3 lectures: Nuclear Physics Particle Physics 1 Particle Physics 2. Nuclear and Particle Physics. Nuclear Physics Topics. Composition of Nucleus features of nuclei Nuclear Models nuclear energy Fission Fusion Summary. About Units. Energy - electron-volt
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opposite of “cathode rays”
nucleus (1900 – 1920)
613C* 612C + n
Both a, gdiscrete spectrum because
Ea, g= Ei – Ef
But b spectrum continuous
Energy conservation violated??
Bohr:: “At the present stage of atomic theory, however, we may say that we have no argument, either empirical or theoretical, for upholding the energy principle in the case of β-ray disintegrations”
F. A. Scott, Phys. Rev.48, 391 (1935)Puzzle with Beta Spectrum
Positron track going
upward through lead
energy units MeV/c2
Problem: Estimate the lowest possible energy of a neutron contained in a typical nucleus of radius 1.33×10-15 m.
E = p2/2m = (cp)2/2mc2
x p = h/2 x (cp) = hc/2
(cp) = hc/(2 x) = hc/(2 r)
(cp) = 6.63x10-34 Js * 3x108 m/s / (2 * 1.33x10-15 m)
(cp) = 2.38x10-11 J = 148.6 MeV
E = p2/2m = (cp)2/2mc2 = (148.6 MeV)2/(2*940 MeV) = 11.7 MeV
At t = 1/,
N is 1/e (0.368)
of the original amount
In each potential well, the lowest energy states are occupied.
Because of the Coulomb repulsion the proton well is shallower than that of the neutron.
But the nuclear energy is minimized when the maximum energy level is about the same for protons and neutrons
Therefore, as Z increases we would expect nuclei to contain progressively more neutrons than protons.
U has A = 238, Z = 92Fermi-Gas Model of Nucleus
+ about 200 MeV energy
1H + 1H → 2H + e+ + n
e+ + e- → g + g
2H + 1H → 3He + g
3He + 3He → 4He + 1H + 1H
1 pp collision in 1022→ fusion!
Sir Fred Hoyle
7.65 MeV above 12C ground state