Evidence for a change in the nuclear mass surface with the discovery of the most neutron-rich nuclei with 17<Z <25

The results of measurements of the production of neutron-rich nuclei by the fragmentation of a 76-Ge beam are presented. The cross sections were measured for a large range of nuclei including fifteen new isotopes that are the most neutron-rich nuclides of the elements chlorine to manganese (50-Cl, 53-Ar, 55,56-K, 57,58-Ca, 59,60,61-Sc, 62,63-Ti, 65,66-V, 68-Cr, 70-Mn). The enhanced cross sections of several new nuclei relative to a simple thermal evaporation framework, previously shown to describe similar production cross sections, indicates that nuclei in the region around 62-Ti might be more stable than predicted by current mass models and could be an indication of a new island of inversion similar to that centered on 31-Na.Comment: 4 pages, 3 figures, to be published in Physical Review Letters, 200

Production cross sections of neutron rich isotopes from a 82Se beam

Production cross sections for neutron-rich nuclei from the fragmentation of a 82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions of 122 neutron-rich isotopes of elements $11 \le Z \le 32$ were determined by varying the target thickness. Production cross sections with beryllium and tungsten targets were determined for a large number of nuclei including several isotopes first observed in this work. These are the most neutron-rich nuclides of the elements $22 \le Z \le 25$ (64Ti, 67V, 69Cr, 72Mn). One event was registered consistent with 70Cr, and another one with 75Fe. A one-body Qg systematics is used to describe the production cross sections based on thermal evaporation from excited prefragments. The current results confirm those of our previous experiment with a 76Ge beam: enhanced production cross sections for neutron-rich fragments near Z=20.Comment: Talk given at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

Reactivity Initiated Accident Test Series RIA Scoping Test Quick Look Report

The Reactivity Initiated Accident Scoping Test (RIA-ST) was successfully completed August 30, 1978. The test was introductory to the RIA Series 1 tests and was designed to investigate and resolve several anticipated problem areas prior to performance of the first test of the series, Test RIA 1-1. The RIA Scoping Test, as performed, consisted of four separate single-rod experiment phases. The first three phases were performed with shrouded fuel rods of 5.8 wt.% enrichment. They were subjected to power bursts resulting in total fuel surface energies ranging from 205 to 261 cal/q at the axial peak elevation. The fourth phase consisted of a 20 wt.% enriched, shrouded fuel rod which was subjected to a power hurst that deposited a total radially averaged energy of 527 cal/g. The primary objectives of the Scoping Test were defined as follows: (1) Determine the applicability of extrapolating low-power steady state calorimetric measurements and self-powered neutron detector (SPND) output to determine fuel rod energy depositions during a power burst. (2) Determine the enerqy deposition failure threshold for unirradiated fuel rods at BWR hot-startup coolant conditions. (3) Determine the magnitudes of oossible pressure pulses resulting from rod failure. (4) Determine the sensitivity of the test instrumentation to high transient radiation exposures. In general, the energy deposition values for the Scoping Test derived from the SPND output were 25% higher than those obtained from the core ion chamber data. Determining which values are correct will require radiochemical analysis of the fuel rods which will take several months. At present, it apoears that the SPND derived energies are in error because of excellent agreement between the calculated and measured power calibration results and the agreement between the predicted failure threshold and that seen using the core ion chamber derived energies. Meeting the second objective was accomplished during the first three test phases by subjecting the fuel rods to energy depositions which bracketed the failure threshold. The failure threshold in terms of total pellet surface energy at the axial flux peak was found to be between 218 cal/g where no rod failure occurred and 256 cal/g where · rod failure did occur. The experiment predictions indicated that the failure threshold would be 262 cal/g at the pellet surface. Only the fourth experiment phase (527 cal/g) resulted in a pressure pulse upon rod failure. The best indication of source pressure was the reading from a 69 MPa EG&amp;G pressure transducer at the flow shroud inlet. This pressure transducer indicated a pressure pulse upon rod failure of 28.2 MPa with a rise time of 1.6 ms. The source pressure was attenuated considerably outside the shroud region as indicated by pressure transducers in the upper plenum of the in-pile tube and in the flow bypass region. The maximum pressure indicated outside the flow shroud was 2.1 MPa. In general, instrumentation sensitivity to radiation was minimal. The most significant instrumentation problem during the power bursts was a false flowrate indication by the flow turbines. This problem is being examined. The Kaman and Bell &amp; Howell pressure transducers showed the least sensitivity to radiation of the pressure measurement devices. The EG&amp;G transducers were most sensitive. The locked linear variable differential transformer (LVDT) gave no indication of radiation sensitivity as its response during the burst was a straight line. The strain gages were very sensitive to radiation, indicating a strain increase of 70% with the second burst of RIA-ST-1. The Type S thermocouple did not exhibit significant radiation sensitivity. In addition, the RIA Scoping Test has provided data on the consequences of fuel rod failure during a RIA event at BWR hot startup conditions. Posttest examination of the fuel rods from the first two phases of the test revealed large quantities of UO{sub 2} fuel missing from the cladding. Fuel rod failures for energy depositions near the failure threshold in previous closed capsule tests without forced coolant flow resulted in only a slight amount of fuel loss

Shape evolution in 116,118 Ru: Triaxiality and transition between the O(6) and U(5) dynamical symmetries

116Ru and 118Ru have been studied via β-delayed γ-ray spectroscopy of nuclei produced in fragmentation reactions at the Radioactive Ion-Beam Factory (RIBF) facility. Level schemes with positive-parity states up to spin J=6 have been constructed. The re

Beta decay of the Tz=-2 nucleus 64Se and its descendants

International audience; The beta decay of the Tz=-2 nucleus 64Se has been studied in a fragmentation reaction at RIKEN-Nishina Center. 64Se is the heavies Tz=-2 nucleus that decays to bound states in the daughter nucleus and the heaviest case where the mirror reaction 64Zn(3He,t)64Ga on the Tz=+2 64Zn stable target exists and can be compared. Beta-delayed gamma and proton radiation is reported for the 64Se and 64As cases. New levels have been observed in 64As, 64Ge (N=Z), 63Ge and 63Ga. The associated T1/2 values have been obtained