Experimental study of time reversal invariance and atomic final state effects in nuclear transitions

Citation

Gimlett, James L. (1980) Experimental study of time reversal invariance and atomic final state effects in nuclear transitions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/n7sw-jy41. https://resolver.caltech.edu/CaltechTHESIS:10272016-131924862

Abstract

Experiments have been performed to test time reversal invariance in nuclei using gamma transitions of oriented ¹⁹¹Ir and ¹³¹Xe. The phase angle η associated with the imaginary part of the ratio of reduced matrix elements of the gamma transition was measured through observation of the angular distribution of the linear polarization from oriented nuclei. Interaction of the gamma ray with the atomic electron cloud can cause an additional phase shift ξ which is indistinguishable from the time-reversal phase η. Such an atomic final state effect has been observed for the 129 keV transition in ¹⁹¹Ir. Nuclear orientation was achieved with a large magnetic field (the hyperfine field of Ir in iron) and low temperature (20 to 30 mK obtained with a dilution refrigerator). A Compton polarimeter was used to measure linear polarization of the E2-Ml gamma ray. The matrix-element ratio was found to have an imaginary part corresponding to a phase angle (η+ξ) = (-4.8 ± 0.2) x 10^-3. This measurement is in agreement with the most recent final state calculations which give ξ = (-4.3 ± 0.4) x 10^-3. A limit |η| < 10^-3 is deduced for the time-reversal phase. In another experiment a phase angle η = (-1.2 ± 1.1) x 10^-3 was measured for the E2-Ml 364 keV transition in ¹³¹Xe, for which atomic final state effects are small. Both measurements are consistent with time reversal invariance.

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