Gamma Detector Array Research Articles

A novel active collimator for compton-suppressed clover HPGe detector and its role in a hybrid gamma detector array

A new active collimator (AC) detector has been designed as a replacement of the heavy metal collimator for the Compton-suppressed clover High Purity Germanium (HPGe) detector, aiming to enhance the performance of the 4π hybrid gamma detector array for nuclear spectroscopy experiments. This replacement promises enhanced functionality and efficiency in detecting gamma radiation within the detector array. By utilizing ACs in combination with Compton-suppressed clover HPGe and LaBr3(Ce) detectors, a highly effective setup can be established for a γ-ray multiplicity filter for angular momentum selection in heavy ion collision reactions. This configuration offers notable advantages when studying weak band structures that undergo decay through high-cut multiplicity γ-ray events. Moreover, by summing the energy deposited in all detectors, the hybrid array can also be effectively utilized for calorimetric applications in specific measurements. We have designed and characterized an AC with a Compton-suppressed clover HPGe detector. Significantly, when using the AC configuration with the 60Co source, the absorption of γ-rays in AC and the peak-to-total ratio in clover HPGe were found to be similar to that obtained with the standard design incorporating the heavy metal configuration. The advantages of employing the AC for higher multiplicity events were demonstrated through GEANT4 simulations. The simulations were conducted for the entire array, and the potential benefits are thoroughly discussed, highlighting the improved performance achievable with the AC configuration.

Feasibility study of a novel hash algorithm-based neutron activation analysis system for arms control treaty verification

Information on isotopic composition and geometric structure is necessary for identifying a true warhead. Nevertheless, such classified information should be protected physically or electronically. With a novel Hash encryption algorithm, this paper presents a Monte Carlo-based design of a neutron activation analysis verification module. The verification module employs a thermal neutron source, a non-uniform mask (physically encrypting information about isotopic composition and geometric structure), a gamma detector array, and a Hash encryption algorithm (for electronic encryption). In the physical field, a non-uniform mask is designed to distort the characteristic gamma rays emitted by the inspected item. Furthermore, as part of the Hash algorithm, a key is introduced to encrypt the data and improve the system resolution through electronic design. In order to quantify the difference between items, Hamming distance is used, which allows data encryption and analysis simultaneously. Simulated inspections of simple objects are used to quantify system performance. It is demonstrated that the method retains superior resolution even with 1% noise level. And the performances of anti-statistical attack and anti-brute force cracking are evaluated and found to be very excellent. The verification method lays a solid foundation for nuclear disarmament verification in the upcoming era.

Configuration of gamma detectors in a neutron interrogation system for detection of explosives

This paper investigates the use of a suitable gamma detector array to increase the detectably of explosives in a prompt-gammas neutron activation analysis (PGNAA) system. Monte Carlo simulations (MCNP-4C) were used for analyzing the system. It was found that the system's performance is enhanced by the use of four detectors: three of the are located on the same side as the neutron source and the fourth on the opposite side. Signature-based radiation-scanning, with nine signatures for each detector, is also discussed.

Detectors for in vivo range and dose verification in proton therapy

Particle detection instrumentation to address the in vivo verifications of proton dose and range is under development as part of a proton therapy research program focused on patient quality assurance. For in vivo proton range verification, a collimated gamma detector array is under construction to indirectly measure the position of the Bragg peak for each proton beam spot to within 1–2 mm precision. For dose flux verification, a proton fluence detector based on the technology of the Micromegas is under construction. This detector has an active area of about 100 cm2, coordinate resolution of better than 1 mm, and handling of incident proton beam fluxes of 109–1013 particles/s.

Incomplete fusion in 16O+159Tb

In heavy-ion induced reactions, incomplete fusion (ICF) has been found to be a process of greater importance and of distinct nature even at slightly above the barrier energies where complete fusion (CF) is supposed to be dominant. However, the studies are limited to a few projectile target combinations only. To confirm the distinctly different decay patterns observed in case of CF and ICF residues, and to understand the role of high ℓ-values in the onset of ICF, a particle-γ-coincidence technique has been employed to measure spin-distributions and feeding intensity profiles of CF and ICF residues populated via xn/pxn/αxn-channels in 16O+159Tb interactions at Elab≈83.5±1.5, 88.5±1.5, 93.5±1.5 and 97.6±1.4 MeV. The Gamma Detector Array and the Charged Particles Detector Array have been used to detect prompt γ-rays in coincidence with charged particles (p and α). CF-α and ICF-α channels have been identified from backward (B)- and forward (F)-α-gated-γ-spectra, respectively. Reaction dependent decay patterns (thus, the feeding intensity profiles) have been observed in different α emitting channels. The CF channels are found to be widely populated and strongly fed over a broad spin range. In case of ICF-α channels, narrow range feeding was observed only for high-spin states or the low spin states were not populated. The mean ℓ-values involved in the production of ICF-αxn-channels are found to be higher than those involved in the production of CF-αxn-channels associated with fusion-evaporation reactions.

A charged particle detector array for detection of light charged particles from nuclear reactions

A 4π charged particle detector array (CPDA), for detecting low-Z charged particles from nuclear reactions, was built to improve selection of fusion evaporation channels for in-beam gamma spectroscopy measurements at Inter University Accelerator Centre, New Delhi. The array consists of fourteen fast–slow plastic phoswich detectors coupled to photomultiplier tubes through indigenously developed optical light guides. This paper describes design of optical light guide, target chamber, front-end electronics and presents in-beam performance of the array. Custom made analogue electronic device enables online selection of nuclear reaction channel. The charged particle detection efficiency and improvement in peak to background ratio obtained using CPDA in conjunction with a gamma-detector array demonstrates its usefulness in selection of specific nuclear reaction channel. This array has been used in a number of nuclear spectroscopic and reaction investigations.

Design and construction of a target chamber and associated equipments for the BARC Charged Particle Detector Array

A 60 cm diameter spherical high-vacuum target-chamber with side-opening hemispherical-lids, two ancillary-chambers, beam-line-tubes, tees and other high-vacuum components, and chamber-lid handling systems have been designed, constructed and installed for the Charged Particle Detector Array in BARC-TIFR Pelletron-LINAC Facility, Mumbai. This array of several tens of Si-CsI detector modules and other ancillary-detectors will be used for investigations in fusion-fission dynamics, nuclear structure at elevated temperatures and angular momenta, exotic nuclear clusters and related fields. This paper describes the unique features of the system that aid different coincidence experiments, the chamber fabrication experience and the pump-down characteristics with a turbo molecular pump. Unlike many other target chambers in use, this chamber allows multiple overall geometrical configurations to be set to reach experimental goals. For instance, by replacing a hemispherical-lid from one side with a flat-lid, the overall configuration becomes hemispherical. This way, high geometrical efficiency can be provided to an ancillary gamma detector array by allowing it to move close to target from the flat-lid side, although with some sacrifice of geometrical efficiency for charged particles. In experiments where a further improvement of geometrical efficiency for a gamma array is desired, a third compact-cylinder configuration can also be arrived at. Thinned portion of the lids of the chamber also allow neutron coincidence measurements with charged particles and gamma rays.

Seven-quasiparticle bands inCe139

The high spin states in the $^{139}\mathrm{Ce}$ nucleus have been studied by in-beam $\ensuremath{\gamma}$-spectroscopic techniques using the reaction $^{130}\mathrm{Te}(^{12}\mathrm{C},3n)^{139}\mathrm{Ce}$ at ${E}_{\mathrm{beam}}=65$ MeV. A gamma detector array, consisting of five Compton-suppressed Clover detectors was used for coincidence measurements. 15 new levels have been proposed and 28 new $\ensuremath{\gamma}$ transitions have been assigned to $^{139}\mathrm{Ce}$ on the basis of $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence data. The level scheme of $^{139}\mathrm{Ce}$ has been extended above the known 70 ns ${\frac{19}{2}}^{\ensuremath{-}}$ isomer up to $~6.1$ MeV in excitation energy and $\frac{35}{2}\ensuremath{\hbar}$ in spin. The spin-parity assignments for most of the newly proposed levels have been made using the deduced Directional Correlation from Oriented states of nuclei (DCO ratio) and the Polarization Directional Correlation from Oriented states (PDCO ratio) for the de-exciting transitions. The observed level structure has been compared with a large basis shell model calculation and also with the predictions from cranked Nilsson-Strutinsky (CNS) calculations. A general consistency has been observed between these two different theoretical approaches.

Study of yrast band in 155Tm

The nucleus 155Tm has been studied by a detailed in-beam gamma spectroscopy following the reaction 144Sm( 14N, 3 n) 155Tm, at a beam energy, E lab = 70 MeV , using a Compton suppressed gamma detector array. More than 25 new gamma transitions have been placed in the proposed scheme and the latter has been extended upto a spin-parity of (51/2 −) at an excitation energy ∼ 6 MeV.

The automatic liquid nitrogen filling system for GDA detectors

An indigenously developed automatic liquid nitrogen (LN2) filling system has been installed in gamma detector array (GDA) facility at Nuclear Science Centre. Electro-pneumatic valves are used for filling the liquid nitrogen into the high purity germanium detector cryostat. The temperature of the out-flowing gas/liquid from the cryostat is monitored using platinum resistor thermometer. The program allows for automatic filling at regular intervals with temperature monitoring from a remote terminal.

High spin spectroscopy of 139Pr

The high spin states in N=80 139Pr have been investigated by in-beam γ-spectroscopic techniques following the reaction 130Te (14N, 5n) reaction at E=75 MeV, using a gamma detector array, consisting of seven 23% compton-suppressed high purity germanium detectors and a multiplicity ball of fourteen bismuth germanate elements. Based on γ-γ coincidence data, the level scheme of 139Pr has been considerably extended up to 7.2 MeV excitation. Tentative spin-parity assignments are done for the newly proposed levels on the basis of the DCO ratios corresponding to strong gates and the available information from the earlier light ion experiments.

High Spin States in 70 Ge [Erratum: APH N.S., Heavy Ion Physics 11 (2000) 189

High spin states in70Ge nucleus have been studied in two different experiments using heavy ion fusion evaporation reaction. The Gamma Detector Array comprising of eight Compton-suppressed High Purity Ge detectors, was used in conjunction with a Recoil Mass Spectrometer — the HIRA — in order to identify and measure the transitions of this weakly populated nucleus. The level scheme is extended up to an excitation energy of13MeV for spin-parity 21- with several newly observed transitions placed in it. A rotational like band is also observed in this nucleus for the first time.

γ-ray spectroscopy of odd-odd62Cu

Excited states of the odd-odd ${}^{62}\mathrm{Cu}$ isotope were populated and studied via the ${}^{16}\mathrm{O}$ $(65 \mathrm{MeV}{)+}^{52}\mathrm{Cr}$ reaction using a gamma detector array equipped with a charged-particle detector array for reaction channel separation. On the basis of $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence relations and angular distribution ratios, an extended level scheme was constructed up to ${E}_{x}=10.88$ MeV and ${J}^{\ensuremath{\pi}}{=(14}^{+})\ensuremath{\Elzxh},$ and ${(14}^{\ensuremath{-}})\ensuremath{\Elzxh},$ and this result was interpreted in terms of shell model calculations with a restricted basis of the ${f}_{5/2},$ ${p}_{3/2},$ ${p}_{1/2},$ and ${g}_{9/2}$ orbitals outside a ${}_{28}^{56}\mathrm{Ni}$ core.

High spin states in 63Cu

Excited states of 63Cu were populated via the 52Cr+10O (65 MeV) reaction using the gamma detector array equipped with charged particle detector array for reaction channel separation. On the basis of γ-γ coincidence relations and angular distribution ratios, a level scheme was constructed up to E n=7 MeV and J π=23/2(+). The decay scheme deduced was interpreted in terms of shell model calculations, with a restricted basis of the f 5/2, p 3/2, p 1/2, g 9/2 orbitals outside a 56 28Ni core.

New determination of the Ba-Mo yield matrix for252Cf

Using triple-coincidence events of prompt fission gamma rays from 1995 Gammasphere data on spontaneous fission of ${}^{252}\mathrm{Cf},$ we made a careful analysis of the yield matrix of coincident pairs of barium $(Z=56)$ and molybdenum $(Z=42)$ fission fragments. Branching from gamma bands $(K=2)$ and octupole bands $(K=0)$ are presented for even-even partners, where observable. From this reanalysis the previously proposed ``extra-hot-fission mode'' (up to ten neutrons evaporated) as determined by twofold coincidences of 1993 Gammasphere data is much weaker, but not excluded. This finding is in agreement with a recently published similar study from the Legnaro gamma-detector array.

Band structure of 79Br

High-spin states of 79Br have been studied in the reaction 76 Ge( 7Li , 4nγ) at 32 MeV. A gamma-detector array with twelve Compton-suppressed HPGe detectors was used. The positive-parity yrast states, interpreted as a rotationally aligned g 9 2 proton band, and the negative-parity ground state band have been extended to spins of ( 33 2 + ) and ( 25 2 − ), respectively. Lifetime measurements indicate that both bands have a similar quadrupole deformation of β 2 ∼ 0.2. The positive-parity α = −1 2 band has been identified. Several new inter-band transitions are observed. A cranked-shell model analysis shows that the νg 9 2 alignments occur in the positive-parity and the negative-parity bands at rotational frequencies of ℏω ∼ 0.6 and 0.4 MeV, respectively. The level energies and the electromagnetic properties of the g 9 2 band can be well reproduced by a particle-rotor model calculation with an axially symmetric core.

High spin states in doubly-odd142Pm

The high spin states in the N=81 odd-odd ${}^{142}\mathrm{Pm}$ have been investigated by in-beam \ensuremath{\gamma}-spectroscopy following the reaction ${}^{133}\mathrm{Cs}{(}^{13}\mathrm{C}{,4n)}^{142}\mathrm{Pm}$ at E=63 MeV and using a gamma detector array. Thirty new $\ensuremath{\gamma}$ rays have been assigned to ${}^{142}\mathrm{Pm}$ on the basis of the $\ensuremath{\gamma}$-ray singles and $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidence data. The level scheme of ${}^{142}\mathrm{Pm}$ has been extended considerably above the known 2 ms isomer at 883.0 keV and spin-parity assignments for several levels have been made. The proposed level structure is discussed in the light of available data for the neighboring odd-odd isotones.

Alignments and new band structures in the doubly odd nucleus 80Rb

The high spin structure of 80Rb has been investigated using the reaction 51V( 32S,2pn) at a beam energy 105 MeV. The level scheme was established from γ-γ and recoil-γ-γ coincidence measurements obtained using the Gamma Detector Array consisting of eight Compton suppressed Ge detectors coupled to the recoil mass separator HIRA. Rotational states upto an excitation energy 13 MeV and a spin 25ħ were studied. Band crossings at ħω = 0.63 and 0.73 MeV in the negative parity band, due to successive g 9 2 proton and neutron alignment, were observed for the first time. Evidence has also been found for a hitherto unknown sideband. The yrast positive parity bands in 78Kr and 80Rb have similar transition energies beyond a rotational frequency ħω ≈ 0.55 MeV. This is the only known example of identical bands in nuclei differing by two quasiparticles, in this mass region.

Status of NSC Pelletron Laboratory

The status of the 15 UD Pelletron Laboratory at the Nuclear Science Centre is described. Compressed geometry acceleration tubes will be used to achieve 16 MV terminal potential. Two major projects, recoil mass spectrometer and gamma detector array, are already funded by the University Grants Commission. The accelerator installation is expected to start in July 1989.