11 Matching Results

Search Results

Advanced search parameters have been applied.

Lifetimes of high-spin states of /sup 160/ /sup 161/Yb

Description: Recoil-distance measurements of lifetimes of high-spin states of /sup 160/ /sup 161/Yb are described. While the results for the ground band of /sup 160/Yb are not inconsistent with centrifugal stretching, the addition of one or more quasineutrons seems to cause a reduction in collectivity which depends on frequency but not, for the case examined, on the type of quasineutron. 9 references.
Date: January 1, 1982
Creator: Fewell, M.P.; Baktash, C.; Guidry, M.W.; Hattula, J.S.; Johnson, N.R.; Lee, I.Y. et al.
Partner: UNT Libraries Government Documents Department

Recent experiments at Brookhaven: level structure of N = 86 isotones /sup 156/Yb and /sup 150/Gd

Description: States of the N = 86 isotones /sup 156/Yb and /sup 150/Gd have been studied by means of the /sup 144/Sm(/sup 16/O,4n)/sup 156/Yb, /sup 113/In(/sup 46/Ti,p2n)/sup 156/Yb, and /sup 124/Sn(/sup 30/Si,4n)/sup 150/Gd reactions. Levels have been established to spin 36 h-bar and over 12.5 MeV in excitation in /sup 150/Gd and to beyond spin 25 h-bar in /sup 156/Yb. The systematics of levels in the N = 86 isotones from /sup 150/Gd to /sup 156/Yb are described, and the near-spherical shell model description for states in this region to near spin 30 h-bar is discussed. A T/sub 1/2/ = 6 ns, 72-keV isomeric transition in /sup 156/Yb has been discovered, and an E1 multipolarity is assigned to this transition. The spin-parity of the isomeric state is established as 11/sup -/. 6 figures.
Date: January 1, 1980
Creator: Sunyar, A W
Partner: UNT Libraries Government Documents Department

Evolution of nuclear shapes at high spins

Description: The dynamic electric quadrupole (E2) moments are a direct reflection of the collective aspects of the nuclear wave functions. For this, Doppler-shift lifetime measurements have been done utilizing primarily the recoil-distance technique. The nuclei with neutron number N approx. 90 possess many interesting properties. These nuclei have very shallow minima in their potential energy surfaces, and thus, are very susceptible to deformation driving influences. It is the evolution of nuclear shapes as a function of spin or rotational frequency for these nuclei that has commanded much interest in the lifetime measurements discussed here. There is growing evidence that many deformed nuclei which have prolate shapes in their ground states conform to triaxial or oblate shapes at higher spins. Since the E2 matrix elements along the yrast line are sensitive indicators of deformation changes, measurements of lifetimes of these states to provide the matrix elements has become the major avenue for tracing the evolving shape of a nucleus at high spin. Of the several nuclei we have studied with N approx. 90, those to be discussed here are /sup 160,161/Yb and /sup 158/Er. In addition, the preliminary, but interesting and surprising results from our recent investigation of the N = 98 nucleus, /sup 172/W are briefly discussed. 14 refs., 5 figs.
Date: January 1, 1985
Creator: Johnson, N.R.
Partner: UNT Libraries Government Documents Department

High-spin properties of some nuclei around A = 160

Description: Two new types of behavior have been observed in /sup 156/Er. The first is a terminating band ending on a 42+ fully aligned state. The second is a strong cross feeding among four negative parity bands, due most likely to a severe reduction or collapse of the neutron pairing. In /sup 158/Er we have found two sequences feeding the 38+ level; one slow and one fast. This suggests that some feeding goes through regions of oblate (or nearly so) shapes, and some does not. Lifetimes have been determined for levels around 30+ in /sup 166/Yb, which seem to be longer than is easily explained. 23 refs, 8 figs.
Date: May 1, 1985
Creator: Stephens, F.S.
Partner: UNT Libraries Government Documents Department

Limits of studying high-spin states by discrete-line gamma-ray spectroscopy

Description: Recent (HI, xn) data on rotational Yb and Hf nuclei are used to describe the motivations and techniques for pushing discrete-line spectroscopy to the realm of the weakly populated yrast and non-yrast states. Three aspects of these studies are discussed: extraction of moments of inertia in different aligned bands, observation and understanding of high-frequency band crossings, and dependence of feeding patterns on nuclear structure.
Date: January 1, 1980
Creator: Riedinger, L.L.
Partner: UNT Libraries Government Documents Department

Multiquasiparticle configuration effects deduced from the very high frequency discrete lines spectroscopy of /sup 165/Yb

Description: New experimental data are presented for /sup 165/Yb in which three already known rotational bands are extended up to very high angular frequencies. We do not observe, below h-bar omega/sub c/ approx. 0.45 MeV in any of these three bands the second discontinuity occuring for h-bar omega/sub c/ approx. 0.42 MeV in N = 90 nuclei. Furthermore, we observe in these three sequences a dealignment of high enough amplitude that it cannot be explained in terms of a single quasi-neutron configuration, and must then be due to a collective effect. A gradual decrease of the neutron pairing with increasing angular frequencies is suggested.
Date: January 1, 1982
Creator: Schuck, C.; Bendjallah, N.; Diamond, R.M.; Ellis-Akovali, Y.; Lindenberg, K.H.; Newton, J.O. et al.
Partner: UNT Libraries Government Documents Department

gamma. -ray decay and nuclear shapes in /sup 158/Yb

Description: The decay of the entry states in /sup 158/Yb populated in the reactions of 149 MeV /sup 20/Ne with /sup 144/Nd and /sup 146/Nd has been investigated with a 4 ..pi.. multidetector system gated by a Ge counter. The average exitation energy, the ..gamma..-ray spectra and the angular distributions as a function of multiplicity show several changes in the ..gamma..-ray decay. These changes suggest a transition from prolate to particle aligned oblate configuration at I approx. 28. At I 38 to 48 collective transitions with dipole and quadrupole component are observed. Possible explanations for these transitions are discussed in terms of nuclear shapes. Furthermore, above I approx. 48 the dipole component disappears suggesting a further change toward more triaxial shape. 19 references.
Date: January 1, 1982
Creator: Jaeaeskelaeinen, M.; Sarantites, D.G.; Dilmanian, F.A.; Woodward, R.; Puchta, H.; Beene, J.R. et al.
Partner: UNT Libraries Government Documents Department

Evolution of nuclear shapes in /sup 157/-/sup 161/Yb as a function of spin and neutron number

Description: The population distributions of the entry states, the entry lines <E*> versus multiplicity, the energy spectra and the angular distributions of the continuum ..gamma..-rays as a function of multiplicity in /sup 157/-/sup 161/Yb from the reactions of 136 MeV and 149 MeV /sup 20/Ne with /sup 144/Nd and /sup 146/Nd have been investigated with a 4pi multidetector system gated with a Ge detector. The observed entry lines and ..gamma..-decay modes indicate change for N = 87 - 9l Yb isotopes suggests an evolution of nuclear shapes from prolate at low spins to particle aligned oblate structure for /sup 157/Yb and /sup 158/Yb followed by the onset of high-K bands built on largely deformed oblate states at increasingly higher spin between 38 and 50 n with increasing neutron number for /sup 157/-/sup 161/Yb. Furthermore evidence for an evolution to triaxial shape at I approx. = 50 for /sup 158/Yb was found. 23 references.
Date: January 1, 1982
Creator: Jaeaeskelaeinen, M.; Sarantites, D.G.; Dilmanian, F.A.; Woodward, R.; Puchta, H.; Beene, J.R. et al.
Partner: UNT Libraries Government Documents Department

Research highlights with the spin spectrometer

Description: The excitation energy and angular momentum dependence of the entry states in fusion reactions measured with the spin spectrometer is discussed. A new decay mode involving the onset of localized stretched dipole radiation at half the accompanying stretched E2 collective radiation is found in /sup 157 -161/Yb. The appearance of this mode correlates smoothly with neutron number and spin. Possible interpretations are presented in terms of the evolution of the nuclear shapes from prolate to aligned-quasiparticle oblate to collective oblate and then to triaxial. Evidence for nuclear deformation that increases with spin at very high excitation is presented based on ..cap alpha..-particle angular distributions measured relative to the spin direction, using a new method for deriving the spin alignment.
Date: January 1, 1982
Creator: Sarantites, D.G.; Jaeaeskelaeinen, M.; Dilmanian, F.A.; Puchta, H.; Woodward, R.; Beene, J.R. et al.
Partner: UNT Libraries Government Documents Department

Population and decay of high-spin states in /sup 157-161/Yb: evolution of nuclear shapes as a function spin and neutron number

Description: The population and decay of the entry states in /sup 157-161/Yb and /sup 155-158/Er from the reactions of 136- and 149-MeV /sup 20/Ne with /sup 144/Nd and /sup 146/Nd have been investigated with the Spin Spectrometer gated with a Ge detector. Statistical-model calculations reproduce the main features of the entry state populations. The entry lines, <E/sup */> as a function of multiplicity, M/sub ..gamma../ show changes in slope at high M/sub ..gamma../ which are due to changes in the decay mode as a result of changes in nuclear structure. Energy spectra of the continuum ..gamma..-rays and angular distributions as a function of M/sub ..gamma../ show the onset of a dipole component localized at 650 +- 100 keV accompanied by an equally intense quadrupole component at twice the energy that continues to evolve to higher energies with increasing multiplicity. For /sup 157/ /sup 158/ /sup 159/ /sup 160/ /sup 161/Yb the dipole component appears at M/sub ..gamma../ = 21,22,23,25, and 27 (at spin I approx. = 38,40,42,45, and 50), respectively. At precisely these multiplicities the entry lines show a decrease in slope. In /sup 158/Yb the dipole component disappears at M/sub ..gamma../ = 28 and the entry line resumes its original slope. The results are consistent with the following picture. At low spins for /sup 157/ /sup 158/Yb the nuclear shapes evolve from prolate to slightly oblate particle-aligned structures. At I approx. = 38,40,42,45, and 50 the /sup 157/ /sup 158/ /sup 159/ /sup 160/ /sup 161/Yb nuclei, respectively, develop high-K rotational bands which may be built on oblate structures with large deformation (epsilon approx. = 0.3). At I = 49 a transition to triaxial shape appears to occur in /sup 158/Yb.
Date: January 1, 1982
Creator: Jääskeläinen, M.; Sarantites, D. G.; Dilmanian, F .A.; Woodward, R.; Puchta, H.; Beene, J. R. et al.
Partner: UNT Libraries Government Documents Department

Gamma-spectrometry with Compton suppressed detectors arrays

Description: Recent results of experiments performed with two different Compton-suppressed detectors arrays in Daresbury and Berkeley (/sup 163,164/Yb and /sup 154/Er, respectively), are presented together with a brief description of the national French array presently under construction in Strasbourg. 25 refs., 15 figs.
Date: January 1, 1985
Creator: Schueck, C.; Hannachi, F.; Chapman, R.; Lisle, J.C.; Mo, J.N.; Paul, E. et al.
Partner: UNT Libraries Government Documents Department