dose rate task 9 result conversion may be incorrect

[py1sl]

task 9 dose rate on a surface states
"The cell tally has units of pSv cm² per source particle (p is pico). Therefore, the tally result must be divided by the surface area of the sphere to make the units into pSv, and then multiplied by the activity (in Bq) of the source to get pSv per second."

I believe it should not be activity but gammas emitted per second, so in the case of Co60 where there are approximately two gamma rays emitted per decay it should be twice the activity.

[shimwell]

Thanks for reporting this @py1sl

[shimwell]

I see this is currently in the code for task 9 part 1. Wondering if this looks ok?

dose_in_pSv = tally_result / (4 * math.pi * math.pow(200, 2))

source_activity = 56000 # in decays per second (Bq)
dose_rate_in_pSv = dose_in_pSv * 56000

print('The surface dose = ', dose_rate_in_pSv, 'pico Sv per second')

[py1sl]

I think in should be
dose_in_pSv = tally_result / (4 * math.pi * math.pow(200, 2))

gamma_per_second = 112000 # in decays per second (Bq) * emission rate (approx 2 for Co60)
dose_rate_in_pSv = dose_in_pSv * gamma_per_second

print('The surface dose = ', dose_rate_in_pSv, 'pico Sv per second'

Assuming that the initial units are picoSv cm2 per source particle and you wanted a 56kBq Co60 source

[py1sl]

same issue in task 9 part 2 as well

[shimwell]

ah so i was missing that * emission rate (approx 2 for Co60) part. Thanks for that. I shall correct soon