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 Experimental Investigation and R-matrix Analysis of Low-lying Levels in 5He and 5Li

1988 ◽  
Vol 41 (4) ◽  
pp. 525 ◽  
Author(s):  
CL Woods ◽  
FC Barker ◽  
WN Catford ◽  
LK Fifield ◽  
NA Orr
Keyword(s):  
Matrix Analysis ◽  
Scattering Data ◽  
Matrix Formalism ◽  
Satisfactory Description ◽  
Model Calculations ◽  
R Matrix ◽  
Channel Radius ◽  
Direct Reactions ◽  
Method Of Production ◽  
Parameter Values

The ~cle-unstable nuclei SHe and Su have been studied via the 4He<,U,6U)SHe and 4He( Li,6He)SU stripping reactions at beam energies of 50 MeV and the 6U(12C, 13N)SHe and 6Li(13C, 14C)SU pickup reactions at 90 MeV. The experimental data clearly demonstrate a dependence of the lineshapes on the method of production of the mass-5 nuclei (in this case pickup or stripping). The observed lineshapes were analysed using the R-matrix formalism in a two-level approximation for each r value, with parameter values deduced from fits to the available 4He + nucleon scattering data. A best channel radius of 5�5 � 1� 0 fm was determined from the stripping data, and the corresponding set of R-matrix parameters also provided a satisfactory description of the pickup data. This channel radius is significantly larger than that employed in most previous analyses. Properties of the lowest ~ - and ! - sta~s of SHe and sU, observed via direct reactions, ate deduced from the parameter values. These properties are compared with results from earlier experimental analyses and the inferred properties of positive-parity states are compared with the results of recent shell-model calculations.

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 8Be Level Properties from the Low-energy 7Li(p, γo)8Be Cross Section

1996 ◽  
Vol 49 (6) ◽  
pp. 1081 ◽  
Author(s):  
FC Barker
Keyword(s):  
Shell Model ◽  
Cross Section ◽  
Low Energy ◽  
Cross Section Data ◽  
Model Calculations ◽  
R Matrix ◽  
Section Data ◽  
Extensive Data

R-matrix fits to 7Li(p, γo)8Be cross section data for Ep ≤ 1500 keV give reduced width amplitudes of the 1+ levels of 8Be at 17.64 and 18.15 MeV having signs in agreement with shell model calculations, contrary to previous fits to less-extensive data.

States inC14fromσTandσel(θ)forC13+n: Measurement,R-matrix analysis, and model calculations

1981 ◽  
Vol 23 (5) ◽  
pp. 1883-1897 ◽  
Author(s):  
R. O. Lane ◽  
H. D. Knox ◽  
P. Hoffmann-Pinther ◽  
R. M. White ◽  
G. F. Auchampaugh
Keyword(s):  
Matrix Analysis ◽  
Model Calculations ◽  
R Matrix

scholarly journals Calculation of the 13N(p, ?)14O Cross Section at Low Energies

1985 ◽  
Vol 38 (5) ◽  
pp. 657 ◽  
Author(s):  
FC Barker
Keyword(s):  
Experimental Data ◽  
Excited State ◽  
Shell Model ◽  
Cross Section ◽  
Energy Region ◽  
Model Calculations ◽  
R Matrix ◽  
Considerable Uncertainty ◽  
First Excited State ◽  
Low Energies

R-matrix formulae are used to calculate the 13N(p, ?) 140 cross section in the energy region of astrophysical interest. Values of the R-matrix parameters are determined by fitting experimental data in 14C and 14N as well as 140, and by making use of shell model calculations where necessary. With the presently available data, there is considerable uncertainty in the predicted cross section, but this could be reduced appreciably by a measurement of the lifetime of the first excited state of 14C. With the preferred channel radius of about 5 fm, the predicted cross section is lower than those found in two previous calculations, which are discussed in some detail.

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.

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