The ($n,2n$) cross section of the radioactive isotope ${}^{241}\mathrm{Am}$ ($T_{1/2}=432.6$ y) has been measured in the incident neutron energy range from 7.6 to 14.5 MeV in steps of a few MeV using the activation technique. Monoenergetic neutron beams were produced via the ${}^2\mathrm{H}$($d,n$)${}^3\mathrm{He}$ reaction by bombarding a pressurized deuterium gas cell with an energetic deuteron beam at the TUNL 10-MV Van de Graaff accelerator facility. The induced γ-ray activity of ${}^{240}\mathrm{Am}$ was measured with high-resolution HPGe detectors. The cross section was determined relative to Al, Ni, and Au neutron activation monitor foils, measured in the same geometry. Good agreement is obtained with previous measurements at around 9 and 14 MeV, whereas for a large discrepancy is observed when our data are compared to those reported by Perdikakis et al. near 11 MeV. Very good agreement is found with the END-B/VII evaluation, whereas the JENDL-3.3 evaluation is in fair agreement with our data.

We present a new direct simulation Monte Carlo method for solving the relativistic Boltzmann equation. We solve numerically the two-dimensional Boltzmann equation using this new algorithm. We find that elliptic flow from this transport calculation smoothly converges toward the value from ideal hydrodynamics as the number of collisions per particle increases, as expected on general theoretical grounds but in contrast with previous transport calculations.

Polarization and relaxation of radon isotopes by spin exchange with laser optically pumped rubidium were studied in preparation for electric dipole moment measurements with octupole deformed ${}^{223}\mathrm{Rn}$. γ-ray anisotropies provided a measure of nuclear polarization produced by spin exchange with laser polarized rubidium vapor, and the temperature dependence over the range 130 to ${220}^{°}$C was measured to parametrize the spin exchange polarization and the quadrupole-dominated wall relaxation rate. These results provide quantitative data for developing electric dipole moment measurements of octupole-deformed ${}^{223}\mathrm{Rn}$ and other radon isotopes.

We have determined a value for the ${}^1{S}_0$ neutron-neutron scattering length ($a_{\mathit{nn}}$) from high-precision measurements of time-of-flight spectra of neutrons from the ${}^2\mathrm{H}$$({\pi }^{-},n\hspace{1em}\gamma )\hspace{1em}n$ capture reaction. The measurements were done at the Los Alamos Meson Physics Facility by the E1286 Collaboration. The high spatial resolution of our γ-ray detector enabled us to make a detailed assessment of the systematic uncertainties in our techniques. The value obtained in the present work is $a_{\mathit{nn}}=-18.63\pm 0.10$ (statistical) ± 0.44 (systematic) ± 0.30 (theoretical) fm. This result is consistent with previous determinations of $a_{\mathit{nn}}$ from the ${\pi }^{-}d$ capture reaction. We found that the analysis of the data with calculations that use a relativistic phase-space factor gives a more negative value for $a_{\mathit{nn}}$ by 0.33 fm over the analysis done using a nonrelativistic phase-space factor. Combining the present result with the previous ones from ${\pi }^{-}d$ capture gives $a_{\mathit{nn}}=-18.63\pm 0.27(\mathrm{expt})\pm 0.30$ fm (theory). For the first time the combined statistical and systematic experimental uncertainty in $a_{\mathit{nn}}$ is smaller than the theoretical uncertainty and comparable to the uncertainty in the proton-proton ${}^1{S}_0$ scattering length ($a_{\mathit{pp}}$). This average value of $a_{\mathit{nn}}$ when corrected for the magnetic-moment interaction of the two neutrons becomes −18.9 ± 0.4 fm, which is 1.6 ± 0.5 fm different from the recommended value of $a_{\mathit{pp}}$, thereby confirming charge symmetry breaking at the 1% confidence level.

In this study, we investigate the pre-equilibrium effect by using new evaluated geometry dependent hybrid model for the ${}^{208}\mathrm{Pb}$ ($p,\mathit{xn}$) reaction at 25.5 and 62.9 MeV incident proton energies. We also suggest that the initial neutron and proton exciton numbers for the nucleon induced precompound reactions be calculated from the neutron and proton density by using an effective nucleon-nucleon interaction with Skyrme force. We calculate the initial exciton numbers obtained from SKM${}^{*}$ and SLy4 for a proton induced reaction on target nuclei ${}^{208}\mathrm{Pb}$. The obtained results have been investigated and compared with the pre-equilibrium calculations and experimental results.

A simultaneous optical model calculation of elastic scattering, complete fusion, and breakup cross sections for energies around the Coulomb barrier is presented for reactions involving the weakly bound projectile ${}^9\mathrm{Be}$ on the medium size target ${}^{144}\mathrm{Sm}$. In the calculations, the nuclear polarization potential $U$ is split into a volume part $U_F$, which is responsible for fusion reactions, and a surface part $U_{\mathrm{DR}}$, which accounts for direct reactions. A simultaneous ${\chi }^2$ analysis of elastic and complete fusion data shows that the extracted optical potential parameters of the real $V_F$ and imaginary $W_F$ parts of $U_F$ and the corresponding parts $V_{\mathrm{DR}}$ and $W_{\mathrm{DR}}$ of $U_{\mathrm{DR}}$ satisfy separately the dispersion relation. Energy-dependent forms for the fusion and direct reaction potentials indicate that, at the strong absorption radius, the direct reaction potentials dominate over the fusion potentials$.$ Moreover, the imaginary direct reaction potential results in a rather smooth function of $E$ around the barrier energy. These findings show that the threshold anomaly, usually present in reactions with tightly bound projectiles, is not exhibited for the system ${}^9\mathrm{Be}+{}^{144}\mathrm{Sm}$. Within this formalism, the effect of breakup reactions on complete fusion is studied by turning on and off the potentials responsible for breakup reactions.

The transverse broadening of jets produced in deep-inelastic scattering (DIS) off a large nucleus is studied in the collinear limit. A class of medium enhanced higher twist corrections are resummed to calculate the transverse momentum distribution of the produced collinear jet. In contrast to previous approaches, resummation of the leading length enhanced higher twist corrections is shown to lead to a two-dimensional diffusion equation for the transverse momentum of the propagating jet. Results for the average transverse momentum obtained from this approach are then compared to the broadening expected from a classical Langevin analysis for the propagation of the jet under the action of the fluctuating color Lorentz force inside the nucleons. The set of approximations that lead to identical results from the two approaches are outlined. The relationship between the momentum diffusion constant $D$ and the transport coefficient $\widehat{q}$ is explicitly derived.

We present the relativistic calculation of the β-decay of tritium in a hadron model. The elementary particle treatment (EPT) of the transition ${}^3\mathrm{H}$ $\to$${}^3\mathrm{He}$ $+e^{-}+{\overline{\nu }}_e$ is performed in analogy with the description of the β-decay of neutron. The effects of higher order terms of hadron current and nuclear recoil are taken into account in this formalism. The relativistic Kurie function is derived and presented in a simple form suitable for the determination of neutrino masses from the shape of the endpoint spectrum. A connection with the commonly used Kurie function is established.

The neutron partial decay width of one-particle resonant levels that are the bandhead states in odd-$N$ deformed nuclei is estimated in the formalism with a real-energy variable, using the width of one-particle resonance calculated in terms of eigenphase. It is shown that because of the presence of various ($\ell j$) components in a given one-particle resonant level of deformed nuclei, the neutron decay width can be quite different from the one obtained from assuming a spherically symmetric nuclear shape. As a numerical example, the formalism is applied to the case of the nucleus ${}_4^{13}$Be${}_9$, which lies outside the neutron drip line by 100–200 keV. Considering that the core of the nucleus consisting of four protons and eight neutrons is most likely prolately deformed, we point out the possibility that two lowest lying levels have $I^{\pi }=1/2^{+}$ for the $N=9$ nucleus, and the higher lying one may have a neutron decay width that is much narrower than the one expected for an $s_{1/2}$ level at the same resonance energy. The structure of some ${\Omega }^{\pi }=1/2^{+}$ one-particle resonant levels, which are smoothly connected to weakly bound one-particle levels as the potential strength becomes stronger, is also analyzed using the present formalism.

In this article we study the lowest eigenvalues of random Hamiltonians for both fermion and boson systems. We show that an empirical formula of evaluating the lowest eigenvalues of random Hamiltonians in terms of energy centroids and widths of eigenvalues is applicable to many different systems. We improve the accuracy of the formula by considering the third central moment. We show that these formulas are applicable not only to the evaluation of the lowest energy but also to the evaluation of excited energies of systems under random two-body interactions.

We investigate to what extent a description of ${}^{12}\mathrm{Be}$ as a three-body system made of an inert ${}^{10}\mathrm{Be}$ core and two neutrons is able to reproduce the experimental ${}^{12}\mathrm{Be}$ data. Three-body wave functions are obtained with the hyperspherical adiabatic expansion method. We study the discrete spectrum of ${}^{12}\mathrm{Be}$, the structure of the different states, the predominant transition strengths, and the continuum energy spectrum after high-energy fragmentation on a light target. Two $0^{+}$, one $2^{+}$, one $1^{-}$, and one $0^{-}$ bound states are found; the first four are known experimentally, whereas the $0^{-}$ is predicted as an isomeric state. An effective neutron charge, reproducing the measured $B(E1)$ transition and the charge rms radius in ${}^{11}\mathrm{Be}$, leads to a computed $B(E1)$ transition strength for ${}^{12}\mathrm{Be}$ in agreement with the experimental value. For the $E0$ and $E2$ transitions, the contributions from core excitations could be more significant. The experimental ${}^{10}\mathrm{Be}$-neutron continuum energy spectrum is also well reproduced, except in the energy region corresponding to the $3/2^{-}$ resonance in ${}^{11}\mathrm{Be}$ where core excitations contribute.

We propose the quark mean field model including derivative coupling between quarks and scalar mesons in nuclear matter. This model concisely interprets an increasing size of the nucleon as well as a modification of coupling constant in the nuclear environment.

We discuss the flavor of leading jet partons as a valuable probe of nuclear matter. We point out that the coupling of jets to nuclear matter naturally leads to an alteration of jet chemistry even at high transverse momentum $p_T$. In particular, quantum chromodynamics (QCD) jets coupling to a chemically equilibrated quark gluon plasma in nuclear collisions will lead to hadron ratios at high transverse momentum $p_T$ that can differ significantly from their counterparts in $p+p$ collisions. Flavor measurements could complement energy loss as a way to study interactions of hard QCD jets with nuclear matter. Roughly speaking they probe the inverse mean free path $1/\lambda$ while energy loss probes the average squared momentum transfer ${\mu }^2/\lambda$. We present some estimates for the rate of jet conversions in a consistent Fokker-Planck framework and their impact on future high-$p_T$ identified hadron measurements at RHIC and LHC. We also suggest some novel observables to test flavor effects.

We explore the abundance of light clusters in core-collapse supernovae at post-bounce stage in a quantum statistical approach. Adopting the profile of a supernova core from detailed numerical simulations, we study the distribution of light bound clusters up to α particles ($2⩽A⩽4$) as well as heavy nuclei ($A>4$) in dense matter at finite temperature. Within the frame of a cluster-mean-field approach, the abundances of light clusters are evaluated accounting for self-energy, Pauli blocking, and effects of continuum correlations. We find that deuterons and tritons, in addition to ${}^3\mathrm{He}$ and ${}^4\mathrm{He}$, appear abundantly in a wide region from the surface of the proto-neutron star to the position of the shock wave. The appearance of light clusters may modify the neutrino emission in the cooling region and the neutrino absorption in the heating region and, thereby, influence the supernova mechanism.

Similarities in the ${}^6\mathrm{Li}$ and ${}^6\mathrm{He}$ elastic scattering from ${}^{12}\mathrm{C}$ at about 35 MeV/nucleon are manifested in the ability of an optical model potential that differs only in having a weaker imaginary strength for ${}^6\mathrm{He}$ than for ${}^6\mathrm{Li}$ to describe both data sets equally well. However, the weaker absorption seen in the ${}^6\mathrm{He}+{}^{12}\mathrm{C}$ data is counter to expectations of the effect of coupling to breakup channels, confirmed by continuum discretized coupled channels calculations. Coupled reaction channels calculations including couplings to the strongest transfer channels are also unable to account for this phenomenon.

The dynamic polarization potential (DPP) contribution to the effective deuteron-nucleus interaction is evaluated by means of coupled reaction channel (CRC) calculations followed by $S$-matrix-to-potential inversion. The full coupled channel $S$ matrix $S_{l^{\text{'}}l}^J$ is inverted using the iterative-perturbative algorithm to yield a potential that includes a complex $T_R$ tensor term as well as central and spin-orbit components. The differences between the various components of the inverted potential and the corresponding terms in the bare potential of the CRC calculation constitute a local equivalent representation of the complete DPP that is generated by the reaction channel coupling. The magnitude of the DPP, the real part in particular, is much less than that found in earlier calculations in which the nonorthogonality terms were omitted. The characteristic features of the tensor part of the DPP were traced to breakup and reorientation processes in the entrance deuteron channel that had been included with the pickup. The contribution of stripping to the deuteron-nucleus interaction is also discussed.

We present the neutral- and charged-current reactions by incident neutrino (antineutrino) scattering on the nucleon and on the ${}^{12}\mathrm{C}$ target in the quasi-elastic region within the framework of a relativistic single-particle model. The incident energies at 500 MeV and 1 GeV are used for the scattering. Effects of strangeness are studied thoroughly on the cross sections, the ratios between the neutral- and charged-current reactions, and the asymmetries by incident neutrino and antineutrino. We find that there exists some cancellation of the strange quark contributions between the knocked-out protons and neutrons in the neutrino (antineutrino)-nucleus scattering. The effect of strangeness is exhibited more strongly on the asymmetry than on the ratio or cross section. On a difference of the asymmetry, the effect of strangeness appears strongly, but on a summation of the asymmetry, the effect almost disappears in the low and middle kinetic energies of the knocked-out nucleon.

Measurements of the double-differential ${\pi }^{\pm }$ production cross section in the momentum range $100⩽p⩽800$ MeV/$c$ and angle range $0.35⩽\theta ⩽2.15$ rad in proton-beryllium, proton-carbon, proton-aluminium, proton-copper, proton-tin, proton-tantalum, and proton-lead collisions are presented. The data were taken with the large-acceptance HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 to 12.9 GeV/$c$ hitting a target with a thickness of 5% of a nuclear interaction length. Tracking and identification of the produced particles was performed by using a small-radius cylindrical Time Projection Chamber (TPC) placed inside a solenoidal magnet. Incident particles were identified by an elaborate system of beam detectors. Results are obtained for the double-differential cross sections $d^2\sigma /(dpd\theta )$ at six incident proton beam momenta [3, 5, 8, and 8.9 GeV/$c$ (Be only) and 12 and 12.9 GeV/$c$ (Al only)]. They are based on a complete correction of static and dynamic distortions of tracks in the HARP TPC, which allows the complete statistics of the collected data set to be used. The results include and supersede our previously published results and are compatible with these. Results are compared with the GEANT4 and MARS Monte Carlo simulation.

We study the effect of effective mass on pairing correlations in the ground states of superfluid nuclei ${}^{124}\mathrm{Sn}$ and ${}^{136}\mathrm{Sn}$. Various parameter sets of Skyrme interactions and relativistic Lagrangians are adopted to study pairing correlations across a wide range of effective mass. It is shown that surface-type pairing interaction gives an almost constant pairing gap as a function of the effective mass, while volume-type pairing interaction shows rather strong dependence of the pairing gap upon the effective mass. The local pair potentials of various effective interactions are also examined in relation to the effective mass.

We perform Hartree-Fock-Bogoliubov (HFB) calculations for semi-magic calcium, nickel, tin, and lead isotopes and $N=20,28,50$, and 82 isotones using density-dependent pairing interactions recently derived from a microscopic nucleon-nucleon interaction. These interactions have an isovector component so that the pairing gaps in symmetric and neutron matter are reproduced. Our calculations well account for the experimental data for the neutron number dependence of binding energy, two-neutron separation energy, and odd-even mass staggering of these isotopes. This result suggests that by introducing the isovector term in the pairing interaction, one can construct a global effective pairing interaction that is applicable to nuclei in a wide range of the nuclear chart. It is also shown with the local density approximation that the pairing field deduced from the pairing gaps in infinite matter reproduces qualitatively well the pairing field for finite nuclei obtained with the HFB method.