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Keywords:

nuclear-orientation, transition, forces, impurities, asymmetry, tb-159, table, fe, Science & Technology, Physical Sciences, Physics, Nuclear, Physics, NUCLEAR-FORCES, TRANSITION, NONCONSERVATION, IMPURITIES, TABLE, nucl-ex, 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics, 5106 Nuclear and plasma physics

Abstract:

This paper reports measurements made using the technique of online nuclear orientation which reexamine the gamma decay of isomeric Hf-180(m) and specifically the 501 keV 8(-)-6(+) transition. The irregular admixture of E2 to M2/E3 multipolarity in this transition, deduced from the forward-backward asymmetry of its angular distribution, has for decades stood as the prime evidence for parity mixing in nuclear states. The experiment, based on ion implantation of the newly developed mass-separated Hf-180(m) beam at the CERN online isotope mass separator (ISOLDE) facility into an iron foil maintained at millikelvin temperatures, produces higher degrees of polarization than were achieved in previous studies of this system. The value found for the E2/M2 mixing ratio, epsilon=-0.0324(16)(19), is in close agreement with the previous published average value epsilon=-0.030(2), in full confirmation of the presence of the irregular E2 admixture in the 501 keV transition. The temperature dependence of the forward-backward asymmetry has been measured over a more extended range of nuclear polarization than previously possible, giving further evidence for parity mixing of the 8(-) and 8(+) levels and the deduced E2/M2 mixing ratio.