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Asked by to Becky, Clara, Daniel, Simon, Thomas on 16 Mar 2014. This question was also asked by .
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Daniel Roach answered on 16 Mar 2014:
Neutrons do indeed have a mass. The mass of the neutron is 1.674 x 10-27 kg.
So that’s 0.000000000000000000000000001674 kg! I hope I’ve counted the number of zeros right:)
Neurons, being cells in the brain, are much, much bigger… but not sure how much mass they contain.
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Thomas Elias Cocolios answered on 16 Mar 2014:
All particles we know of in the universe have mass, except the photon. As such, the neutron has mass too (let’s thank Daniel for the value!).
In nuclear physics, though, we do not like to work with kg (have you seen all those 0’s!). Instead, we work in ‘Atomic Mass Units’ (a.m.u.), which have actually been used to redefine the mass altogether. As such, the definition of mass is that 1 mol of carbon-12 is 12 a.m.u. (where 1 mol = 602,214,129,000,000,000,000,000 atoms).
In those units, the neutron (which you’d expect to be 1) has actually 1.00866491600 a.m.u. And the proton, 1.007276466812 a.m.u. That tiny difference (~0.0014 a.m.u.) is actually the reason why a free neutron (i.e. one that is not in a nucleus) is radioactive and decays into a proton (within 10 minutes).
Finally, the weird particles whose mass we are still looking for are the neutrinos (is that what you might have been enquiring about?). Those are very tiny particles that are emitted in the beta decay process (e.g. when the neutron decays to a proton). We know it must exist to balance the equations and to was eventually found. We actually now know that there are millions flying through the Earth, and through us all, all the time! They just go on their way and live us alone. Through the observation of what is known as ‘flavour oscillation’, we know that they must have a mass too. We just do not know how big that value is and thousands of physicists work on that topic all over the world (like in Manchester!) I personally involved in many measurements that contribute to solving this puzzle, such the determination of nuclear form factors with transfer reactions, and Q-value measurements with ISOLTRAP at CERN.
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Clara Nellist answered on 19 Mar 2014:
To extend on the answers given by Simon and Thomas, in particle physics we don’t like working in kg or a.m.u.
We use Einstein’s equation E = mc^2 (where ^2 just means squared) to talk about mass (m) and energy (E) as the same thing. We work in something called eV. This is the energy required to push 1 electron through 1 volt (or electric potential difference).
This is now very useful for us, because we start to ignore the c’s in our maths by making them = to 1 (called natural units) and we can talk about mass and energy almost interchangeably!
This means that a neutron has a mass of 939 MeV. Where the MeV means mega-electron volt and it’s = 1,000,000 eV, which is a 1 with 6 zeros after. There’s also GeV (1 with 9 zeros) and TeV (1 with 12 zeros). In contrast, the neutrino (if that was the second part of your question) has a mass of *less* than about 0.23 eV. I say less than, because we know it’s small, but not how small. We’re still trying to measure it.
If you see anything written about the Large Hadron Collider there will be a lot things written in eV. For example, when running at the highest energy, the LHC will have a collision energy of 14 TeV. Also the newly discovered Higgs boson has a mass of 125 GeV. These are nice easy to read numbers for us! 🙂
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Simon Albright answered on 19 Mar 2014:
Yes, the neurons substantially more than the neutrons!
Neurons are cells so made of many many atoms.
Neutrons are one the particles that makes up an atom.I think Thomas, Clara and Daniel have covered the details though so I’ll leave with an amusing joke instead:
2 atoms are walking down the street, the first one turns to his friend and says “I think I just lost an electron!”, the friend says “Are you sure?” and the first one says:
“Yes, I’m positive!”
Comments
u11wetherallp commented on :
Thank you, and wow thats alot of big numbers