Analysis of the threshold anomaly in proton elastic scattering on A ∼- 30 mass nuclei

The threshold anomaly in energy-averaged excitation functions of proton elastic scattering on A ∼- 30 mass nuclei is analyzed in the framework of the Lane model for p-wave threshold effects. A quantitative correlation between the strength of the threshold anomaly and the 2p-wave neutron strength function is reported.     

Theoretical studies of proton capture reactions in A～25 proton-rich nuclei

The direct proton capture and resonance proton capture properties of stellar reactions 22Mg(p,γ)23Al and 26Si(p,γ)27P are studied by employing a mean-field potential obtained from the Skyrme-Hartree-Fock(SHF) model.Calculations with the SHF potential reproduce well the loosely-bound structure of the ground states as well as the widths of the resonant states in these nuclei.With the obtained potential we estimate the reaction rates of direct proton capture and resonance proton capture to nuclei 23Al and 27P....     

Shell-model calculations of stellar weak interaction rates. I. Gamow-Teller distributions and spectra of nuclei in the mass range A = 45–65

Electron capture and beta-decay rates on nuclei in the mass range A = 45–65 play an important role in many astrophysical environments. The determination of these rates by large-scale shell-model calculations is desirable, but it requires to reproduce the Gamow-Teller strength distributions and spectra of the pf shell nuclei. We show in this paper that large-scale shell-model calculations, employing a slightly monopole-corrected version of the well-known KB3 interaction, fulfill these necessary requirements. In particular, our calculations reproduce the experimentally available GT₊ and GT₋ strength distributions and the nuclear halflives, and describe the nuclear spectra appropriately.     

Microscopic calculation of proton capture reactions in the mass 60–80 region and its astrophysical implications

Microscopic optical potentials obtained by folding the DDM3Y interaction with the densities from the Relativistic Mean-Field approach have been utilized to evaluate S-factors of low-energy (p, γ) reactions in the mass 60–80 region and to compare with experiments. The Lagrangian density FSU Gold has been employed. Astrophysical rates for important proton capture reactions have been calculated to study the behaviour of rapid proton nucleosynthesis for waiting point nuclei with mass less than A = 80.     

Diffuseness parameter of even-even nuclei in the range of 58 ≤ A ≤ 250 and the coupled channel optical model

An interaction potential with a radial dependence in the Woods-Saxon form is used to describe low energy neutron data in the context of the coupled channel optical model. A single value of the diffuseness parameter was used for even-even nuclides over a wide range of A: a = 0.65 fm. Traditional and nontraditional magic and nonspherical nuclei were exceptions. The deviations can be used to find or verify the existence of nontraditional magic numbers.     

Statistical properties of excited nuclei in the mass range 47 ? A ? 59

Level densities and their energy dependences for nuclei in the mass range of 47 ?? A ?? 59 were determined from the results obtained by measuring neutron-evaporation spectra in respective (p, n) reactions. The spectra of neutrons originating from the (p, n) reactions on ⁴⁷Ti, ⁴⁸Ti, ⁴⁹Ti, ⁵³Cr, ⁵⁴Cr, ⁵⁷Fe, and ⁵⁹Co nuclei were measured in the proton-energy range of 7?C11 MeV. These measurements were performed with the aid of a fast-neutron spectrometer by the time-of-flight method over the base of the EGP-15 pulsed tandem accelerator installed at the Institute for Physics and Power Engineering (Obninsk, Russia). A high resolution of the spectrometer and its stability in the time of flight made it possible to identify reliably discrete low-lying levels along with the continuum part of neutron spectra. Our measured data were analyzed within the statistical equilibrium and preequilibrium models of nuclear reactions. The respective calculations were performed with the aid of the Hauser-Feshbach formalismof statistical theory supplemented with the generalized model of a superfluid nucleus, the back-shifted Fermi gas model, and the Gilbert-Cameron composite formula for nuclear level densities. Nuclear level densities for ⁴⁷V, ⁴⁸V, ⁴⁹V, ⁵³Mn, ⁵⁴Mn, ⁵⁷Co, and ⁵⁹Ni and their energy dependences were determined. The results are discussed and compared with available experimental data and with recommendations of model-based systematics.     

A new method for the calculation of Sommerfeld screening parameter σ1 in x-ray spectra

The paper describes a new method for the calculation of the Sommerfeld screening parameter σ₁. It requires neither the knowledge of the energy separations of spin doublet levels nor is it based on the application of the Hertz law. The only data required for the calculation are the experimental energy values of the level concerned for the series of elements belonging to the same subshell in which the element in the question is situated. As an illustration the values of σ₁ are calculated for the L ₁, L ₂ and L ₃ levels for elements belonging to the 4f subshell and these are found to be in excellent agreement with those published earlier by Gokhale and Misra. The method brings out the constancy of σ₁ (L ₂ L ₃)−σ₁(L ₁) in a natural way and may thus be regarded as providing theoretical explanation of the Hertz law.     

Effect of 120 keV proton irradiation on mass loss and chemical structure of AG-80 epoxy resin

The AG-80 resin is a new type of thermosetting matrix for advanced carbon/epoxy composites. Mass loss effect and the related outgassing are major concerns for its application in space. The changes in mass loss, outgassing and chemical structure under 120 keV proton exposure were investigated for the AG-80 epoxy resin. The variation in chemistry was characterised by X-ray photoelectron spectroscopy. Experimental results show that by increasing the proton fluence, the surface colour of specimens becomes darker. Mass loss ratios ascend remarkably until the fluence of approximately 6.3×10¹⁵ cm^?2 and then tend to level off. The surface roughness of specimens exhibits an increasing trend followed by a decreasing trend as a function of proton fluence. Under the exposure, the C?C, C?H, C?N and C?O bonds are broken, a variety of molecule ions with smaller molecular weight are formed and carbon is enriched in the surface layer of the specimens. The changes in mass loss and surface roughness of the AG-80 epoxy resin could be attributed to the formation of the molecule ions and the enrichment of carbon content in the surface layer due to proton radiation.     

Rigidity dependence of cosmic-ray escape length obtained from a comparison of proton and iron spectra in the energy range 3–3000 GeV

A simple leaky-box model of cosmic-ray propagation in the Galaxy is quite suitable for analysis of cosmic-ray nuclei energy spectra and composition at energies under 1 GeV [1, 2]. Within this model the full information about the cosmic-ray propagation in the Galaxy is compressed into a single parameter, viz., escape length, X _e , which characterizes the mean grams of matter that are passed by cosmic-rays from sources to the Earth. In this paper we analyze the worldwide data on proton and iron cosmic-ray spectra that have been collected in experiments and obtain the rigidity dependence of the escape length from the measured rigidity dependence of the proton/iron ratio. This agrees well with the one estimated by a standard manner from the secondary/primary nuclei ratio. However, at R > 300 GV the behavior of X _e (R) distinctly changes, which can point to a change of the proton/iron ratio in cosmic-ray sources.     

Evidence for nonhadronic degrees of freedom in the transverse mass spectra of kaons from relativistic nucleus-nucleus collisions?

We investigate transverse hadron spectra from relativistic nucleus-nucleus collisions within two independent transport approaches that are based on quark, diquark, string, and hadronic degrees of freedom. Both transport models show their reliability for elementary pp as well as light-ion (C+C, Si+Si) reactions. However, for central Au+Au (Pb+Pb) collisions above approximately 5A GeV the measured K+/- transverse mass spectra have a larger inverse slope parameter than expected from the calculation. Thus, the pressure generated by hadronic interactions in the transport models above approximately 5A GeV is lower than observed in the experimental data. This finding shows that the additional pressure--as expected from lattice QCD calculations at finite quark chemical potential and temperature--is generated by strong partonic interactions in the early phase of central Au+Au (Pb+Pb) collisions.     

Observations of “pairing-free” Kπ = 1+ rotational bands in deformed odd-odd A ∼ 100 nuclei

Rotational bands with K^π = 1⁺ in the odd-odd nuclei ^100,102₃₉Y and ^102,104₄₁Nb are postulated from β⁻ decay of t heir even-even parents. Each two-quasiparticle band has a moment of inertia very close to that of a rigid spheroidal nucleus with deformation β ∼ 0.3, hence these bands are nearly “pairing free”.     

Evolution of proton shells in 20 ⩽ Z ⩽ 28 and 20 ⩽ N ⩽ 50 nuclei and dispersive optical model

Experimental single-particle proton energies in spherical and nearly spherical 20 ? Z ? 28 medium-mass nuclei and their counterparts evaluated with the aid of data formirror nuclei were analyzed on the basis of the dispersive optical model. The parameters of the dispersive optical potential were extrapolated to the region of unstable nuclei, and the values obtained in this way were then used to predict the single-particle proton energies in the 20 ? N ? 50 nuclei under study. The evolution of the particle-hole energy gap was traced, and features peculiar to single-particle spectra of magic and nonmagic nuclei were revealed by comparing single-particle energies with proton-separation energies.     

Transverse mass spectra of strange and multi–strange particles in Pb–Pb collisions at 158 A GeV/c

The WA97 experiment has measured the transverse mass spectra for negative hadrons () and strange particles produced at mid–rapidity in Pb–Pb collisions. The increased statistics of analysed data samples allowed us to perform a study of the spectra of , , , and as a function of the collision centrality. The data, which correspond to the most central 40% of the total inelastic cross section, have been divided into four centrality classes according to the estimated number of nucleons taking part in the collision. The spectra, analysed separately for each centrality bin, exhibit only weak ( 15%) centrality dependence. The deviation of the inverse slope from the linear dependence on the particle mass is confirmed even for the most central Pb–Pb collisions. Received: 5 January 2000 / Revised version: 28 February 2000 / Published online: 14 April 2000     

Argon ion laser-induced BaS B1Σ+-A1Σ+, A′1Π, a3Π, and X1Σ+ fluorescence spectra: Analysis of A ∼ A′, A ∼ a,and A′ ∼ a perturbations

The 333.6-, 351.1-, and 363.8-nm lines of a cw argon ion laser are found to coincide with the BaS B¹Σ⁺-X¹Σ⁺ (12, 0) R(17), (6, 0) P(35), and (3, 0) R(125) transitions, respectively. Fluorescence transitions from the laser-prepared upper levels terminating in X¹Σ⁺v = 0–28, A¹Σ⁺v = 1–3, A′¹Π v = 1–13, and a³Π₁v = 3–12 are assigned. These results are combined with a previous analysis of the extensively perturbed BaS A¹Σ⁺-X¹Σ⁺ system [R. F. Barrow, W. G. Burton, and P. A. Jones, Trans. Farad. Soc.67, 902–906 (1971)]. Every observed perturbation of the BaS A¹Σ⁺ state is electronically and vibrationally assigned. The levels a³Π₀v = 10–13, a³Π₁v = 12–14, a³Π₂v = 15, and A′¹Π v = 10–13 are sampled via their perturbations of A¹Σ⁺v = 0–2. Although the mutual interactions of the a³Π, A′¹Π, and A¹Σ⁺ states approach Hund's case (c) limit, a complete deperturbation is performed from a case (a) starting point. Of the five lowest energy electronic states of BaS, only b³Σ⁺ remains uncharacterized. Principal deperturbed molecular constants are (in cm^?1, 1σ uncertainties in parentheses):

     

	$\text{T}{}_{\mathrm{e}}$	$\text{ω}{}_{\mathrm{e}}$	$\text{ω}{}_{\mathrm{e}}\text{x}{}_{\mathrm{e}}$	$\text{B}{}_{\mathrm{e}}\text{× 10}{}^2$	$\text{α}{}_{\mathrm{e}}\text{× 10}{}^4$	$\text{R}{}_{\mathrm{e}}\text{(}\text{A}\text{?}\text{)}$
$\text{A}{}^1\text{Σ}{}^{\mathrm{+}}$	14 498.6(1)	287.7(1)	1.15(5)	9.365(5)	5.0(10)	2.633
$\text{A′}{}^1\text{Π}$	12 095(6)	258.9(5)	0.7	8.21(5)	3.6(5)	2.813
$\text{a}{}^3\text{Π}{}_{\mathrm{i}}$	11 835(6)	259.6(5)	0.7	8.21	3.6	2.813
$\text{X}{}^1\text{Σ}{}^{\mathrm{+}}$	0	379.50(4)	0.91(1)	10.334(1)	3.4(2)	2.507