Leigh's account of having a Tc-99m test brought back memories of a similar
test I had about three years ago for a bone scan. In my case they wanted to
image the various bones, including the tailbone and spine, so they did not put
a lead apron over me as Leigh had. Instead, I had to go to the bathroom just
before each scan, because the isotope tended to accumulate in the bladder and
so they had to have it emptied so it wouldn't dominate the image. After the
hospital tests were concluded I decided to see just how "hot" I had become,
and also to check out the isotope they were using. The technician who
administered the injection told me what it was, so I looked it up on my Chart
of Nuclides and found that it had a 6.0 h half life and 140 keV gamma
energy. With a NaI(Tl) counter and MCA [stands for Multi-channel
analyzer, Brian--and electronic analog-to-digital converter with 8k memory
locations in my case] I confirmed the energy of the peak, and started a long
series of counts to determine the half life. I also put a dosimeter in my
pocket to wear constantly for the next several days to monitor the exposure
that way. In order to get a reproducible geometry to make the half-life
measurement, I had to screen the detector with lead bricks, then place my
hand behind the bricks in a reproducible way. The count rate several hours
after the injection was over 300,000 counts in 10 seconds with my hand.
Not enough to glow, but hot enough! I got good decay data, and confirmed
the 6.0 h half life over the next 100 hours. Interesting what physicists will
do, isn't it? The only down side of all this was that somehow the students
got the idea that one gets radioactive being in the nuclear physics lab!
Rondo Jeffery
Weber State University.