How did we weigh the smallest particles such as the Neutron, proton, and electron?

Question

Understand that I know about the e/m experiment for the electron, and how magnetic & electric fields could be used to get exact measurements for both charged particles( Any details on the experiments for them would be great too though!) My main question applies toward the Neutron, with no charge it is hard to manipulate a single one, weigh it, and find a result. The only way I can imagine finding the result is taking a ion (Deuterium) of a small atom and - the weight of the proton. Problem is I don't know how this takes into account the binding energy. I'm not sure how methods of weighing/mass derivation work so I could be wrong about some of this. Again any answer would be great.

Answer 1

What is typically done was to recognize that there were particles sometimes detected that wouldn't leave ionizing trail since it wasn't charged. Instead these particles would interact with nuclides (the nucleus of a specific type of isotope) creating a signal using a scintillator (signal amplifier) and an oscilloscope (signal detector). I'm simplyfying enormously, of course.

By filtering out other signal events and tracking these types of particle events, physicists could use collision-energy/momentum high energy physics to determine what the mass was estimated to be. By amassing large amounts of statistical data on the mass, they could remove random errors, and assuming there was nothing wrong their detector or thier math (systematic errors), one could calculated the mass of and neutron to a fairly high accuracy.

The same process can be used for charged particles - electron, protons quarks - by smashing atoms together in a cloud chamber and following the tracks made by a the charges in E+M fields. As you know one can find not only the C/m ratio but with collision physics again you can track the mass, momentum, and energys for a variety of particles.

Answer 2

i dont think we know the value of thier weight. i was taught that protons and neutrons weight count was equal to one. and that the electron is so small that its weight is counted as zero but is actually something like 1/2167 that of a proton.

Answer 3

outstanding question, and excellent reasoning.  You are right on all counts. You also made me realise that I had never ask myself this question, and should have, so I went to the original literature.

The binding energy you refer to has been determined by measuring the energy of the gamma ray emitted when a proton and a neutron combine to make a deuterium nucleus. (You do this using

E = h nu = hc/lambda and finding lambda by diffraction through a crystal). Then convert this binding energy to mass units using

E = c^2

and now you can write

proton mass + neutron mass - binding energy = deuteron mass

with proton and deuteron e/m and e determined by methods you know about, and neutron mass your only unknown

Answer 4

With expensive equipment

One of the ways was with hydrogen atom

The weight of a proton is somewhat close to the weight of a hydrogen atom, which is the smallest of all atoms. The weight of a neutron is almost the same as a proton. If you divide the weight of a hydrogen atom by 1837, you will get the weight of an electron. Thus electron is the lightest of the subatomic particles.

hopefully that helps

Answer 5

There are lots of ways to do this, with varying degrees of cost and accuracy.  For example, for charged particles, you can accelerate them in an electric field and then let them pass through a magnetic field which causes them to bend.  By looking at the amount that they bend, it's possible to figure out their mass (for the same amount of charge, a heavier particle bends less).

Another possibility is to use scattering-- basically you bounce the particles of other known masses or entities and by looking at their behavior (e.g., how fast they bounce off, or at what angle) you can determine their mass.

Of course there are lots of other exotic laboratory techniques as well.  This is an active area of research too.