[PDF] Probing Nuclear Correlations With Pion Nucleus Double Charge Exchange eBook

Author :
Publisher :
Page : pages
File Size : 48,43 MB
Release : 1988
Category :
ISBN :

GET BOOK

In this paper we have calculated the lowest order pion double charge reaction mechanism using shell model wavefunctions of medium weight nuclei. We have the sequential reaction mechanism in which the pion undergoes two single-charge exchange scatterings on the valence neutrons. The distortion of the incoming, intermediate, and outgoing pion are included. The closure approximation is made for the intermediate states with an average excitation energy used in the pion propagator. The double-charge exchange is assumed to take place on the valence nucleons which are assumed to be in one spherical shell model orbital. 34 refs., 5 figs., 3 tabs.

Author :
Publisher :
Page : pages
File Size : 33,36 MB
Release : 1988
Category :
ISBN :

GET BOOK

A review is given of pion double-charge exchange reactions at incident energies of 25 to 65 MeV and leading to nuclear isobaric- analog states and to ground states. The large effects on the cross-section magnitudes and angular distribution shapes produced by spatial correlations in nuclear wave functions are demonstrated. The data on 1f7/2 nuclei at 35 MeV obtained in the last few years are used to establish the general validity of the two-amplitude shell model description for these transitions. Recent measurements on the energy dependence between 20 and 65 MeV of forward-angle cross sections are presented and discussed. 19 refs., 15 figs., 2 tabs.

Author :
Publisher :
Page : pages
File Size : 13,17 MB
Release : 1984
Category :
ISBN :

GET BOOK

Recognizing the importance of both the reaction mechanism and nuclear structure aspects of the DCX, a new reaction theory was proposed in 1981 which offers a consistent treatment of these two equally important components of pion DCX. In this theory, the density square-dependent interaction is derived from the dynamical consideration of true pion absorption on a nucleon pair inside the nucleus. The strength of this new pion-nucleus interaction can then be calculated from the knowledge of the second-order pion-nucleus optical potential. With no free parameters for the pion-nucleus interaction and with the use of the coexistence nuclear model, the theory gives satisfactory descriptions of the magnitude and the shape of 5° excitation functions as well as of the differential cross sections for the DCX reactions 18O(.pi., .pi.−) 18Ne(DIAS) and 42Ca(.pi., .pi.−) 42Ti(DIAS) between 120 and 290 MeV. Our basic conclusions are: (1) the TSSCX mechanism alone cannot describe pion DCX; (2) the position of the first minimum in the differential cross section is very sensitive to the inclusion of density square-dependent interaction; and (3) on the other hand, the magnitude of the cross section is very sensitive to the inclusion of pair correlations (core excitation in the case with 18O and 42Ca).

Author :
Publisher :
Page : pages
File Size : 40,8 MB
Release : 1987
Category :
ISBN :

GET BOOK

Double-charge-exchange reactions induced by pions are shown to furnish a direct means of detecting nucleon-nucleon correlations in nuclei. For the particular case of double isobaric analog transitions the effect of correlations is easily isolated and quite strong. Examination of the properties of the position correlations implicit in the nuclear shell model provides an explanation of several experimentally observed features of double-charge-exchange reactions, including in particular, their dependence on the number of valence neutrons present. An explicit demonstration of the role played by nucleon-nucleon correlations is presented for the double-charge-exchange cross-sections of 42Ca, 44Ca and 48Ca, recently measured at LAMPF. Our analysis explains why the cross section for the double-charge-exchange reaction on 48Ca, in which 28 neutron pairs participate, is comparable and indeed smaller than the corresponding cross-section for 42Ca with its single valence neutron pair. It also predicts the variation of angular distributions over the family of isotopes. 13 refs., 3 figs.

Author : Torleif Erik Oskar Ericson
Publisher : Oxford University Press, USA
Page : 506 pages
File Size : 47,23 MB
Release : 1988
Category : Language Arts & Disciplines
ISBN :

GET BOOK

The pion plays an outstanding role in nuclear physics as a generator of the nuclear force and as an important part of the nuclear many-body problem. At the same time, pion beams are used as probes to explore the nucleus and its interactions. As pion physics has matured over the years, a rich and diverse variety of phenomena has been uncovered. The aim of this book is to examine the underlying physical picture behind these phenomena in a systematic and coherent way. The authors emphasize the interplay between physical concepts and experimental facts more than the formal tools, which are presented in a series of appendices. The book is directed towards advanced students as well as research workers.

Author : William R Gibbs
Publisher : World Scientific
Page : 622 pages
File Size : 22,90 MB
Release : 1990-09-24
Category :
ISBN : 9814611875

GET BOOK

What do you associate with chemistry? Explosions, innovative materials, plastics, pollution? The public's confused and contradictory conception of chemistry as basic science, industrial producer and polluter contributes to what we present in this book as chemistry's image as an impure science. Historically, chemistry has always been viewed as impure both in terms of its academic status and its role in transforming modern society. While exploring the history of this science we argue for a characteristic philosophical approach that distinguishes chemistry from physics. This reflection leads us to a philosophical stance that we characterise as operational realism. In this new expanded edition we delve deeper into the questions of properties and potentials that are so important for this philosophy that is based on the manipulation of matter rather than the construction of theories./a

Author :
Publisher :
Page : pages
File Size : 42,88 MB
Release : 1989
Category :
ISBN :

GET BOOK

Recent measurements of pion double-charge exchange (DCX) at energies 20 to 70 MeV are providing a new means for studying nucleon-nucleon correlations in nuclei. At these energies the nucleus is relatively transparent, allowing simpler theoretical models to be used in interpreting the data and leading to a clearer picture. Also the contribution to DCX of sequential charge-exchange scattering through the intermediate analog state is suppressed near 50 MeV and transitions through non-analog intermediate states become very important. Recent theoretical studies by several groups have shown that while transitions through the analog route involve relatively long nucleon-nucleon distances, those through non-analog intermediate states obtain nearly half their strength from nucleon pairs with less than 1 fermi separation. Thus DCX near 50 MeV is an excellent way to study short-range nucleon-nucleon correlations. 31 refs., 29 figs., 4 tabs.

Author :
Publisher :
Page : pages
File Size : 17,49 MB
Release : 1987
Category :
ISBN :

GET BOOK

Pion double charge exchange to both the double-analog state and the ground state is studied for medium weight nuclei. The relative cross section of these two transitions and the importance of nuclear structure as a function of pion kinetic energy is examined. 16 figs., 5 tabs.