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Shapira, Dan

Publications and source records attributed to Shapira, Dan.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Examining the role of transfer coupling in sub-barrier fusion of Ti 46 , 50 + Sn 124

In this study, the presence of neutron transfer channels with positive Q values can enhance sub-barrier fusion cross sections. Recent measurements of the fusion excitation functions for 58 Ni+ 132,124 Sn found that the fusion enhancement due to the influence of neutron transfer is smaller than that in 40 Ca + 132,124 Sn although the Q values for multineutron transfer are comparable. The purpose of this study is to investigate the differences observed between the fusion of Sn + Ni and Sn + Ca. Methods: Fusion excitation functions for 46,50 Ti + 124 Sn have been measured at energies near the Coulomb barrier. As a result, a comparison of the barrier distributions for 46 Ti+ 124 Sn and 40 Ca+ 124 Sn shows that the 40 Ca+ 124 Sn system has a barrier strength resulting from the coupling to the very collective octupole state in 40 Ca at an energy significantly lower than the uncoupled barrier. In conclusion, the large sub-barrier fusion enhancement in 40 Ca induced reactions is attributed to both couplings to neutron transfer and inelastic excitation, with the octupole vibration of 40 Ca playing a major role.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Time-of-flight mass measurements of neutron-rich chromium isotopes up to N = 40 and implications for the accreted neutron star crust

Here, we present the mass excesses of 59-64 Cr, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of 64Cr is determined for the first time, with an atomic mass excess of -33.48(44) MeV. We find a significantly different two-neutron separation energy S 2n trend for neutron-rich isotopes of chromium, removing the previously observed enhancement in binding at N = 38. Additionally, we extend the S 2n trend for chromium to N = 40, revealing behavior consistent with the previously identified island of inversion in this region. We compare our results to state-of-the-art shell-model calculations performed with a modified Lenzi-Nowacki-Poves-Sieja interaction in the fp shell, including the g 9/2 and d 5/2 orbits for the neutron valence space. We employ our result for the mass of 64 Cr in accreted neutron star crust network calculations and find a reduction in the strength and depth of electron-capture heating from the A = 64 isobaric chain, resulting in a cooler than expected accreted neutron star crust. This reduced heating is found to be due to the >1-MeV reduction in binding for 64 Cr with respect to values from commonly used global mass models.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Mass Measurement of 56Sc Reveals a Small A=56 Odd-Even Mass Staggering, Implying a Cooler Accreted Neutron Star Crust

We present the mass excesses of 52-57Sc, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The masses of 56Sc and 57Sc were determined for the first time with atomic mass excesses of -24.85(59)((+0)(-54)) MeV and -21.0(1.3) MeV, respectively, where the asymmetric uncertainty for 56Sc was included due to possible contamination from a long-lived isomer. The 56Sc mass indicates a small odd-even mass staggering in the A = 56 mass chain towards the neutron drip line, significantly deviating from trends predicted by the global FRDM mass model and favoring trends predicted by the UNEDF0 and UNEDF1 density functional calculations. Together with new shell-model calculations of the electron-capture strength function of 56Sc, our results strongly reduce uncertainties in model calculations of the heating and cooling at the 56Ti electron-capture layer in the outer crust of accreting neutron stars. We find that, in contrast to previous studies, neither strong neutrino cooling nor strong heating occurs in this layer. We conclude that Urca cooling in the outer crusts of accreting neutron stars that exhibit superbursts or high temperature steady-state burning, which are predicted to be rich in A approximate to 56 nuclei, is considerably weaker than predicted. Urca cooling must instead be dominated by electron capture on the small amounts of adjacent odd-A nuclei contained in the superburst and high temperature steady-state burning ashes. This may explain the absence of strong crust Urca cooling inferred from the observed cooling light curve of the transiently accreting x-ray source MAXI J0556-332.

Meisel, Z.↗
DOE OSTI2015

Tracking rare-isotope beams with microchannel plates

A system of two microchannel-plate detectors has been successfully implemented for tracking projectile-fragmentation beams. The detectors provide interaction positions, angles, and arrival Limes of ions at the reaction target. Furthermore, the current design is an adaptation of an assembly used for low-energy beams (~1.4 MeV/nucleon). In order to improve resolution in tracking high-energy heavy-ion beams, the magnetic field strength between the secondary-electron accelerating foil and the microchannel plate had to be increased substantially. Results from an experiment using a 37-MeV/nucleon 56 Ni beam show that the tracking system can achieve sub-nanosecond timing resolution and a position resolution of ~1 mm for beam intensities up to 5 x 10 5 pps.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

2π1ν states populated in 135Te from 9Be-induced reactions with a 132Sn beam

γ-ray transitions in 134Te, 135Te, and 136Te were measured from 9Be-induced reactions with a radioactive 132Sn beam at a sub-Coulomb barrier energy of 3 MeV per nucleon using particle-γ coincidence spectroscopy. The transitions were selected by gating on alpha-like particles in a CsI detector following a combination of (9Be,α1n), (9Be,α2n), and (9Be,α3n) incomplete fusion-evaporation reactions. Distorted-wave Born approximation calculations suggest little to no contribution from the (9Be,7He), (9Be,6He), and (9Be,5He) direct reactions.γ-ray transitions from previously known 2+Ⓧν2f7/2 and 4+Ⓧν2f7/2 multiplet members in 135Te are observed. A new γ ray is observed, assigned to the third-excited state in 135Te, and new 2+Ⓧν2f7/2 multiplet members are suggested. In addition, spin assignments are made by using recent one-neutron transfer data. The updated experimental data for 135Te are compared to shell-model calculations for a relatively complete set of states up to the yrast 15/2-,4+Ⓧν2f7/2 multiplet member at 1505 keV.

Allmond, James M.↗
DOE OSTI2014

Double-magic nature of 132Sn and 208Pb through lifetime and cross-section measurements

Single-neutron states in 133Sn and 209Pb, which are analogous to single electrons outside of closed atomic shells in alkali metals, were populated by the (9Be,8Be) one-neutron transfer reaction in inverse kinematics using particle-gamma coincidence spectroscopy. In addition, the s1/2 single-neutron hole-state candidate in 131Sn was populated by (9Be,10Be). Doubly closed-shell 132Sn (radioactive) and 208Pb (stable) beams were used at sub-Coulomb barrier energies of 3 MeV per nucleon. Level energies, gamma-ray transitions, absolute cross sections, spectroscopic factors, asymptotic normalization coefficients, and excited-state lifetimes are reported and compared to shell-model expectations. The results include a new transition and precise level energy for the 3p1/2 candidate in 133Sn, new absolute cross sections for the 1h9/2 candidate in 133Sn and 3s1/2 candidate in 131Sn, and new lifetimes for excited states in 133Sn and 209Pb. This is the first report on excited-state lifetimes of 133Sn, which provide a unique signature of the single-neutron states and 132Sn double-shell closure.

Allmond, James↗
DOE OSTI2013

Experimental study of the β - γ and β - n γ decay of the neutron-rich nucleus 85 Ga

We studied the β-decay properties of neutron-rich 85 Ga produced in proton-induced fission of 238 U at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Data consisted of β-γ and β-γ-γ coincidences were collected at the Low-energy Radioactive Ion Beam Spectroscopy Station after high-resolution on-line mass separation. For the first time, the excited states in the N=53 isotone 85 Ge were established from β-delayed γ decay of 85 Ga. The level scheme of the N=52 isotone 84 Ge was improved and includes now 0 + , 2 + , (2) + , 4 + , and (0) + states populated in the β-delayed-neutron-γ decay of 85 Ga. Advanced shell-model calculations were used to analyze experimental data on 85 Ge and 84 Ge.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Single-neutron levels near the N=82 shell closure

The (d, p) reaction was measured with the radioactive ion beams of {sup 126}Sn and {sup 128}Sn in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory, utilizing the Super ORRUBA silicon detector array. Angular distributions of reaction protons were measured for several states in {sup 127}Sn and {sup 129}Sn to determine angular momentum transfers and deduce spectroscopic factors. Such information is critical for calculating direct (n,{gamma}) cross sections for the r-process as well as for constraining shell model parameters in the A Almost-Equal-To 130 region. Combined with previous experiments on {sup 130}Sn and {sup 132}Sn, these results will provide a complete set of (d, p) reaction data on even tin isotopes between stable {sup 124}Sn and doubly-magic {sup 132}Sn.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Sub-barrier fusion enhancement with radioactive 134Te

The fusion cross sections of radioactive 134Te + 40Ca were measured at energies above and below the Coulomb barrier. The evaporation residues produced in the reaction were detected in a zero-degree ionization chamber providing high efficiency for inverse kinematics. Both coupled-channel calculations and comparison with similar Sn + Ca systems indicate an increased sub-barrier fusion probability that is correlated with the presence of positive Q-value neutron transfer channels. In comparison, the measured fusion excitation functions of 130Te + 58,64Ni, which have positive Q-value neutron transfer channels, were accurately reproduced by coupled-channel calculations including only inelastic excitations. The results demonstrate that the coupling of transfer channels can lead to enhanced sub-barrier fusion but this is not directly correlated with positive Q-value neutron transfer channels in all cases.

Kohley, Zachary W↗
DOE OSTI2012

Time-of-Flight Mass Measurements of Exotic Nuclei

Atomic masses play an important role in nuclear physics and astrophysics. The need of experimental mass values for unstable nuclides has triggered the development of a wide range of mass measurement techniques, with devices installed at many laboratories around the world. We have implemented a time-of-flight magnetic-rigidity (TOF-B ) technique at the National Superconducting Cyclotron Laboratory (NSCL) that includes a position measurement for magnetic rigidity corrections and uses the A1900 separator and the S800 spectrograph. We performed a successful first experiment measuring masses of neutron-rich isotopes in the region of Z 20 30, important for calculations of processes occurring in the crust of accreting neutron stars. The masses of 16 nuclei were determined, for 61V, 63Cr, 66Mn, and 74Ni for the first time, with atomic mass excesses of 30.510(890) MeV, 35.280(650) MeV, 36.900(790) MeV, and 49.210(990) MeV, respectively. The mass resolution achieved was 1.8 10 4.

Matos, M.↗
DOE OSTI2012

Fusion probability for neutron-rich radioactive Sn induced reactions

Evaporation residue cross sections for $^{124,126,127,128}$Sn+$^{64}$Ni and $^{132}$Sn+$^{58}$Ni have been measured to study the effects of neutron excess in neutron-rich radioactive nuclei on fusion. For the reactions with $^{64}$Ni, the fusion probability does not decrease with increasing neutron excess in Sn, contrary to the result of the stable beam Sn+Zr measurement. A comparison of the reduced evaporation residue cross sections for $^{126}$Sn+$^{64}$Ni and $^{132}$Sn+$^{58}$Ni, which make the same compound nucleus, shows that the fusion probability is indistinguishable for reactions involving the same atomic elements but different isotope combinations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Time delays in heavy-ion-induced fission of medium-Z nuclei, measured by crystal blocking

Time delays in fission induced by bombardment of Mo with 170- and 180-MeV {sup 32}S, 225- and 240-MeV {sup 48}Ti, and 300-MeV {sup 58}Ni have been measured by observation of crystal blocking of fission fragments. In contrast to earlier measurements with a W target, the results are consistent with fission of a compound nucleus in competition with mainly neutron emission. Most of the fissions happen on a time scale much shorter than attoseconds but there is a significant component of fission with much longer lifetimes. The measurements are reproduced with a standard statistical model, including a Kramers correction to fission widths from the viscosity of hot nuclear matter. These new results support the interpretation of our earlier measurements with a W target, which indicate that there is a transition in heavy-ion-induced fission at large atomic number and mass, from multichance fission in the standard Bohr-Wheeler picture to fission without formation of a compound nucleus. The process is slowed down by nuclear viscosity, with measured delays of order attoseconds.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Fusion of 124,132Sn with 40,48Ca

Fusion excitation functions for the reactions of {sup 124,132}Sn with {sup 40,48}Ca were measured at energies near and below the Coulomb barrier. Weak sub-barrier fusion enhancement accounted for by coupling to the first 2{sup +} and 3{sup -} states in the target and projectile was observed for {sup 124,132}Sn+{sup 48}Ca. However, the {sup 124,132}Sn+{sup 40}Ca fusion cross sections are very strongly enhanced below the barrier and this difference survives even after correcting for trivial size effects. Although the enhancement appears to be related to the existence of large positive Q values for neutron transfer reactions, it is not proportional to the magnitudes of those Q values, which are much larger for {sup 132}Sn+{sup 40}Ca than for {sup 124}Sn+{sup 40}Ca.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗