1. Apr 17, 2013

Von Neumann

Question:

Recently I've conducted an experiment measuring the dose rate (in μR/h) from various samples (Ba-133, Cs-137, Co-60), at varying distances. In determining the efficiency of paper as a shield, it is required to convert the activity of the source to units of dinsintegrations/second (dps). On each of the sources was a label that stated the half-life. Additionally, each source said "1 μCi". So therefore, since 1 μCi = 3.7 x 10^4 dps, that would be the activity in dps. Correct? However, I don't understand how all of the sources could have the same activity in dps, but have different half-lives.

Note: the half-lives given on the sources for Ba-133, Cs-137, and Co-60 are 10.5, 30.2, and 5.27 years, respectively.

2. Apr 17, 2013

Staff: Mentor

Why? It should be sufficient to know the measured rate with and without shield.

Simple: they contain a different number of radioactive atoms.

If the sources are new. Activity goes down with time, while the labels do not change.

3. Apr 19, 2013

Von Neumann

Yes that does seem to be quite obvious, sorry.

Furthermore, I am looking to estimate my total extra exposure in mR (dose above background) due to performing the experiment by taking into account how long I was near each source, the strength of the source, and its approximate distance from me.

If I take my distance as 0 inches (since I was holding each source throughout experiment) and the time as roughly 10 minutes per source, how would I go about doing this? Perhaps, since I have the measured values of the dose rate at 0 inches from each source, could I multiply the dose rate by the amount of time in order to get this result?

4. Apr 20, 2013

Staff: Mentor

That should give a reasonable upper limit on your dose rate. Even if you touched the radioactive part of the probe (I hope you did not), not all decay products have hit you.

5. Apr 20, 2013

Von Neumann

Yes, I was holding the sources. However, I don't believe my professor would have the class conduct a lab that would endanger our health in any way. The sources were in specially prepared cases from Oak Ridge National Laboratory.