Welcome to Physics Group
Variable Energy Cyclotron Centre, Kolkata

Change of electron capture nuclear decay rate in different environments

Is it possible to change the decay rate of a radioactive substance by external means such as pressure, temperature, chemical environment etc.? The answer given in the text books is “No”. However the electron capture radioactive decay(meaning the capture of an orbital electron by the nucleus) should be slightly affected by the external environment. The electron capture decays taking place deep inside massive stars are expected to be faster than observed terrestrially. Perhaps such decays taking place deep inside the earth are also faster than we normally see. At VECC, we are studying the change of electron capture decay rate of ⁷Be, ¹⁰⁹In, ¹¹⁰Sn etc. under pressure and in different chemical environments to learn about such effects. We compressed large radioactive atoms such as ¹⁰⁹In, ¹¹⁰Sn etc. by implanting them in a small lattice and recently observed about 1% increase of decay rate.  

Nuclear Orbiting Reaction

It is well-known that the nuclei fuse to form a compound nucleus, if they collide with sufficient kinetic energy to overcome the Coulomb barrier. However occasionally in some cases, instead of fusing, the two nuclei form a quasi-bound dinuclear system which would preferentially break apart into the entrance channel without ever undergoing complete fusion. It is generally assumed that the thermal equilibrium of the dinuclear orbiting complex is achieved quickly, but still the two nuclei would maintain their identities inhibiting their fusion.  

Fragments emission studies in light Heavy-ion collision

Study of fragment emission  mechanisms for light   heavy-ion (A_proj.+ A_target < 60) collisions, at energies (<10 MeV /u ) is subject of great interest in the recent years.  The origin of these fragments extends from quasi-elastic, deep-inelastic transfer and orbiting, to fusion–fission processes; and in some cases the structure of the nuclei has been found to play an important role. Many interesting features, e.g., quasi molecular resonance, super deformed bands, orbiting etc. have been seen for nuclear reactions involving   alpha like   nuclei. Although, there is no apparent link between these phenomena, they are believed to originate from highly deformed configuration of these systems. The occurrence of such highly deformed configurations and their evolution with excitation energy are studied at VECC through charged particle spectroscopy.

Gamma Ray Spectroscopy

Many of the secrets of an atomic nucleus, a tiny object but a potential source of huge energy, can be understood by putting it under “extreme conditions” and studying how it survives such a stress. Gamma ray spectroscopy is one of the powerful tools for such study and to “visualize” the shape and shell structure of a nucleus. The “extreme conditions” of large isospin (neutron-proton asymmetry), high excitation and large angular momentum are achieved in a nucleus by producing them in a variety of direct and indirect nuclear reactions using energetic beam of particles from an accelerator. The gamma rays, emitted from the produced nuclei, carry the information of the shape of a nucleus and the quantum states of the protons and the neutrons inside it. These gamma rays are detected using several high resolution, state-of-the-art, Hyper Pure Germanium (HPGe) Detectors. Several ancillary detectors for detecting charged particles, neutrons and to measure gamma multiplicity are also used in conjunction with the HPGe detectors to achieve better sensitivity. Several such experiments have been performed using the experimental facilities at VECC, at BARC-TIFR Pelletron, Mumbai, Inter University Accelerator Centre, New Delhi and also at various facilities abroad. In these experiments, combined with nuclear model calculations, we try to understand the new symmetries in nuclei (manifested in tetrahedral shape, chiral bands, magnetic rotation etc.), the change in shell structure in extremely neutron rich nuclei, shape change and shape coexistence in nuclei, formation of high spin isomers in nuclei, etc. 

Resonance Particle Spectroscopy

Resonance particle spectroscopy is a quite powerful technique in nuclear physics to study the space-time characteristics of particle emission mechanism in nuclear reactions. This is a unique tool to study the structures and properties of the particle-unbound resonance states in nuclei by detecting their decay products in coincidence. One of the major research goals of the charged particle detector array, is to carry out systematic resonance spectroscopy studies of (a) the alpha-cluster structure of light alpha-like nuclei using K130 cyclotron and other accelerators in India, and, (b) the structures of exotic particle-unstable resonances of stable nuclei and nuclei away from alpha-stability line, which will be produced in intermediate energy nuclear reactions using K500 superconducting cyclotron. Recently, studies on 2-alpha structure of 8Be, and 3-alpha structure of Hoyle state of 12C, have been carried out. Hoyle state of 12C is specially interesting as it is claimed to be either a 3-alpha-chain structure or a gas-like condensate. Our new measurements are expected to throw new light on the structures of these resonances. 

Study of the Fusion-fission and Quasi-fission Dynamics

We have an active research program to explore the role of entrance channel on fusion-fission dynamics.

One of the major aspects of today’s nuclear physics research is to look for the dynamical effect which inhibits the fusion process. These studies are important since they give a clue for picking up the right kind of target and projectile combination for the formation of super heavy elements (SHE). A comprehensive study of fission fragment mass and angular distribution at near barrier energies was embarked on for heavy ion induced fission reactions experimentally, to have an insight of the dynamics of the fusion-fission reactions. The experiments are carried out with pulsed heavy ions from the accelerators (IUAC Pelletron, New Delhi, BARC-TIFR Pelletron, Mumbai, VECC Cyclotron, Kolkata) available in India using the detectors developed indigenously in the laboratory. For the first time, a direct evidence of orientation dependent quasi-fission reaction was established. A novel and powerful tool to look for the onset of a non-statistical reaction mechanism in heavy ion induced fission was unearthed. 

High Energy Photon Spectroscopy

Hot nuclei are formed in heavy ion fusion reaction where the relative kinetic energy of the colliding nuclei is converted into internal excitation energy and high angular momentum of the compound nuclei. These systems are unstable and decay by emission of particles (neutron, proton, alpha-particle, etc.) and heavier fragments. Apart from particle emission, the system can also decay by emitting  gamma-rays. The decay of Giant Dipole Resonance (GDR) is one of the way through which the energy is released from the system in the form of electromagnetic radiation (8-20 MeV).