Average Value Of Spin Research Articles

Compilation and Evaluation of Isomeric Fission Yield Ratios

Fission yields are essential data for reactor physics, forensics, and astrophysics. In some cases, the fission yield of a fragment is divided between the ground state and a long-lived excited state, and the relative population of the two states is referred to as the isomeric ratio. In this work, we present a comprehensive compilation of experimental isomeric fission yield ratios for all target and projectile combinations. When possible, these data are combined to provide recommended isomeric fission yield ratios for low energy neutron-induced fission and spontaneous fission. The recommended ratios are compared to the traditional Madland-England model, which attempts to describe the isomeric ratios with a single parameter relating to the angular momentum of the fragment. It is found that the model does not reliably reproduce isomeric ratios outside the few nuclei it was fitted to, and its simplified treatment of the statistical process following population in fission results in average spin values, which are neither constant nor follow a recently observed saw-tooth pattern.

Polarizing neutron by light‐irradiated graphene

We study the spin orientation of the neutron scattered by light‐irradiated graphene and calculate the average value of spin z‐component of the neutron in terms of a generating functional technique. Our calculation results indicate that there is a remarkable neutron polarization effect when a neutron penetrates graphene irradiated by a circularly polarized light. We analyse the dynamical source of generating this effect from the aspect of photon‐mediated interaction between the neutron spin and valley pseudospin. By comparing with the polarization induced by a magnetic field, we find that this polarization may be equivalent to the one led by a magnetic field of several hundred Teslas if the photon frequency is in the X‐ray frequency range. This provides an approach of polarizing neutrons. image

Decoupling the effect of temperature on GDR widths in excited compound nucleus 144Sm

We measured giant dipole resonance (GDR) γ-rays in the 28Si + 116Cd reaction at ∼105 and 120 MeV excitation energies. The resonance widths were extracted as a function of temperature at different angular momentum values to decouple the effect of these two variables on resonance widths. The high energy GDR γ-rays from the decay of compound nucleus (CN) 144Sm were measured using a large NaI(Tl) detector in coincidence with a sum-spin multiplicity filter. The experimental data were analyzed under the framework of statistical decay of CN. The GDR cross sections were also calculated with a thermal shape fluctuation model (TSFM), which incorporates the temperature and spin dependent shell corrections within the Nilsson–Strutinsky approach. The GDR widths were extracted in the temperature range 1.5–2.2 MeV. The measured widths indicate that the increase of GDR widths with temperature at different average spin values follows a similar trend and is borne out by theoretical calculations. Present calculation shows that TSFM satisfactorily reproduces the GDR cross section as well as widths in the temperature range 1–2.2 MeV over a wide range of angular momentum.

Spin accumulation in the electron transport with Rashba interaction

The nonequilibrium transportation of two-dimensional electrons through a narrow channel is investigated under the influence of the Rashba interaction. By introducing suitable lifetime in the Green's function, the average spin values can be calculated from the ballistic regime to the diffusive regime. It is shown that the spin accumulation is a combined effect of the spin current and disorders. In the diffusive regime, disorders offer a mechanism to stop the spin current and generate the spin accumulation. In the ballistic regime, spins are more spread out and do not have definite signs. Further consideration indicates that the inclusion of ferromagnetic spin–spin interaction increases the spin accumulation near the edge.

Transport through a single discrete level for non-collinear magnetic polarizations of the electron reservoirs

Spin-polarized transport through a non-interacting single-level quantum dot coupled to two ferromagnetic leads with non-collinear magnetizations is analyzed theoretically by the non-equilibrium Green function technique. It is shown that spin of an electron that has tunnelled on the dot precesses around an effective exchange field before it leaves the dot. The exchange field originates from interaction between the electron and external electrodes. Electric current, tunnel magnetoresistance, and average value of spin accumulated on the dot are calculated for an arbitrary angle between magnetic moments of the electrodes.

Strong coupling in the Kondo problem at low temperatures

An average value of spin of a localized electron coupled with conduction electrons via exchange interaction is found for the ground state as a function of magnetic field. For magnetic fields μH∼0.5 T k ( T k is the Kondo temperature) there is an inflection point, wheras for a strong magnetic field μH⪢ T k, the deviation of the average spin from saturated value is proportional to ( T k/ μH) 2.

Coupled-channels analyses of scattering and fusion cross sections of 16O+152,154Sm, 186W systems at sub- and near-Coulomb barrier energies.

Coupled-channels calculations are performed to predict fusion, elastic scattering, and inelastic scattering cross sections for the $^{16}\mathrm{O}$${+}^{152,154}$Sm and $^{16}\mathrm{O}$${+}^{186}$W systems at sub- and near-Coulomb barrier energies, taking into account the lowest rotational states of the target up to ${\mathit{I}}^{\mathrm{\ensuremath{\pi}}}$=${8}^{+}$ explicitly. It is shown that experimental data of fusion cross sections taken recently with high precision, partial fusion cross sections, and also average spin values of compound nuclei formed after fusion are well reproduced by the calculations using optical potential parameters that can reproduce elastic and inelastic scattering data. The fusion-barrier distribution, defined as the second derivative of the fusion cross section ${\mathit{d}}^{2}$(E\ensuremath{\sigma})/${\mathit{dE}}^{2}$, is also calculated and compared with experimental data. Particular attention is focused on effects of the ${\mathit{Y}}_{4}$ deformation of the target on various physical quantities.

Distribution of fusion barriers

Heavy ion fusion cross sections and compound nucleus average spin values obtained from distribution of fusion barriers are discussed. Various shapes of distribution functions are studied using a truncated Gaussian distribution function (TGD). It is shown that fusion cross section and average spin values are less sensitive to different parametrization of TGD function, whereas the second derivative of the product of energy and fusion cross sections (w.r.t. energy), obtained from the corresponding TGD functions are significantly different depending on the shape of the barrier distribution function. It is also shown byχ 2 analysis of fusion cross section data that some systems favour a narrow Gaussian distribution function whereas others, for which the vibrational and rotational collective states are less important, favour a flat barrier distribution. A physical interpretation of the dynamical process that gives rise to different barrier distribution is given in the framework of microscopic coupled channel calculations.

A new polarization potential for heavy ion fusion spin distribution

The real part of the polarization potential which depends on both energy and angular momentum is calculated in a simple way using dispersion relation. A barrier penetration model (BPM) has been used to explain the fusion cross-section and compound nucleus spin distribution for32S+64Ni system in the energy range 50–75 MeV. It is also shown that the polarization potential which only depends on energy, is not adequate to give rise to correct spin distribution even after including any radial dependence. The proposed polarization potential with implicitE andl dependences is able to explain both fusion cross-section and average spin values.

Hyperfine fields in Sm1−xGdxAl2 alloys—Microscopic evidence for ferromagnetic coupling between rare earth spins

The results of hyperfine field studies on Sm1−xGdxAl2 alloys for 0?x?0.5 are reported. The hyperfine field at Al, H(Al), has been measured to be +32.5 kOe in SmAl2 and −47 kOe in GdAl2. In Sm1−xGdxAl2 alloys, we find that the magnitude of H(Al) increases with increasing x and further H(Al) becomes negative even with small replacement of Sm by Gd. H(Al) in these compounds is proportional to the average value of spin per rare earth ion. The observed behaviour can be understood in terms of a ferromagnetic coupling between the spins of Sm and Gd.