An experimental study of beta decay using the radiations from oriented nuclei

Abstract

Here we wish to specify the coefficients of the possible Legendre polynomials, P, (p»J), which have as an argument the cosine of the angle between^, a unit vector in the direction of electron emission, and J, a unit vector in the direction of the initial state nuclear spin. The degree to which the latter can be considered a unique direction in space is given by the products of all nuclear matrix elements of tensor rank L and L' times their associated energy-dependent lepton functions. The bgClLO's, which from A(kLL') consist of only bQ(OO), b^dl), and b^laa), multiply the isotropic tenii P" and give the shape factor, which is the departure of the spectral shape from that of an allowed transition, for unoriented nuclei.In general the higher terms of a distribution or correlation function must be divided by this isotropic term as a step in the interpretation of an experimental angular distribution as a function of energy.Let us now consider the beta distribution function as applied to a 7/2" -5/2 transition. ---b^dl) +bQ (22) Experimental Information on CeThe present information on the decay of Ce is shown in figure 1.Several spectral shape measurements have been made, [28,29,30,31] with some disagreement on the endpoint energies, but with no reports of other than an "allowed" shape.In general, data taken in the region between 4-35 and 580 kev has been extrapolated and subtracted from the total spectrum to yield an "allowed" spectrum for the 435 kev transition, although the lower region is somewhat masked by conversion and Auger electrons.In two cases P -Y coincidences were used to separate the inner beta branch [29,32], which was found to be "allowed" in shape in the higher energy region for which measurements were reported. These investigations are sjtressed because the present results indicate that for the 580 kev spectrum there should be some deviation from an"allowed"shape which might be observed in a careful measurement. ionic radii involved in the nuclear paramagnetic resonance determination.As mentioned in the previous section, a simultaneous measurement of the gamma angular distribution and linear polarization in a nuclear orientation experiment [20] gave the ratio of electric quadrupole to magnetic dipole amplitude in the gamma transition as 0.08 ± 0,02. This experiment also gives information on the contribution of different tensor rank operators in the inner beta transition, but this effect is obscured by the uncertainty in the gamma-mult ipole mixing ratio. pulse-height channels.The gamma distribution is sampled by three 2" x 2" Nal counters, connected in parallel, lying in an equatorial plane with respect to the c-axis of the source crystal and spaced 3.5 inches from the activity. The crystal was then mounted in the apparatus, the dewars were slipped on, and the assembly was slowly cooled to the temperature of liquid nitrogen. At this point the helium space and experimental space were evacuated, helium gas was introduced and liquid helium then added.Pumping on the liquid helium reduced the temperat...