scholarly journals 2- States of 8Be

1977 ◽  
Vol 30 (2) ◽  
pp. 113 ◽  
Author(s):  
FC Barker
Keyword(s):  
Shell Model ◽  
Cross Sections ◽  
Matrix Theory ◽  
Matrix Approximation ◽  
Model Calculations ◽  
R Matrix ◽  
Rapid Changes ◽  
The Cross ◽  
Proper Account

The cross sections for several reactions populating sBe in the region of the 7Be+n threshold show rapid changes, which have been attributed to a 2- threshold state. An analysis of these data using R matrix theory shows that there is considerable isospin mixing in the threshold state, implying another 2 - state nearby. A two-level R matrix approximation provides a good fit to all the relevant data, with parameters consistent with shell model calculations and with properties of sLi. Proper account must be taken of the neutron threshold in order to explain the isospin mixing. The threshold state is expected to show different widths in different reactions.

scholarly journals Isospin Mixing in 4¯ States of 12C

1983 ◽  
Vol 36 (5) ◽  
pp. 649 ◽  
Author(s):  
FC Barker
Keyword(s):  
Shell Model ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Matrix Theory ◽  
Bound State ◽  
Model Calculations ◽  
R Matrix ◽  
Parameter Values

Fits are made to measured 12C(n�,no:)12C cross sections in terms of an isospin-mixed doublet of 4- 12C levels near 19�5 MeV, using the R-matrix theory of nuclear reactions. Parameter values are restricted by information from other reactions and from bound-state shell model calculations.

scholarly journals The Boundary Condition Parameter in R-Matrix Theory

1972 ◽  
Vol 25 (4) ◽  
pp. 341 ◽  
Author(s):  
FO Barker
Keyword(s):  
Boundary Condition ◽  
Finite Number ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Matrix Theory ◽  
R Matrix ◽  
The Cross

In the general R-matrix theory of nuclear reactions, all measurable quantities such as the cross sections scc' should be independent of the choice of the boundary condition parameters Bc although the values of the level parameters E? and ??c depend on the Bc. For applications involving only a finite number of levels ?, it is not obvious that this is still the case as completeness arguments can no longer be used. It is shown here that scc' can be made independent of the choice Bc of for any finite number of levels and any number of channels, and the resulting formulae giving the dependence of E? and ??c on Bc are derived. An application is made to the pair of 5/2- levels of 7Li near 7 MeV excitation.

Elastic and inelastic scattering of 40 MeV polarized protons from 90Zr and 92Zr

1979 ◽  
Vol 57 (4) ◽  
pp. 540-549 ◽  
Author(s):  
R. de Swiniarski ◽  
Dinh-Lien Pham ◽  
G. Bagieu ◽  
H. V. Geramb
Keyword(s):  
Inelastic Scattering ◽  
Cross Sections ◽  
Imaginary Component ◽  
Spin Orbit ◽  
Model Calculations ◽  
Analyzing Powers ◽  
Elastic And Inelastic Scattering ◽  
Polarized Protons ◽  
The Cross ◽  
Good Agreement

Analyzing powers and cross sections have been measured for elastic and inelastic scattering of 40 MeV polarized protons from 90Zr and 92Zr. The analysis has been carried out in the DWBA within the framework of the macroscopic and microscopic models. Furthermore, the coupled-channels calculations using the vibrational model and the full Thomas form for the spin–orbit potential give a very good description for both the cross sections and the analyzing powers of the iow-lying2+, 3−, 5−, and 4+ states in 92Zr and the 2+ and 3− in 90Zr. The cross section and analyzing power for the first 2+ state in these nuclei were compared with previous results at 30 and 20.3 MeV, and from this comparison a certain energy dependence of the relative strength of the spin–orbit deformation to the central deformation could be observed. Microscopic model calculations with tensor and spin–orbit components included in the projectile–target real interaction and with an exact treatment of knock-on' exchange have been performed for the 2+ states in these nuclei. An attempt has also been made in order to include the imaginary component in the N–N interaction. For these calculations, rather good agreement was obtained especially for the 2+ state in 92Zr but poor agreement for 90Zr. Finally, valence plus core polarization calculations have also been done and showed a very good agreement between theory and experiment for those 2+ transitions.

Structure of 12B from measurement and R-matrix analysis of σ(θ) for 11B(n, n)11B and 11B(n, n')11B∗(2.12 MeV), and shell-model calculations

1983 ◽  
Vol 394 (1-2) ◽  
pp. 221-244 ◽  
Author(s):  
P.E. Koehler ◽  
H.D. Knox ◽  
D.A. Resler ◽  
R.O. Lane ◽  
D.J. Millener
Keyword(s):  
Shell Model ◽  
Matrix Analysis ◽  
Model Calculations ◽  
R Matrix

scholarly journals Interference Between Levels in Nuclear Reactions

1967 ◽  
Vol 20 (3) ◽  
pp. 341 ◽  
Author(s):  
FC Barker
Keyword(s):  
Nuclear Reaction ◽  
Cross Section ◽  
Nuclear Reactions ◽  
Matrix Theory ◽  
R Matrix ◽  
Single Level ◽  
The Cross

In this note we consider the cross section for a nuclear reaction in which one of the product nuclei is unstable, with two or more levels contributing to its decay. Previously a formula had been derived from R-matrix theory for the case where contributions come from only a single level of the nucleus with a given spin and parity.

scholarly journals Forbidden transitions in nuclear weak processes relevant to neutrino detection, nucleosynthesis and evolution of stars

2019 ◽  
Vol 223 ◽  
pp. 01063
Author(s):  
Toshio Suzuki ◽  
Satoshi Chiba ◽  
Takashi Yoshida ◽  
Koh Takahashi ◽  
Hideyuki Umeda ◽  
...  
Keyword(s):  
Shell Model ◽  
Cross Sections ◽  
Neutral Current ◽  
Expansion Method ◽  
Multipole Expansion ◽  
Reaction Cross ◽  
Model Calculations ◽  
Multipole Expansion Method ◽  
Supernova Explosions ◽  
Model Hamiltonians

The distribution of the spin-dipole strengths in 16O and neutrino-induced reactions on 16O areinvestigated by shell-model calculations with new shell-model Hamiltonians. Chargedcurrent and neutral-current reactioncross sections are valuated in various particle and γ emission channels as well as the total ones at neutrinoenergies up to Eν≈ 100 MeV. Effects of multiparticle emission channels, especially the αp emission channels, on nucleosynthesis of 11B and 11C in core-collapse supernova explosions are investigated. The MSW neutrino oscillation effects oncharged-current reaction cross sections are investigated for future supernova burst. Electron capture rates for a forbidden transition 20Ne(Og.s.+) → 20F(2g.s.+) in stellar environments are evaluated by the multipole expansion method with the use of shell model Hamiltonians, and compared with those obtained by a prescription that treats the transition as an allowed GamowTeller (GT) transition. Different electron energy dependence of the transition strengths between the two methods is found to lead to sizable differences in the weak rates of the two methods.

On threshold resonances

1970 ◽  
Vol 48 (15) ◽  
pp. 1747-1758 ◽  
Author(s):  
C. T. Tindle
Keyword(s):  
Cross Sections ◽  
Matrix Theory ◽  
Threshold Level ◽  
R Matrix ◽  
Neutral Particles ◽  
S Matrix ◽  
Energy Neutron ◽  
Square Well ◽  
Neutron Cross Sections ◽  
Threshold Resonances

A comparison is made of the way R-matrix and S-matrix theories analyze the threshold resonances which occur in the scattering of neutral particles by a square well. Both approaches are found to provide very good approximate formulas. However, modifications of the usual S-matrix expansions must first be made. The behavior of the energy of the threshold level is quite different in the two alternatives. By comparing the two theories in their interpretation of the low-energy neutron cross sections of 1H, 16O, and 208Pb it is concluded that.R-matrix theory provides a better interpretation for unbound levels and S-matrix theory is preferable when the threshold level is bound.

scholarly journals Single photoionization of the Kr-like Rb ii ion in the photon energy range 22–46.0 eV

2019 ◽  
Vol 486 (1) ◽  
pp. 245-250 ◽  
Author(s):  
Brendan M McLaughlin ◽  
James F Babb
Keyword(s):  
Cross Section ◽  
Photon Energy ◽  
Cross Sections ◽  
Large Scale ◽  
Experimental Studies ◽  
Photoionization Cross Section ◽  
Theoretical Work ◽  
Matrix Approximation ◽  
Theoretical Cross Section ◽  
R Matrix

Abstract Single photoionization cross-sections for Kr-like Rb+ ions are reported in the energy (wavelength) range from 22 (564 Å) to 46 eV (270 Å). Theoretical cross-section calculations for this trans-Fe element are compared with measurements from the ASTRID radiation facility in Aarhus, Denmark and from the dual laser plasma technique, at respectively 40 and 35 meV FWHM energy resolution. In the photon energy region 22–32 eV the spectrum is dominated by excitation auto-ionizing resonance states. Above 32 eV the cross-section exhibits classic Fano window resonances features, which are analysed and discussed. Large-scale theoretical photoionization cross-section calculations, performed using a Dirac Coulomb R-matrix approximation are benchmarked against these high-resolution experimental results. Comparison of the theoretical work with the experimental studies allowed the identification of resonance features and their parameters in the spectra in addition to contributions from excited metastable states of the Rb+ ions.

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