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One step of the IRFU GBAR project aims at producing a dense low temperature positronium gaz. In order to characterize the positronium cloud we have tested a detector able to measure gamma energies in the 511 keV domain or lower, which is compact, fast, and insensitive to high magnetic fields. It uses the PreLude 420 scintillating crystal from Saint Gobain and large area Hamamatsu avalanche photodiodes. The performances of the system are presented. It could be used for other purposes.

A lightweight, low-cost multi-panel direction-sensitive radiation detector prototype has been developed at Oregon State University that is designed to be mounted on a small unmanned aerial system to autonomously search for radiation sources while flying close to the ground. The detection system comprises sixteen BGO-SiPM detector panels with an adjustable view angle, and signal outputs are processed in parallel in an FPGA. The minimum detectable activity was calculated to be 1.3 μCi of 137 Cs at 1 m in under 60 s. The counting response of the detector panels were characterized and found to have 4.7% relative standard deviation, indicating good uniformity in overall design and assembly. The detector was also able to estimate the direction of a 12.3 μCi 137 Cs source 100 cm from the device center with 2.3° accuracy in a 95% confidence width of 10.8° in 60 s.

This paper reports on a new Ce-doped Tl-based scintillator , Tl 2 LaCl 5 (TLC), for gamma-ray detection. 10 mm diameter crystals have been successfully grown using the vertical Bridgman method . The emission peak of TLC is detected at 383 nm under X-ray excitation. The light yield of TLC is 76,000 ph/MeV. The samples show excellent energy resolution of 3.4% (FWHM) at 662 keV. The non-proportionality is less than 1%, from 32 keV to 1275 keV. The major scintillation decay time is 36 ns.

High demand for nuclear reaction cross-section measurements relevant for astrophysical processes requires the development of new experimental techniques that allow for investigation of, often very low, cross-sections. For this purpose, a new 4 π Summing NaI(Tl) detector (SuN) has been constructed, which is an 8-fold segmented NaI(Tl) barrel read by 24 photomultipliers. The design of the detector will be presented and detailed results of the commissioning experiments utilizing standard calibration sources and known Al 27 ( p , γ ) Si 28 resonances will be discussed.

Calibrating the gamma-ray detection efficiency of radiation detectors in a field environment is difficult under most circumstances. To counter this problem we have developed a technique that uses a Cerium doped Lanthanum-Tri-Chloride (LaCl 3 :Ce) scintillation detector to provide gated gammas (Guillot-Noel et al. (1999) [1] and van Loef et al. (2001) [2] ). Exploiting the inherent radioactivity of the LaCl 3 :Ce due to the long-lived radioactive isotope 138 La ( t 1/2 =1.06×10 11 yr) allows the use of the 788 and 1436 keV gammas as a measure of efficiency. In this paper, we explore the effectiveness of using the beta-gamma coincidences radiation LaCl 3 :Ce detector to calibrate the energy and efficiency of a number of gamma-ray detectors.

For biomolecular analysis and nuclear medicine, we are developing a novel gamma camera based on a gaseous detector that uses gas electron multipliers (GEMs). To increase the gamma-ray-detection efficiency, we have constructed a novel GEM foil. The gamma-ray-conversion layers of the GEM foils are plated with 3 μm of gold on both surfaces. To evaluate the detection efficiency of the gamma-ray energy that corresponds to 99m Tc, which is the target isotope for our gamma camera, the measurements were performed using 241 Am and 57 Co as gamma-ray sources. Our measured detection efficiency was 0.81% ( 241 Am) and 0.75% ( 57 Co) for the sources, which agreed well with a Monte Carlo simulation based on Geant4. In addition, we were able to increase the efficiency using multiple gold-plated GEM foils.

Sputtered yttrium metal forms a thin hole-barrier contact on both p- and n-type germanium semiconductor detectors. Yttrium contacts can provide a sufficiently high hole barrier to prevent measurable contact leakage current below ∼120 K. Detectors having yttrium contacts produce good gamma-ray spectroscopy data.

Cerium bromide (CeBr 3 ) has become a material of interest in the race for high-resolution gamma-ray spectroscopy at room temperature. This investigation quantified the potential of CeBr 3 as a room-temperature, high-resolution gamma-ray detector. The performance of CeBr 3 crystals was compared to other scintillation crystals of similar dimensions and detection environments. Comparison of self-activity of CeBr 3 to cerium-doped lanthanum tribromide (LaBr 3 :Ce) was performed. Energy resolution and relative intrinsic efficiency were measured and are presented.

Energy-resolution of inorganic-scintillator gamma-ray detectors is discussed. Experiment shows that the resolution can be significantly improved. For the new scintillator LaCl 3 : Ce, an energy resolution of 3.1% was observed at 662 keV.

A low-background gamma-ray detector of NaI(Tl) comprising a core surrounded by an annulus was developed for nuclear astrophysics experiments with radioactive ion beams, mostly for detailed studies of low-energy radiative capture reactions that involve proton and alpha particles. Monte Carlo simulations using EGS4 were performed to calculate the full-energy detection efficiency. The background was satisfactorily reduced as designed. The best S / N ratio for very low-event rate was obtained using the annulus in anticoincidence with the core. A consideration of an experiment of astrophysical interest, the 19 Ne(p,γ) 20 Na reaction, is also briefly discussed.

This paper reviews some of the progress obtained in the understanding of defects in detector grade cadmium zinc telluride material (CZT). Several techniques have been utilized to elucidate some of the issues related to compositional uniformity, effects of precipitates, grain boundaries, and surface defects related to mechanical and chemical treatments. In few cases, special mapping capabilities had to be developed to allow correlations with detector performance.

The total-to-peak ratio of a semiconductor gamma-ray detector was measured on a grid of points in its vicinity. Losses due to pile-up and dead time were corrected by the pulser method. An expression for calculation of the total number of gamma-rays detected from the total number of counts in the spectrum was derived. The usefulness of the approach is demonstrated by presentation and discussion of the measured spatial dependence of the total-to-peak ratio.

Vertical Zone Melt Growth (VZM) is being investigated as a technique for preparation of bulk GaAs crystals with applications as ambient temperature gamma ray detectors/spectrometers. Zone refining (repeated passes of a molten zone across a crystal) and zone levelling (one pass of a molten zone which is gallium rich) are being investigated for improving the purity of bulk GaAs and lowering the deep level donor defect (EL2) concentration. GaAs which has been zone refined and GaAs which has been zone levelled with a gallium rich melt have been grown, characterized and processed as detectors. In this paper, we discuss details of the VZM growth of GaAs and the crystalline and electronic properties achieved by zone levelling and zone refining.

The physical principles the of Nuclear Resonance Absorption (NRA) method and its application to explosives detection are described. In this method, the object to be tested is scanned by a beam of 9.17 MeV gamma rays which undergoes resonant attenuation whenever the beam encounters regions of nitrogen concentration. This resonant component of attenuation is detected using an array of gamma ray detectors containing a nitrogen-rich medium. From the reconstructed spatial distribution of nitrogen density obtained in multi-view scanning, the presence of an explosive can be determined.

The method for determination of the detector efficiency for volume samples [M. Korun and R. Martincic, Appl. Radiat. Isot. 43 (1992) 29] is extended to the case of inhomogeneous samples by introducing two inhomogeneity functions, which describe the distribution of radioisotopes and the distribution of the material in the sample. It is shown by the example of 55Fe, how the efficiency may be assessed even in the case when the distribution of the material in the sample is not known.

Simulation of gamma-ray semiconductor detector generally makes assumptions such as electric field uniformity, constancy of mobilities and trapping times respect to electric field, etc. At least a part of these assumptions are not valid. A way to overcome this problem is to measure the collection efficiency as a function of depth directly. By a particular version of the micro-IBIC technique we measured the collection efficiency on a section of a CdTe detector and we used the experimental data as input for the Monte Carlo code ISIDE for simulating pulse height spectra produced by 57Co. The results obtained by this more realistic approach are presented and can be compared both with other kinds of simulations and with available experimental data.

Measurements have been made to characterize the response of NaI(Tl) and Ge(Li) gamma ray detectors to gamma rays in the energy range of 2.6 to 16.1 MeV. Both absolute efficiency and energy resolution are reported. At 16.1 MeV the absolute full energy efficiency of a 10 cm × 10 cm NaI(Tl) detector is about 2% and the energy resolution is also about 2%. For a 65 cm3 Ge(Li) detector, the full energy peak absolute efficiency at 16.1 MeV is 0.2% (the escape peak efficiencies are 5 times larger), and the fwhm energy resolution is about 0.1%.

An empirical equation describing the photopeak efficiency of Ge(Li) and high purity germanium (HPGe) photon detectors in the energy range from 60 keV to the onset of escape peak losses is presented. The functional parameters are fitted to calibration points obtained from long-lived commercially available standards (241Am, 109Cd, 57Co, 137Cs, 54Mn, 60Co, 22Na). The fitted function is shown to describe 61 efficiency functions of 60 different detectors with an accuracy better than the quoted uncertainty of the calibration sources, including those energy regions where long-lived calibration standards are difficult to obtain. In contrast to other proposed functions, this equation has functional restrictions with respect to the general shape of the photopeak efficiency curve and, therefore, it is well suited to describe the photopeak efficiency, even when fitted only to a few calibration points.

The 80-20 wt.% mixture of paraffin and boric acid was proposed as a shielding material for the gamma-ray detector used in fast neutron experiments. Its neutron shielding capability was evaluated by neutron and gamma-ray transport calculations and compared with that of other materials. As a result, it was found that the borated paraffin will be an effective and economical shielding material against fast neutrons if it is used with a lead shield. Moreover, a heavy shield for the gamma-ray detector has been constructed, and the typical shield performance was investigated for keV-neutron capture experiments.

A simple expression for peak-to-total ratio evaluation of gamma-ray detectors in the energy range 0.3–10 MeV is proposed. The quantities one needs to know for the computation are: detector dimensions and chemical composition, photon cross sections and an empirical energy dependent function which is valid for all the detector materials considered. This procedure seems able to produce peak-to-total values with an accuracy comparable with the most sophisticated Monte Carlo calculations. It has been tested using experimental peak-to-total values of Ge, NaI, CsI and BGO detectors but it is reasonable to suppose that it is valid for any detector material.