E. F. Moore

New neutron-rich nuclei 103,104Zr and the A~100 region of deformation.

Partial decay schemes in the neutron-rich nuclei {sup 103}Zr and {sup 104}Zr have been measured for the first time and rotational bands in {sup 100--102}Zr have been extended to spins of up to 10{h bar} by observing prompt {gamma} rays from the spontaneous fisson of {sup 248}Cm. These nuclei are among the most deformed known at low spin and excitation energy. The level structures in the odd-{ital A} nuclei show that the {ital h}{sub 11/2} intruder orbital plays an important role in stabilizing the deformation in this region.

Excitation energies and spins of the yrast superdeformed band inHg191

The excitation energies and spins of the levels in the yrast superdeformed band of {sup 191}Hg have been determined from two single-step {gamma} transitions and the quasicontinuum spectrum connecting the superdeformed and normal-deformed states. The results are compared with those from theoretical mean-field calculations with different interactions. A discussion of pairing in superdeformed states is also included.

Differential lifetime measurements and configuration-dependent quadrupole moments for superdeformed bands in nuclei near 152Dy☆

Abstract High-precision lifetime measurements have been performed in superdeformed (SD) bands of 151,152 Dy and 151 Tb with the Doppler-shift attenuation method. Differences found in the quadrupole moments Q 0 of the yrast SD bands are understood in terms of shape polarization effects by the high- N intruder orbitals. Q 0 moments are also presented for three excited SD bands in 151 Dy. Recent calculations can account for most of the observations.

Correction factors for γ-ray relative intensities in the 66Ga radioisotope

Abstract We present here strong evidence that recently published values for the relative intensities of γ-ray lines in the 66 Ga(β + + EC) 66 Zn decay are incorrect at the higher energies (∼ 30% too low at 4.8 MeV). In particular, we find that our current results are consistent with a set of correction factors which were first suggested 20 years ago, but have gone largely ignored until now. Our validation of these little known correction factors will have bearing on experiments which use the 66 Ga radioisotope to extrapolate absolute detector efficiencies to higher energies. In particular, we discuss the conclusions of a recent D(p, γ ) 3 He experiment which will be strongly affected by our current results. The astrophysical S -factor data derived from this D(p, γ ) 3 He experiment are now seen to be systematically too low by ∼ 30%.

Superdeformed shapes and configurations in thallium nuclei

Superdeformation studies in {sup 189,191,192}Tl at Gammasphere are discussed. New results on {sup 191}Tl are the observation of interband transitions between the signature partner E2 bands and the measurement of an average quadrupole moment (Q{sub 0} = 18 {+-} 1 eb) for these superdeformed structures. These data enable them to derive absolute M1 strengths and confirm that the 81st proton occupies the [642]5/2 orbital. Tentative data for one superdeformed sequence in {sup 189}Tl are consistent with the prediction of a decrease in quadrupole deformation for the lightest nuclei at the limit of this island of superdeformation.

Lifetime measurements and dipole transition rates for superdeformed states in 190Hg

The Doppler-shift attenuation method was used to measure lifetimes of superdeformed (SD) states for both the yrast and the first excited superdeformed band of 190Hg. Intrinsic quadrupole moments Q o were extracted. For the first time, the dipole transition rates have been extracted for the inter-band transitions which connect the excited SD band to the yrast states in the second minimum. The results support the interpretation of the excited SD band as a rotational band built on an octupole vibration.

Strength distribution of γ-transitions deexciting superdeformed rotational bands

Abstract The strength distribution of the γ rays in the decay-out from superdeformed (SD) states is investigated by applying the maximum likelihood method, with special emphasis on the influence of the lower threshold given by experimental conditions. Clear graphical solutions are found, and a careful estimation of the dispersion in the values of the number of degrees of freedom and of the average strength of the most likely χ 2 distribution is carried out. For the 194 Hg nucleus, 41 primary transitions from the decay-out of SD states are identified above 2600 keV. It is concluded that they represent the strongest 10% of the transitions selected stochastically from a Porter-Thomas distribution. This would support the scenario of a statistical decay of SD states via coupling to a compound state at normal deformation. However, the occurrence of several very strong direct one-step transitions as previously observed in 194 Hg has a very small probability of the order of 10 −4 . This may indicate special selection rules governing the decay. However, based on the absence of strong primary transitions from SD states in adjacent nuclei, the situation in 194 Hg is viewed as a very lucky incidence.

Lifetime measurements of triaxial strongly deformed bands in {sup 163}Tm

With the Doppler Shift Attenuation Method, quadrupole transition moments Q{sub t} were determined for the two recently proposed triaxial strongly deformed (TSD) bands in {sup 163}Tm. The measured Q{sub t} values indicate that the deformation of these bands is larger than that of the yrast signature partners. However, the measured values are smaller than those predicted by theory. This observation appears to be valid for TSD bands in several nuclei of the region.

Absolute intensities of {gamma} rays in {sup 182}Hf decay

The absolute intensities of {gamma} rays produced in the decay of {sup 182}Hf were determined by measuring its {gamma}-ray spectra with high-resolution Ge spectrometers. Because the sample was chemically purified more than 30 years ago, the daughter {sup 182}Ta (t{sub 1/2}=114.43 d) was in secular equilibrium with {sup 182}Hf (t{sub 1/2}=8.90x10{sup 6} yr). The absolute intensities of {sup 182}Hf {gamma} rays were determined with respect to the intensities of {sup 182}Ta {gamma} lines. In order to minimize summing losses from the peak areas, spectra were measured at low absolute efficiencies. The absolute intensity of the 270.4-keV-{gamma} ray was found to be (79.0{+-}0.6)% per {sup 182}Hf {beta}{sup -} decay.

Lifetime measurements of superdeformed bands in 142Sm: A test of the additivity principle for quadrupole moments

Abstract Lifetime measurements with the Doppler shift attenuation method have been performed for the two superdeformed (SD) bands of 142Sm. The inferred transition quadrupole moments, Q0, are 11.7±0.1 eb for the yrast SD band and 13.2+0.8−0.7 eb for the excited SD band. These results are consistent with expectations from mean-field calculations, and indicate that the proposed additivity of contributions of individual orbitals to Q0 is valid for SD nuclei over an extended mass range in the vicinity of 152Dy.