32129688
Systematics of preequilibrium contributions in (n,p) reactions at 14 MeV.
The existing up to data global data on angle integrated energy spectra (AIES) and energy integrated angular distributions (EIAD) of protons from ([ital n],[ital p]) reactions at 14 MeV nominal neutron energy have been analyzed to develop systematics in relative preequilibrium contributions (RPC). The experimental estimates of RPC were obtained either from asymmetric components of the extrapolated EIAD or from the analysis of AIES, by comparison with equilibrium contributions obtained from the Hauser-Feshbach model. The experimentally obtained RPC have been compared with those expected from recent Feschbach-Kerman-Koonin theory as extended by Kalbach [ital et] [ital al]. as well as with theoretical predictions by Brown and Muirhead. The mass number systematics of RPC manifest shell and even-odd effects. The fraction of the precompound nucleus decays obtained from RPC, using the Blann-Griffin model, is constant and small for [ital A][ge]72, and increases to about 1 for small [ital A]'s. The analysis with the Kalbach model yields the dependence of the level density parameters [ital a][sub 1] and [ital a][sub 2] on [ital A]; also values of [ital a][sub 1] and [ital a][sub 2] manifest prominent structures near closed shell nuclei. The values of [ital a][sub 1] for compound nucleus are systematically highermore » than [ital a][sub 2], for the residual nuclei by an amount much larger than expected by usual [ital A] dependence, indicating excitation energy dependence of the single particle level density [ital g]. The excitation energy dependence of [ital g] when explored in the light of Rosenzweig's positive power law, with parameters [ital n] and [ital k], reveals that for most cases 1.2[le][ital n][le]1.5, with no systematic dependence of [ital n] on [ital A], compared to reported theoretical values of [ital n][congruent]1.6 by Rosenzweig, and 0.8[le][ital k][le]3.8 with a trend of slow increase of [ital k] with [ital A].« less
122194176
Search for entrance channel effects in heavy ion induced fusion reactions via neutron evaporation
122026076
Role of nuclear dissipation and entrance channel mass asymmetry in pre-scission neutron multiplicity enhancement in fusion-fission reactions
Pre-scission neutron multiplicities are measured for ${}^{12}\mathrm{C} + {}^{204}\mathrm{Pb}$ and ${}^{19}\mathrm{F} + {}^{197}\mathrm{Au}$ reactions at laboratory energies of 75\char21{}95 MeV for the $^{12}\mathrm{C}$ beam and 98\char21{}118 MeV for the $^{19}\mathrm{F}$ beam. The chosen projectile-target combinations in the present study lie on either side of the Businaro-Gallone mass asymmetry (${\ensuremath{\alpha}}_{\mathrm{BG}}$) and populate the $^{216}\mathrm{Ra}$ compound nucleus. The dissipation strength is deduced after comparing the experimentally measured neutron yield with the statistical model predictions which contains the nuclear viscosity as a free parameter. Present results demonstrate the combined effects of entrance channel mass asymmetry and the dissipative property of nuclear matter on the pre-scission neutron multiplicity in fusion-fission reactions.
120167461
Anomalous behavior of the level density parameter in neutron and charged particle evaporation
The compound nucleus $^{76}\mathrm{Kr}*$ was populated at the excitation energy of $75\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ and angular momentum of $39\ensuremath{\hbar}$ in fusion reactions with two complementary, mass-symmetric $(^{31}\mathrm{P}+^{45}\mathrm{Sc})$ and mass-asymmetric $(^{12}\mathrm{C}+^{64}\mathrm{Zn})$ entrance channels. The neutron evaporation spectra were measured and compared with the predictions of statistical model calculations using the transmission coefficients for the spherical nuclei in the inverse absorption channel, the rotating liquid drop model moment of inertia, and the normal systematic value of $A∕8$ for the level density parameter $a$. The results for the mass-asymmetric reaction are found to be consistent with the predictions of the statistical model calculations. However, for the mass-symmetric reaction $(^{31}\mathrm{P}+^{45}\mathrm{Sc})$, the experimental spectra are found to be harder than the theoretical neutron spectra and the statistical model calculations require a lower value of $A∕10$ for the parameter $a$ to reproduce the shape of the experimental spectra, indicating the neutron to be evaporated at higher temperature for the same excitation energy and angular momentum in symmetric system. According to the dynamical model, the formation time $(37\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}\phantom{\rule{0.3em}{0ex}}\mathrm{sec})$ of the compound nucleus for the symmetric $^{31}\mathrm{P}+^{45}\mathrm{Sc}$ system is significantly higher than that $(29\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}\phantom{\rule{0.3em}{0ex}}\mathrm{sec})$ for the asymmetric $^{12}\mathrm{C}+^{64}\mathrm{Zn}$ system. This may probably lead to the formation of a temperature-equilibrated dinuclear complex that may be responsible for neutron emission at higher temperature in the case of the symmetric system.
37575993
Coulomb excitation studies in antimony isotopes.
Various low-lying energy levels up to 1.145 MeV in {sup 121,123}Sb have been Coulomb excited using 3.0--4.0 MeV proton-beam energies. The reduced transition probabilities of the excited levels have been newly deduced from the measured yields of the deexcitation gamma rays. The values of mixing ratios for a few transitions and the removal of ambiguities in the spin values of some levels have been presented from the angular distribution analysis.
120945477
On improvement of charge resolution of cosmic ray particles using a cellulose nitrate plastic detector
Abstract By employing improved procedures of measurement and analysis we have been able to obtain good charge resolution for stopping cosmic ray nuclei with Z ⩽30 in a cellulose nitrate detector. In a particular, it has been found that ( V t V b ) provides a much more reliable measure of ionisation loss than cone length. A charge resolution of 0.2 charge units for nuclei with Z ≲20 and of 0.3 charge units for nuclei with Z > 20 has been achieved in the present experiment.
16619649
London relation and fluxoid quantization for monopole currents in U(1) lattice gauge theory.
We explore the mechanism of quark confinement in four-dimensional U(1) lattice gauge theory by measuring the color-magnetic current distribution from Dirac magnetic monopoles in the presence of a static quark-antiquark pair. Our results give the first direct evidence that the quarks induce a solenoidal current distribution that screens the color-electric flux of the quarks in an electric analogue of the Meissner effect in a superconductor. We show that the vacuum state of U(1) lattice gauge theory obeys both a dual version of the London equation and an electric fluxoid quantization condition.
36246455
The quasiopen string.
The quasiopen string in D dimensions is defined by the Nambu-Goto action and the boundary conditions (x'+x)(σ α ,τ)=V α (x'-x) (σ α ,τ), where σ=σ 1 and σ 2 denote the ends of the string, x'≡∂x/∂σ, and the V α (α=1,2) are real symmetric orthogonal matrices. (The usual open string corresponds to V 1 =V 2 =−1.) We impose Poincare invariance in d dimensions, d α ) jk =−δ jk for j,k ∈ Poincare sector and (V α ) jk =0 if only one of j,k belongs to the Poincare sector. Further quantization gives D=26 and a mass spectrum with a ground-state mass squared M G 2 =−(1−J i ||theta i ||(1-||theTa I ||)/4)/α', where ||theta i ||≤(½), exp(2iπtheta i ) are the eigenvalues of V 2 V 1 , and α' is the slope parameter in the string action. A choice of theta i giving a tachyon-free spectrum is thus possible if d≤10.
38815785
Baryon-number fluctuations in a quark-hadron phase transition.
Isothermal baryon-number fluctuations arising from a first-order quark-hadron phase transition in the early Universe are obtained by including the quark-gluon interactions up to the order [ital g][sub [ital s]][sup 3] in the perturbative QCD coupling constant in the quark-gluon plasma (QGP) phase and the finite-size volume corrections for the hadrons in the hadron-resonance gas (HRG) and their effects on the primordial nucleosynthesis (PNS) are analyzed. The ratio of the baryon-number densities in the QGP and HRG phases at the critical temperature [ital T][sub [ital c]] is larger than one in the range 150 MeV[lt][ital T][sub [ital c]][lt]260 MeV. However, it is far larger than one even when [ital T][sub [ital c]] is outside this range, thus affecting primordial nucleosynthesis significantly.
11413480
Interacting quasiopen strings.
A 26-dimensional quasiopen string, in which Poincare invariance in some dimensions is broken by new boundary conditions, has also a new mass spectrum. Based on locality we construct vertex operators and generalized dual Veneziano amplitudes with singularities corresponding to the quasiopen mass spectrum.
40983341
Nucleus-nucleus multiplicity distributions and quantum chromodynamics.
A model for nucleus-nucleus multiplicity distributions is proposed and its relations with hadron-proton and hadron-nucleus multiplicity distributions are explored and compared with the experimental data. The values of the parameters are the same for all these processes and owe their origin to the quantum chromodynamical gluon bremsstrahlung mechanism. Some other consequences of the model are also analyzed and compared with the available experimental data.