Question

A sample of radioactive materials emits 1 MeV gamma rays and has an activity of 23 curies, How long can a radiation worker be exposed to the affected area before exceeding the annual exposure limit of 5 rem? The worker is in direct contact with the sample.

Answer 1

The activity is given to be , the energy per photon (gamma ray) is given to be , the mass of the worker is , and the equivalent dosage is given to be . This problem is mostly dealing with unit conversions in radioactive exposure.

Step 1) First find the energy absorbed by the worker. This is equal to the absorbed dosage (in rad) times the mass of the worker. Begin by finding the absorbed dosage in units of rad as found by the equation, where RBE (radioactive biological effectiveness) is equal to 1 for gamma rays. Plug and in to find the absorbed dosage by the worker.

So for gamma rays, 5 rem is equal to 5 rad in dosage.

Step 2) Next convert the units of rad to joules per kilogram. Multiply the 5 rad by the conversion factor .

Step 3) Now we can find the energy absorbed by the 75 kg worker by multiplying the absorbed dosage by the mass of the worker, .

Step 4) Convert the energy absorbed into eV by multiplying by the conversion factor .

Step 5) Now divide the energy absorbed by the worker by the energy emitted by each photon to find how many photons were emitted (to be equivalent to 5 rem dose).

Step 6) Now convert the activity from Ci to units photons per second by multiplying 23 Ci by the conversion factor .

Step 7) Finally divide the number of photons emitted by the activity to find the number of seconds that the worker would have before he reaches the limit of 5 rem.

The time the worker has before he reaches the 5 rem limit is 27.5 seconds.