Prompt fission neutron spectra of n+~(235)U above the(n,nf) fission threshold

Calculations of prompt fission neutron spectra(PFNS) from the235U(n, f) reaction were performed with a semi-empirical method for E n = 7.0 and 14.7 Me V neutron energies. The total PFNS were obtained as a superposition of(n,xnf) pre-fission neutron spectra and post-fission spectra of neutrons which were evaporated from fission fragments, and these two kinds of spectra were taken as an expression of the evaporation spectrum.The contributions of(n,xnf) fission neutron spectra on the calculated PFNS were discussed. The results show that emission of one or two neutrons in the(n,nf) or(n,2nf) reactions influences the PFNS shape, and the neutron spectra of the(n,xnf) fission-channel are soft compared with the neutron spectra of the(n,f) fission channel. In addition,analysis of the multiple-chance fission component showed that second-chance fission dominates the PFNS with an incident neutron energy of 14.7 Me V whereas first-chance fission dominates the 7 Me V case.     

Nuclear Physics Programs for the Future RIBs Facility in Korea

We present nuclear physics programs based on the planned experiments using rare isotope beams (RIBs) for the future Korean Rare Isotope Beams Accelerator facility(KRIA). This ambitious facility has both an Isotope Separation On Line (ISOL) and fragmentation capability for producing RIBs and accelerating beams of wide range mass of nuclides with energies of a few to hundreds MeV per nucleon. Low energy RIBs at Elab = 5 to 20 MeV per nucleon are for the study of nuclear structure and nuclear astrophysics toward and beyond the drip lines while higher energy RIBs produced by inflight fragmentation with the reaccelerated ions from the ISOL enable to explore the neutron drip lines in intermediate mass regions. The planned programs have goals for investigating internal structures of the exotic nuclei toward and beyond the nucleon drip lines by addressing the following issues: how the shell structure evolves in areas of extreme proton to neutron imbalance; whether the isospin symmetry maintains in isobaric mirror nuclei at and beyond the drip lines; how two-proton radioactivity affects abundances of the elements; what the role of the continuum states including resonant states above protondecay threshold in exotic nuclei is in astrophysical nuclear reaction processes, and how the nuclear reaction rates triggered by unbound proton-rich nuclei make an effect on rapid proton capture processes in a very hot stellar plasma.     

Comparison of nuclear reactions for the production of monoenergetic neutron fields with energies below 100 keV

NPL, PTB, IRMM and IRSN are involved, within a scientific cooperation, in a comprehensive study aimed at developing reference low-energy monoenergetic neutron fields. This paper will explain the importance of such developments, highlighted by the over response of neutron survey meters in the keV energy range, and also describe the main difficulties encountered. The variation of the neutron yield with ion beam energy from the neutron threshold up to about 50 keV has been measured at IRSN AMANDE facility for the ⁴⁵Sc(p,n), ⁶⁵Cu(p,n), ⁵¹V(p,n), ⁵⁷Fe(p,n) and ³⁷Cl(p,n) reactions.     

Shell Evolution Study for New Magic Number N =32 via Isochronous Mass Spectrometry

Recent results and progress of mass measurements of neutron-rich nuclei utilizing Isochronous Mass Spectrometry (IMS) based on the HIRFL-CSR complex at Lanzhou are reported. The nuclei of interest were produced through projectile fragmentation of primary 86Kr ions at a realistic energy of 460.65 MeV/u. After in-flight separation by the fragment separator RIBLL2, the fragments were injected and stored in the experimental storage ring CSRe, and their masses were determined from measurements of their revolution times. The re-determined masses were compared and evaluated with other mass measurements, and the impact of these evaluated masses on the shell evolution study is discussed.     

Effects of pairing correlation on neutron drop

In this work, the effects of the pairing correlation on the properties of neutron drops N=6-50 trapped in a harmonic oscillator potential with ω = 10 Me V are investigated by comparing the results given by the Skyrme Hartree-Fock and Hartree-FockBogoliubov theories with the density-dependent delta interaction(DDDI) pairing force. The results showed that the pairing correlation slightly made the neutron drops more bound, and increased the central neutron density, the spin-orbit and pseudo spin-orbit splittings. Thus, the pairing correlation must be accounted for to improve the Skyrme functional compared with the ab initio calculations. Furthermore, although the single-particle energy gaps with or without pairing were similar, the shell closures varied due to pair scattering. Here, the shell closures in neutron drops using the Sk M* parameter set and DDDI pairing force were found at N=8, 16, and 32.     

An empirical fit to estimated neutron emission cross sections from proton induced reactions

Neutron emission cross section for various elements from⁹Be to²⁰⁹Bi have been calculated using the hybrid model code ALICE-91 for proton induced reactions in the energy range 25 MeV to 105 Me V. An empirical expression relating neutron emission cross section to target mass number and incident proton energy has been obtained. The simple expression reduces the computation time significantly. The trend in the variation of neutron emission cross sections with respect to the target mass number and incident proton energy has been discussed within the framework of the model used.     

Study of neutron dose equivalent at the HIRFL deep tumor therapy terminal

The secondary neutron fields at the deep tumor therapy terminal at HIRFL(Heavy Ion Research Facility in Lanzhou) were investigated. The distributions of neutron ambient dose equivalent were measured with a FHT762Wendi-II neutron ambient dose equivalent meter as ~(12)C ions with energies of 165, 207, 270, and 350 Me V/u were bombarded on thick tissue-like targets. The thickness of targets used in the experiments was larger than the range of the carbon ions. The neutron spectra and dose equivalent were simulated by using FLUKA code, and the results agree well with the experimental data. The experiment results showed that the neutron dose produced by fragmentation reactions in tissue can be neglected in carbon-ion therapy, even considering their enhanced biological effectiveness.These results are also valuable for radiation protection, especially in the shielding design of high energy heavy ion medical machines.     

Deformation dependence of symmetry energy coefficients of nuclei

Based on the semi-classical Thomas-Fermi approximation together with the Skyrme energy-density functional, we study the deformation dependence of symmetry energy coefficients of finite nuclei. The symmetry energy coefficients of nuclei with mass number A = 40, 100, 150, 208 are extracted from two-parameter parabola fitting to the calculated energy per particle. We find that the symmetry energy coefficients decrease with the increase of nuclear quadrupole deformations, which is mainly due to the isospin dependence of the difference between the proton and neutron surface diffuseness. Large deformations of nuclei can cause the change of the symmetry energy coefficient by about 0.5 Me V and the influence of nuclear deformations on the symmetry energy coefficients is more evident for light and intermediate nuclei.     

Extending the nuclear chart by continuum: From oxygen to titanium

Nuclear masses ranging from O to Ti isotopes are systematically investigated with relativistic continuum Hartree-Bogoliubov (RCHB) theory, which can provide a proper treatment of pairing correlations in the presence of the continuum. From O to Ti isotopes, there are 402 nuclei predicted to be bound by the density functional PC-PK1. For the 234 nuclei with mass measured, the root mean square (rms) deviation is 2.23 MeV. It is found that the proton drip-lines predicted with various mass models are roughly the same and basically agree with the observation. The neutron drip-lines predicted, however, are quite different. Due to the continuum couplings, the neutron drip-line nuclei predicted are extended further neutron-rich than other mass models. By comparison with finite-range droplet model (FRDM), the neutron drip-line nucleus predicted by RCHB theory has respectively 2(O), 10(Ne), 10(Na), 6(Mg), 8(Al), 6(Si), 8(P), 6(S), 14(K), 10(Ca), 10(Sc), and 12(Ti) more neutrons.     

Prompt neutron multiplicity distribution for 235U(n,f) at incident energies up to 20 MeV

For the n+<'235>U fission reaction, the total excitation energy partition of the fission fragments, the average neutron kinetic energy <ε>(A) and the total average energies E<,γ>(A) removed by γ rays as a function of fission fragment mass are given at incident energies up to 20 MeV. The prompt neutron multiplicity as a function of the fragment mass, ν(A), for neutron-induced fission of <'235>U at different incident neutron energies is calculated. The calculated results are checked with the total average prompt neutron multiplicities ν and compared with the experimental and evaluated data. Some prompt neutron and γ emission mechanisms are discussed.     

Experimental determination of one-and two-neutron separation energies for neutron-rich copper isotopes

A method is proposed to determine the one-neutron S_n or two-neutron S_(2n) separation energy of neutronrich isotopes.Relationships between S_n(S_(2n)) and isotopic cross sections have been deduced from an empirical formula,i.e.,the cross section of an isotope exponentially depends on the average binding energy per nucleon B/A.The proposed relationships have been verified using the neutron-rich copper isotopes measured in the 64 A Me V ~(86)Kr+~9Be reaction.S_n,S_(2n),and B/A for the very neutron-rich ~(77,78,79)Cu isotopes are determined from the proposed correlations.It is also proposed that the correlations between S_n,S_(2n) and isotopic cross sections can be used to find the location of neutron drip line isotopes.     

Precise mass measurement of 68Se, a waiting-point nuclide along the rp process

Mass measurements of 68Ge, 68As, and 68Se have been obtained with the Canadian Penning Trap mass spectrometer. The results determine the mass excess of 68Se as -54 232(19) keV, the first measurement with a precision and reliability sufficient to address the light-curve and energy output of x-ray bursts as well as the abundances of the elements synthesized. Under typical conditions used for modeling x-ray bursts, 68Se is found to cause a significant delay in the rp process nucleosynthesis.     

Pesponse of the Neutron Star Properties to the Equation of State at Low Density

Using the RMF theory to describe the neutron liquid region in the neutron star and the Fermi gas model or FMT, BPS,and BBP model to describe the crust of the neutron star (referred as Fermi gas+RMF and RMF* respectively),the properties of the neutron star are calculated and compared with those from the RMF theory. Although the EOS at low density has negligible influence on the maximum mass of the neutron star, and its corresponding central density, energy density, and pressure, it changes the mass-radius relationship of neutron stars considerably. The differences of the neutron star radius corresponding to maximum mass between the RMF theory and RMF* calculations are 0.23-0.33 km.     

Application of microscopic transport model in the study of nuclear equation of state from heavy ion collisions at intermediate energies

The equation of state (EOS) of nuclear matter, i.e., the thermodynamic relationship between the binding energy per nucleon, temperature, density, as well as the isospin asymmetry, has been a hot topic in nuclear physics and astrophysics for a long time. The knowledge of the nuclear EOS is essential for studying the properties of nuclei, the structure of neutron stars, the dynamics of heavy ion collision (HIC), as well as neutron star mergers. HIC offers a unique way to create nuclear matter with high density and isospin asymmetry in terrestrial laboratory, but the formed dense nuclear matter exists only for a very short period, one cannot measure the nuclear EOS directly in experiments. Practically, transport models which often incorporate phenomenological potentials as an input are utilized to deduce the EOS from the comparison with the observables measured in laboratory. The ultrarelativistic quantum molecular dynamics (UrQMD) model has been widely employed for investigating HIC from the Fermi energy (40 MeV per nucleon) up to the CERN Large Hadron Collider energies (TeV). With further improvement in the nuclear mean-field potential term, the collision term, and the cluster recognition term of the UrQMD model, the newly measured collective flow and nuclear stopping data of light charged particles by the FOPI Collaboration can be reproduced. In this article we highlight our recent results on the studies of the nuclear EOS and the nuclear symmetry energy with the UrQMD model. New opportunities and challenges in the extraction of the nuclear EOS from transport models and HIC experiments are discussed.     

Multielement Analysis of Higherian Major Stimulants Using Instrumental Neutron Activation Analysis (INAA)

Instrumental neutron activation analysis was used for the determination of Na, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Rb, Sb, Cs, La, Ce, Sm, Eu, Dy, Yb, Lu, Hf, Ta, Pa, and U in bitter cola (Garcinia cola), Tatassai (Capsicum spp), sweet pepper (Capsicum annum), chillies (Capsicum spp.), alligator pepper (Aframomum melagueta) and onions (Allium caps) which are the major Nigerian stimulants.     

Monitoring method for neutron flux for a spallation target in an accelerator driven sub-critical system

In this paper, we study a monitoring method for neutron flux for the spallation target used in an accelerator driven sub-critical(ADS) system, where a spallation target located vertically at the centre of a sub-critical core is bombarded vertically by high-energy protons from an accelerator. First, by considering the characteristics in the spatial variation of neutron flux from the spallation target, we propose a multi-point measurement technique,i.e. the spallation neutron flux should be measured at multiple vertical locations. To explain why the flux should be measured at multiple locations, we have studied neutron production from a tungsten target bombarded by a 250 Me V-proton beam with Geant 4-based Monte Carlo simulations. The simulation results indicate that the neutron flux at the central location is up to three orders of magnitude higher than the flux at lower locations. Secondly, we have developed an effective technique in order to measure the spallation neutron flux with a fission chamber(FC), by establishing the relation between the fission rate measured by FC and the spallation neutron flux. Since this relation is linear for a FC, a constant calibration factor is used to derive the neutron flux from the measured fission rate. This calibration factor can be extracted from the energy spectra of spallation neutrons. Finally, we have evaluated the proposed calibration method for a FC in the environment of an ADS system. The results indicate that the proposed method functions very well.     

Time-of-flight mass measurements for nuclear processes in neutron star crusts

We present results from time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory that are relevant for neutron star crust models. The masses of 16 neutron-rich nuclei in the scandium-nickel range were determined simultaneously, with the masses of (61)V, (63)Cr, (66)Mn, and (74)Ni measured for the first time with mass excesses of -30.510(890) MeV, -35.280(650) MeV, -36.900(790) MeV, and -49.210(990) MeV, respectively. With these results the locations of the dominant electron capture heat sources in the outer crust of accreting neutron stars that exhibit super bursts are now experimentally constrained. We find the experimental Q value for the (66)Fe→(66)Mn electron capture to be 2.1 MeV (2.6σ) smaller than predicted, resulting in the transition occurring significantly closer to the neutron star surface.     

Systematics on fission fragment mass distribution of neutron induced 235U fission

Based on the neutron induced fission fragment mass distribution data up to     

Preparation and photoluminescence of Sc-doped ZnO nanowires

We demonstrate bulk synthesis of single-crystal Sc-doped ZnO nanowires by using (Sc+Zn) powders at . These mass nanowires are characterized through X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction, and high-resolution TEM, which have uniform diameters of about 40 nm and microns of several decades in length. The growth of ZnScO nanowires is suggested for self-catalyzed vapor–liquid–solid. In particular, PL spectra of these nanowires show emission peaks that intensely shift to long wavelength with increasing Sc and the doping quantity is found responsible for the different characteristics, in which PL mechanism is explained in detail.