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 0+ States of 8Be

1968 ◽  
Vol 21 (3) ◽  
pp. 239 ◽  
Author(s):  
FC Barker ◽  
HJ Hay ◽  
PB Treacy
Keyword(s):  
Excited State ◽  
Excited States ◽  
Cross Section ◽  
Scattering Data ◽  
Excitation Energies ◽  
R Matrix ◽  
Channel Radius

The light even nuclei with A ;;;. 10 have 0+ excited states near 6 MeV, probably with large (X-particle reduced widths. A similar state in BBe would be very broad. Evidence for 0+ excited states in BBe has been obtained here using many-level R-matrix fits to known (X-(X scattering data, but the excitation energies depend strongly on the assumed channel radius. For a simultaneous fit to the 9Be(p, d)BBe cross section, assuming these higher states are not strongly populated, the channel radius is restricted to (7~~) fm, implying a 0+ excited state at (6=f3) MeV of width (9=f4) MeV.

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 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 Low-lying Levels of 13C and 13N

1980 ◽  
Vol 33 (4) ◽  
pp. 691 ◽  
Author(s):  
FC Barker ◽  
Nasima Ferdous
Keyword(s):  
Shell Model ◽  
Cross Sections ◽  
Scattering Data ◽  
Excitation Energies ◽  
R Matrix ◽  
Fitted Parameter ◽  
Model Predictions ◽  
Transition Matrix Elements ◽  
The One ◽  
Parameter Values

An attempt is made to give a consistent account of observed properties of the low-lying levels of the mirror nuclei 13C and 13N. In the first stage of this analysis, least squares fits of the data are made using R-matrix formulae in the one- and two-level approximations; in the second stage, the resultant parameter values are compared with shell model predictions. Fitted properties include level widths, neutron scattering data, El radiative widths and El capture cross sections .. The R-matrix formulae include external contributions to the El transition matrix elements, calculated using wavefunctions with the correct asymptotic forms. Acceptable fits are obtained for channel radii in the range 4-6 fm, with the lower values preferred. The parameter values obtained in these fits agree with shell model predictions, except for quantities involving the t - levels. Level displacement energies are calculated from the fitted parameter values. A reasonable account is given of two notable asymmetries between 13C and 13N-the very different excitation energies of the first excited states and the very different strengths of the El decays of these states.

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 The ??Decay of 8B, and 2+ States Of 8Be

1969 ◽  
Vol 22 (6) ◽  
pp. 663 ◽  
Author(s):  
GJ Clark ◽  
PB Treacy ◽  
SN Tucker
Keyword(s):  
Elastic Scattering ◽  
Energy Distribution ◽  
Matrix Formalism ◽  
R Matrix ◽  
Channel Radius

The {l-decay of 8B has been investigated by measuring the energy distribution of the <x-particles from subsequent breakup of 8Be. The data have been analysed, in conjunction with data from <X-o< elastic scattering, in a three-level R-matrix formalism. Consistent fits are obtained for a channel radius of 6�0�0�5 fm, and the existence of a broad 2+ state of 8Be near 12�0 MeV, of width 14 MeV, is confirmed.

Statistical Description of Isotope Exchange Processes: A Multisite Model for the 18O Exchange

1982 ◽  
Vol 37 (11-12) ◽  
pp. 1161-1169 ◽  
Author(s):  
Paul Rösch
Keyword(s):  
Active Site ◽  
Isotope Exchange ◽  
Analytical Procedure ◽  
Matrix Formalism ◽  
Model Calculations ◽  
Exchange Processes ◽  
Reaction Solution ◽  
Different Types ◽  
Refinement Procedure

Abstract An analytical procedure has been developed for the determination of isotope exchange processes as exemplified by the 18O exchange catalysed by enzyme-nucleotide complexes. The model is able to handle more than one type of active site per reaction solution and is also able to distinguish between different types of inequivalence of the oxygens of enzyme bound Pi. Use of transition matrix formalism and basic statistical considerations lead directly to the simple model. A data refinement procedure is introduced and model calculations are shown.

scholarly journals The 7Be(p, ?)8B Cross Section at Low Energies

1980 ◽  
Vol 33 (2) ◽  
pp. 177 ◽  
Author(s):  
FC Barker
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Solar Neutrinos ◽  
Model Calculations ◽  
Spectroscopic Factors ◽  
Low Energies ◽  
Standard Values ◽  
Experimental Values ◽  
Parameter Values ◽  
Potential Parameters

The nonresonant part of the 7Be(p, )I)8B cross section at low energies is recalculated by means of a direct-capture potential model, using parameter values determined by fitting 7Li(n, n)7Li and 7Li(n, )I)8Li data. Standard values of the potential parameters and spectroscopic factors give values of the 7Li(n,)I) cross section that are too large. Modified values that fit the thermal-neutron capture cross section predict 7Be(p,)I) cross sections that are much less than the experimental values. Also, shell model calculations predict resonant 7Be(p,)I) cross sections that are smaller than the experimental values. It is suggested that the accepted experimental values of the 7Be(p, )I) cross section may be too large, perhaps due partly to an overlarge accepted value for the 7Li(d, p)8Li cross section, which has been used for normalization purposes. A decrease in the 7Be(p,)I) cross section would reduce the calculated detection rate of solar neutrinos and lessen the discrepancy with the measured value.

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