N. Dokania

Characterization and modeling of a low background HPGe detector

Abstract A high efficiency, low background counting setup has been made at TIFR consisting of a special HPGe detector ( ~ 70 % ) surrounded by a low activity copper+lead shield. Detailed measurements are performed with point and extended geometry sources to obtain a complete response of the detector. An effective model of the detector has been made with GEANT4 based Monte Carlo simulations which agrees with experimental data within 5%. This setup will be used for qualification and selection of radio-pure materials to be used in a cryogenic bolometer for the study of Neutrinoless Double Beta Decay in 124Sn as well as for other rare event studies. Using this setup, radio-impurities in the rock sample from India-based Neutrino Observatory (INO) site have been estimated.

Study of radioactive impurities in neutron transmutation doped Germanium

A program to develop low temperature (mK) sensors with neutron transmutation doped Ge for rare event studies with a cryogenic bolometer has been initiated. For this purpose, semiconductor grade Ge wafers are irradiated with thermal neutron flux from Dhruva reactor at Bhabha Atomic Research Centre (BARC), Mumbai. Spectroscopic studies of irradiated samples have revealed that the environment of the capsule used for irradiating the sample leads to significant levels of 65 Zn, 110m Ag and 182 Ta impurities, which can be reduced by chemical etching of approximately � 50 µm thick surface layer. From measurements of the etched samples in the low background counting setup, activity due to trace impurities of 123 Sb in bulk Ge is estimated to be � 1 Bq/g after irradiation. These estimates indicate that in order to use the NTD Ge sensors for rare event studies, a cooldown period of � 2 years would be necessary to reduce the radioactive background to � 1 mBq/g.

Development of NTD Ge sensors for low temperature thermometry

The development of NTD Ge sensors for use in cryogenic bolometric detector to search for neutrinoless double beta decay (Ovββ) in 124Sn is reported. The samples made from device grade Ge wafers are irradiated with thermal neutrons at Dhruva reactor, Bhabha Atomic Research Centre (BARC), Mumbai. The carrier concentration in irradiated Ge samples is estimated by Hall effect measurement at 77K. The fast neutron induced defects are studied using Positron Annihilation Lifetime Spectroscopy and Channeling. It is found that vacuum annealing of the samples at 600°C for 2 hours is necessary to cure the defects. Sensors are made from annealed NTD samples using Au-Ge Ohmic contact. Preliminary measurements have shown a significantly large dR/dT ~ 2.3 kΩ/mK at 100 mK. Details of these measurements are presented.

Giant dipole resonance studies in Ba isotopes at E/A≈5 MeV

Exclusive measurements of high energy

New limit for the half-life of double beta decay of 94Zr to the first excited state of 94Mo

\gamma

Characterization of PARIS LaBr3(Ce)-NaI(Tl) phoswich detectors up to Eγ ∼ 22 MeV

-rays are performed in

Estimation of low energy neutron flux (En ⩽ 15 MeV) in India-based Neutrino Observatory cavern using Monte Carlo techniques

\rm ^{124}Ba

Study of neutron-induced background and its effect on the search of 0νββ decay in 124Sn

and

Cryogen-free dilution refrigerator for bolometric search of neutrinoless double beta decay (0νββ) in 124Sn

\rm ^{136}Ba

Characterization of Neutron Transmutation Doped (NTD) Ge for low temperature sensor development

at the same excitation energy (