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.

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 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.

Spectroscopic Study of 32S Through the 31P(d,n)32S Reaction

1974 ◽  
Vol 52 (14) ◽  
pp. 1288-1294 ◽  
Author(s):  
A. H. Hussein ◽  
G. C. Neilson ◽  
W. J. McDonald ◽  
W. K. Dawson
Keyword(s):  
Spectroscopic Study ◽  
Shell Model ◽  
Cross Sections ◽  
Differential Cross ◽  
Time Of Flight ◽  
Angular Distributions ◽  
Absolute Differential ◽  
Spectroscopic Factors ◽  
Model Predictions ◽  
Theoretical Predictions

The 31P(d,n)32S reaction has been studied at deuteron energies of 4.0 and 5.45 MeV. Neutron energies were measured by time of flight. Absolute differential cross sections of seven levels in 32S have been measured and compared with the theoretical predictions of both the DWBA and compound statistical theories. Analysis of the angular distributions yielded lP values and absolute spectroscopic factors. These results have been compared with those from other experiments and shell model predictions.

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.

Cluster states in 13C

2006 ◽  
Vol 21 (31n33) ◽  
pp. 2393-2401 ◽  
Author(s):  
Y. Sasamoto ◽  
T. Kawabata ◽  
T. Uesaka ◽  
K. Suda ◽  
Y. Maeda ◽  
...  
Keyword(s):  
Shell Model ◽  
Cross Sections ◽  
Cluster Structure ◽  
Quadrupole Transition ◽  
Cluster States ◽  
Model Predictions

Cross sections for 13 C (α,α′) reactions at Eα = 400 MeV have been measured to obtain the monopole and quadrupole transition strengths. The excitation strengths are compared with the shell-model predictions. It is suggested that the large monopole strengths observed for the [Formula: see text] and [Formula: see text] states in 13 C are attributed to the cluster structure of those states.

scholarly journals Multi-photon above threshold ionization of multi-electron atoms and molecules using the R-matrix approach

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jakub Benda ◽  
Zdeněk Mašín
Keyword(s):  
Cross Sections ◽  
Outer Region ◽  
Angular Distributions ◽  
Matrix Formalism ◽  
Computationally Efficient ◽  
Threshold Ionization ◽  
R Matrix ◽  
Atoms And Molecules ◽  
Above Threshold Ionization ◽  
Transition Matrix Elements

AbstractWe formulate a computationally efficient time-independent method based on the multi-electron molecular R-matrix formalism. This method is used to calculate transition matrix elements for the multi-photon ionization of atoms and molecules under the influence of a perturbative field. The method relies on the partitioning of space which allows us to calculate the infinite-range free-free dipole integrals analytically in the outer region, beyond the range of the initial bound wave function. This approach is valid for an arbitrary order, that is, any number of photons absorbed both in the bound and the continuum part of the spectrum (below- and above-threshold ionization). We calculate generalized multi-photon cross sections and angular distributions of different systems (H, He, $$\hbox {H}_{{2}}$$ H 2 , $$\hbox {CO}_{{2}}$$ CO 2 ) and validate our approach by comparison with data from the literature.

scholarly journals Delayed Alpha Spectra from the Beta Decay of 8Li and 8B

1989 ◽  
Vol 42 (1) ◽  
pp. 25 ◽  
Author(s):  
FC Barker
Keyword(s):  
Phase Shift ◽  
Shell Model ◽  
Satisfactory Agreement ◽  
Beta Decay ◽  
Matrix Elements ◽  
R Matrix ◽  
Intruder State ◽  
Parameter Values ◽  
Gamow Teller ◽  
D Wave

Many-level R-matrix fits are made to the ()(-()( scattering d-wave phase shift and to ()(-spectra from BLi and BB ,8-decay measured by Wilkinson and Alburger (1971). With the requirement that the parameter values are the same in the fits to the phase shift and the ()(-spectra data, the best overall fits are obtained for a channel radius of about 6�5 fm, implying a broad 2+ intruder state of BBe at about 9 MeV. There is satisfactory agreement between the Gamow-Teller matrix elements extracted from the fits and shell model values.

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