Antineutrons, protons, electrons

[dayglo]

Is it theoretically possible to have:

a) a helium atom with 2 protons, 2 electrons, and 2 antineutrons
b) a helium atom with 2 negatrons, 2 positrons, and 2 neutrons
c) a helium atom with 2 protons, 2 positrons and 2 neutrons

etc...

 

[The_Duck]

No:

a) Protons and antineutrons will not play nice together. One way to think about it is to note that protons contain up and down quarks, while antineutrons contain up and down antiquarks. These quarks and antiquarks will annihilate with each other and so you can't get a stable nucleus composed of protons and antineutrons.

b) What's a negatron? An antiproton? If so, this will have the same problem as a).

c) The protons will repel the positrons (because both have positive charge), so the positrons will go flying off into space.