# Modes of nuclear decay **URL:** \ **Category:** Factual Questions\ **Created:** [July 10, 2013, 6:52pm UTC](https://boards.straightdope.com/t/modes-of-nuclear-decay/663160 "2013-07-10T18:52:02Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [July 10, 2013, 6:52pm UTC](https://boards.straightdope.com/t/modes-of-nuclear-decay/663160/1 "2013-07-10T18:52:02Z")
I just read an article in the July-August issue of The American Scientist about supernovas. It was primarily about the discovery of dark energy and the acceleration of expansion. But it began by discussing type 1a supernovas. It claimed that the main element produced in that type of supernova was Ni-56. After an amusing discussion of how much the amount produced in a typical supernova was made in nickels, he then mentioned that in about a week most of it would have decayed into Co-56 and then into Fe-56, which is the standard–and stable–isotope. How does this come about? I was aware of two kinds of decay. Beta decay happens when a neutron emits an electron and becomes a proton. This increases the atomic number, while leaving the atomic mass unchanged. This is what happens when U-239 (created when a U-238 nucleus captures a neutron) decays into Np-239, which in turn decays into Pu-239, which is long-lived, although not stable. The second kind I am aware of involves the emission of an He nucleus which lowers the atomic number by 2 and the atomic mass by 4. I was unaware of any reaction that could leave the atomic mass unchanged while reducing the atomic number by 1. Could a proton emit a positron and change into a neutron. The neutron has slightly more mass, but perhaps there is enough energy around to cause it. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [July 10, 2013, 6:57pm UTC](https://boards.straightdope.com/t/modes-of-nuclear-decay/663160/2 "2013-07-10T18:57:57Z")
Yes that is exactly what happens (along with a neutrino of course). It occurs in proton rich nuclei. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [July 10, 2013, 7:25pm UTC](https://boards.straightdope.com/t/modes-of-nuclear-decay/663160/3 "2013-07-10T19:25:44Z")
> [@Hari\_Seldon](#): > > I was unaware of any reaction that could leave the atomic mass unchanged while reducing the atomic number by 1. Could a proton emit a positron and change into a neutron. The neutron has slightly more mass, but perhaps there is enough energy around to cause it. The fancy phrase for this is [ß[sup]+[/sup] (“beta-plus”) decay](http://en.wikipedia.org/wiki/Positron_emission), or positron emission. Roughly speaking, a nucleus “wants” to have a given number of neutrons to balance out the repulsive electric forces between its protons. If it has “too many” neutrons, it’ll convert one neutron to a proton via ß[sup]-[/sup] decay; but if it has “too many” protons, it’ll convert one proton to a neutron via ß[sup]+[/sup] decay. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [July 10, 2013, 9:54pm UTC](https://boards.straightdope.com/t/modes-of-nuclear-decay/663160/4 "2013-07-10T21:54:13Z")
Ni-56 decays via electron capture (EC). No positron is emitted. In EC, an electron in a low-lying atomic shell (K- or L-shell typially) combines with a proton to produce a neutron and a neutrino. This decay mode is sometimes called “K-capture” or “L-capture”, although you don’t hear “L-capture” very often. Co-56 decays either by electron capture (81% of the time) or positron emission (19% of the time). > [@Hari Seldon](#): > > I was aware of two kinds of decay. There are loads. Some others: proton emission, neutron emission, double-beta decay (which can be dominant in neutron-rich isotopes that, due to spin-related energy reasons, cannot undergo normal beta decay), double electron capture, gamma emission, carbon-14 emission (think: alpha decay, but bigger.) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 10, 2013, 10:25pm UTC](https://boards.straightdope.com/t/modes-of-nuclear-decay/663160/5 "2013-07-10T22:25:11Z")
You’ve heard of PET scans, in the medical field? That stands for “positron emission tomography”, and uses isotopes that decay via positron emission. **Hari Seldon** , why would carbon-14 emission in particular be a notable decay channel? I’d expect carbon-12, if anything, since multiples of the helium nucleus tend to be relatively stable. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [July 10, 2013, 11:22pm UTC](https://boards.straightdope.com/t/modes-of-nuclear-decay/663160/6 "2013-07-10T23:22:11Z")
> [@Chronos](#): > > **Hari Seldon** , why would carbon-14 emission in particular be a notable decay channel? I’d expect carbon-12, if anything, since multiples of the helium nucleus tend to be relatively stable. I assume you meant me and not **Hari**? If a nucleus is in rough enough shape to jettison so much of itself, it probably wants to get rid of more neutrons than protons if it’s to return to the stable line of isotopes. Carbon-14 is also rather stable, as unstable nuclei go, with a decay energy of only 156 keV. Eight isotopes are known to decay via carbon-14 emission. None via carbon-12. A smattering of other nuclei also make the list of known decay products (mostly neutron-laden neon, magnesium, and silicon nuclei). ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [July 10, 2013, 11:25pm UTC](https://boards.straightdope.com/t/modes-of-nuclear-decay/663160/7 "2013-07-10T23:25:35Z")
> [@Chronos](#): > > **Hari Seldon** , why would carbon-14 emission in particular be a notable decay channel? I’d expect carbon-12, if anything, since multiples of the helium nucleus tend to be relatively stable. Pop quiz for **Hari Seldon**! (But **Pasta** spoiled it. :() ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [July 11, 2013, 12:33pm UTC](https://boards.straightdope.com/t/modes-of-nuclear-decay/663160/8 "2013-07-11T12:33:41Z")
Thanks to all. I didn’t know any of this.