## Physics Questions People Ask Fermilab

Is Antineutron the Same as Neutron?

You Wrote:
My name is Killian Lobato. I am a year 13 IB student in St. Julians Portugal. I have come across in my physics book the idea of anti matter. Anti matter is the same as its opposing matter but has an opposite charge. Now as the nuetron has no charge what makes its anti particle different. The idea i have is that the Anti Neutron is the fussion of an anti proton and an anti electron (a positron, i do not know the anti particle of proton).

Hello Killian,
thanks for your very interesting question. When you talk about particles, the charge and the mass are not the only possible descriptive elements we use. If you try to describe a person around you, you would use many items such as weight, hight, color of eyes, color of hair, ... ) Similarly, particles are described by many quantities, such as charge, mass, spin, isospin, lepton number, ... . In case of antiparticles, some of the above listed items are the same as for the particle( as for instance mass, spin, ... ) but some of them are different ( as for instance charge ( if the particle is charged), or lepton number, or ... .

In the case of a neutron, you are very much right, the charge cannot be opposite, since it does not have a charge. The trick is however, that the neutron is not an ELEMENTARY particle!!!

It is made from 3 other smaller particles, called QUARKS! Namely, the neutron is made out of one quark called Up quark and two quarks called Down quarks. ( just for reference, the proton is made out of two Up quarks and one Down quark). These quarks HAVE CHARGE!!! The charge of the Up is +2/3*1.606*10^-19 C and the charge of the Down is -1/3*1.606*10^-19 C. ( That way you can see, the neutron is really neutral and the proton has really charge +1.606*10^-19 C )

Now, the antineutron, is made out of one ANTI Up ( which has a charge -2/3*1.606*10^-19 C and two ANTI Downs ( each of them having a charge +1/3*1.606*10^-19 C), and that makes him very different from a neutron.

Your idea about the fusion reaction to create an antineutron is perfect, and it really could happen in laboratories such as Fermilab, where we have all the components necessary for the reaction. I say all the components, because you were missing a little particle essential for the fusion, namely the NEUTRINO.

Let us look at an ordinary neutron. If he is in an atomic nucleus, he is perfectly stable, and could stay there practically forever. However if a neutron is outside a nucleus, it becomes very unstable, and within 15 minutes it decays into an electron, a proton and an antineutrino!!!

In your case, an antineutron ( just do the charge conjugation) would decay into an antiproton ( that is it's name) a positron and a neutrino. Therefore if you take those three particles and let them undergo a fusion reaction, you get a ANTINEUTRON .

I hope this helped to understand this little mystery about antiparticles.

Cheers
Arnold Pompos

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