physics geeking: nuclear decay

[danaeris]

OK, so in beta decay, let's say you start off with 120/60 Nd.

You'll wind up with
120/59 Pr + e+ + nu
or
120/61 Pm + e- + anti-nu

Now, it was always my understanding that 120= protons + neutrons, and the second number (60, 59, and 61 respectively)= # of protons. What is puzzling me is... how can these guys be losing or gaining a proton, and have the mass number stay 120?

The reactions do not show a neutron being added to the system or a proton leaving the system. I HAD been assuming that the proton becomes a positron and a neutrino, but that doesn't explain the other case at all nor does it explain the constant mass number. So here's the explanation I came up with:

in Case 1
proton -> neutron + e+ + nu

in Case 2
neutron -> proton + e- + anti-nu

Is that correct? Anyone know? It looks like it works. But that doesn't mean its right.

Comments

[dicedork.livejournal.com]

These protons go straight to my hips.

Seriously though Beta Decay sounds like a really sugary snack.

[danaeris.livejournal.com]

I just can't keep myself away from that beta beta pi.

It tastes so good, seems endless, and each bite is different -- it never even repeats itself!

[dicedork.livejournal.com]

I suppose I asked for that.

[danaeris.livejournal.com]

Aw, c'mon. There's nothing quite like extremely silly, punish, late-night geeking. You know you secretly wanted this. ;p

[dicedork.livejournal.com]

I'm only barely able to hang on in the math and physics geeking department. Now if you want to quote Yoda or do your Jean Luc Picard impression, I'm all for that....

[danaeris.livejournal.com]

mmm, yes. Hang on, you do. Do not barely hang on. Just hang on. yes.

[98.livejournal.com]

It is correct.

[qedrakmar.livejournal.com]

If you're unsure, you could always just check a Table of Nuclides, of which there are many available on the net.

Off the top of my head, Proton -> Neutron + Positron + Something for conservation, but I don't remember what that something is. I would expect it to have mass equal to the energy of the positron expulsion, so a neutrino makes sense.

[auros]

I'm pretty sure the "something" is a neutrino of some flavor, but I forget which. (I guess probably an electron neutrino. The others are what, Tau, and, uh... something else. *g*)

Anyways, yeah, a neutron can decay into a proton and an electron. The electron is the "beta particle" of "beta radiation" or "beta decay". (And of course an "alpha particle" is basically a helium nucleus.)

I'm not totally sure what would happen in a beta decay where you emitted a positron instead of an electron. I remember that it's possible, but it seems like that would leave you with a negatively-charged heavy particle (as contrasted with a light particle like an electron, or a near-massless particle like a neutrino) in the nucleus, which is weird. Maybe it's actually a proton that emits the positron, thus turning it into a neutron?