arXiv subjects

R. G. Pillay

Publications and source records attributed to R. G. Pillay.

28 records · Page 2Linked to original sources

arXiv2015

Radiation Background Studies for 0$νββ$ decay in $^{124}$Sn

Radiation background studies pertaining to $0νββ$ decay in $^{124}$Sn have been carried out. A TiLES setup has been installed at TIFR for this purpose. Neutron-induced background is studied in the TIN.TIN detector materials using fast neutron activation technique. The neutron flux ($E_n\leq15$ MeV) resulting from SF and ($α, n$) interactions for the rock in the INO cavern is estimated using MC simulations. A two layer composite shield of borated paraffin (20 cm) + Pb (5 cm) is proposed for the reduction of neutron flux.

physics.ins-det↗

arXiv2014

Characterization of neutron transmutation doped (NTD) Ge for low temperature sensor development

Development of NTD Ge sensors has been initiated for low temperature (mK) thermometry in The India-based Tin detector (TIN.TIN). NTD Ge sensors are prepared by thermal neutron irradiation of device grade Ge samples at Dhruva reactor, BARC, Mumbai. Detailed measurements have been carried out in irradiated samples for estimating the carrier concentration and fast neutron induced defects. The Positron Annihilation Lifetime Spectroscopy (PALS) measurements indicated monovacancy type defects for all irradiated samples, while Channeling studies employing RBS with 2 MeV alpha particles, revealed no significant defects in the samples exposed to fast neutron fluence of $\sim 4\times10^{16}/cm^2$. Both PALS and Channeling studies have shown that vacuum annealing at 600 $^\circ$C for $\sim2$ hours is sufficient to recover the damage in the irradiated samples, thereby making them suitable for the sensor development.

physics.ins-det↗

arXiv2014

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 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, $^{110}$Ag and $^{182}$Ta impurities, which can be reduced by chemical etching of approximately $\sim50 μ$m 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 $\sim$ 1 Bq/gm after irradiation. These estimates indicate that in order to use the NTD Ge sensors for rare event studies, a cool down period of $\sim$ 2 years would be necessary to reduce the radioactive background to $\le$ 1 mBq/gm.

physics.ins-det↗

arXiv2014

Study of neutron-induced background and its effect on the search of 0$νββ$ decay in $\rm^{124}Sn$

Neutron-induced background has been studied in various components of the TIN.TIN detector, which is under development for the search of Neutrinoless Double Beta Decay in $\rm^{124}Sn$. Fast neutron flux $\sim10^{6}~n~cm^{-2}s^{-1}$ covering a broad energy range ($ \sim0.1$ to $ \sim18$~MeV) was generated using $^{9}Be(p,n)^{9}B$ reaction. In addition, reactions with quasi-monoenergetic neutrons were also studied using $^{7}Li(p,n)^{7}Be$ reaction. Among the different cryogenic support structures studied, Teflon is found to be preferable compared to Torlon as there is no high energy gamma background ($E_γ>$ 1 MeV). Contribution of neutron-induced reactions in $\rm ^{nat, 124} $Sn from other Sn isotopes (A = 112 -- 122) in the energy region of interest, namely, around the $Q_{ββ}$ of $\rm^{124}Sn$ ($E \sim$ 2.293 MeV), is also investigated.

physics.ins-det↗

arXiv2014

Carbon Irradiated SI-GaAs for Photoconductive THz Detection

We report here a photoconductive material for THz generation and detection with sub-picosecond carrier lifetime made by C12 (Carbon) irradiation on commercially available semi-insulating (SI) GaAs. We are able to reduce the carrier lifetime of SI-GaAs down to sub-picosecond by irradiating it with various irradiation dosages of Carbon (C12) ions. With an increase of the irradiation dose from ~1012 /cm2 to ~1015 /cm2 the carrier lifetime of SI-GaAs monotonously decreases to 0.55 picosecond, resulting in strongly improved THz pulse detection compared with normal SI-GaAs.

cond-mat.mtrl-sci↗

arXiv2014

Characterization and modeling of a low background HPGe detector

A high efficiency, low background counting setup has been made at TIFR consisting of a special HPGe detector ($\sim$ 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 $^{124}$Sn 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.

physics.ins-det↗

arXiv2013

Highly Efficient and Electrically Robust Carbon Irradiated SI-GaAs Based Photoconductive THz Emitters

We demonstrate here an efficient THz source with low electrical power consumption. We have increased the maximum THz radiation power emitted from SI-GaAs based photoconductive emitters by two orders of magnitude. By irradiating the SI-GaAs substrate with Carbon-ions up to 2 micron deep, we have created lot of defects and decreased the life time of photo-excited carriers inside the substrate. Depending on the irradiation dose we find 1 to 2 orders of magnitude decrease in total current flowing in the substrate, resulting in subsequent decrease of heat dissipation in the antenna. This has resulted in increasing maximum cut-off of the applied voltage across Photo-Conductive Emitter (PCE) electrodes to operate the device without thermal breakdown from ~35 V to > 150 V for the 25 micron electrode gaps. At optimum operating conditions, carbon irradiated (10^14 ions/cm^2) PCEs give THz pulses with power about 100 times higher in comparison to the usual PCEs on SI-GaAs and electrical to THz power conversion efficiency has improved by a factor of ~ 800.

cond-mat.mtrl-sci↗

arXiv2013

Electromagnetic transition from the 4$^+$ to 2$^+$ resonance in $^8$Be measured via the radiative capture in $^4$He+$^4$He

An earlier measurement on the 4$^+$ to 2$^+$ radiative transition in $^8$Be provided the first electromagnetic signature of its dumbbell-like shape. However, the large uncertainty in the measured cross section does not allow a stringent test of nuclear structure models. The present paper reports a more elaborate and precise measurement for this transition, via the radiative capture in the $^4$He+$^4$He reaction, improving the accuracy by about a factor of three. The {\it ab initio} calculations of the radiative transition strength with improved three-nucleon forces are also presented. The experimental results are compared with the predictions of the alpha cluster model and {\it ab initio} calculations.

nucl-ex↗

arXiv2012

Role of the cluster structure of $^7$Li in the dynamics of fragment capture

Exclusive measurements of prompt $γ$-rays from the heavy-residues with various light charged particles in the $^7$Li + $^{198}$Pt system, at an energy near the Coulomb barrier (E/$V_b$ $\sim$ 1.6) are reported. Recent dynamic classical trajectory calculations, constrained by the measured fusion, $α$ and $t$ capture cross-sections have been used to explain the excitation energy dependence of the residue cross-sections. These calculations distinctly illustrate a two step process, breakup followed by fusion in case of the capture of $t$ and $α$ clusters; whereas for $^{6}$He + $p$ and $^{5}$He + $d$ configurations, massive transfer is inferred to be the dominant mechanism. The present work clearly demonstrates the role played by the cluster structures of $^7$Li in understanding the reaction dynamics at energies around the Coulomb barrier.

nucl-ex↗

arXiv2000

Local magnetism of isolated Mo atoms at substitutional and interstitial sites in Yb metal : Experiment and Theory

Using TDPAD experiment and local spin density calculations, we have observed large 4d moments on isolated Mo atoms at substitutional and octahedral interstitial lattice sites in Yb metal, showing Curie-Weiss local susceptibility and Korringa like spin relaxation rate. As a surprising feature, despite strong hybridization with the Yb neighbours, interstitial Mo atoms show high moment stability with small Kondo temperature. While, magnetism of Mo, at substitutional site is consistent with Kondo type antiferromagnetic d-sp exchange interaction, we suggest that moment stability at the interstitial site is strongly influenced by ferromagnetic polarization of Yb-4f5d band electrons.

cond-mat↗