# I say, I say, I say! What's the difference between a neutron and an antineutron?.....
**URL:** https://boards.straightdope.com/t/i-say-i-say-i-say-whats-the-difference-between-a-neutron-and-an-antineutron/175524
**Category:** Factual Questions
**Created:** [May 15, 2003, 8:20pm UTC](https://boards.straightdope.com/t/i-say-i-say-i-say-whats-the-difference-between-a-neutron-and-an-antineutron/175524 "2003-05-15T20:20:18Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)
#### Post date: [May 15, 2003, 8:20pm UTC](https://boards.straightdope.com/t/i-say-i-say-i-say-whats-the-difference-between-a-neutron-and-an-antineutron/175524/1 "2003-05-15T20:20:18Z")
Well obviously there is some difference, but apart from the fact that when one collides with the other they anilihate each other, how can you tell one from the other?
The only possible way I could think of is using the conservation of hadrons if you so one being formed in a particle reaction, but if you just have a particle that is a neutron or an antineutron how could you tell which it was?
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [May 15, 2003, 8:23pm UTC](https://boards.straightdope.com/t/i-say-i-say-i-say-whats-the-difference-between-a-neutron-and-an-antineutron/175524/2 "2003-05-15T20:23:51Z")
They have opposite spin. You can tell from that.
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### Author:  [@Keeve](https://boards.straightdope.com/u/Keeve)
#### Post date: [May 15, 2003, 8:30pm UTC](https://boards.straightdope.com/t/i-say-i-say-i-say-whats-the-difference-between-a-neutron-and-an-antineutron/175524/3 "2003-05-15T20:30:45Z")
IANAParticlePhysicist, but my guess is that the antineutron has negative mass.
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### Author:  [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)
#### Post date: [May 15, 2003, 8:31pm UTC](https://boards.straightdope.com/t/i-say-i-say-i-say-whats-the-difference-between-a-neutron-and-an-antineutron/175524/4 "2003-05-15T20:31:57Z")
Sorry that should of been baryons, not hadrons.
Spin would seem to be the only way to tell the two apart then without destroying them.
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### Author:  [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)
#### Post date: [May 15, 2003, 8:34pm UTC](https://boards.straightdope.com/t/i-say-i-say-i-say-whats-the-difference-between-a-neutron-and-an-antineutron/175524/5 "2003-05-15T20:34:33Z")
sorry right the fiirst time, it was hadrons (I was once upon a time studying physics in a degree course but along time ago).
Keeve, antiparticles have postive mass, infact 'cept for hypothetical exotic particles, all particles have postive mass.
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### Author:  [@FriendRob](https://boards.straightdope.com/u/FriendRob)
#### Post date: [May 15, 2003, 9:20pm UTC](https://boards.straightdope.com/t/i-say-i-say-i-say-whats-the-difference-between-a-neutron-and-an-antineutron/175524/6 "2003-05-15T21:20:57Z")
Well, if you could peer into it, you would see that it has a quark with charge -2/3 (anti-up) and two quarks with charge +1/3 (anti-down). A neutron would have quarks of the opposite charges. Problem is, it takes an awful lot of energy to scatter off a quark, so you would blow apart the antineutron (almost) for sure. But hey, I’m a theorist, and I answered the question. Find an experimentalist to figure out HOW to do it.
BTW, a neutron or antineutron is both a hadron (particle made of quarks) and a baryon (particle made of 3 quarks).
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### Author:  [@FriendRob](https://boards.straightdope.com/u/FriendRob)
#### Post date: [May 15, 2003, 9:32pm UTC](https://boards.straightdope.com/t/i-say-i-say-i-say-whats-the-difference-between-a-neutron-and-an-antineutron/175524/7 "2003-05-15T21:32:33Z")
Also, the spin is the _same_ for both. Both have “spin 1/2”, which means if you measure one component of the spin it can be either +1/2 h-bar or -1/2 h-bar.
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### Author:  [@dtilque](https://boards.straightdope.com/u/dtilque)
#### Post date: [May 15, 2003, 9:36pm UTC](https://boards.straightdope.com/t/i-say-i-say-i-say-whats-the-difference-between-a-neutron-and-an-antineutron/175524/8 "2003-05-15T21:36:08Z")
Free neutrons are not stable and will decompose into a proton and electron. Half-life of about 12 minutes or so, I think.
A free anti-neutron will decompose into a anti-proton and anti-electron.