Particle Stripping Research Articles

Effective two-body forces in light and medium mass nuclei

From the spectroscopic information provided by single particle stripping reactions, we have extracted average effective two-body interaction between nucleons in thep-, sd-, andfp- shells. Using the derived interaction parameters, we have calculated the energy centroids of the level spectra of residual nuclei obtained via single nucleon stripping reactions involving light and medium mass nuclei as targets.

The transfer reactions induced by 38 MeV 19F ions on 27Al

The reactions induced by 38 MeV 19F on 27Al have been studied using the Tandem Van de Graaff accelerator at Harwell together with a mass identification system based on a combination of a Buechner magnetic spectrograph and position sensitive silicon detectors in the focal plane of the magnet. Comparison of the elastic scattering measurements with Coulomb cross sections provided an absolute normalisation to the measured reaction yields. Transfer reactions were measured as a function of emitted particle energy and angle for single nucleon pick-up and stripping and for 2, 3 and 4 particle stripping. Essential features of the experimental technique are outlined and the experimental results are presented. The significance of the energy spectra and angular distributions are discussed. The results of DWBA analyses of one-nucleon transfer reactions yield spectroscopic factors for levels in 28Si, 28Al and 26Al which are in fair agreement with those obtained in other studies.

Study of the 9Be(n, α)6He reaction in the neutron energy range from 12.2 to 18.0 MeV

Angular distributions of α-particles emitted in the 9Be(n, α0)6He reactions have been measured at neutron energies of 12.2, 14.1 and 18.0 MeV. Excitation functions for forward emission of the reaction products have been determined in the neutron energy range 12.2–18.0 MeV. The results indicate the dominance of heavy particle stripping in the mechanism of the 9Be(n, α0)6He reaction in the investigated neutron energy range.

NLi6(α,d)Be8reaction and the importance of exchange processes

The $^{6}\mathrm{Li}(\ensuremath{\alpha},d)^{8}\mathrm{Be}_{\mathrm{g}.\mathrm{s}.}$ reaction is studied in the expectation that exchange contributions will be enhanced relative to the more usual light particle stripping process. Angular distributions of deuterons were measured at bombarding energies of 20 and 24 MeV and are found to exhibit back-angle peaking characteristic of the exchange process. Calculations including only a direct stripping mechanism are not able to account for the back-angle peaking and disagree with the back-angle data by more than two orders of magnitude. A two-mode finite-range distorted-wave Born-approximation analysis including cluster exchange contributions accurately describes the observed backward peaking at both energies. The importance of exchange contributions is attributed to favorable kinematic conditions and large cluster amplitudes associated with the exchange process.

On three particle stripping reactions

The formalism for the coupled-channel analysis of stripping reactions of complex nuclear projectiles by nuclei is presented. The general adiabatic approximation is developed. The indirect transitions that are considered are those which arise via intermediate rotational excitations of the target and product nuclei, i.e. the adiabatic approximation for rotational bands is used. At the same time the generalized DWBA procedure is considered for the intrinsic states. Also the antisymmetrization problem is solved. A new method for the calculation of the matrix elements of the (α,n) stripping reaction with finite range effective forces is developed. The method is based on an expansion of the radial functions which describe the relative motion in terms of harmonic oscillator wave functions multiplied by a Gauss one. Effective forces of Gauss type are assumed between the outgoing neutron and each captured nucleon

Analyse de la réaction 16O(n, α) 13C à 14 MeV par la méthode des ondes distordues

The 16O(n, α) 13C reaction is studied by using the DWBA method. The following combinations are investigated: first, knock-on and heavy particle stripping, second, pick-up and heavy particle stripping. The differential cross sections are theoretically calculated using a graphical method. The results obtained are then compared with the plane wave ones.

The [formula omitted] and [formula omitted] reactions near 445 MeV

Ground state group (p, α) angular distributions have been obtained at energies between 30.5 MeV and 45 MeV. It appears that an energy range free from significant resonance effects has been found for the (p, α) reaction. The main process for the 19 F(p, α) 16 O and the 112 C(p, α) 9 B reactions is direct triton pickup, however, the backward angle region is quite different for the two angular distributions and the 12 C(p, α) 9 B reaction probably contains significant heavy particle stripping.

The [formula omitted] reaction induced by 14.4 MeV neutrons

The differential cross section of the 9 Be(n, α 0) 6 He reaction has been measured with a counter telescope discriminating 4He and 6He particles. The angular distribution is compared with heavy particle stripping theory. The total cross section is σ = 11.7 ± 1.8 mb.

Rearrangement collisions and heavy particle stripping

The formal theory of rearrangement collisions is discussed, following the works of Day et al. and Robson, using a different representation. It was found that heavy particle stripping could arise from the process of antisymmetrization, as discussed previously by Robson, just as from the residual interaction. The latter contribution, which was found to be larger in magnitude than the earlier one, takes place when the state of the core of the target nucleus is changed by the reaction. The reaction C 13(p, n)N 13 is considered as an illustration, in which the heavy particle stripping contribution arising from core excitation was calculated.

Rearrangement collisions and heavy particle stripping: M. El-Nadi and T. H. Rihan. Atomic Energy Establishment, Cairo, U.A.R.

Rearrangement collisions and heavy particle stripping: M. El-Nadi and T. H. Rihan. Atomic Energy Establishment, Cairo, U.A.R.

The direct exchange contributions to the reaction 12C(α, p) 15N between 20 MeV and 40 MeV

A treatment of the exchange interactions, heavy particle stripping and knock-out stripping is developed for (α, p) reactions using plane wave theory which takes into account interference between the two reaction amplitudes. A comparison with experiment for the reaction 12C(α, p) 15N is made. The theory has some success in predicting the angular and the energy positions of the maxima and minima, but detailed agreement with experiment is rather poor.

The (p, α) reaction mechanism at 45 MeV

A non-resonant increase in the yield of alpha particles at backward angles has been observed in the reaction 12C(p, α) 9B which does not appear in the reaction 19F(p, α) 16O. This is interpreted as a contribution from the direct exchange process, heavy particle stripping.

Exclusion principle and nuclear reaction mechanism

Effects of the Exclusion Principle in specific reference to direct reactions are studied in detail by formulating a simple one-dimensional model in the two channel approximation. The fact that a target wavefunction can be described by different systems of cluster wavefunctions on account of the indistinguishability of nucleons is exploited to bring out the connections between the various aspects of the reaction mechanism and the forward and the backward reaction amplitudes. The coupled integro-differential equations of the model are solved by a matrix method, and an iteration method respectively for low and high energies of the incident particle in the entrance channel. The exact solution of the coupled integro-differential equations takes into account the Exclusion Principle and the effects of rescattering and target recoil. The result shows that the direct reactions are long distance or “surface” phenomena. An evidence is presented that this is a consequence of the Exclusion Principle. The exact result is compared with various approximate results. The latter include the cases; 1. antisymmetrization is completely neglected; 2. antisymmetrization is performed on the target wavefunctions only; 3. plane wave Born approximation; 4. distorted wave Born approximation. The result obtained by target antisymmetrization coincides with the exact result only for high energies of the incident particle. The practical use of this result obtained by use of the two equivalent clusterwavefunctions which describe the target wavefunction is discussed in connection with heavy particle stripping.

A study of the reactions O 17(He 3, α0), O 18(He 3, α0) and O 18(He 3, α1)

The angular distribution of the alpha particles from each of the reactions O 17( He 3, α 0) O 16, O 17( He 3,α 0), O 18( He 3,α 0) and O 18( He 3,α 1) O 17∗ has been measured over an angular range of 0–160° at thirteen values of incident energy between 2.68 and 6.47 MeV. The experimental results and a comparison of these results with the theoretical prediction of a plane-wave direct-reaction theory with two modes, pick-up and heavy particle stripping, are presented.

The magnitude of exchange effects in (d, p) reactions

The angular distributions in (d, p) reactions are frequently interpreted in terms of deuteron stripping, heavy particle stripping and knock-on processes. It is shown that, in general, distortion effects cause the heavy particle stripping cross section to be of order 1/ A compared to the deuteron stripping cross section. The knock-on cross section is also shown to be smaller and less sharply peaked than the deutron stripping cross section when proper account is taken of the finite size of the deuteron. Thus only when special selection rules suppress the contribution of deuteron stripping are these exchange effects important.

Exchange terms in direct nuclear reaction theories

An internally consistent formulation of the problem of exchange effects in direct nuclear reactions is given. By using convenient Distorted Wave Born Approximation forms, it is shown that in the limit of an infinitely massive target the usual “heavy particle stripping” matrix elements have the scattering properties which the exchange matrix elements should have. It is thus concluded that these forms are correct, and their properties are discussed in plane-wave and other approximations.

A STUDY OF THE Be9(He3, n)C11 REACTION

The energy spectra and angular distributions of the emergent neutrons from the Be9(He3, n)C11 reaction have been obtained for an incident He3-particle energy of 2 Mev with the technique of observing proton recoil in photographic emulsions. The cross sections were normalized to Be9(He3, p)B11 data observed simultaneously at 90° to the beam. The lack of similarity in the (He3, n) and (He3, p) mirror reactions to some residual states suggests a direct interaction mechanism rather than compound nucleus. An attempt to analyze some of the data in terms of double particle stripping has been made.

Direct inelastic scattering of nucleons

The forward and backward peakings observed in the angular distributions in nucleon collisions, are interpreted theoretically as forward knock on and heavy particle stripping, processes. Some experimental data on C 13(p, n)N 13 at varying proton energies were chosen and satisfactory fits were obtained.

Numerical methods in the distorted wave theory of heavy particle stripping

An investigation of some possible methods of calculating the heavy particle stripping amplitude in the distorted wave approximation is carried out. The validity of the zero-range approximation analogous to that used in ordinary stripping is examined and results indicate that its range of validity is very restricted. A less aproximate method is investigated involving a finite-range interaction and harmonic oscillator functions which yields a calculable result. Numerical calculations are presented for the reaction F 19(d, p)F 20 and the various approximations compared. A comparison of the finite-range calculation with experiment indicates the need for a two-mode stripping theory for this reaction.

(n, α) reactions on light nuclei at 14 MeV

Angular distributions of alpha particles from (n, α) reactions on light nuclei (carbon, nitrogen and oxygen) have been studied. The result shows that the pick-up and heavy particle stripping processes play a role in the reaction mechanism.