News for hackers. Stuff that matters.

A comment on Physicists Pin Down Nuclear Reaction from Moments After the Big Bang. Parent comment

Re:Physicists Pin Down Nuclear Reaction from Moments After t... by ISL on Thursday November 12, 2020 @01:43AM (#25067143)
The protons that make up more than half of your mass are also mostly from the big bang.

Some of the hydrogen in the world around us is deuterium, again mostly from the big bang. When your body was assembled, and when you drink water/breathe, some of the generally-hydrogen sites in our bodies happen, instead, to be deuterated.

[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by warent on Thursday November 12, 2020 @03:24AM (#25067697)
Aren't 100% of the protons that make up your body from the big bang?
[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by p1mrx on Thursday November 12, 2020 @04:07AM (#25067933)
They're from the big bang indirectly, but they haven't all been protons the whole time.

For example: https://en.wikipedia.org/wiki/Beta_decay

[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by miemo23 on Thursday November 12, 2020 @04:06AM (#25067923)
well neutrons decay in about 10min (avg) into fresh new protons (plus an electron) so perhaps not
[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by robocat on Thursday November 12, 2020 @02:26PM (#25073819)
Half-life ~10 minutes, which has a mean of ~15 minutes. Per https://en.wikipedia.org/wiki/Free_neutron_decay
[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by saagarjha on Thursday November 12, 2020 @05:41AM (#25068499)
*free neutrons
[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by sandfly on Thursday November 12, 2020 @09:55AM (#25070497)
Is the free electron immediately captured by the H+ particle, or is the energy high enough that this can produce an acidic gas of H+?
[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by ISL on Thursday November 12, 2020 @12:56PM (#25072564)
The energy release in neutron beta-decay is ~780 keV. This should be compared with the hydrogen binding energy of ~13 eV.

Hence, there is far too much energy released for the electron to stay bound in essentially any case. If the neutrino carries away all the energy (with momentum conservation soaked up mostly by the recoiling proton), it could re-bind, but that process should be exceedingly rare. In that case, the result would see an (excited, probably) hydrogen atom recoiling away from the invisible neutrino.

[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by corty on Thursday November 12, 2020 @11:54AM (#25071741)
Conservation of momentum dictates that proton and electron will move away from each other. The decay energy might be absorbed by a nearby nucleus in an medium to a large part, leaving only a small momentum for both particles so they can form an atom, but usually it won't. In the average low-density case, the proton and electron will find other partners only after quite some cooldown.

In very rare cases most of the energy might also be carried away by the neutrino that is produced as well, so decay to hydrogen is not impossible in a vacuum.

[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by DrAwdeOccarim on Thursday November 12, 2020 @06:37AM (#25068748)
Wow, I didn't know that. Do you have a reference?
[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by magicalhippo on Thursday November 12, 2020 @06:48AM (#25068806)
https://en.wikipedia.org/wiki/Free_neutron_decay

https://phys.org/news/2020-09-mystery-neutron-lifetime.html

[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by DrAwdeOccarim on Friday November 13, 2020 @06:59AM (#25081352)
TIL. Thanks so much for sharing, this is wild...Reminds me of pair-production. Nuclear physics is so fascinating.
[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by delibes on Thursday November 12, 2020 @07:53AM (#25069287)
Just being a bit pedantic ... more than half? Atoms typically have more neutrons than protons, and neutrons also weigh slightly more. Surely I'm >50% neutrons by mass?
[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by ISL on Thursday November 12, 2020 @09:07AM (#25069954)
Agreed -- I should have gone with "roughly half" or "almost half". As I wrote last night, I incorrectly recalled that n/p is often below 1 -- if I had thought for a moment about high-Z nuclei, the error would have been obvious.

A great place for a reader to begin to reach their own conclusions is here: https://en.wikipedia.org/wiki/Neutron%E2%80%93proton_ratio

Thank you for the correction.

[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by marcosdumay on Thursday November 12, 2020 @08:49AM (#25069785)
Hydrogen mostly does not have neutrons. You have a lot of those.
[ Parent | on HN ]
Re:Physicists Pin Down Nuclear Reaction from Moments After t... by CapriciousCptl on Thursday November 12, 2020 @09:03AM (#25069906)
It’s probably close to 50%. 80% of your mass is water and carbon. Hydrogen makes up 10% taken by itself but generally didn’t have a neutron which balances out the comparatives rare bigger elements with more neutrons.
[ Parent | on HN ]