2
$\begingroup$

For example, the ground state of a nuclei is $0^+$, and we can excite $1^-$ state with a circular polarized gamma photon, which has a spin angular momentum $1\hbar$. This satisfies the selection rule for E1 (electric dipole) transition.

However, if we want a high spin state, say $2^+$, excited from the ground state, and since we need a photon who carries $2\hbar$ angular momentum to satisfy the angular momentum conservation, what kind of gamma photons is that? I know the decay from $2^+$ to $0^+$ can be an E2 (electric quadruple) transition, but is that quadruple gamma field needed for the same excitation, or we can just use a normal gamma beam?

$\endgroup$
1
$\begingroup$

Most high-spin spectroscopy is done on nuclei created in collisions. The volume of phase space for a beam-target or beam-beam collision to be exactly head-on is very small, so in the rest frame of the collision there is always some angular momentum; that angular momentum may be carried after the collision by rapidly-spinning daughter nuclei. A useful homework problem is to take your favorite heavy-nucleus accelerator, make some assumptions about the ratio of the impact parameter to the nuclear radius, and estimate the angular momentum involved in a collision. (The answer at RHIC.)

You can also populate high-spin states in the excited daughter products of decays and fissions.

I'm not aware of any experiment that has produced an ingoing quadrupole gamma ray field; I'm not sure that's a thing.

$\endgroup$
  • $\begingroup$ Plane waves naturally include all multipole components, with an excitation rate of the order of $(a/\lambda)^\ell$ for a system of size $a$. With optical radiation this is possible (octupole example). Nuclear transitions have a smaller system size, but the wavelength can also be much shorter - at 200 MeV the wavelength is ~1 fm, so as you approach that range quadrupole and higher multipoles become more naturally accessible? $\endgroup$ – Emilio Pisanty Dec 8 '17 at 23:17
  • $\begingroup$ A lot of Couloumb interaction, particularly for low-level stages. This conference paper iopscience.iop.org/article/10.1088/1742-6596/322/1/012004/pdf contains useful information. $\endgroup$ – ZeroTheHero Dec 9 '17 at 3:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.