# A question about dose rates

Hi:
I have most recently been using G4 to measure the dose rate parameters of our newly designed radioactive sources, but now I am having some problems with the dose rate measurements.

We designed the I-125 radioactive source activity of 0.5mCi, according to the formula this 0.5mCi radioactive source can produce `1.85*10E8` decays per second. I used G4 with`/run/beamOn 185 , 1850 and 18500` particles respectively.

And counting the absorbed doses in SD, I found that these absorbed doses basically showed a linear relationship. So I used the command `/run/beamOn 185000` in the final experiment and multiplied the absorbed dose by 1000 to get the absorbed dose of 5mCi I-125 in the detector in one second.

But I don’t know if this method of mine is feasible, so I would like to ask for your advice. Also I have another question.

I see more in some papers that use `MCNP` to calculate absorbed dose, they use `MCNP *f4 tally` to calculate `energy fluence (MeV/cm2)` and then use `mass-energy absorption coefficients` to convert energy fluence to absorbed dose rate.

According to my understanding, I count the absorbed dose of SD in one second in G4, so that I can get the absorbed dose rate in `Gy/s`, and then I multiply this value by 3600 to get the absorbed dose rate in `Gy/h`.

Based on the above description my questions are as follows:

The first question is whether I can conclude that G4 shows a linear relationship when counting the absorbed dose, such that I can use the command /run/beamOn 185000000 instead of /run/beamOn 185000 or even less and multiply it by the corresponding multiplier.The resulting absorbed dose rate of SD in one second was obtained.

The second question is whether the way I calculated the absorbed dose rate using G4 is correct, which is to first derive` Gy/s` and then multiply by 3600 to get` Gy/h`.

The third question is whether there is a big difference between the absorbed dose rate calculation method of `MCNP` and the absorbed dose rate counted by `G4`. If my absorbed dose rate calculation method is correct is it possible that there is not much error between these two.

Thank you all for your responses.

1 Like

Hello @Jodie_Comer !
I have the same question as you right now. Did you find the answer and does this method work fine for your purposes?
I will be really glad to hear from you.