I think all of us old geezers should schedule our thallium stress tests at
a suitable time for lecture demonstrations. When I got mine, I was the second
most active source in the department, second only to our 5 Ci PU-Be neutron
source. With a NaI counter I was easily detectable from 20 ft away. To spare my
wife a little unnecessary exposure, I slept on the couch that evening.
Previously
one of my colleagues returned from the doctor after his. I grabbed a NaI
detector to see if I could see the single Tc peak. I was fiddling with the MCA
and he was holding the detector to his chest. The spectra were all washed out,
no peaks visible. Then I realized that he was the most active source I had ever
tried to get a spectrum from and the problem was that he was so active that
pulse pileup was destroying the spectra. I backed the detector off a couple of
feet and found the Tc peak as expected.