Part 1 Flashcards
Strong force
Nucleus loses material (alpha-decay, fission)
Weak force
Changes proton/neutrino ratio (beta-decay)
EM force
De-excitation by gamma-ray emission
Alpha decay
Heavy nuclei
Beta decay
All nuclei at each side of stability valley
Gamma decay
All nuclei in excited states
Proton emission
Few nuclei along proton drip line
Spontaneous fission
Mass, A>230
Spin-orbit coupling
LS-coupling arises from term in the nuclear potential. V(r) = V(r)_ws + W(r)LdotS. Causes splitting of levels and energy shift proportional to j(j+1) - l(l+1) - s(s+1). (With s=1/2)
Nuclear shell structure
Each nuclear state has intrinsic spin J and parity pi. Protons and neutrons pair up, every pair has parity, pi=1.
Even-even Nuclei
0+
Odd A Nuclei
Have one unpaired nucleon. The spin of the nucleus is equal to that of the unpaired nucleon. Parity=(-1)^l where l is the orbital angular momentum of the unpaired nucleon.
Odd-odd Nuclei
Unpaired proton with j_p and an unpaired neutron with j_n. Total spin of the nucleus is the vector sum of the two values and can take values between |j_p – j_n| and |j_p + j_n| in unit steps. Parity is given by (-1)^(l_p+l_n), where l_p and l_n are orbital angular momenta of the unpaired proton and neutron.
Fermi-Kurie plot
Can be calculated from beta spectra. Allows us to determine if an observed transition is allowed vs forbidden, and allows better determination of the end point energy. Straight line means no orbital angular momentum – pure fermi decay.
FT value
Comparative half-life. Correlation between Log(ft) and type of transition. The lowest permitted order of ‘forbiddeness’ will dominate the transition.
Three types of gamma-decay excited states
Single nucleon excitation states.
Vibrational excited states.
Rotational excited states.
Gamma decay: Single nucleon excitation states
Best for lowest-lying excitations of oddA nuclei near closed shells.
A low-lying states: last particle (valence nucleon) is excited to the next shell.
Higher energy states: braking a pair at a lower configuration in the shell structure.
Gamma decay: Vibrational excitation states
Occur when a nucleus oscillates about a spherical equilibrium shape. Form of the excitations can be represented by a multipole expansion.
