Speaker
Micha Hass
(Weizmann Institute of Science)
Description
Since the discovery of parity violation in beta decay, Parity Non-Conservation (PNC)
in bound nuclei has provided a means to address the parity violating term in the
nuclear Hamiltonian due to the weak interaction component. The few cases identified
as promising ones have been studied but showed marginal or no effects.
In the case of 180Hf(8-) isomer, the PNC effect was studied nearly four decades ago
by observing its 501 keV gamma decay from a polarized source which showed a large
effect of ~10 standard deviations, i.e. 1.66±0.18%. Since then it has been the only
bound nucleus where the parity violation in its gamma decay is clearly and
unambiguously observed. This very uniqueness of the 180mHf case, and the
availability of a 180mHf(8-) beam from ISOLDE, are the basis for the present renewed
interest in this PNC case.
The 180mHf beam with 3.105 particles/s was implanted into a magnetized Fe host in
the NICOLE dilution refrigerator and is polarized using the low temperature
orientation method. The gamma decays from a total of ~5.1013 implanted 180mHf
nuclei are observed in 4 HPGe detectors placed at 90 degrees to each other and at a
distance of ~12 cm from the Fe foil and ~1cm from the cryostat wall. The direction
of magnetic field was changed every ~5 hrs. to left (L) or right (R) by changing the
direction of the current sent through the coil. This ensured minimization of
systematic errors.
The measured 0 to 180 degree asymmetry from a preliminary analysis yields A(gamma)
=1.14±0.052% in basic agreement with the earlier measurement. A careful analysis of
the complete data is underway and is expected to further improve upon the error.
The complete results, together with a detailed discussion, will be presented.
Author
Micha Hass
(Weizmann Institute of Science)
