Nucleon transfer reactions with exotic beams at ATLAS

We present some recent results from studies of light nuclei using exotic beams from ATLAS at Argonne National Laboratory. Light nuclei far from stability provide ideal testing grounds for modern theoretical methods, and may provide information about astrophysical environments. We focus on the nuclei ⁹Li and ⁷He, populated with the (d,p) and (d,³He) reactions.     

Recent advances in exotic nuclear beams

Not intended to be a review of the field, the present paper is the written version of a talk given at the APAC 1999 conference. It only aims at an outline of the important effort nowadays made for experiments with exotic beams. A comparatively long list of references is given where more complete information can be found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Elastic scattering via quark structure of nucleons

In the framework of the Glauber multiple-scattering theory, the elastic collisions of proton-proton (pp) at the center-of-mass energies = 23.5, 30.7, 44.7, and 52.8 GeV and alpha-proton (p) at = 88 and 89 GeV are analyzed by considering the quark structure of their constituents. The differential cross-section containing the full multiple-scattering series between their quarks is calculated using Gaussian forms for the quark density and quark-quark (QQ) scattering amplitudes. The results obtained from the quark model and the conventional nucleon model are compared with the experimental data. The comparison shows that the nucleon model reproduces the experimental data more satisfactorily than the quark model, and both approaches have limited success in describing the data at such energies. The agreement with the experimental data is improved by the inclusion of the phase variation.     

Elastic scattering of positrons by xenon atoms

Summary Partial and total cross-sections of positron scattering by Xe atoms are calculated at twenty values of incident energy ranging from 0.01 Ry to 4.00 Ry. The calculations are carried out via model potential (describing the positron target interaction) and a polarization potential introduced previously by Lane and Geltmann (1967). The comparison between our results and those obtained by other authors shows significant agreement and supports our simple model scattering process. The author of this paper has agreed to not receive the proofs for correction.     

Elastic scattering of electrons by hydrogen molecules

Elastic scattering of electrons by hydrogen molecules has been investigated in the intermediate energy range 100–2000 eV. The direct scattering amplitude consists of first Börn and second Börn minus distortion term. The contribution of exchange has been included through Ochkur approximation. The elastic differential cross-sections agree with experimental data.     

Nuclear structure studies on halo nuclei by direct reactions with radioactive beams

The investigation of direct reactions with exotic beams in inverse kinematics gives access to a wide field of nuclear structure studies in the region far off stability. The basic concept and the methods involved are briefly discussed. The present contribution will focus on the investigation of light neutron-rich halo nuclei. Such nuclei reveal a new type of nuclear structure, namely an extended neutron distribution surrounding a nuclear core. An overview on this phenomenon, and on the various methods which gave first evidence and qualitative confirmation of our present picture of halo nuclei, is given. To obtain more quantitative information on the radial shape of halo nuclei, elastic proton scattering on neutron-rich light nuclei at intermediate energies was recently investigated for the first time. This method is demonstrated to be an effective means for studying the nuclear matter distributions of such nuclei. The results on the nuclear matter radii of ⁶He and ⁸He, the deduced nuclear matter density distributions, and the significance of the data on the halo structure is discussed. The present data allow also a sensitive test of theoretical model calculations on the structure of neutron-rich helium isotopes. A few examples are presented. The investigation of few-nucleon transfer reactions in inverse kinematics may provide new and complementary information on nuclear structure, as well as astrophysical questions. The physics motivation and the experimental concept for such experiments, to be performed due to momentum matching reasons at low incident energies around 5–20 MeV/u at the new generation low energy radioactive beam facilities SPIRAL, PIAFE, etc., is briefly discussed.     

Elastic scattering of electrons by argon atoms

The partial wave method with a central potential has been applied to investigate the elastic scattering of electrons by the argon atoms in the intermediate energy range (100 eV − 1 keV). The central potential includes the effects of the static field, exchange and polarization. The results are in good accord with recent experimental data. A brief account of this investigation was presented at the X Int. Conf. on the Physics of Electronic and Atomic Collisions held at Paris in July 1977.     

Elastic scattering of electrons and positrons by cadmium atoms

ABSTRACT

The differential, integrated elastic, total and momentum transfer cross sections along with Sherman function for the elastic scattering of electrons and positrons by cadmium atoms have been evaluated from the partial wave solution of the Dirac relativistic scattering equations for a projectile-atom complex potential at the energy range 6.4 eV < E < 1.0 keV. For various scattering quantities, a comparison of our results exhibits better agreement with the experimental data than the other available theoretical values.     

Elastic and inelastic scattering of 58Ni +90,94Zr

Pure elastic and inelastic scattering cross sections have been measured for the systems ⁵⁸Ni +^90,94Zr at energies near the Coulomb barrier where not only quasi-elastic and fusion but also deep-inelastic process come into play. Coupled channels calculations including both projectile and target inelastic excitations can successfully explain the elastic and inelastic scattering angular distributions with an energy-independent semi-empirical bare potential. The calculation reproduces also the sum of the total quasi-elastic, fusion and deep-inelastic cross sections. Received: 14 September 1998 / Revised version: 21 October 1998     

Elastic and vibrational excitation cross-sections in the Ps-H2 scattering: a perturbative approach

Summary A detailed account is reported of a perturbative calculation of the elastic and vibrational excitation cross-sections for the positronium-H₂ molecule scattering. The problem is studied in the context of the multichannel scattering theory for identical particles; the first-order exchange amplitude and the second-order direct amplitude are evaluated for energy from zero to the positronium excitation threshold. The lowest-order Padé approximant is also constructed and this suggests the occurrence of a strong enhancement in the vibrational cross-section and in the related energy loss in matter at the positronium excitation threshold. In comparison with a short preliminary account presented elsewhere, various improvements are introduced both in the physical approximations and in the numerical calculations.

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Riassunto Si dà un resoconto particolareggiato di un calcolo perturbativo della sezione d'urto elastica e di eccitazione vibrazionale per la collisione positronio su molecola d'idrogeno. Il problema è studiato nel contesto della teoria dello scattering a molti canali per sistemi di particelle identiche; sono calcolate l'ampiezza di scambio al primo ordine e l'ampiezza diretta al secondo ordine per energie da zero alla soglia di eccitazione del positronio. è anche valutata l'approssimante di Padé piú bassa e questo suggerisce la comparsa di una forte esaltazione della sezione d'urto vibrazionale e della perdita di energia nella materia attorno alla soglia di eccitazione del positronio. Rispetto ad un breve resoconto preliminare presentato in precedenza si sono apportati diversi miglioramenti sia nelle approssimazioni di carattere fisico che nelle valutazioni numeriche.

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Резюме Проводится пертурбационное вычисление поперечных сечений упругого рассеяния и вибрационного возбуждения в процессе рассеяния позитрония на молекуле H₂. Рассматриваемая проблема исследуется в связи с теорией многоканального рассеяния тождественных частиц. Вычисляются обменная амплитуда первого порядка и прямая амплитуда второго порядка в области энергий от нуля до порога возбуждения позитрония. Также определяется низший порядка Падэ приближения, предполагая наличие сильного увеличения в вибрационном поперечном сечении и в энергетических потерях в веществе на пороге возбуждения позитрония. По сравнению с существующими подходами, предлагаются различные улучшения в физических приблизениях и в численных расчетах.

     

Fission experiments with secondary beams

Nuclear fission from excitation energies around 11 MeV was studied at GSI, Darmstadt for 76 neutron-deficient actinides and pre-actinides by use of relativistic secondary beams. The characteristics of multimodal fission of nuclei around ²²⁶Th are systematically investigated and related to the influence of shell effects on the potential-energy and on the level density between saddle point and scission. A systematic view on the large number of elemental yields measured gave rise to a new interpretation of the enhanced production of even elements in nuclear fission and allowed for a new understanding of pair breaking in fission.     

Enhanced raman scattering spectra for gaussian light beams

We show that effect of light-induced focusing of the low-frequency Raman scattering components and defocusing of the high-frequency components in the field of a gaussian exciting beam lead to a slight shift of the enhanced Raman line relative to the center of the spontaneous Raman line on the low-frequency side. We propose and provide a rationale for an efficient algorithm for calculating the average power for enhanced Raman scattering, based on numerical solution of the wave equation for the field of the Stokes beam developing from spontaneous Raman scattering. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 230–236, March–April, 2007.     

Elastic scattering of electrons by helium atoms in high energy higher order Born approximation

The differential cross-sections forē-helium elastic scattering are calculated by using Yateshigh-energy higher order Born approximations, through 0 (K _i ^{Emphasis>−2} ) of the incident electron momentum, and comparisons have been made with the recent theoretical and experimental results.     

Elastic scattering of electrons from oxygen and ozone molecules at high energies

Elastic differential cross-sections for thee-O₂ ande-O₃ systems are obtained in the independent atom model at high energies (E _i ⩾ 300 eV). The basic atomic scattering amplitudes are obtained in the partial wave method through a sum of static exchange and polarization potentials. Oure-O₂ results agree with experiments except for small angles. No data are available for O₃, for comparison.     

Elastic scattering of 9Be on light target nuclei

The elastic scattering of ⁹Be on the target nuclei ⁹Be, ¹²C, ¹³C and ¹⁶O was measured at projectile energies of 14, 20 and 26 MeV. All angular distributions show a diffraction-like structure. In addition, excitation curves were measured for the scattering of ⁹Be on ⁹Be at three different angles in the energy range of 9–22 MeV. An optical potential having parameters independent of mass number and energy and reproducing all the measured angular distributions in the forward angular region was found and compared with that for the scattering of ⁹Be on medium and heavy nuclei.     

Nuclear physics with simple and multi-element detectors and with stable and radioactive beams

The phenomenon of fusion barrier distributions is discussed in the context of a problem already investigated in some detail with simple detection systems, but possessing avenues to studies with multi-detector arrays. The complementarity of research with simple and complex detectors, as well as with stable and radioactive beams, will be highlighted.     

The use of exotic heavy ion transfer reactions to study light neutron rich nuclei

The ¹⁸O + ^{207, 208}Pb reaction at E = 93 MeV has been used to measure the mass excesses of ^{21, 22}O ¹⁹N and ¹⁷C. values of 8.095 ± 0.075, 9.29 ± 0.18, 15.96 ± 0.15 and 21.10 ± 0.22 MeV, respectively, were obtained. These results are in good agreement with previous measurements. A comparison with current theoretical predictions is also presented.