How do you calculate the mass of proton or a neutron?

Question

How do you calculate the mass of proton or a neutron?

Answer 1

Wikipedia comments,’... After the discovery of the electron by J.J. Thomson, Goldstein suggested that since the atom is electrically neutral there must be a positively charged particle in the atom and tried to discover it. He used the "canal rays" observed to be moving against the electron flow in cathode ray tubes. After the electron had been removed from particles inside the cathode ray tube they became positively charged and moved towards the cathode. Most of the charged particles passed through the cathode, it being perforated, and produced a glow on the glass. At this point, Goldstein believed that he had discovered the proton. When he calculated the ratio of charge to mass of this new particle (which in case of the electron was found to be the same for every gas that was used in the cathode ray tube) was found to be different when the gases used were changed. The reason was simple. What Goldstein assumed to be a proton was actually an ion. He gave up his work there, but promised that "he would return." However, he was widely ignored.'

In 1919, Rutherford discovered protons were emitted when alpha particles bombarded nitrogen nuclei. The reaction 14N(α,p)17O was also the first transmutation of elements.

A proton's charge-mass ratio may be measured by allowing a proton of known velocity to enter a magnetic field and then measuring the angle of deflection. Hence, using the known value for the charge of a proton the mass may be calculated.

Wikipedia further adds, 'In 1930 Walther Bothe and H. Becker in Germany found that if the very energetic alpha particles emitted from polonium fell on certain light elements, specifically beryllium, boron, or lithium, an unusually penetrating radiation was produced. At first this radiation was thought to be gamma radiation, although it was more penetrating than any gamma rays known, and the details of experimental results were very difficult to interpret on this basis. The next important contribution was reported in 1932 by Irène Joliot-Curie and Frédéric Joliot in Paris. They showed that if this unknown radiation fell on paraffin or any other hydrogen-containing compound it ejected protons of very high energy. This was not in itself inconsistent with the assumed gamma ray nature of the new radiation, but detailed quantitative analysis of the data became increasingly difficult to reconcile with such a hypothesis. Finally, in 1932 the physicist James Chadwick in England performed a series of experiments showing that the gamma ray hypothesis was untenable. He suggested that in fact the new radiation consisted of uncharged particles of approximately the mass of the proton, and he performed a series of experiments verifying his suggestion.'

Chadwick wrote, '...It is possible to prove that the mass of the neutron is roughly equal to that of the proton, by combining the evidence from the hydrogen collisions with that from the nitrogen collisions. In the succeeding paper, Feather records experiments in which about 100 tracks of nitrogen recoil atoms have been photographed in the expansion chamber. The measurement of the tracks shows that the maximum range of the recoil atoms is 3•5 mm. in air at 15 °C. and 760 mm. pressure, corresponding to a velocity of 4•7 x 108 cm. per second according to Blackett and Lees. If M, V be the mass and velocity of the neutron then the maximum velocity given to a hydrogen atom is

up = (2M / M + 1) • V

and the maximum velocity given to a nitrogen atom is

un = (2M / M + 14) • V

whence

M + 14 / M + 1 = up / un = 3•3 x 109 / 4•7 x 108 ,

...



and

M = 1•15.

The total error in the estimation of the velocity of the nitrogen recoil atom may easily be about 10 per cent., and it is legitimate to conclude that the mass of the neutron is very nearly the same as the mass of the proton.'

Answer 2

E=mc^2.now u have to know enargy of proton and c=is speed of light.m=E/c^2.

Answer 3

It is very easy if you have a copy of the periodic table of elements handy. The atomic mass is mass of the atom. The mass of an atom is made up primarily by the protons and neutrons. I would round down to the nearest even number. I say to round down because electrons do make up part of the mass, just not very much if it, and divide by two. That is the mass of the protons and the neutrons. Then divide that number by the amount of protons in the atom, and that gives you the mass of one proton. Same thing applies for a neutron.

Answer 4

Just use the accepted values. Calculating the real thing would take some pretty crazy scientific equipment.