Simulating transuranium isotope yields upon explosive nucleosynthesis with allowance for elements of process dynamics

A two-group model of transuranium isotope production under the conditions of explosive nucleosynthesis is studied. The slow neutron effect on the yields of transuranium isotopes is considered. The static model of multiple neutron capture is supplemented with features of dynamics with allowance for the adiabatic expansion of matter at t ?? 10^?6 s. The results from calculations in the two-group model for mass numbers A = 246?C257 are compared to those of the Par experiment.     

Production of transuranium elements in a binary model under conditions of pulse nucleosynthesis

A model for the production of transuranium isotopes under the conditions of pulse nucleosynthesis in a powerful neutron flux (∼10²⁴−10²⁵ neutron cm⁻²) is considered. The explosive nature of the process allows us to separate it into two parts: the process of multiple neutron captures (t < 10⁻⁶ s) and the process of the subsequent β-decays for neutron-rich nuclei. The model of multiple captures neutron includes a variation of the cross section of the (n, γ) reaction as a result of the adiabatic expansion of the explosive nucleosynthesis area. A binary mixture of ²³⁸U and ²³⁹Pu is used as the initial isotope composition.     

Production of neutron-deficient nuclei around N = 126 by proton-induced spallation

Many isotopes of Np, Pu, Am, and Cm around the N = 126 shell still have not been produced in the laboratory. This study aims to investigate the cross sections and yields of the neutron-deficient nuclei of Np, Pu, Am, and Cm produced in the proton-induced spallations of transuranium elements. The isospin-dependent quantum molecular dynamics (IQMD) model is applied to study the dynamical process of reaction, and the subsequent decay process is simulated by the GEMINI++ model. The IQMD-GEMINI++ model is applied to calculate the cross section, kinetic energy, and angular distribution of the isotopic productions around N = 126. The Lindhand, Scharff, and Schiott theory is applied to calculate the energy loss of different heavy nuclei in the target material. A comparison between the data and the calculations shows that the IQMD-GEMINI++ model can reproduce the production cross sections of the neutron-deficient nuclei in spallation within approximately 1.5 orders of magnitude. The maximum cross section of the undiscovered isotopes of Np, Pu, Am, and Cm is about 10^?5 mb, while the kinetic energies of the productions are all less than 16 MeV. The angular distribution shows that the emission direction of production is mostly at a backward angle. The range of production in the target is within the range of 10^?7 to 10^?5 cm. This range is the effective target thickness for the online identification of undiscovered isotopes. Based on the effective thickness of the target and assuming an intensity of 120 μA for the proton beam, the yields of the undiscovered neutron-deficient nuclei are calculated. Productions of the undiscovered isotopes of Np, Pu, Am, and Cm by the proton-induced spallations of transuranium elements are feasible. However, experimental techniques for online identification of neutron-deficient nuclei produced in proton-induced spallation should be developed.     

Calculation of transuranium element synthesis in intensive neutron fluxes under adiabatic conditions

The creation of transuranium isotopes based on intense pulsed nucleosynthesis is considered. The model of multiple neutron captures takes into account the variation of the (n, γ)-cross section resulting from adiabatic expansion of the explosive nucleosynthesis area. The calculated yields of transuranium isotopes obtained under conditions close to a “Par” nuclear explosion, enable us to improve the agreement between the model results and the experimental data within the wide range of atomic mass number A = 248–257, provided the adiabatic conditions are taken into account.     

Determination of the fission barrier of232Pu from β-delayed fission and the problem of the first barrier

A delayed fission activity with a half-life of (55±7) s and a production cross section of (5±1)nb has been observed in the irradiation of²³⁷Np with 104 MeVα particles. It is tentatively assigned to the electron capture decay of²³²Am followed by fission of²³²Pu With a probability of (1.3 _?0.8 ⁺⁴ )· 10^?2 A barrier height of (5.3±0.4) MeV is extracted for²³²Pu exceeding theoretical barrier heights by about 2MeV. Systematic deviations between experimental and theoretical barrier heights previously observed in particular for U and Th isotopes are now also established for neutron deficient Pu isotopes indicating severe defects in the procedure of calculating static fission barriers.     

The peninsula of neutron nuclear stability in the vicinity of N = 258

The properties of extremely neutron-excessive nuclei with Z ?? 70, including the region of transuranium elements, are calculated beyond the previously theoretically known neutron drip line (NDL). The calculations are based on the Hartree-Fock approach using Skyrme forces (SkM*, SkI2, SLy4, Ska) with allowance for axial deformation and pairings in the BCS approximation. It is shown that the series of isotones with neutron number N = 258 outside of 2n NDL forms a peninsula of stable nuclei (PSN) with respect to the emission of one neutron. For SkM* forces, a PSN is formed by ³⁴⁴Rn, ³⁴⁶Ra, ³⁴⁸Th, and ³⁵⁰U nuclides.     

Effect of absorbing microinhomogeneities on optical damage to Alkali-Halide crystals

Micropores up to 30?C100 ??m in size (bulk density ??10⁵ cm^?3) are obtained in NaCl, KCl, KBr, and RbI via the effect of a pulse of a CO₂ laser with power density 10⁶?C10⁷ W cm^?2 up to 5 ??s long. When a pore appears, plasma formation is initiated. The average temperature is ??5500 K and the pressure is ??10⁴ kg cm^?2. The dependence of the average weight of the material removed from the pore on the energy of the crystal lattice is found. Pore formation occurs mainly via the effect of the radiation pulse, due to evaporation at the absorption wave front (velocity, 5 m s^?1) and plastic deformation. The annealing kinetics of micropores and the effect of the ionizing radiation on the bulk pore formation in NaCl crystals are investigated.     

On the Possibility of Delayed Fission of Nuclei in the Region of Superheavy Transuranium Elements

Delayed fission of atomic nuclei was discovered in 1966. It is observed primarily in odd–odd nuclei for which the energy released in beta decay (K capture) is commensurate with the fission barrier in the nucleus formed after this process. Delayed fission was found in four nuclide regions: neutrondeficient isotopes in the Pb region, neutron-deficient isotopes in the Ac and Pa regions, and neutrondeficient and neutron-rich isotopes of transuranium elements. In the wake of investigations into the properties of isotopes of superheavy transuranium elements, numerous calculations were performed in order to determine the masses of new nuclei and to predict their decay properties. Explored and predicted properties of superheavy-element nuclides, where, for some odd–odd nuclei of transuranium elements, the K-capture energy is commensurate with the fission barriers in the corresponding daughter nuclei formed after K capture, are analyzed. Estimates of the delayed-fission probability are presented for some isotopes of elements whose charge number Z ranges from 103 to 107.     

Ternary fission yields of 241Pu(nth,f)

Ternary events in the thermal neutron induced fission of ²⁴¹Pu(n,f) were studied with the recoil separator LOHENGRIN at the high-flux reactor of the Institut Laue Langevin in Grenoble. Yields and energy distributions could be determined for most isotopes of the elements hydrogen to oxygen. Also several heavier nuclei up to ³⁰Mg could be observed. Yields were measured for 42 isotopes, for further 17 isotopes upper limits could be deduced. For the first time the halo nuclei ¹¹Li, ¹⁴Be and ¹⁹C were found in neutron induced fission with yields of some 10⁻¹⁰ per fission.     

Production of Transuranium Nuclides in Pulsed Neutron Fluxes from Thermonuclear Explosions

The production of transuranium nuclides in pulsed neutron fluxes from thermonuclear explosions has been studied within the kinetic model of the astrophysical r-process taking into account the time dependence of external parameters and processes accompanying the beta decay of neutron-rich nuclei. Neutron fluxes depending on the time in the range of ~10^–6 s have been simulated within the developed adiabatic binary model. The probabilities of beta-delayed processes have been calculated within the microscopic theory of finite Fermi systems. The yields of transuranium nuclides Y(A) have been calculated for three experimental thermonuclear explosions Mike (Y_M), Par (Y_P), and Barbel (Y_B) (United States). The rms deviations of the calculations from experimental data are 91, 33, and 29% for Y_M, Y_P, and Y_B, respectively. These deviations are much smaller than those for other known calculations and are comparable with the proposed exponential approximation ensuring rms deviations of 56, 86.8, and 60.2% for Y_M, Y_P, and Y_B, respectively. The even–odd anomaly in the observed yields of heavy nuclei is explained by the dominant effect of processes accompanying the beta decay of heavy neutron-rich isotopes.     

Implications on the chiral quark bag from the deuteron asymptoticD-state

Fission yields of^124–132In in the thermal neutron fission of²³⁵U were determined for the first time. Charge displacementsΔZ=Z _p?Z _UCD were calculated for the corresponding mass chains. Both fission yields and charge displacement values were compared with those obtained by systematics by Wahl et al. and Wolfsberg. It was found that the fission yields of the In isotopes obey the gaussian distribution. The displacement function of Wolfsberg seems to give the better representation of the experimental results. Half-lives of^124–131In were determined from beta decay curves.     

On the search for density isomers in interaction of relativistic12C nuclei with lead

A Pb target was bombarded with¹²C nuclei of an energy of 15 and 43 GeV. The target was periodically transported to the inside of the neutron multiplicity detector which allowed measuring time distributions for events of multiple emission of delayed neutrons. Abnormal neutron emitters have not been found. Upper limits of probabilities of their production were estimated for the half-life range 10–10⁵ s and for different mean multiplicities of neutrons¯n. The values obtained are within the interval from 1.4·10^?9 (for¯n=12)to 4·10^?6(for¯n=2).     

Alpha decay of new neutron deficient gold,mercury, and thallium isotopes

In fusion evaporation reactions of a⁹²Mo beam with targets of neutron deficient Rb — Mo isotopes very neutron deficient isotopes of elements between Au and Po have been produced. The new isotopes^{173, 174}Au,^{175, 176}Hg, and¹⁷⁹Tl were identified by alpha spectroscopy. The mass excess value of¹⁷⁶Hg could be linked to known values of theN?Z=16 chain. The location of the new isotopes with respect to the proton drip line is discussed. A new high energyα transition of (7.20±0.02) MeV andT _1/2=(1.4±0.5) ms has been found in the reaction⁹²Mo+⁸⁹Y→¹⁸¹Tl^* at an excitation energy of 37 MeV. It is tentatively assigned to isotopes produced in 2-particle evaporation channels.     

Developments at the SLOWRI facility at RIKEN: precision optical spectroscopy of 7,9,10,11Be+ ions

Precision optical spectroscopy of radioactive Be isotopes produced in projectile fragmentation has been performed for the first time at the prototype SLOWRI facility of RIKEN RI-Beam Factory. The ground state hyperfine constants of ⁷Be⁺ and ¹¹Be⁺ were determined with relative accuracies of 6 × 10^?7 and 3 × 10^?8, respectively, by laser-microwave double resonance spectroscopy of laser-cooled ions in a trap. The optical transition energies from the ground S-state to the excited P-state of Be isotope ions were also measured to determine the nuclear charge radii from the isotope shifts. Development of the universal slow RI-beam facility??SLOWRI??based on the rf-carpet ion guide technique is progressing at RIKEN RI-beam factory. An additional capability of providing parasitic slow RI-beams from the projectile fragment separator BigRIPS is also discussed.     

Average neutron resonance parameters and radiative capture cross sectins for the isotopes of molybdenum

The neutron capture cross sections of the stable molybdenum isotopes have been measured with high energy resolution (ΔE/E ? 0.2 %), between 3 and 90 keV neutron energy, at the 40 m station of ORELA. Average resonance parameters are extracted for s- and p-wave resonances. The s-wave neutron strength function is close to 0.5 × 10^?4 for all isotopes, but the p-wave strength function exhibits a well defined peak near At~ 95.Both s- and p-wave radiative widths decrease markedly as further neutrons are added to the closed shell. The p-wave radiative widths are generally greater than the s-wave widths showing the presence of non-statistical γ-decay mechanisms.Valence neutron theory fails to explain the magnitude of the p- to s-wave radiative width disparity and doorway state processes are invoked. In particular, the data for ⁹⁸Mo appear to violate the usual valence theory, since the correlations between radiative and neutron strengths are small. Further, the radiative widths are smaller than can be explained on the valence model. An explanation for the loss of valence strength is advanced.Interpolated resonance parameters allow an estimate for the unknown cross section for ⁹⁹Mo(n, γ).     

On the neutronization radius of magnetic neutron stars: The field and temperature dependences of the chemical potential and minimum number density of a degenerate magnetized electron gas

The temperature and field dependences of the chemical potential and the field dependence of the Fermi energy for a degenerate relativistic electron gas in a magnetic field have been analyzed by numerical and analytical methods. An analytical expression has been derived for the dependence of the minimum electron number density and the corresponding neutronization radius on the magnetic field strength in a collapsing star upon its subsequent transformation into a neutron one. We believe that a similar relation also holds for the equilibrium neutron star radius. Our results refine the conclusions reached previously [1] in the case of a nonzero temperature and the influence of the star??s proton component on the neutronization process as well as confirm and generalize them in terms of a significant (by an order of magnitude or severalfold) decrease in the equilibrium radius of a neutron star in a superstrong (10¹⁴?C10¹⁷ G) magnetic field compared to the case where there is no such field. We point out that there may exist a separate class of stellar objects??very small magnetar neutron stars that we propose to name ??minimagnetars??. We hypothesize that they can be the final evolutionary stage of stars before their collapse into a black hole.     

Target mass correction on the 3He polarized structure function

The diffusion-effusion model has been used to analyse the release and yields of Fr and Cs isotopes from uranium carbide targets of very different thicknesses (6.3 and 148 g/cm²) bombarded by a 1 GeV proton beam. Release curves of several isotopes of the same element and production efficiency versus decay half-life are well fitted with the same set of parameters. Comparison of efficiencies for neutron-rich and neutron-deficient Cs isotopes enables separation of the contributions from the primary (p + ²³⁸U) and secondary (n + ²³⁸U) reactions to the production of neutron-rich Cs isotopes. A rather simple calculation of the neutron contribution describes these data fairly well. The FLUKA code describes the primary and secondary-reaction contributions to the Cs isotopes production efficiencies for different targets quite well.     

Conversion electron measurement of isomeric primary transitions in196, 198, 199, 200, 201Pb

The transition energies of nine low energy primary transitions from high spin isomers in^{196, 198, 199, 200, 201}Pb have been measured with conversion electron spectroscopy usinge ^? e ^? ande ^? γ coincidences.B(E2) values as deduced from the measured lifetimes and transition energies are discussed in terms of seniority shell model configurations and of a quasiparticle Tamm-Dancoff approach using the surface delta interaction. A revised discussion of the effectiveE2 charge in neutron deficient Pb isotopes is presented.     

On a source of outgoing electrons in a pulsed gas discharge

It has been shown that explosive electron emission is delayed by 10^?10 s with respect to field emission in a pulsed subnanosecond discharge in atmospheric air. A pulse of outgoing electrons is observed for approximately the same time in air. Correspondingly, field emission is a source of these electrons. Owing to the sharp nonlinearity of the emission current density as a function of the electric field j(E), the real duration of the current pulse of the outgoing electrons is equal to about 10^?11 s.