study of heavy ion reactions using dielectric track detectors

Abstract

Matter in all forms and states is made up of atoms. All atoms contain a ‎central region of very high density, which is called the 'Atomic Nucleus' or ‎simply the 'Nucleus'. Understanding the structure of nucleus and its ‎behaviour under different conditions, constitutes the core objective of ‎nuclear physics research. One of the major sources of information about the ‎nucleus, are the experiments in which a high energy particle is scattered off ‎a nucleus, or triggers changes inside the nucleus as a result of its collision. ‎The very discovery of nucleus was based on the observed angular ‎distributions of scattered α-particles incident on thin gold foils. ‎Conventionally light projectiles, such as electrons, pions, protons, neutrons, ‎and α-particles have been used for studying nuclear properties. However, ‎the scope of such experiments was greatly enlarged with the advent of ‎accelerators capable of imparting high energies to heavier masses. The ‎projectiles with masses heavier than α-particles are dubbed as 'heavy ions'. ‎Essentially these are bare nuclei which interact with the target nucleus to ‎initiate nuclear processes of different characteristics. Currently there are a ‎number of accelerators available in different laboratories of the world, where ‎it is possible to accelerate projectiles of masses throughout the periodic ‎table with energies from a few MeV (106 electron volt) to several TeV (1012 ‎electron volt).‎

The present project is concerned with the study of nuclear reactions using a ‎particle detection system called Dielectric Track Detectors (DTD). These ‎detectors are capable of registering and storing the tracks of all particles ‎with charge numbers (Z) greater than the Z-thresholds for different ‎materials. Complete kinematical analysis is, therefore, possible by the ‎measurement of correlated tracks pertaining to the reaction products of an ‎isolated reaction event.‎

Using the heavy ion accelerator, UNILAC at GSI (Darmstadt, Germany) we ‎have arranged exposures of uranium ions on gold targets, with mica sheets ‎serving as DTD. The energy of the incident ions was 16.7 MeV/nucleon (i.e. ‎‎16.7 x 238 MeV for each ion). We have also used a previous exposure of ‎l.37 MeV/nucleon uranium ions incident on Bi targets, with a view to study ‎nuclear interactions of the projectiles with the detector nuclei, rather than ‎the usual projectile-target interactions. The experimental and theoretical ‎work done in this project involved the following steps.‎

‎1. Target-detector assemblies were prepared at PINSTECH and sent for ‎exposures at the accelerator facility. The exposed detectors were then ‎retrieved for off-line analysis at PINSTECH.‎ ‎2. The optical scanning was done after optimizing track etching process. ‎Each individual event was fully recorded with the help of a tracing tube and ‎a depth measuring instrument.‎ ‎3. Computer programs were developed to convert geometrical parameters of ‎tracks into kinematical parameters such as masses & energies.‎ ‎4. The observed data was used for achieving the following results of basic ‎importance in nuclear physics.‎ i.‎ determination of total and partial cross sections for different ‎reaction channels,‎ ii.‎ separation of elastic events from the total set of binary data iii.‎ determination of masses, velocities and scattering angles of ‎reaction products,‎ iv.‎ interpretation of kinematical data on the basis of models such as ‎sequential fission and fusion-fission model.‎

The experimental procedures developed for this study along with theoretical ‎models and computer codes would be useful for the analysis of heavy ion ‎reactions using DTDs in future studies. This work has resulted in three ‎publications in reputed international journals and two in the national ‎journals / proceedings.‎