- #1

Von Neumann

- 101

- 4

**Question:**I'm looking to estimate my total extra exposure (dose above background) by taking into account account roughly how long I was near each source, the strength of the source, and its approximate distance from me. I believe it's useful to use the following equation,

[itex]\frac{dD}{dt}=\frac{dD_{0}}{dt}e^{-cx}[/itex]

where [itex]\frac{dD_{0}}{dt}[/itex] is the dose rate at

*x=0*and

*c*is the absorption coefficient.

The dose rates measured at

*x=0*for the 3 sources, as well as the calculated absorption coefficients are

Ba-133: 277 μR/h , c=0.303/in.

Cs-137: 107 μR/h , c=0.375/in.

Co-60: 117 μR/h , c=0.360/in.

*note that the background radiation has been subtracted from the dose rates shown.

So if I take the time

*t*spend near each source as 10 minutes, and the distance from each source as

*x=0 in.*(as I was holding the sources as we varied the distance in the first part of the experiment) I can approximate the exposure as

[itex]\frac{dD_{0}}{dt}\cdot[/itex][itex]t[/itex]

and then sum these for from each source. So therefore I get,

Ba-133: 277 μR/h * (10 min) * (1 h/ 60 min) = 0.0462 mR

Co-60: 107 μR/h * (10 min) * (1 h/ 60 min) = 0.0195 mR

Cs-137: 117 μR/h * (10 min) * (1 h/ 60 min) = .0178 mR

Thus as my total extra exposure I get,

0.0462 mR + 0.0195 mR + 0.0178 mR = 0.0835 mR

Is this reasoning correct? Thank you in advance for any input.