Polarization measurements of proton capture gamma rays

Abstract

The linear polarization has been measured of eight different gamma rays of widely differing energies (Eγ = 0.8 - 8.0 MeV) emitted at resonances in the 24Mg(p, γ)25Al, 30Si(p, γ)31P, and 32S(p, γ)33Cl reactions. The gamma rays emitted at 90° to the proton beam were Compton scattered in a 2″ NaI scintillation crystal and then detected in two 4″ NaI scintillation counters.

For six of the eight gamma rays mentioned above previous angular distribution measurements had left just two alternatives for either the spin or the parity of the corresponding resonance level, or for the E2/Ml mixing ratio. The present polarization measurements have resolved these ambiguities with the following results:

a. the 2.85 and 2.86 MeV levels in 33C1 have Jπ = 5/2+ and 3/2-, respectively;

b. the 2.69 and 2.24 MeV gamma rays observed at the 418 keV 24Mg(p, y) 25A1 resonance, and the 2.85 MeV gamma ray at the 580 keV 32S(p, γ)33Cl resonance have predominantly Ml character, while the 8.04 MeV gamma ray at the 776 keV 30Si(p, γ)31P reaction has predominantly E2 character.