The?positron?or antielectron is the antiparticle or the antimatter counterpart of the electron. The?positron?has an electric charge of +1 e, a spin of 1/2, and has the same mass as an electron.

The half-life of Plutonium is given to be 24000 years. It is stored for a period of 72000 years. So, the number of half-life periods = 72000/24000 = 3 The fraction that remains is given by 1/2³ = 1/8

0 - 1.00 5 days - half decays - 0.50 remains 10 days - half of the .50 decays, 0.25 remains 15 days - half of the 0.25 decays - 0.125 remains At 15 days, 7/8 has decayed, 1/8 remains.

Alternatively, you could think about this intuitively. If 3/4 decayed, then that means that only one quarter is left. How many half lives does that take? Well, after one half life, you have 1/2 of the original. After another half life, you have 1/2 1/2=1/4 . S two half lives have passed