anti-Compton Shield Research Articles

Direct Observation of Competing M1 and M3 Transitions in ^{10}B.

Excited states in ^{10}B were populated with the ^{10}B(p,p^{'}γ)^{10}B^{*} reaction at 8.5MeV and their γ decay was investigated via coincidence γ-ray spectroscopy. The emitted γ rays were measured using large-volume LaBr_{3}:Ce and CeBr_{3} detectors placed in anti-Compton shields. This allowed the observation of weak γ-ray transitions, such as the M3 transition between the J^{π},T=0^{+},1 isobaric analog state (IAS) and the J^{π},T=3^{+},0 ground state and the E2 transition between the J^{π},T=2_{1}^{+},0 state and the IAS, i.e., performing measurements of branching ratios at the level of λ≥10^{-4}. For the first time in ^{10}B, the competing M1 and M3 transitions from the decay of the IAS have been observed in a γ spectroscopy experiment. The experimental results are compared with abinitio no-core shell model calculation using the newest version of the local position-space chiral N^{3}LO nucleon-nucleon interaction. The calculations reproduce correctly the ordering of the bound states in ^{10}B, and are in reasonable agreement with the observed branching ratios and reduced transition probabilities.

Lung counting with a highly segmented HPGe detector

A highly segmented High-Purity Germanium (HPGe) detector was used to measure 241Am activity located inside the lungs of an anthropomorphic phantom with various active and passive shield configurations. It was found that the background suppression shield does not play a significant role in reducing the Minimum Detectable Activity (MDA) after veto, based on the segmentation in the depth direction of the HPGe, when measuring low-energy gamma rays. A reduction of up to 57% in the MDA was achieved. The MDA could be further improved by a thinner lateral segmentation and an optimized anti-Compton shield coupled with an active or passive backplate. The new detector application would be particularly useful in mobile whole-body counting units, where the natural background radiation poses a challenge when measuring low-energy gamma rays.

γ-ray spectroscopic study of self-conjugate 10B nucleus with inelastic proton scattering

A γ-ray spectroscopic study of 10B is reported. Excited states in 10B were populated in inelastic proton scattering and their γ-decays were measured with the ELIFANT array, a state-of-the-art spectrometer with large volume LaBr3:Ce and CeBr3 detectors placed in anti-Compton shields and having unprecedented efficiency for high-energy γ rays. A few weak transitions were observed in the experiment, namely M3 transition between Jπ, T = 0+1, 1 isobaric analog state to the Jπ, T = 3+1,0 ground state and E2 transition between the Jπ, T = 2+1,0 state and the isobaric analog state. The results are compared to a new set of ab initio no-core shell model calculation using the newest version of the local position-space chiral N3LO nucleon-nucleon interaction, which correctly reproduces the spectrum of the excited states in 10B, a problem of the theory in previous years.

A new detector concept based on the prompt gamma radiation analysis for In vivo boron monitoring in BNCT.

The problem of boron concentration monitoring during the boron neutron capture therapy (BNCT) therapy is one of the main challenges of this type of radiotherapy and is directly related to the nature of the interaction of neutrons with mater. Among the available in vivo methods of boron monitoring positron emission tomography seems to be very promising but it requires a new boron carrier with a β+ emitter, which is not yet clinically available. An alternative solution may be the prompt gamma radiation analysis (PGRA) based on the secondary radiation emitted in the interaction of neutrons with the patient's tissues. This method requires, however, compact gamma radiation detection systems sustaining high counting rates and characterized by very good energy resolution. In this contribution, we present state-of-the-art solutions for monitoring in BNCT based on PGRA. Moreover, we describe a new concept of such a system based on position-sensitive scintillator detectors equipped with an anti-Compton shield and data analysis supported with modern artificial intelligence algorithms.

Anti-Compton shield for Compex germanium detector modules

A bismuth-germanate (BGO) anti-Compton shield (ACS) for Compex germanium detector modules was designed, built, and characterised. BGO performance was evaluated for light output and energy resolution. The response of the ACS shield and its impact on germanium detector spectra was measured for standard 60Co, 133Ba, and 137Cs sources. The results were compared to comprehensive Geant4 simulations. The ∼70% improvement of the peak-to-total ratio for the 137Cs 662-keV γ-ray peak is in good agreement with expectations from the simulations. A 133Ba source exemplifies decay schemes of odd-A superheavy nuclei. Congruence between measured and simulated spectra indicates that the Compex plus ACS multi-detector module is well understood.

Active Collimator for the BGO Anti-Compton Shield of the HPGe Clover Detector

Active Collimator for the BGO Anti-Compton Shield of the HPGe Clover Detector

Testing and modeling HpGe detector with anti-Compton shield

Testing and modeling HpGe detector with anti-Compton shield

Spectroscopy of Neutron Induced Reactions with the $\nu $-ball Spectrometer

The ʋ-ball is a high-efficiency hybrid spectrometer which consists of both germanium (Ge) detectors and associated anti-Compton BGO shields, coupled to lanthanum bromide (LaBr3) detectors. The hybrid configuration provides a combination of both excellent energy and timing resolutions. The ʋ-ball geometry allows the coupling with the LICORNE directional neutron source at the ALTO facility of the IPN, Orsay. This opens the possibility to perform precise spectroscopy of neutron induced reactions and was used for two experiments during the recent experimental campaign. These two experiments are described here: 1. Spectroscopy of the neutron-rich fission fragments produced in the 238U(n; f) and 232Th(n; f) reactions; 2. Spectroscopy above the shape isomer in 238U. The 238U(n; f) and 232Th(n; f) reactions produce hundreds of neutron-rich nuclei on which gamma-ray spectroscopy can be performed. The main goal of the experiment aiming to populate the shape isomer in 238U is the measurement of the gamma-ray and fission decay branches as well as determination of level scheme in the super-deformed minimum. The shape isomer is populated by 238U(n; n') reaction, which gives a very advantageous population cross section over other reactions. More detailed descriptions of these two ʋ-ball experiments will be presented here.

Measurement of the strengths of the resonances at 417, 458, 611, 632 and 1222 keV in the 22Ne(p, γ)23Na reaction

The 22Ne(p, γ)23Na reaction is part of the NeNa cycle of hydrogen burning. This cycle plays a key role in the nucleosynthesis of the elements between 20Ne and 27Al in red giant stars, asymptotic giant stars and classical nova explosions. The strengths of the resonances at proton energies above 400 keV are still affected by high uncertainty. In order to reduce this uncertainty, a precision study of some of the most intense resonances between 400 keV and 1250 keV has been performed at the HZDR 3 MV Tandetron. The target, made of 22Ne implanted in a 0.22 mm thick Ta backing, has been characterized using the 1222 keV and 458 keV resonances, well known in literature. Subsequently, the strengths of the resonances at 417, 458, 611, 632 and 1222 keV were determined. Two HPGe detectors equipped with active anti-Compton shielding have been used.

Measurement of photoelectron yield of the CDEX-10 liquid argon detector prototype

The China Dark Matter Experiment (CDEX) is a low background experiment at China Jinping Underground Laboratory (CJPL) designed to directly detect dark matter with a high-purity germanium (HPGe) detector. In the second phase, CDEX-10, which has a 10 kg germanium array detector system, a liquid argon (LAr) anti-Compton active shielding and cooling system is proposed. To study the properties of the LAr detector, a prototype with an active volume of 7 liters of liquid argon was built and operated. The photoelectron yields, as a critically important parameter for the prototype detector, have been measured to be 0.051–0.079 p.e./keV for 662 keV γ rays at different positions. The good agreement between the experimental and simulation results has provided a reasonable understanding and determination of the important parameters such as the surviving fraction of the excimers, the absorption length for 128 nm photons in liquid argon, the reflectivity of Teflon and so on.

Geant4 simulation study of Indian National Gamma Array at TIFR

A Geant4 simulation code for the Indian National Gamma Array (INGA) consisting of 24 Compton suppressed clover high purity germanium (HPGe) detectors has been developed. The calculated properties in the energy range that is of interest for nuclear γ-ray spectroscopy are spectral distributions for various standard radioactive sources, intrinsic peak efficiencies and peak-to-total (P/T) ratios in various configurations such as singles, add-back and Compton suppressed mode. The principle of operation of the detectors in add-back and Compton suppression mode have been reproduced in the simulation. The reliability of the calculation is checked by comparison with the experimental data for various γ-ray energies up to 5 MeV. The comparison between simulation results and experimental data demonstrate the need of incorporating the exact geometry of the clover detectors, Anti-Compton Shield and other surrounding materials in the array to explain the detector response to the γ-ray. Several experimental effects are also investigated. These include the geometrical correction to angular distribution, crosstalk probability and the impact of heavy metal collimators between the target and the array on the P/T ratio.

Comparison of two spectrometric counting modes for fast analysis of selected radionuclides activity

The two counting modes: a normal with a single HPGE detector and second with the additional anti-Compton shield of the annular NaI(Tl) detector have been compared for fast determination of the activity concentration of thorium 232Th in the building materials. The 232Th activity concentration was calculated by measurement of its decay products: 212Pb, 212Bi and 208Tl as well 228Ac content. Although the Compton suppression mode applied in gamma spectrometry systems in general increase sensitivity of the analysis, but in case of 583 keV the most abundant 208Tl γ-line, the significant reduction of photon counting rate was observed.

Determination of Gamma Angular Distribution from the Shape of Spectral Line for the First Excited State of Carbon Nucleus

An experiment investigating gamma emission in hadron therapy was performed at Cyclotron Centre Bronowice (CCB), Cracow, Poland, using two different phantom materials—carbon and poly(methyl methacrylate) PMMA. The measurements were carried out at 70 MeV proton beam energy and the gamma quanta were registered with the use of HP Ge detector with scintillation anti-Compton shielding. Although the primary aim was to establish a solid experimental data base for future applications in prompt gamma imaging, the data have also been analyzed with regards to the position and shape of the spectral line stemming from deexcitation of the carbon excited state 4.44 MeV. Measurements potentially useful to determine the cross section were performed only at 90° laboratory polar angle. However, benefiting from the very good energy resolution it turned out possible to extract information on angular distribution of the C* (4.44 MeV) deexcitation by analyzing the associated line shape. This paper presents the scheme of model calculations assuming the whole process can be divided into two stages: excitation of carbon nuclei by impinging protons and deexcitation of the C* (4.44 MeV) state.

Study of the material photon and electron background and the liquid argon detector veto efficiency of the CDEX-10 experiment**Supported by National Natural Science Foundation of China (11175099, 10935005, 10945002, 11275107, 11105076) and State Key Development Program of Basic Research of China (2010CB833006)

The China Dark Matter Experiment (CDEX) is located at the China Jinping Underground Laboratory (CJPL) and aims to directly detect the weakly interacting massive particles (WIMP) flux with high sensitivity in the low mass region. Here we present a study of the predicted photon and electron backgrounds including the background contribution of the structure materials of the germanium detector, the passive shielding materials, and the intrinsic radioactivity of the liquid argon that serves as an anti-Compton active shielding detector. A detailed geometry is modeled and the background contribution has been simulated based on the measured radioactivities of all possible components within the GEANT4 program. Then the photon and electron background level in the energy region of interest (<10−2events·kg1·day−1·keV−1 (cpkkd)) is predicted based on Monte Carlo simulations. The simulated result is consistent with the design goal of the CDEX-10 experiment, 0.1cpkkd, which shows that the active and passive shield design of CDEX-10 is effective and feasible.

Perspectives for the gamma-ray spectroscopy at LNL: the GALILEO project

GALILEO is a new 4π high-resolution γ-ray array in which GASP tapered detectors and Gammapool Cluster detectors will be used together. The array will be located at the Laboratori Nazionali di Legnaro and it will make use of the stable beams provided by the Tandem-ALPI-PIAVE accelerator complex and, in the future, of the exotic radioactive ion beams provided by SPES. The project requires the transformation of the original EUROBALL 7-capsules cluster detectors into triple cluster detectors and several R&D activities are ongoing for the development of a triple cluster cryostat and for building the corresponding anti-Compton shields. The development of the front-end, digital sampling, preprocessing and readout electronics is taking advantage of the most recent advances obtained within the AGATA project. A strong physics case was made for the building of the GALILEO array based on Letters of Intent submitted by several research groups from all over the world. In the present paper a brief summary of the status and the perspectives of the GALILEO project is given.

Coincidence Techniques in Gamma-ray Spectroscopy

Abstract In many different gamma-ray detection systems, the events are registered in coincidence, i.e. within short time interval, by two or more detectors. Depending on purpose of an experiment, these events can be rejected (anticoincidence counting) or acquired (coincidence counting). The construction, setup and application of several coincidence systems in Laboratory for nuclear physics of Department of Physics in Novi sad are presented. The anti-Compton shield for HPGe detector based on big annular NaI(Tl) detector and corresponding measurement which proved existing of 283 keV level in Ba-137 populating by beta decay of Cs-137, is described. The application of this system (in addition with NaI(Tl) plug detector) where HPGe detector is actively shielded by NaI(Tl) detector for investigation of double beta decay of positron emitters (Cr-50, Zn-64,) is also shown. The improving of detection limit of HPGe detector by the active shield consisting of five plastic scintillation detectors is presented, as well as the measurements of cross sections for X-ray production, induced by interaction of cosmic-ray muons with massive lead shield. We found that the prompt and delayed coincidence events between plastic veto detector and Ge detector can be sharply divided in two groups. Also, the bremsstrahlung and annihilation events can be time resolved from (n,n’) events, although all these events belong to the group of delayed events.

Measurements of the pair production cross section close to the threshold energy

We have measured the total cross section for production of ${e}^{+}{e}^{\ensuremath{-}}$ pairs by photons in the Coulomb field of Ge nuclei. Up to 10${}^{16}$ $\ensuremath{\gamma}$ quanta per second were produced by thermal-neutron capture reactions of a natural gadolinium target, placed inside the high-flux reactor of the ILL Grenoble. Out of this stream of $\ensuremath{\gamma}$ rays various strong discrete $\ensuremath{\gamma}$ lines were extracted using the GAMS5 Bragg spectrometer of the ILL. A well-collimated beam of reflected $\ensuremath{\gamma}$ rays irradiated a germanium detector placed inside an anti-Compton shield, consisting of eight bismuth germanate crystals, assembled as a pair spectrometer. Using this new technique we have measured, for the first time, the pair production cross section at only 18.2 keV above the 1022-keV threshold. Our measurements indicate that the pair production cross section, expressed in units of Bethe-Heitler, grows monotonously toward low energies and does not support the claim of other works of a maximum at $\ensuremath{\sim}$65 keV.

Measurement of 15 MeV γ-rays with the Ge cluster detectors of EUROBALL

A measurement of the response to 15.1 MeV γ-rays has been made for the Ge cluster detectors in the EUROBALL array. Each cluster detector consists of seven germanium capsules surrounded by a single anticompton shield of BGO. The reaction D( 11B,γ) 12C+n at E beam =19.1 MeV has been employed. The “adding-back” of signals simultaneously present in the capsules composing each cluster detector has been made on an event by event basis. The intensity in full-energy peak increases by a factor of three as compared to that of the spectrum obtained by summing the individual spectra of the 7 capsules. The pulse height to energy conversion is found to be very linear from few hundreds keV to 15 MeV. The efficiency is discussed relative to that of large volume BaF 2 scintillators.

Progress in Activation Analysis at the Atomic Institute Vienna

Fields in which progress has been achieved at the Atomic Institute Vienna are discussed briefly. The use of short and medium lived nuclides for activation analysis (AA). Construction of out-core parts of a fast transfer system. Combined sample catcher sample-changer for AA allowing cyclic and pseudocyclic AA. A system for discontinuous or continuous irradiation of liquid samples. Counting with an anticompton shield and quantitative correction of random coincidences. Screening analyses with the fast irradiation and measurement system. Improved peak-evaluation of gamma-spectra. Epithermal AA by a neutron converter. Following short-lived nuclide measurement, automatic sample transfer into a well-type detector enabling sensitive counting of nuclides with short half-lives. Use of large samples to increase the detection limits of ng to pg at activation with moderate neutron flux. Flux determination by liquid scintillation counting.

Status of the MUNU experiment

The MUNU experiment, a low background 1 m 3 time projection chamber surrounded by active anti-Compton shielding, is now under way at the Bugey nuclear reactor. It is dedicated to the experimental study of ν ee − scattering down to 500 keV. The experiment is sensitive to a ν e magnetic moment down to 3 × 10 −11 Bohr magneton.