Bhushan N. Joshi

Effective α-α t-Matrix Interaction at Medium Energies

The α-α transition operator-effective interaction, tαα(E, r) has been evaluated using phenomenological α-α optical potentials at several bombarding energies, Eα from 77 to 200 MeV. The results are obtained by solving the Schrodinger equation with appropriate optical potentials for various partial waves and then clubbing these with their respective optical potentials and initial state plane waves. The change of the α-α optical potential with or without hard core has been shown to influence the effective α-α t-matrix interactions drastically. The behaviour of the calculated tαα(E, r) effective interaction indicates towards a solution of the large anomalies found in the (α, 2α) reaction analyses.

A Bi-Dimensional Multi-Wire Cathode Strip Detector for Fission Fragments

A large area bi-dimensional position sensitive multi-wire cathode strip detector (MCSD) has been developed for the detection of fission fragments (FFs). The performance of the detector has been characterized with FFs from 252Cf and α particles from 241Am-239Pu sources. The position information is obtained from the measurement of time delay signals of the cathode strips (X-direction) and split-cathode wires (Y-direction) with respect to the timing signal from the anode wires. The position resolution is found to be about 1.0 and 1.5 mm in X-and Y-directions respectively.

Nucleon-Nucleon t-matrix Effective Interaction for (p, 2p) Reactions

In (p, 2p) reactions the p-p interaction is the main knockout interaction which acts in its full glory. Recent finite range (p, 2p) calculations used a parametrized spin-isospin dependent finite range tNN (r) - effective interaction operator which is a function of the distance between the nucleons alone. In the present work we have evaluated the nucleon-nucleon (N-N) t-matrix effective interaction using the Reid soft core N-N interaction potential. In this we find that the proper t- matrix effective interaction is not only a function of spin and isospin of the interacting nucleons but is a strong function of the relative orbital angular momentum, L also. The radial behaviour of the tL (r) is also found to be very unconventional in that it is found to go to zero at r = 0 while in the conventional usage the t(r) is taken to peak at r = 0 because of its representation in terms of Yukawa functions. This very different behaviour of our calculated N-N t-matrix effective interaction operator is expected to make large changes in the Finite Range (FR-DWIA) predictions for (p, 2p) reaction cross sections. Besides this it is hoped that the marked differences one obtains in the behaviour of these tL(r)s from different realistic N-N interactions through their resulting fits obtained for the (p, 2p) reactions will provide us a tool to select the proper N-N interaction out of the many available in literature.

Heavy Cluster Knockout Reaction {sup 16}O({sup 12}C,2{sup 12}C){sup 4}He and the Nature of the {sup 12}C-{sup 12}C Interaction Potential

The heavy cluster knockout reaction (16)O((12)C,2(12)C)(4)He performed for the first time, reveals the true nature of the (12)C-(12)C interaction. The observed cross section is enhanced by almost 2 orders of magnitude over the conventional zero range distorted wave impulse approximation (DWIA) predictions. An attractive (12)C-(12)C optical potential, as obtained in the folding model, does not explain the enhanced cross section in the finite range (FR) DWIA framework. The inclusion of a hard core of fairly long range ∼3.65  fm explains the data. The present investigation of (16)O((12)C,2(12)C)(4)He along with the (12)C-(12)C elastic scattering also proves beyond doubt that the folding models deep attractive heavy ion potentials are unsuitable to describe the highly overlapping heavy ions. The application of FR-DWIA opens up new avenues to use the heavy core knockout for the detailed investigation of heavy as well as Borromean halo nuclei.

WITNESSING THE HADRONIC COLLISION EVENTS AT CLOSE QUARTERS

It is seen that in the three body final state of a nucleon knockout reaction the residual nucleus not only bears testimony to the dynamics of the knocked out nucleon before the event but also can testify the happening at the time of the hard collision event. This arises mainly because of the distorting optical potentials of the residual nucleus with the knockout partners. In 40Ca(p, 2p) knockout reaction the optical distortion effects are large enough to be able to differentiate between strong peripheral bruising or the deep interpenetration of the two protons at the time of knockout. Similar effect is witnessed in the proton knockout using pions. Many stronger evidences of the effect of varying behaviour of the knockout vertex exist in the nucleon cluster knockout reactions which were only viewed as unexplained large anomalies. Evidences are provided where the different short distance behaviour of the knockout vertex t-matrix effective interaction produced huge differences in the finite range (FR) distorted wave impulse approximation (DWIA) predictions of various knockout reactions. These observations enhance the possibility of observing the multiquark objects (dibaryons, pentaquark eta.) through nucleon knockout reactions if they are produced at the knockout vertex by the incident hadron beam.