c) for 5rem / year

rem / hour = 5 / 8760 = 0.57 mrem / hour

so the number of hours it can work = 0.57 / 20.73 = 51.81 hours / week