D R Chakrabarty

Bio: D R Chakrabarty is an academic researcher from Tata Institute of Fundamental Research. The author has contributed to research in topics: Pelletron. The author has an hindex of 1, co-authored 1 publications receiving 5 citations.

A multi NaI(Tl) detector array for medium energyγ-ray spectroscopy

Abstract: An array of seven hexagonal NaI(Tl) detectors has been set up for measuringγ-ray spectra in the energy region 5 MeV ≤E γ ≤ 40 MeV with good accuracy. This is in contrast to earlier set ups which mostly used one large sized (about 10 inchesφ × 15 inches long)NaI(Tl) detector. This set up has been made for the study ofγ decay of GDR based on high spin states and ultra-dipole radiations. The array has been provided with the following features: a) TOF discrimination against neutrons, b) pile up detection and elimination, c) active and passive shielding to cut down background and d) an array of trigger counters for multiplicity dependence measurements. The well known program EGS4 has been used to determine the response of the array forγ-rays in the energy region 5–40 MeV and several test measurements have been carried out to confirm the validity of the calculated response functions. Some typicalγ-ray spectra fromα and16O induced reactions measured at VECC, Calcutta and Pelletron accelerator at TIFR are also shown.

A large high-energy gamma-ray spectrometer at NSC

Abstract: A large NaI HIgh energy Gamma Ray Spectrometer (HIGRASP) has been designed and constructed at NSC, New Delhi. The spectrometer has been working quite satisfactorily for the last two years and has achieved the set goals. Detailed design considerations have resulted in very good energy resolution (2.5% at 22.5 MeV) and line shape of the gamma-ray spectrum. Experiments to study giant dipole resonance decay from hot rotating nuclei and nuclear Bremsstrahlung gamma emission have been successfully carried out using this spectrometer. The design, construction and response of the detector is discussed in detail.

Characterization of a 2 × 2 array of large square bars of LaBr 3 :Ce detectors with γ-rays up to 22.5 MeV

Abstract: LaBr3:Ce scintillators have recently become commercially available in sizes large enough for measurements of high energy gamma-rays. In this communication, we report our studies on properties and response of large volume square bars ( 2 ′ ′ × 2 ′ ′ × 8 ′ ′ ) of LaBr3:Ce detectors, individually, and in a compact array of four square bars, with gamma-rays up to 22.5 MeV. The properties studied are, uniformity of the crystal, internal radioactivity, energy resolution, timing resolution, linearity of the response and detection efficiencies. The response of the detectors for 22.5 MeV γ -rays produced from 11B( p , γ )12C capture reaction and for 15.1 MeV γ -rays produced from 12C( p , p ′ γ )12C inelastic scattering reaction are studied in detail. The measured absolute efficiencies (both total detection and photo-peak) for 662 keV gamma-rays from 137Cs are compared to those obtained using realistic GEANT4 simulations. The primary aim of the array is to measure high energy gamma-rays (5–50 MeV) produced from the de-excitation of excited Giant Dipole Resonance (GDR) states, radiative capture reactions, nuclear Bremsstrahlung process and inelastic scattering process. The highly satisfactory performance of the array provides the impetus for future efforts toward building a bigger array.

New numerical simulation method to calibrate the regular hexagonal NaI(Tl) detector with radioactive point sources situated non-axial

Abstract: Scintillation crystals are usually used for detection of energetic photons at room temperature in high energy and nuclear physics research, non-destructive analysis of materials testing, safeguards, nuclear treaty verification, geological exploration, and medical imaging. Therefore, new designs and construction of radioactive beam facilities are coming on-line with these science brunches. A good number of researchers are investigating the efficiency of the γ-ray detectors to improve the models and techniques used in order to deal with the most pressing problems in physics research today. In the present work, a new integrative and uncomplicated numerical simulation method (NSM) is used to compute the full-energy (photo) peak efficiency of a regular hexagonal prism NaI(Tl) gamma-ray detector using radioactive point sources situated non-axial within its front surface boundaries. This simulation method is based on the efficiency transfer method. Most of the mathematical formulas in this work are derived analytically and solved numerically. The main core of the NSM is the calculation of the effective solid angle for radioactive point sources, which are situated non-axially at different distances from the front surface of the detector. The attenuation of the γ-rays through the detector’s material and any other materials in-between the source and the detector is taken into account. A remarkable agreement between the experimental and calculated by present formalism results has been observed.

Measurement of cosmic-ray muon flux in the underground laboratory at UCIL, India, using plastic scintillators and SiPM

Abstract: A measurement of cosmic muon flux, in the newly established underground laboratory at the Uranium Corporation of India Limited (UCIL), Jaduguda, Jharkhand, India, has been carried out. Several future low background experiments are planned in this laboratory. The experimental set up for muon flux measurements consists of four plastic scintillators, with three of these coupled to photomultiplier tubes (PMT) to generate a coincidence trigger for acquiring data. The fourth scintillator has been coupled to a Silicon Photomultiplier (SiPM) whose signals were processed with respect to the coincidence trigger. In this scintillator, a mean light yield of 22 photoelectrons per muon event was observed and the measured time resolution was 1.3 ns. The muon flux measurement at the underground laboratory at 555 m ( 1554 ± 45 m w.e.) depth level was ( 2 . 79 ± 0 . 13 ( s t a t ) ± . 20 ( s y s t ) ) × 1 0 − 7 c m − 2 s e c − 1 s r − 1 . This agrees well with model predictions. This paper describes the detector system, analysis techniques, and results of measurement at the surface and the underground laboratory.

Decoupling the effect of temperature on GDR widths in excited compound nucleus (144)Sm

Abstract: We measured giant dipole resonance (GDR) γ-rays in the 28Si + 116Cd reaction at ~105 and 120 MeV excitation energies The resonance widths were extracted as a function of temperature at different angular momentum values to decouple the effect of these two variables on resonance widths The high energy GDR γ-rays from the decay of compound nucleus (CN) 144Sm were measured using a large NaI(Tl) detector in coincidence with a sum-spin multiplicity filter The experimental data were analyzed under the framework of statistical decay of CN The GDR cross sections were also calculated with a thermal shape fluctuation model (TSFM), which incorporates the temperature and spin dependent shell corrections within the Nilsson–Strutinsky approach The GDR widths were extracted in the temperature range 15–22 MeV The measured widths indicate that the increase of GDR widths with temperature at different average spin values follows a similar trend and is borne out by theoretical calculations Present calculation shows that TSFM satisfactorily reproduces the GDR cross section as well as widths in the temperature range 1–22 MeV over a wide range of angular momentum