# Where do all the neutrons go? **URL:** \ **Category:** Factual Questions\ **Created:** [April 6, 2001, 2:54pm UTC](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067 "2001-04-06T14:54:16Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\ **Post date:** [February 11, 2016, 9:16pm UTC](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067/21 "2016-02-11T21:16:37Z")
> [@John\_Mace](#): > > How many neutrons have disappeared in 15 years? Can neutrons from radiation turning to hydrogen substantially mitigate hydrogen losses from the atmosphere? ---
**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\ **Post date:** [February 12, 2016, 1:52am UTC](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067/22 "2016-02-12T01:52:47Z")
> [@John\_Mace](#): > > How many neutrons have disappeared in 15 years? What John Mace is trying to say is: ZOMBIE THREAD!!! 😛 ---
**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\ **Post date:** [February 12, 2016, 1:53am UTC](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067/23 "2016-02-12T01:53:57Z")
> [@beowulff](#): > > As any Future Nukular Engineer should know, Neutrinos are almost massless, and have a tiny cross-section for interaction with normal matter. So, they will keep going in whatever direction the started at for many light-years. Surely they are influenced by gravity, though! ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [February 12, 2016, 2:07am UTC](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067/24 "2016-02-12T02:07:24Z")
> [@tracer](#): > > Surely they are influenced by gravity, though! Sure, but so is Hydrogen, and that escapes from the Earth’s gravity, and it’s vastly more massive… ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [February 12, 2016, 3:18am UTC](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067/25 "2016-02-12T03:18:14Z")
Specifically, a proton + electron + neutrino weighs about 1.4 \* 10[sup]-30[/sup]kg less than a neutron. A neutrino has mass on the order of 10[sup]-37[/sup] kg (and may be a bunch less). If even a small fraction of the energy liberated in the decay ends up in the neutrino the kinetic energy is going to totally dominate the mass energy, which is the sign of something moving real fast. These things are almost certain to be born moving faster than escape velocity. ---
**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:** [February 12, 2016, 3:25am UTC](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067/26 "2016-02-12T03:25:55Z")
I don’t think that there’s anything short of a black hole that could prevent a neutrino of typical energy from escaping via its gravity. I mean, theoretically, you could have a neutrino of sufficiently low energy that it could be captured by a neutron star, or a regular star, or a planet… but typical neutrino energies are so far above that level that it wasn’t even until a couple of decades ago that we realized they even had a mass. EDIT: And there **leahcim** goes giving actual numbers. To which I would add that in a decay, the lightest byproduct typically ends up with the largest share of the energy, far more than “even a small fraction”. ---
**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\ **Post date:** [February 16, 2016, 6:02pm UTC](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067/27 "2016-02-16T18:02:00Z")
> [@Chronos](#): > > I don’t think that there’s anything short of a black hole that could prevent a neutrino of typical energy from escaping via its gravity. True, but even a weak gravitational field should _deflect_ neutrinos to some extent – if only with the same degree of gravitational lensing that affects light. The claim was that neutrinos “will keep going in whatever direction the[y] started at for many light-years,” and I’m saying that unless they’re unaffected by gravity, that can’t be completely true. ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [February 16, 2016, 8:00pm UTC](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067/28 "2016-02-16T20:00:59Z")
> [@tracer](#): > > The claim was that neutrinos “will keep going in whatever direction the[y] started at for many light-years,” and I’m saying that unless they’re unaffected by gravity, that can’t be completely true. **Sheldon:** More wrong? Wrong is an absolute state and not subject to gradation. **Stuart:** Of course it is. It is a little wrong to say a tomato is a vegetable, it is very wrong to say it is a suspension bridge. It is a little wrong to say neutrinos travel in a perfectly straight line. It is very wrong to say say that they gather in the centre of the Earth. One would be hard-pressed to detect the difference between the path of a neutrino escaping from a decay on the surface of the earth and a straight line. I can’t even imagine what a particle that wasn’t affected by gravity would be like. It would definitely be a much weirder entity than just one that isn’t affected by the strong force. ---
**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:** [February 16, 2016, 8:40pm UTC](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067/29 "2016-02-16T20:40:26Z")
> [@](#): > > The claim was that neutrinos “will keep going in whatever direction the[y] started at for many light-years,” and I’m saying that unless they’re unaffected by gravity, that can’t be completely true. Well, first of all, that depends on what you mean by “the same direction”, because if they’re just affected by gravity, then the path they’re taking is the closest thing there is to a straight line. And even if we define “straight” using some global coordinate system, it would indeed be many, many lightyears before they ever got close enough to a significant enough mass that they’d deflect by any measurable amount. [Previous page](https://boards.straightdope.com/t/where-do-all-the-neutrons-go/61067.md?page=1)