3 ms·

I take issue to the generalization that short half lives = more danger. That is just not true. Tc-99m is used in diagnostic medicine, it has a half-life of 6 hr

• Tuna-Fish 9y ago
  One mg of Sr-90 has an activity of ~140 uCi. One mg of Tc-99m has an activity of ~5Ci. You probably understand the differences in the implications of handling an amount of material that emits 140uCi compared to one that emits 5Ci. In medical radiology, the amounts of radioactive isotopes are measured in Bq because the samples are so heavily diluted that it's the only thing you can sensibly measure. This easily hides the fact that when you are talking about roughly equal amounts, Tc-99m is roughly 29 years/6 hours ~=40000 times more dangerous than Sr-90. You just never use equal amounts, when you receive a sample of Tc-99m it's about 40000 times smaller than the Sr-90 sample.
• cperciva 9y ago
  Because Tc-99m is used in extremely small quantities.
• Tuna-Fish 9y ago
  > I take issue to the generalization that short half lives = more danger. That is just not true. On this I have to concede that it's not strictly true because some decay events produce more/ more dangerous radiation than others, and much more importantly, the decay of some isotopes start a long decay chain where all the successor isotopes decay much faster than the original. However, both of those effects are relatively small constant multipliers next to the 9 order of magnitude difference between decay rate of an isotope with a half-life of 16 million years compared to an isotope with a half-life of 8 days.