what is the half life of neptunium-139?

Question

the radioactive substance neptunium-139 decays to 73.6% of its original amount after 24 hours. Whar is the hals life of neptunium-139?

Answer 1

This page lists the half life of the various isotopes, but I don't see 139, just 235 etc.

Its really just a math question, about exponential decay. The half life is approximately 48 hours. If it decayed to half (0.5 or 50%) of its value in 48 hours, it would decay to root 2, 0.707 or 70.7% per day. Its actually decaying to 0.736 per day, so 48 hours isn't quite right. You need some maths expert on Yahoo Answers to work it out. I can't remember how to do it.

If you copy what I've written into your question's additional information, someone else can do the rest.