arXiv subjects

D. van der Knijff

Publications and source records attributed to D. van der Knijff.

22 records · Page 2Linked to original sources

arXiv2005

Compound and quasi-compound states in low-energy scattering of nucleons from 12C

A multi-channel algebraic scattering theory has been used to study the properties of nucleon scattering from 12C and of the sub-threshold compound nuclear states, accounting for properties in the compound nuclei to ~10 MeV. All compound and quasi-compound resonances observed in total cross-section data are matched, and on seeking solutions of the method at negative energies, all sub-threshold states in 13C and 13N are predicted with the correct spin-parities and with reasonable values for their energies. A collective-model prescription has been used to define the initiating nucleon-12C interactions and via use of orthogonalizing pseudo-potentials, account is made of the Pauli principle. Information is extracted on the underlying structure of each state in the compound systems by investigating the zero-deformation limit of the results.

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arXiv2004

On Raynal's posting in arXiv (nucl-th/0407060)

With nucl-th/0407060, Jacques Raynal uses the arXiv in a way which does not conform to standard professional practices. His posting contains many statements that are beyond the borders of acceptable scientific disputes, with the scope to defame colleagues by manifestly false or misleading statements. In this comment we reject the three ``critiques'' expressed by Raynal. 1. The fact that we possibly misquoted our references. 2. The role of the Pauli principle in these kind of calculations. 3. The nature and limits of our coupled-channel potential model. Raynal's postings unfairly detract from the importance of our work, which we published in Nuclear Physics A728, 65 (2003), on a new approach, Multi-Channel-Algebraic-Scattering (MCAS), for coupled-channel calculations. With the MCAS approach we were able to identify systematically all low-energy compound resonances, and to include effectively the Pauli principle in collective, geometrical-type, macroscopic models of multichannel interaction. This represents a clear advantage with respect to the current distribution of the ECIS formulation.

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arXiv2004

Raynal's use of the word "aberrant" appears more appropriate for his ECIS formulation

Recently, we published a paper (Nucl. Phys. A 728 (2003) 65; see nucl-th/0306068) presenting a new calculational method for nucleon-nucleus elastic scattering at low energies. That method is particularly appropriate for analyses in the region of narrow resonances. The method is based upon the sturmian representation of the S-matrix, and allows inclusion of nonlocality effects due to Pauli principle. It also provides a systematic identification of narrow-resonance spectra and subthreshold bound states. A phenomenological test calculation for low-energy (below 4 MeV) neutrons on 12-C (including the first two excitations of the target) was presented to illustrate the validity of the approach. The model calculation received a violent criticism (see nucl-th/0312038) by the developer of a method (ECIS) which to date cannot handle nonlocality effects and cannot be used easily to identify all narrow resonances. We demonstrate that Raynal's opposition to our development is not well founded by the arguments he presents. Indeed the work we published shows, on rewording the title of nucl-th/0312038, that it is ``aberrant'' phenomenologically to analyze resonant low-energy nucleon-nucleus processes with coupled-channel methods without taking into account the nonlocalities due to the Pauli principle; problems typically encountered in the ECIS formulation.

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arXiv2003

An algebraic solution of the multichannel problem applied to low energy nucleon-nucleus scattering

Compound resonances in nucleon-nucleus scattering are related to the discrete spectrum of the target. Such resonances can be studied in a unified and general framework by a scattering model that uses sturmian expansions of postulated multichannel interactions between the colliding nuclei. Associated with such expanded multichannel interactions are algebraic multichannel scattering matrices. The matrix structure of the inherent Green functions not only facilitates extraction of the sub-threshold (compound nucleus) bound state spin-parity values and energies but also readily gives the energies and widths of resonances in the scattering regime. We exploited also the ability of the sturmian-expansion method to deal with non-local interactions to take into account the strong non-local effects introduced by the Pauli principle. As an example, we have used the collective model (to second order) to define a multichannel potential matrix for low energy neutron-C12 scattering allowing coupling between the 0+ (ground), 2+ (4.4389 MeV), and 0+ (7.64 MeV) states. The algebraic S matrix for this system has been evaluated and the sub-threshold bound states as well as cross sections and polarizations as functions of energy are predicted. The results are reflected in the actual measured data, and are shown to be consistent with expectations as may be based upon a shell model description of the target and of the compound nucleus.

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