I need to calculate the dose rate leaking from sealed Co-60 sources.
Let's say the activity of a source is 7 TBq. The source is tube shaped, 2 mm radius and 10 mm in height.
There is 5 cm of tungsten and 3 cm lead in the radiation's way.
The measured dose rate according the NCRP report 102: "the maximum and the average leakage kerma rates through the housing shall not exceed 100 uGy/h"
How could I calculate if the 5 cm tungsten and 3 cm lead will be enough to limit the leakage dose rate to the 100 uGy/h range?
We have built a Monte Carlo model of the above scenario and ran the simulation.
There are a number of particles with a given energy arriving to the other side of the shielding. We save the state of these particles in a phase-space. So in this phase space we have the type of the particle: e-, gamma, position, direction, energy.
Calculating dose from the particle energies.
Dose is Joule/kg, so we need a volume with some material in which the energy of the particles will be absorbed. So we put a 1 cm^3 lead cube next to the area where the energy is the most dense in the phase space. Restart all the particles. Now we look at how much energy was absorbed in the lead cube and divide by the weight of the cube. The result is somewhat sensitive to the size of the cube because the shielding is not homogeneous.
Calculate dose rate.
Activity is 7 TBq which is 7x10^12 decays/s for Co-60 let's say that that is 7x10^12 gammas of 1.1732 MeV plus 7x10^12 gammas of 1.3325 MeV. So modelling 14x10^12 initial events would equal to 1 sec of real time. Let's say we model 1x10^9 events so now we can say have how much of real time is simulated and thus we have the dose rate.
This is what I would like to verify.