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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Isospin aspects in nuclear reactions involving Ca beams at 25 MeV/nucleon

Isospin dependence of dynamical and thermodynamical properties observed in reactions {sup 40}Ca+ {sup 40,48}Ca and {sup 40}Ca + {sup 46}Ti at 25 MeV/nucleon has been studied. We used the CHIMERA multi-detector array. Strong isospin effects are seen in the isotopic distributions of light nuclei and in the competition between different reaction mechanisms in semi-central collisions. We will show also preliminary results obtained in nuclear collision {sup 48}Ca + {sup 48}Ca at 25MeV/nucleon, having very high N/Z value in the entrance channel (N/Z = 1.4). The enhancement of evaporation residue production confirms the strong role played by the N/Z degree of freedom in nuclear dynamics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Even-odd effects in Z and N distributions of fragments emitted at intermediate energies

Even-odd effects in Z and N distributions of light fragments emitted at forward angles in nuclear collisions {sup 40}Ca + {sup 40}Ca, {sup 40}Ca + {sup 48}Ca, and {sup 48}Ca + {sup 48}Ca at 25 MeV/nucleon and identified in charge and mass with the Chimera multidetector have been analyzed. The amplitude of even-odd staggering effects seems to be related to the neutron to proton ratio N/Z of the entrance channels. A qualitative explanation of this effect, taking into account the deexcitation phase of primary excited fragments, is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Fusion of calcium isotopes and of nearby systems

Very recent data on {sup 40,48}Ca+{sup 40,48}Ca are presented. In all cases fusion hindrance far below the barrier has been observed. Coupled-channel effects influence the threshold energy for hindrance. The excitation functions of the two symmetric systems are similar, while the case of {sup 40}Ca+{sup 48}Ca is different both above and below the barrier, possibly due to couplings to transfer channels with Q > 0. Other systems in the same mass region show different trends that have to be related to the nuclear structure of the colliding nuclei. Investigating the behavior of lighter systems will be interesting also from the astrophysical point of view.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Projectile fragmentation of {sup 40,48}Ca and isotopic scaling in a transport approach

We investigate theoretically projectile fragmentation in reactions of {sup 40,48}Ca on {sup 9}Be and {sup 181}Ta targets using a Boltzmann-type transport approach, which is supplemented by a statistical decay code to describe the de-excitation of the hot primary fragments. We determine the thermodynamical properties of the primary fragments and calculate the isotope distributions of the cold final fragments. These describe the data reasonably well. For the pairs of projectiles with different isotopic content we analyze the isotopic scaling (or isoscaling) of the final fragment distributions, which has been used to extract the symmetry energy of the primary source. The calculation exhibits isoscaling behavior for the total yields as do the experiments. We also perform an impact-parameter-dependent isoscaling analysis in view of the fact that the primary systems at different impact parameters have very different properties. Then the isoscaling behavior is less stringent, which we can attribute to specific structure effects of the {sup 40,48}Ca pair. The symmetry energy determined in this way depends on these structure effects.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Reaction Dynamics And Nuclear Structure Via Deep Inelastic Collisions With Heavy-Ions: Search For Particle-Vibration Couplings in {sup 49}Ca

The deep inelastic reaction (DIC){sup 48}Ca+{sup 64}Ni, at an energy approximately 2.5 times above the Coulomb barrier, was studied using the CLARA-PRISMA setup at the Laboratori Nazionali di Legnaro. Total cross sections and angular distributions, both energy integrated and associated to the population of selected excited states, are measured for the most intense reaction channels. The {gamma}-decay of the most intense reaction products is also studied. The use of angular distributions and polarization measurements of {gamma} transitions allows to firmly establish spin and parity of excited states. Both reaction and gamma spectroscopy studies demonstrate the relevance of DIC with heavy ions for the investigation of moderately neutron rich systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Observation of new neutron-rich isotopes at the NSCL

Recently, increased primary beam intensities at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University and advances in experimental techniques allowed probing further into unknown regions of the table of the isotopes with fragmentation and in-flight fission reactions. Recent measurements at the NSCL have demonstrated that primary beams of {sup 48}Ca at 141 MeV/u and {sup 76}Ge at 132 MeV/u can be used to produce new isotopes {sup 40}Mg, {sup 42,43}Al, {sup 44}Si, {sup 52}Ar, {sup 50}Cl, {sup 52,53}Ar, {sup 55,56}K, {sup 57,58}Ca, {sup 59,60,61}Sc, {sup 62,63}Ti, {sup 65,66}V, {sup 68}Cr, {sup 70}Mn in the proximity of the neutron dripline. Also, experiments with {sup 238}U(81 MeV/u) and {sup 208}Pb(86 MeV/u) beams in order to measure production yields and possibly observe several neutron rich isotopes in the first time have recently been performed at the NSCL. A search for new neutron-rich isotopes with {sup 48}Ca and {sup 76}Ge beams was carried out using the recently developed two-stage fragment separator technique.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Consistent description of hindrance in sub-barrier fusion of {sup 48}Ca with {sup 36}S, {sup 48}Ca, and {sup 96}Zr

Recent fusion reaction data for the systems {sup 36}S+{sup 48}Ca, {sup 48}Ca+{sup 48}Ca, and {sup 96}Zr+{sup 48}Ca are analyzed within the coupled-channel formalism. The heavy-ion entrance channel potential is calculated employing an improved double-folding prescription. The nonlocal kernel arising from the knock-on exchange component of the effective N-N interaction is localized within the lowest order of the Perey-Saxon approach, including full recoil. The single-particle densities entering the folding integrals are prescribed according to the density matrix expansion method. The investigation is more elaborated because each case is tested with four different types of N-N effective forces: The two standard parametrizations of the density-independent M3Y force (Reid and Paris) and two parametrizations of the density-dependent Gogny force (D1S and D1N). A consistent description of all three reactions is achieved by keeping fixed the nuclear structure input for {sup 48}Ca. The inclusion of 2{sup +} and 3{sup -} phonon states in the coupled-channel calculation, within an energy excitation window identical for all three reactions explains better the hindrance in extreme sub-barrier fusion cross sections. The interactions providing the best fit to the data are not pointing to a possible maximum in the astrophysical S factor, thereby confirming the conclusion reached by the Legnaro group for these cases.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

{gamma} spectroscopy around doubly magic {sup 48}Ca by heavy-ion transfer reactions

{gamma} spectroscopy of neutron-rich nuclei around {sup 48}Ca is performed by the heavy-ion transfer reaction {sup 48}Ca on {sup 64}Ni at 282 MeV, with the PRISMA-CLARA setup at Legnaro Laboratory. Angular distributions, polarizations and lifetimes analysis probe spin and parities of several excited states, shading lights on their configuration. In the one neutron transfer channels, {sup 49}Ca and {sup 47}Ca, states arising by coupling a single particle to the 3{sup -} phonon of {sup 48}Ca are observed, showing the robustness of nuclear collectivity in rather light systems. The work demonstrates the feasibility of complete in-beam {gamma}-spectroscopy with heavy-ion transfer reactions and provides a method that can be further exploited in the future with heavy targets and radioactive beams.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Precision lifetime measurements of the first 2{sup +} and 4{sup +} states in {sup 56}Cr at the N=32 subshell closure

Excited states in {sup 56}Cr have been populated after {sup 48}Ca({sup 11}B,p2n) reactions at a beam energy of 32 MeV. The Cologne plunger device surrounded by a {gamma}-detector array of one EUROBALL cluster detector and five Ge detectors was employed to determine lifetimes with the recoil distance Doppler shift method. {gamma}{gamma}-coincidence data were analyzed using the differential decay curve method and precise lifetimes for the first 2{sup +} and 4{sup +} state of {tau}=5.49(14) ps and {tau}=3.15(11) ps, respectively, were extracted. The corresponding B(E2; 2{sup +}{yields}0{sup +})=11.33(31) W.u. quantifies with a high accuracy the puzzling discrepancy between experimental B(E2) values in N=32 isotones and theoretical results from large-scale shell model calculations employing modern effective nucleon-nucleon interactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Experimental study of the {sup 238}U({sup 36}S,3-5n){sup 269-271}Hs reaction leading to the observation of {sup 270}Hs

The deformed doubly magic nucleus {sup 270}Hs has so far only been observed as the four-neutron (4n) evaporation residue of the reaction {sup 26}Mg+{sup 248}Cm, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of {sup 270}Hs in the 4n evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict that the reactions {sup 48}Ca+{sup 226}Ra and {sup 36}S+{sup 238}U result in higher cross sections due to lower reaction Q values, in contrast to simple arguments based on the reaction asymmetry, which predict opposite trends. Calculations using hivap predict cross sections for the reaction {sup 36}S+{sup 238}U that are similar to those of the {sup 26}Mg+{sup 248}Cm reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction {sup 36}S+{sup 238}U and the observation of {sup 270}Hs, which is produced in the 4n evaporation channel, with a measured cross section of 0.8{sub -0.7}{sup +2.6} pb at 51-MeV excitation energy. The one-event cross-section limits (68% confidence level) for the 3n, 4n, and 5n evaporation channels at 39-MeV excitation energy are 2.9 pb, while the cross-section limits of the 3n and 5n channel at 51 MeV are 1.5 pb. This is significantly lower than the 5n cross section of the {sup 26}Mg+{sup 248}Cm reaction at similar excitation energy.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Synthesis of superheavy elements at the Dubna gas-filled recoil separator

A survey of experiments at the Dubna gas-filled recoil separator (Laboratory of Nuclear Reactions, JINR, Dubna) aimed at the detection and study of the “island of stability” of superheavy nuclei produced in complete fusion reactions of {sup 48}Ca ions and {sup 238}U–{sup 249}Cf target nuclei is given. The problems of synthesis of superheavy nuclei, methods for their identification, and investigation of their decay properties, including the results of recent experiments at other separators (SHIP, BGS, TASCA) and chemical setups, are discussed. The studied properties of the new nuclei, the isotopes of elements 112–118, as well as the properties of their decay products, indicate substantial growth of stability of the heaviest nuclei with increasing number of neutrons in the nucleus as the magic number of neutrons N = 184 is approached.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Development of collective structures over noncollective excitations in {sup 139}Nd

High-spin states in {sup 139}Nd were investigated using the reaction {sup 96}Zr({sup 48}Ca,5n) at a beam energy of 195 MeV and {gamma}-ray coincidences were acquired with the Euroball spectrometer. Apart from several dipole bands at medium excitation energy, three quadrupole bands have been observed at high spin. Linking transitions connecting two of the high-spin bands to low-energy states have been observed. Calculations based on the cranked-Nilsson-Strutinsky formalism have been used to assign configurations for the high-spin quadrupole bands.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

High-spin spectroscopy in {sup 125}Xe

Levels excited up to 39.8 MeV and 119/2 units of angular momentum have been populated in {sup 125}Xe by the {sup 82}Se({sup 48}Ca,5n){sup 125}Xe reaction. High-fold {gamma}-ray coincidence events were measured using the Gammasphere Ge detector array. Nine regular rotational bands extending from levels identified previously up to almost 60 ({h_bar}/2{pi}) have been identified, and three of these have been connected to low-lying levels having well-established spins and parities. Configurations have been assigned to six of the bands based on alignment properties, band crossings, and comparison with theoretical cranked shell model calculations (CSM). Transition quadrupole moments have been measured for these bands in the spin range 31-55 ({h_bar}/2{pi}) and were found to be in agreement with the CSM calculations. The corresponding quadrupole deformation {epsilon}{sub 2} ranges from 0.28 to 0.34 at a {gamma} deformation of 0 deg. and from 0.29 to 0.36 at a {gamma} value of 5 deg.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗