β-delayed proton decays near the proton drip line

Simply speaking, the drip line is the margin in chart of the nuclides where the nu-clides with the lower limits of detectable lifetime survive. The N/Z ratios of the nuclides on the drip line are extreme. Synthesis of the nuclei near the drip line and study of their exotic decays deal with the physics under extreme conditions, and therefore become one of the frontiers in nuclear physics today. The rare-earth nuclei near the proton drip line have been predicted to be highly deformed[1]. They a…     

Decay properties of neutron-deficient nuclei in the region Z = 86–92

Neutron deficient isotopes of elements Z = 86-92 have been produced by heavy-ion fusion reactions ¹²C + ²⁰⁸Pb, ²⁰⁹Bi, ²²Ne + ²⁰⁸Pb, ⁵¹V + ¹⁷⁰Er, and ⁵⁰Ti + ¹⁷⁰Er. The evaporation residues were investigated by means of α- and α-γ-spectroscopy after in-flight separation from the projectile beam by the velocity filter SHIP and implantation into a 16-strip position-sensitive Si-detector. New or improved decay data for ^{225, 226}U, ^{216, 217m, 218}Pa, ^{215, 216, 217}Th, ^{214, 215, 216, 216m}Ac, ²¹⁴Ra and ²¹³Rn have been obtained. Received: 5 April 2000 / Accepted: 28 July 2000     

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.     

Neutron drip line of Z=9–11 isotopic chains

A recent experimental breakthrough identified the last bound neutron-rich nuclei in fluorine and neon isotopes. Based on this finding, we perform a theoretical study of Z = 9, 10, 11, 12 isotopes in the relativistic mean field(RMF) model. The mean field parameters are assumed from the PK1 parameterization, and the pairing correlation is described by the particle number conservation BCS(FBCS) method recently formulated in the RMF model. We show that the FBCS approach plays an essential role in reproducing experimental results of fluorine and neon isotopes. Furthermore, we predict ~(39)Na and ~(40)Mg to be the last bound neutron-rich nuclei in sodium and magnesium isotopes.     

Decay spectroscopy of neutron-rich nuclei with A ≃ 100

We review structure data obtained by decay spectroscopy of neutron-rich nuclei of mass close to 100. Emphasis is put on the contribution of experiments at IGISOL in the nineties. They confirmed the earlier postulated shape coexistence in the fast shape-transition region between N = 58 (spherical ground states and low collectivity) and N = 60 (strong axial deformation). A detailed spectroscopic study of the A = 99 chain established the upper-Z limit of the N = 56 shell closure region with ⁹⁹Nb, owing to striking similarities with ⁹⁷Y. A consequence of the N = 56 closure is that the s _1/2 odd-neutron becomes the ground state of the most neutron-rich N = 57 isotones, starting with ⁹⁹Mo, instead of the degenerated d _5/2 and g _7/2 subshells familiar in the tin region. Consequences on the change of spin on astrophysical r-process calculations are briefly discussed. Finally, we say a few words about neutron-rich rhodium and palladium isotopes near the neutron midshell where regular and intruder states coexist very close to each other.     

Shell model calculations for the allowed Gamow-Teller β-decays of light nuclei

The allowed Gamow-Teller β-decay information of Li,Be,B,C,and N isotopes under the frame work of nuclear shell model is calculated herein.Theoretical results of Q values,half-lives,excitation energies,log ft values,branching fractions,and β-delayed proton/neutron emission probabilities are tabulated and compared with experimental data.The deviations from the observations are also analyzed.The 11Be nucleus is well known for its anomaly ground state Jπ=1/2+.Thus,we compared the theoretical energy levels with the experimental data and the agreements for low excitation states are consistent.The quenching factor is also evaluated and discussed.     

De–excitation of compound nuclei with A around 56: reduction of the emission barriers for protons and alpha particles

This paper contributes to the discussion on the phenomena of the enhanced emission of low–energetic charged particles during compound nuclei decay. The decay of compound nuclei ⁵²Fe, ⁵⁶Ni, and ⁵⁹Cu was studied. Energy spectra and emission angles of evaporated charged particles were measured in coincidence with gamma rays to determine the corresponding evaporation residue nucleus. Additionally, evaporation residue distributions were determined with the Munich rf recoil spectrometer. In this way, detailed channel–specific evaporation data were obtained for theoretical analysis. We extracted evaporation barriers and compared them with corresponding fusion barriers. The main result was revealed to be a lowering of the evaporation barrier for protons and alpha particles relative to the fusion barriers. But the observed effect is not as intensive as reported in recent studies. Received: 15 June 1998 / Revised version: 5 November 1998     

Structure of neutron-rich nuclei around A ⋍ 100

Neutron-rich isotopes of Mo (Z=42) around A ⋍ 100 have been investigated within the formalisms of cranked Nilsson Strutinsky and CHFB, to study several interesting features of nuclear structure in this mass region. The total energy/routhian surfaces have been generated for the isotopes of Mo ranging from A ⋍ 96 − 112, as a function of deformation (β ₂ and γ) for ground state and higher angular momentum states. Results of calculations using two different formalisms have been compared and combined to have a better understanding of the underlying mechanism of shape evolution.     

On the possibility for precision measurements of differential cross sections for elastic proton–proton scattering at the Protvino accelerator

Elastic-scattering data were analyzed, and it was concluded on the basis of this analysis that precisionmeasurements of differential cross sections for elastic proton–proton scattering at the accelerator of the Institute for High Energy Physics (IHEP, Protvino, Russia) over a broad momentum-transfer range are of importance and topical interest. The layout of the respective experimental facility detecting the scattered particle and recoil proton and possessing a high momentum-transfer resolution was examined along with the equipment constituting this facility. The facility in question is able to record up to a billion events of elastic proton–proton scattering per IHEP accelerator run (20 days). Other lines of physics research with this facility are briefly discussed.     

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.     

A new complex line soliton for the two-dimensional KdV–Burgers equation

Making use of a extended tanh method with symbolic computation, we find a new complex line soliton for the two-dimensional (2D) KdV–Burgers equation. Its real part is the sum of the shock wave solution of a 2D Burgers equation and the solitary wave solution of a 2D KdV (KP) equation, and its imaginary part is the product of the shock wave solution of a 2D Burgers equation and the solitary wave solution of a 2D MKdV (MKP) equation.     

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 least-squares/finite element method for the numerical solution of the Navier–Stokes-Cahn–Hilliard system modeling the motion of the contact line

In this article we discuss the numerical solution of the Navier–Stokes-Cahn–Hilliard system modeling the motion of the contact line separating two immiscible incompressible viscous fluids near a solid wall. The method we employ combines a finite element space approximation with a time discretization by operator-splitting. To solve the Cahn–Hilliard part of the problem, we use a least-squares/conjugate gradient method. We also show that the scheme has the total energy decaying in time property under certain conditions. Our numerical experiments indicate that the method discussed here is accurate, stable and efficient.     

Method study of parameter choice for a circular proton–proton collider

In this paper we show a systematic method of appropriate parameter choice for a circular proton–proton collider by using an analytical expression for the beam–beam tune shift limit, starting from a given design goal and technical limitations. A suitable parameter space has been explored. Based on the parameter scan, sets of appropriate parameters designed for a 50 km and 100 km circular proton–proton collider are proposed.