While looking at a table of helium isotopes it said that helium-8 turns into Tritium(hydrogen-3) and helium-5 through fission and beta decay.

But the pathway to helium-5 isn't so direct. It is more like this

helium-8 -> hydrogen-3 and hydrogen-5 (fission) -> helium-5 (beta decay)

But the table of hydrogen isotopes said nothing about hydrogen-5 going through beta decay. All it had there was double neutron emission producing tritium which after 12 years turns into helium-3 via beta decay.

Does this mean that I discovered that hydrogen-5 does go through beta decay but not nearly as often as double neutron emission?


Sorry, you haven't. I don't know where your information is from but I think there is an error in your decay chain. For the 0.9% of $\ce{^8_2He}$ decays that proceed via spontaneous fission your equation should look more like this: $$\ce{^8_2He ->[fission] ~^3_1T + ^5_1He + \beta ^{-}}$$ $$\ce{ ^5_1He ->[neutron~emission] n + ^4_2He} $$

|improve this answer|||||
  • $\begingroup$ Looking at the A=8 energy level diagrams (tunl.duke.edu/nucldata/figures/08figs/menu08.shtml) gives a slightly different picture. 0.9% of the time you get He-8 undergoing beta decay to Li-8, which than can fission in to He-5 and T. 16% of the time the beta decay instead lands on Li-8 levels that decay to Li-7 + neutron. 84% of the time it decays to an even lower Li-8 energy level, drops to the ground state, and then will beta decay to Be-8. Nuclear energy level diagrams are quite useful. $\endgroup$ – Jon Custer Dec 15 '15 at 23:00
  • $\begingroup$ I am aware of the other decay modes. I chose to focus on the one pertinent to the question. I have updated the question to be more explicit about this. $\endgroup$ – A.K. Dec 15 '15 at 23:06
  • $\begingroup$ For clarity it seem that there should be two separate equations. One for $\ce{^8_2He}$ and one for $\ce{^5_1He}$. $\endgroup$ – MaxW Dec 15 '15 at 23:23
  • $\begingroup$ But fission of helium produces 2 hydrogens. So the larger hydrogen(hydrogen-5 in this case) goes through beta decay. $\endgroup$ – Caters Dec 16 '15 at 2:59
  • 1
    $\begingroup$ This is because fission not only splits the nucleus but it also splits the electrons. So to get helium-5 from helium-8 it first has to go through fission into tritium and hydrogen-5. Then it has to go through beta decay and capture that electron in the 1s orbital to turn into helium-5 $\endgroup$ – Caters Dec 17 '15 at 21:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.