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High-spin states of the neutron-rich 152Nd nucleus have been reinvestigated by measuring the prompt $ \gamma$ -rays in the spontaneous fission of 252Cf . The ground-state band and a side negative-parity band have been updated. A new band based on the 2243.7keV isomeric state has been identified. The half-life for the isomeric state has been measured to be 63(7)ns. The projected shell model is employed to study the band structure of this nucleus. The results show that the calculated levels of the bands are in good agreement with the experimental ones, and the isomeric state and the negative-parity band are based on the proton $ \pi$5/2-[532] ⊗ $ \pi$9/2+[404] and neutron $ \nu$3/2-[521] ⊗ $ \nu$5/2+[642] two-quasiparticles configurations, respectively. [ABSTRACT FROM AUTHOR]

Two similar sets of odd-parity bands are observed in each of three even–even neighbors, 108,110,112Ru, from a study of prompt spontaneous-fission gamma rays at Gammasphere. A careful study of the odd-parity levels of these nuclei shows evidence for the features of chiral doubling. Comparisons are made with reported other candidates for chiral doubling. [ABSTRACT FROM AUTHOR]

High-spin, even-parity bands in neutron-rich 108, 110, 112Ru nuclei were reinvestigated and considerably expanded by measuring many-fold prompt γ-ray coincidence events following the spontaneous fission of 252Cf with Gammasphere. Our high statistics data allow us to detect weaker transitions and bands not previously published. Also, gamma branching ratios, which are important for theory, are carefully measured from all levels. In 110Ru, we find a doubling of levels for both ground and quasi-gamma bands above the 8+ levels. There are likely two-phonon quasi-gamma bands in 110, 112Ru, as well as a bandhead level in 108Ru. The odd–even spin energy band staggering observed in the quasi-gamma bands in 108, 110, 112Ru and the doubling of levels in 110Ru present a challenge to theory. [ABSTRACT FROM AUTHOR]

Rotational bands in 110,112Ru and 108Mo have been investigated by means of γ-γ-γ and γ-γ(θ) coincidences of prompt γ rays emitted in the spontaneous fission of 252Cf. New ΔI = 1 negative parity doublet bands are found. These bands in 110,112Ru and 108Mo have all the properties expected for chiral vibrations. Microscopic calculations that combine the TAC mean-field with random phase approximation support this interpretation. [ABSTRACT FROM AUTHOR]

IBM-1 calculations for the fission products 108,110,112Ru have been carried out. The even–even isotopes of Ru can be described as transitional nuclei situated between the U(5) (spherical vibrator) and SO(6) (γ-unstable rotor) symmetries of the interacting Boson Model. At first, a Hamiltonian with only one- and two-body terms has been used. Excitation energies and B(E2) ratios of gamma transitions have been calculated. A satisfactory agreement has been obtained, with the exception of the odd–even staggering in the quasi-γ bands of 110,112Ru. The observed pattern is rather similar to the one for a rigid triaxial rotor. A calculation based on a Hamiltonian with three-body terms was able to remove this discrepancy. The relation between the IBM and the triaxial rotor model was also examined. [Copyright &y& Elsevier]

We have used our analysis of γ-γ-γ data (5.7 × 1011 triples and higher folds) taken with Gammasphere from prompt γ rays emitted in the spontaneous fission of 252Cf to study the collective bands in 104,106,108Mo. The one-phonon and two-phonon γ-vibrational bands and known two-quasiparticle bands in neutron-rich 104,106Mo were extended to higher spins. The one-and two-phonon γ-vibrational bands have remarkably close energies for transitions from the same spin states and identical moments of inertia. Several new bands are observed and are proposed as quasiparticle bands in 104,106Mo, along with the first β-type vibrational band in 106Mo. The quasiparticle bands have essentially constant moments of inertia near the rigid-body value that indicate blocking of the pairing interaction. Candidates for chiral doublet bands in 106Mo are strong. These are the first reported chiral vibrational bands in an even-even nucleus. [ABSTRACT FROM AUTHOR]

For the first time, average angular momenta of the ternary fission fragments100, 102Zr,106Mo,144, 146Ba and138, 140, 142Xe from the α-accompanied fission of252Cf were obtained from relative intensities of prompt γ-ray transitions with the use of the statistical model calculation. Average values of the angular momenta were compared with the corresponding values for the same fission fragments from the binary fission of252Cf. Results indicate the presence of a decreasing trend in the average values of angular momenta induced in ternary fission fragments compared to the same binary fission fragments. On the average, the total angular momentum extracted for ternary fission fragments is ∼1.4 ℏ lower than in binary fission. Consequently, results indicate that the mechanism of the ternary α-particles emission may directly effect an induction of angular momenta of fission fragments, and possible scenarios of such mechanisms are discussed. Further, the dependence of the angular momenta of106Mo and140Xe on the number of emitted neutrons from correlated pairs of primary fragments was obtained also showing a decreasing dependence of average angular momenta with increasing number of emitted neutrons. Consequences are briefly discussed. [ABSTRACT FROM AUTHOR]

The levels in [sup 162]Gd were identified in spontaneous fission studies. Its transition energies are remarkably similar to those in [sup 160]Gd. From that work, an analysis of yrast bands in even-even proton to neutron-rich Ba to Pb nuclei led to the discovery of a new phenomenon, shifted identical bands (SIB). SIBs are yrast bands in neighboring nuclei (a, b) with moments of inertia which are identical when shifted by a constant amount κ, so J[sub 1a](1 + κ) = J[sub 1b], from 2[sup +] to 8[sup +] and higher to 16[sup +]. Out of over 700 comparisons, 55 SIBs were found from stable to the most neutron-rich Ce-W nuclei with &κmacr; between 1.5% and 13%, where the spread in κ is less than ±1%, and only four identical bands (&κmacr; ≅ 0). As examples, we found for [sup 158]Sm-[sup 160]Gd, &κmacr; = (-3.2[sup +0.1, sub -0.2]) % (where the ± is the total spread in κ from -3.1 to -3.4); [sup 156]Nd-[sup 160]Gd, 10 (-10.6 [sup +0.4, sub 0.2])%; [sup 158]Sm-[sup 160]Sm, (3.4[sup +0.5, sub -0.3])%. The J[sub 1] values were fitted to a variable moment of inertia model with parameters J[sub 0] and C whose values correlate with the SIB J[sub 1] values. The SIBs are not correlated either with deformation or with the N[sub p]N[sub n] product of the IBA model. [ABSTRACT FROM AUTHOR]

We reinvestigated the neutron multiplicity yields of Ba-Mo, Ce-Zr, Te-Pd, and Nd-Sr from the spontaneous fission of 252Cf by (i) using both γ-γ-γ-γ and γ-γ-γ coincidence data, (ii) using up to date level scheme structures, and (iii) crosschecking analogous energy transitions in multiple isotopes, we have achieved higher precision than previous analyses. Particular attention was given to the Ba-Mo pairs where our results clearly confirm that the Ba-Mo yield data have a second hot fission mode where 8-10, and now 11 neutron evaporation channels are observed. These are the first observations of the 11 neutron channel. These 8-11 neutron channels are observed for the first time in the Ce-Zr pairs, but are not observed in other fission pairs. The measured intensities of the second mode in Ba-Mo and Ce-Zr pairs are ~1.5(4)% and ~1.0(3)%, respectively. These high neutron number evaporation modes can be an indication of hyperdeformation and/or octupole deformation in 143-145Ba and in 146,148Ce at scission to give rise to such high neutron multiplicities. [ABSTRACT FROM AUTHOR]

Level structures in the neutron-rich 144Ba nucleus have been reinvestigated by measuring prompt γ rays in the spontaneous fission of 252Cf. The previous s=+1 octupole band structure with reflection asymmetric shape has been expanded, and a side quadrupole band structure based on a 3+ state with reflection symmetric shape is identified. Thus, the results show the coexistence of reflection asymmetric and symmetric shapes in 144Ba. This is a first identification of such a shape coexistence structure in a nuclear structure. The other structural characteristics are discussed. [ABSTRACT FROM AUTHOR]

High spin band structures of neutron-rich 152-158Pm isotopes have been obtained from the measurement of prompt γ rays of isotopically identified fragments produced in fission of 238U+9Be and detected using the VAMOS++ magnetic spectrometer and EXOGAM segmented Clover array at GANIL and also from the high statistics γ-γ-γ and γ-γ-γ-γ data from the spontaneous fission of 252Cf using Gammasphere. The excited states in 157Pm and those above the isomers in even-A Pm isotopes 152,154,156,158Pm have been identified for the first time. The spectroscopic information on the rotational band structures in odd-A Pm isotopes has been extended considerably to higher spins and the possibility of the presence of reflection asymmetric shapes is explored. The configuration assignments are based on the results of cranked relativistic Hartree-Bogoliubov calculations. From the systematics of bands in odd-A Pm isotopes and weak population of opposite parity bands, octupole deformed shapes in neutron-rich Pm isotopes beyond N=90 seem unlikely to be present. [ABSTRACT FROM AUTHOR]

Neutron-rich 107Mo has been reinvestigated by analyzing the large statistics γ-γ-γ and γ-γ-γ-γ coincidence data from the spontaneous fission of 252Cf at the Gammasphere detector array. Two new bands have been identified. The potential-energy surface calculations of this nucleus have been performed. The calculations show evidence for the 5/2+[413] configuration of the ground-state band and 7/2-[523] configuration for the 348-keV excited band, as assigned in previous work. The two bands newly established are proposed to be one- and two-phonon γ-vibrational bands built on the 7/2-[523] Nilsson orbital, respectively, in the current paper. Triaxial projected shell-model (TPSM) calculations have been performed to explain the level structure and are found in fair agreement with experimental data. In particular, the TPSM study confirms the γ- and γγ-vibrational structure for the two observed excited band structures. Systematics of the one- and two-phonon γ-vibrational bands in the A~100 Mo series is also discussed. [ABSTRACT FROM AUTHOR]

We report the results of a β-decay study of fission products 86Br, 89Kr, 89Rb, 90gsRb, 90mRb, 90Kr, 92Rb, 139Xe, and 142Cs performed with the Modular Total Absorption Spectrometer (MTAS) and on-line mass-separated ion beams. These radioactivities were assessed by the Nuclear Energy Agency as having high priority for decay heat analysis during a nuclear fuel cycle. We observe a substantial increase in β feeding to high excited states in all daughter isotopes in comparison to earlier data. This increases the average γ-ray energy emitted by the decay of fission fragments during the first 10000 s after fission of 235U and 239Pu by approximately 2% and 1%, respectively, improving agreement between results of calculations and direct observations. New MTAS results reduce the reference reactor νe flux used to analyze reactor νe interaction with detector matter. The reduction determined by the ab initio method for the four nuclear fuel components, 235U, 238U, 239Pu, and 241Pu, amounts to 0.976, 0.986, 0.983, and 0.984, respectively. [ABSTRACT FROM AUTHOR]

The β decay of 124Cd into levels in 124In was reinvestigated at the Holifield Radioactive Ion Beam Facility. Fifty-MeV protons were bombarded on uranium targets and the induced fission products were mass separated and deposited on a moving tape in the center of an array of γ detectors. The resulting γ-γ coincidences revealed appreciable disagreement with previous work and has resulted in a revised ordering of the low-energy states in 124In. The resulting partial decay scheme has four energy levels, three of which are new. [ABSTRACT FROM AUTHOR]

Level structures of neutron-rich 140Xe nucleus have been reinvestigated by using a triple γ coincidence study from the spontaneous fission of 252Cf. Several new levels and transitions are identified. The previously observed s=+1 octupole band structure is confirmed and expanded. Another set of the ΔI=2 positive and negative parity bands connected by strong E1 transitions is proposed as the s=-1 octupole band structure. Thus, the s=±1 doublet octupole bands are completed in 140Xe. The experimental B(E1)/B(E2) branching ratios indicate that the octupole correlations in 140Xe are weak. The other characteristics of the s=±1 octupole bands have been discussed. [ABSTRACT FROM AUTHOR]

The β decays of neutron-rich nuclei near the doubly magic (78)Ni were studied at the Holifield Radioactive Ion Beam Facility using an electromagnetic isobar separator. The half-lives of (82)Zn (228±10  ms), (83)Zn (117±20  ms), and (85)Ga (93±7  ms) were determined for the first time. These half-lives were found to be very different from the predictions of the global model used in astrophysical simulations. A new calculation was developed using the density functional model, which properly reproduced the new experimental values. The robustness of the new model in the (78)Ni region allowed us to extrapolate data for more neutron-rich isotopes. The revised analysis of the rapid neutron capture process in low entropy environments with our new set of measured and calculated half-lives shows a significant redistribution of predicted isobaric abundances strengthening the yield of A>140 nuclei.

The discovery of a new chemical element with atomic number Z=117 is reported. The isotopes (293)117 and (294)117 were produced in fusion reactions between (48)Ca and (249)Bk. Decay chains involving 11 new nuclei were identified by means of the Dubna gas-filled recoil separator. The measured decay properties show a strong rise of stability for heavier isotopes with Z > or = 111, validating the concept of the long sought island of enhanced stability for superheavy nuclei.

Spectra of the E2 quasicontinuum gamma rays feeding different spin regions of the 154Dy yrast line have been extracted. These are compared with corresponding theoretical spectra obtained by numerical simulations based on temperature-dependent Hartree-Fock theory, with thermal shape fluctuations. In this manner, different regions of the spin-energy plane can be examined. The results support the predictions of a smeared-out phase transition at high spin above the yrast line.

The Shuttle Activation Monitor (SAM) experiment was flown on the Space Shuttle Columbia (STS-28) from 8-13 August, 1989 in a 57 degrees, 300 km orbit. One objective of the SAM experiment was to determine the relative effect of different amounts of shielding on the gamma-ray backgrounds measured with similarly configured sodium iodide (NaI) and bismuth germante (BGO) detectors. To achieve this objective twenty-four hours of data were taken with each detector in the middeck of the Shuttle on the ceiling of the airlock (a high-shielding location) as well as on the sleep station wall (a low-shielding location). For the cosmic-ray induced background the results indicate an increased overall count rate in the 0.2 to 10 MeV energy range at the more highly shielded location, while in regions of trapped radiation the low shielding configuration gives higher rates at the low energy end of the spectrum.

An X2/2B level solar flare occurred on 12 August, 1989, during the last day of the flight of the Space Shuttle Columbia (STS-28). Detectors on the GOES 7 satellite observed increased X-ray fluxes at approximately 1400 GMT and a solar particle event (SPE) at approximately 1600 GMT. Measurements with the bismuth germanate (BGO) detector of the Shuttle Activation Monitor (SAM) experiment on STS-28 showed factors of two to three increases in count rates at high latitudes comparable to those seen during South Atlantic Anomaly (SAA) passages beginning at about 1100 GMT. That increased activity was observed at both north and south high latitudes in the 57 degrees, 300 kilometer orbit and continued until the detector was turned off at 1800 GMT. Measurements made earlier in the flight over the same geographic coordinates did not produce the same levels of activity. This increase in activity may not be entirely accounted for by observed geomagnetic phenomena which were not related to the solar flare.