Impact Parameter Dependent X Ray Investigations in Heavy Ion Heavy Atom Collisions

Author(s):
Sarvesh Kumar , Inter University Accelerator Center, Aruna Asaf Ali Marg, New Delhi; Kajol Chakraborty, Amity Institute of Applied Sciences, Amity University, Noida, (U. P.); Lakshmi Dagar, Amity Institute of Applied Sciences, Amity University, Noida, (U. P.); Punita Verma, Kalindi College, University of Delhi, New Delhi

Keywords:
Heavy Atom Collisions, X Ray Investigations

Abstract:
The discovery of x-rays in 1895 marked the beginning of quantitative studies of atomic collisions. These investigations have made important contributions in formulation of modern concepts and theory of atomic physics. It is well known that x-rays emitted during heavy-ion collisions stem from the innermost shells of a quasi-molecule formed during the collision. These x-rays and impact parameter dependence of their emission probability holds crucial information about molecular orbital x-ray emission or charge exchange during interaction with solid targets. These super heavy quasi-molecules can be approached in relatively slow heavy ion-atom collisions which are slow compared to the orbital velocity of innermost electrons of concern. In order to probe the inner shell levels, vacancies have to be provided there. Since the vacancy production probability is primarily determined by electron emission into final states at the Fermi surface of the united atom, the energy transfer is essentially given by the binding energy of the bound state considered. In our investigations it has been calculated that to achieve the above desired system, an impact parameter range of (0.016-0-.023) a.u. is required. The experimental work has been planned to be done at Inter University Accelerator Center, India. 127 I-ions will be bombarded on heavy solid targets of 53I, 79Au and 83Bi. Targets of different thickness will be used to extrapolate to near “zero target thickness”‚(thinnest to 250 ¼g/ cm2) which are approximately the conditions under single collision conditions. The characteristic x-rays from the collision partners as well as MO x-rays will be detected by available x-ray detectors (a Si (Li) and a low energy Ge detector) to cover the entire energy range of K and L x-rays of the collision partners. For measurement of recoils at backward angles SBD/ (gas or annular) proportional counter will be used. A coincidence will be set up between the backward angle particle detectors and the x-ray to extract the impact parameter dependency of x-ray emission. Experimental data will then be compared with the data from correlation diagrams drawn on the basis of Self Consistent Field-Dirac Fock Slater (SCF-DFS) calculations for these systems for interpretation. Such a type of comparison will give a concrete idea about the couplings of the inner shells during such a slow ion-atom collision. A part of the investigations were presented as M.Sc. dissertation work of the second author.

I. AIM OF THE EXPERIMENT
The purpose of planning an impact parameter dependent ion atom collision experiment was to study the dependency of impact parameter on x-rays emitted during heavy ion heavy atom collision. This dependency holds crucial information about the inner shell couplings and hence vacancy transfer in a quasi-molecule (atomic energy levels of projectile and target overlap and hence the system behaves as a united atomic system) during a slow ion-atom collision. A detailed literature survey of similar experiments done in the past across the globe showed that for studying the above mentioned collisions, an impact parameter range of (0.016-0.023) atomic units was required. Thus a suitable experimental set up has been planned keeping the desired impact parameter range in mind at Inter University Accelerator Centre (IUAC). To examine the impact parameter of scattered projectile and emitted x-rays in coincidence (observing the scattered projectile and x-rays emitted from the target simultaneously) a particle detector (parallel plate avalanche counter available at IUAC) will be used to detect the scatteredprojectile and Low energy germanium detectors (LeGe) will be used to detect the x-rays. As a part of pre-experimental preparations a detailed theoretical analysis was done for the planned experimental set up. Correlation diagrams for the chosen projectile target combinations have been drawn which will be used to analyze the results after performing the experiment.
After performing the experiment we would be able to get a concrete idea about how superheavy systems (combined atomic number of target and projectile should be greater than 130) behave under the conditions of single ion-atom collisions.

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