Helium Isotopes, Radioactive Decay and Half-Life

This is a periodic table tile for the element helium.
This is a periodic table tile for the element helium. Todd Helmenstine
by Anne Marie Helmenstine, Ph.D.
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
Updated January 29, 2019

It takes two protons to make a helium atom. The difference between isotopes is the number of neutrons. Helium has seven known isotopes, ranging from He-3 to He-9. Most of these isotopes have multiple decay schemes where the decay type depends on the overall energy of the nucleus and its total angular momentum quantum number.

This table lists helium isotopes, half-life, and type of decay:

IsotopeHalf-LifeDecay
He-3StableN/A
He-4Stable
≈ 0.5 x 10-21 sec - 1 x 10-21 sec		N/A
p or n
He-51 x 10-21 secn
He-60.8 sec
5 x 10-23 sec - 5 x 10-21 sec		β-
n
He-73 x 10-22 sec - 4 x 10-21 secn
He-80.1 sec
0.5 x 10-21 sec - 1 x 10-21 sec		β-
n/α
He-9unknownunknown
p
n
α
β-		proton emission
neutron emission
alpha decay
beta- decay