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Activity of 225Ac was measured by the digital anti-coincidence spectroscopy technique using a 4πα–γ detector configuration, composed of a sandwich type 4π plastic scintillator and Ge detectors. Ultrathin plastic scintillators were used for selective detection of α-particles emitted from 225Ac and its progenies, and the α-counting efficiencies of a 4π plastic scintillation detector for individual nuclides in the decay chain were determined as well. A list-mode multichannel analyzer was employed to record coincidence/anti-coincidence events for off-line analyses. The time difference distribution spectra revealed α-particle emission following 213Po decay without β-particle interference from 213Bi. • Selective α-particle detection using ultrathin plastic scintillators for 225Ac. • Individual α-efficiencies determined by 4πα(PS)–γ(Ge) anti-coincidence spectroscopy. • α-particles from short-lived 213Po(T 1/2 = 3.7 μs) detected without interference. • Effect of β-particle from 213Bi confirmed from γ–α/β time difference distribution. • Results were consistent with those obtained using the CN method with LSC. [ABSTRACT FROM AUTHOR]

A systematic study is conducted to understand the digital time of flight (TOF) response for a pair of fast scintillator detectors; BaF 2 –LaBr 3 , BaF 2 -BC501A, and LaBr 3 -BC501A respectively. Coincidence signals from each detector pair, irradiated by 22Na source, are acquired by LeCroy HDO5000A digital oscilloscope. While operating the oscilloscope at 2.5 giga samples per second (GSPS) and 500 mega samples per second (MSPS) of sampling rates, over 10 k coincidence signals were collected for each pair of detectors. Data at different sampling rates; 1.66 GSPS, 1.25 GSPS, 833 MSPS, 625 MSPS, 333 MSPS, and 250 MSPS were generated by down-sampling method. Using anode signal, the photon arrival time marker is determined by digital constant fraction (DCF) algorithm for each detector pair on event-by-event basis. For a given rate, the algorithm is optimized at various delay and fraction values to get the minimum TOF dispersion. Mentioned pairs reveals the TOF resolution (FWHM) as; 0.58 ns, 0.79 ns, 0.907 ns and 0.53 ns, 0.94 ns, 1.08 ns at 250 MSPS and 2.5 GSPS respectively. While analysing the events, a saturation in the TOF width is observed from 500 MSPS onward. The saturated dispersion values for the aforementioned pairs are found to be 0.53 ns, 0.94 ns, and 1 ns respectively. Effect is being understood by calculating the optimum DCF transition region distribution for BC501A and LaBr 3 detectors, reveals a constant curvature profile at different rates. To further explain the saturation effect on computational ground, a simple pulse fitting approach is adopted using Landau distribution. Event-by-Event processing of fitted pulses followed by TOF resolution calculation reproduces the experimental numbers. [ABSTRACT FROM AUTHOR]

A network of specialist laboratories support the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) with re-measurements of radionuclide samples, including xenon gas. The measurement of four xenon fission product radionuclides ( 133 Xe, 135 Xe, 131m Xe and 133m Xe) can be used to detect an underground nuclear explosion. Laboratories use a range of techniques to measure the radionuclides, including beta-gamma (β − γ) coincidence spectrometry. These highly-sensitive measurements are capable of detecting concentrations of down to 500 atoms of 133 Xe in a few cm 3 of xenon. In some detector systems, detection of the metastable isomers ( 131m Xe and 133m Xe) can be more challenging due to interferences between the signatures of different radionuclides. Recent work has shown that using high-purity Germanium (HPGe) high-resolution gamma detectors, these interferences can be reduced, lowering the dependence of the detection limits on radionuclide sample isotopic composition. One downside of these detectors is the reduction in detection efficiency, which impacts the overall detection sensitivity; so assessing different detector systems is a priority for radionuclide laboratories. This work presents a coincidence detector system comprising of a plastic scintillator gas cell and a large-crystal high-purity germanium detector. The energy resolution, coincidence detection efficiency, MDA and interference factors are determined from measurements of synthetic radioxenon gas samples. • A plastic scintillator and HPGe β − γ coincidence system has been configured for the measurement of isotopes of radioxenon • Calculations show that this type of setup can improve the detection limits compared to other systems. • High-resolution γ -detectors can separate Xe and Cs X-rays, decreasing interference. [ABSTRACT FROM AUTHOR]

We report a new high-precision lifetime measurement of the first excited 5 / 2 + state of 133Cs using NaI(Tl) and LaBr 3 (Ce) detectors. The time difference between the coincident decays of two successive states was measured using fast-timing electronics. The 356-keV (1 / 2 + → 5 / 2 + ) gamma transition was tagged by the successive 81-keV (5 / 2 + → 7 / 2 + ) transition of 133Cs. The half-life of the first excited 5 / 2 + 133Cs state was measured as T 1 / 2 = 6.283 ± 0.004 (stat.) ± 0.011 (syst.) ns. [ABSTRACT FROM AUTHOR]

A scintillating fiber array detector for measuring gross beta counting is developed to monitor the real-time radioactivity in drinking water. The detector, placed in a stainless-steel tank, consists of 1096 scintillating fibers, both sides of which are connected to a photomultiplier tube. The detector parameters, including working voltage, background counting rate and stability, are tested, and the detection efficiency is calibrated using standard potassium chloride solution. Water samples are measured with the detector and the results are compared with those by evaporation method. The results show consistency with those by evaporation method. The background counting rate of the detector is 38.131 ± 0.005 cps, and the detection efficiency for β particles is 0.37 ± 0.01 cps/(Bq/l). The MDAC of this system can be less than 1.0 Bq/l for β particles in 120 min without pre-concentration. [ABSTRACT FROM AUTHOR]

X-ray transmission imaging (XRT) is widely used for sorting materials. However, conventional single-energy and dual-energy X-ray systems have poor ability to discriminate between materials with similar atomic number (Z), and the count rate of available multi-energy XRT detectors could not support high-speed industrial applications. This paper presents the design of a detector that can potentiality achieve high-speed multi-energy X-ray imaging using Geant4 simulations. This detector consisted of five detection layers (with three scintillator materials: CsI, GOS and CdWO 4), two metal filters, which allows X-ray imaging at five energies. Validation simulation showed that the 15% more accurate than a dual-layers detector in the classification of Mg and Al alloys. • A five-layer structure scintillator imaging detector was designed using Geant4 simulations. • The energy response in each layer of this detector is clearly differentiated, permitting multi-energy X-ray imaging. • The readout equipment employed in dual-layer detectors can be used in a five-layers detector with the same imaging speed. • Stimulations showed that this imaging system can be used to differentiate between materials with similar atomic numbers, such as Mg and Al alloys. [ABSTRACT FROM AUTHOR]

Dose-rate monitoring instruments measure the ambient dose equivalent and hence are crucial for protecting workers from radiation exposure. Although plastic scintillation detectors (PSDs) are ideal equipment for dosimetry, they are rarely used owing to the lower detection efficiency than other scintillation detectors. In this study, we acquired ten types of G(E) functions to utilize a PSD in spectroscopic dosimetry using the least-square and first-order methods. The energy response of PSD was much improved in terms of dose evaluation. • Measurement of ambient dose equivalent using a plastic scintillation detector. • Detector with an EJ-276G plastic scintillator coupled to a silicon photomultiplier. • G(E) function obtained using the least-square and first-order methods. • Ensemble G(E) function showed the most stable and superior performance. [ABSTRACT FROM AUTHOR]

The dosimetry of small fields has become tremendously important with the advent of intensity-modulated radiation therapy (IMRT) and stereotactic radiosurgery, where small field segments or very small fields are used to treat tumors. With high dose gradients in the stereotactic radiosurgery or radiotherapy treatment, small field dosimetry becomes challenging due to the lack of lateral electronic equilibrium in the field, x-ray source occlusion, and detector volume averaging. Small volume and tissue-equivalent detectors are recommended to overcome the challenges. With the lack of a perfect radiation detector, studies on available detectors are ongoing with reasonable disagreement and uncertainties. The joint IAEA and AAPM international code of practice (CoP) for small field dosimetry, TRS 483 (Alfonso et al., 2017) provides guidelines and recommendations for the dosimetry of small static fields in external beam radiotherapy. The CoP provides a methodology for field output factor (FOF) measurements and use of field output correction factors for a series of small field detectors and strongly recommends additional measurements, data collection and verification for CyberKnife (CK) robotic stereotactic radiotherapy/radiosurgery system using the listed detectors and more new detectors so that the FOFs can be implemented clinically. The present investigation is focused on using 3D gel along with some other commercially available detectors for the measurement and verification of field output factors (FOFs) for the small fields available in the CK system. The FOF verification was performed through a comparison with published data and Monte Carlo simulation. The results of this study have proved the suitability of an in-house developed 3D polymer gel dosimeter, several commercially available detectors, and Gafchromic films as a part of small field dosimetric measurements for the CK system. • Different commercial small field detectors are used to measure the field output factors for robotic CyberKnife system. • Tissue equivalent radiochromic EBT3 films were calibrated, and measurements of field output factor are performed. • Locally fabricated and patented 3D polymer is also used to measure the field output factors for CK. • The measured data were compared with Monte Carlo simulated data using BEAMnrc and DOSRZnrc codes. • The measured field output factors with all the detectors and techniques are found suitable for CK. [ABSTRACT FROM AUTHOR]

Combination of two or three dissimilar scintillator materials as a radiation detector has found major role in environmental radiation monitoring. In this paper, a three-layer Phoswich detector including BC-400, YAG, and CsI was designed to efficiently discriminate gamma-ray in the beta events up to 3.2 MeV using a simple rise-time discrimination method. MCNPX Monte Carlo code was used to obtain interaction probability of beta and gamma-rays as well as optimum thicknesses of the layers in the designing process. The optical transport of the system was simulated by GEANT4. In this regard, the pulses from simultaneous beta-gamma emitter sources were detected and discriminated based on pulse's rise-time so that the minimum number of gamma-ray contaminating events was observed in the beta spectrum. The results showed that using the proposed configuration and the method, output pulses with a rise-time shorter than 9 ns have been successfully detected as a beta particle while those with rising time longer than 15 ns have been identified as gamma-ray events. Overall results revealed that using the proposed system, an individual spectrum of beta particles or gamma-rays can be recorded from a simultaneous beta-gamma emitter source that minimizes contribution of the other radiation. • A Phoswich detector was designed for simultaneous beta-gamma radiation. • Scintillator materials used in the detector structure should have different decay time constant. • GEANT4 simulation was used for scintillation lights transport. • A pulse discrimination method based on the pulse rise time has been proposed for pulse processing. • Beta-rays were successfully discriminated against gamma-rays by the proposed detector and associated pulse processing method. [ABSTRACT FROM AUTHOR]

Neutron gamma density measurement using dual gamma detectors (NGD-GD) is a popular density measurement method. Compared with other NGD methods, the NGD-GD method has many advantages in tool optimization, cost control, and density precision; however, it is easily affected by the salinity of formation water. To improve the NGD-GD method, the influence mechanism of formation water salinity was discussed, and a feasible improvement scheme using characteristic gamma information was proposed. A special boron sleeve gamma detector was designed to record the capture gamma rays from the boron-10 element. By analyzing the gamma spectrum, pure boron-10 gamma information was extracted from the total capture gamma spectrum for density calculation. Finally, a new NGD method with boron sleeve gamma detectors (NGD-BD) was developed. Results depict that although the NGD-BD method has a slight decrease in density accuracy and precision compared with the NGD-GD method, its performance is significantly improved in high-brine formations, and oil and gas formations. In addition, the NGD-BD method exhibits better performance in terms of density accuracy, density precision, and environmental impact than another NGD method that uses hydrogen capture gamma information. Moreover, the NGD-BD method is easily implemented with low cost and has little impact on existing NGD tools, and hence, it can coexist with other NGD methods to improve logging quality. Overall, the NGD-BD method is a very promising alternative to the NGD-GD method. [ABSTRACT FROM AUTHOR]

A compact gamma-ray sensor composed of a cadmium sulfide (CdS) photoresistor and a small-sized cesium iodine doped thallium scintillator is introduced for intense gamma-ray monitoring. The sensor exhibits radiation-resistant ability and a linear output response over a wide dose range. The dose rate at several conditions was measured for confirmation of feasibility. Experimental results demonstrated its advantage for gamma-ray measurements in intense fields as an inexpensive, robust, compact, and high-sensitivity device. • A new gamma-ray sensor that combined scintillation (cesium iodine doped thallium) with photoconductivity (cadmium sulfide). • It can be used for monitoring intense radiation sources. • Its built-in structure is simple to adapt to multiple measurements. • It is robust and inexpensive, with high sensitivity, and high spatial resolution. • Its compactness is afforded by the CdS small area, and the flexible size of a scintillator. [ABSTRACT FROM AUTHOR]

A previously proposed hybrid analytical–numerical method for efficiency calibration of a NaI detector for a point γ -source is extended and applied for other shapes of sources. The shapes include line, disk, and cylindrical sources of various dimensions and locations with respect to the right circular cylindrical NaI detector. The results obtained by this method have been evaluated through comparison with Monte Carlo (MC) calculations. A relative maximum difference of 3.5% is found between the two methods. • A novel hybrid method was extended to include other gamma–source forms. • A developed C code was used to calculate the peak efficiency numerically. • The results were validated by means of the MCNPX. • The hybrid method is a time–efficient for peak efficiency calculations. [ABSTRACT FROM AUTHOR]

In this paper, a well typed phoswich detector consisting of CsI and plastic scintillators has been designed. This detector can measure Beta and Gamma rays simultaneously. Beta signals, Gamma signals and combination signals can be distinguished using Pulse Shape Analysis. 137Cs, 241Am and 133Ba radioactive sources have been used to test this detector. It clearly shows that this phosiwch detector can be used for low level radioactivity measurement with Beta-Gamma coincidence method. • Low level radioactivity measurements are an important part of radiation measurements. • However, it is pretty difficult to perform the low level radioactivity measurements. • A well typed phoswich detector has been designed for low level radioactivity measurement with Beta-Gamma coincidence method. [ABSTRACT FROM AUTHOR]

Over the last decade one of the most significant technological advances made in the field of radiation detectors for nuclear medicine was the development of Silicon Photomultipler (SiPM) sensors. At present only a small number of SiPM based radiation detectors for Single Photon Emission Computed Tomography (SPECT) applications have been explored, and even fewer experimental prototypes developed. An in-silico investigation into the optimal design of a Philips DPC3200 SiPM photosensor-based thin monolithic scintillator detector for SPECT applications was undertaken using the Monte Carlo radiation transport modelling toolkit Geant4 version 10.5. The performance of the 20 different SPECT radiation detector configurations, 4 scintillator materials (NaI(Tl), GAGG(Ce), CsI(Tl) and LaBr 3 (Ce)) and 5 thicknesses (1–5 mm), were determined through the use of seven figures of merit. It was found that a crystal thickness range of 4–5 mm was required for all four materials to ensure acceptable energy resolution, sensitivity and spatial resolution performance with the Philips DPC3200 SiPM. Any thinner than this and the performance of all four materials was found to degrade rapidly due to a high probability of material specific fluorescence x-ray escape after incident gamma/x-ray photoelectric absorption. When factoring in each material's magnetic resonance imaging compatibility, hygroscopy, and cost, it was found that CsI(Tl) represents the most promising material to construct tileable Philips digital SiPM based thin monolithic scintillator detectors for SPECT applications. • Geant4 was used to optimise SiPM based thin monolithic scintillator SPECT detectors. • For Philips SiPMs, four materials and impact of their crystal thickness was explored. • A critical minimum crystal thickness of 3 mm was determine for all materials. • CsI(Tl) was determined to represent the most promising material for Philips SiPMs. [ABSTRACT FROM AUTHOR]

We found that problems of α/β pulse-height overlapping can be solved by use of ultra-thin plastic scintillator sheets. In order to determine individual α-counting efficiencies for nuclides in the 223Ra decay-chain, the 4πα−γ anti-coincidence spectrometry technique was employed with a 4πα-γ detector configuration composed of a source sandwiched between ultra-thin plastic scintillator sheets and a Ge detector. This technique was applied to the activity measurements of 223Ra. This type of sandwich source is useful to prevent possible leakage of 219Rn gas. • Selective α-rays detection can be performed with very thin plastic scintillator. • Individual α-efficiencies can be determined by anti-coincidence spectrometry. • α-efficiency does not depend on energies when ultra thin scintillator was used. • The leakage of 219Rn can be avoided by source sandwiched with scintillators. [ABSTRACT FROM AUTHOR]

Determination of the uranium enrichment is an important safeguards verification task, routinely carried out using non-destructive assay methods. The enrichment-meter method is one of the most widely used passive non-destructive X- and gamma-ray based methods used for such tasks. Among its advantages is the highly constrained physical nature of its underlying formalism, allowing it to be used with high-resolution HPGe detectors, as well as with low-resolution NaI detectors. Due to attractive features and spectroscopic performance, CdZnTe and LaBr 3 (Ce) detectors raised interest in their application to such tasks as well. However, their spectroscopic performance is different to that of the traditional detectors in many ways. Application of the enrichment-meter method requires determination of the net peak areas corresponding to 235U signature photopeaks. The latter requires an adequate algorithm to select the region-of-interest boundaries, which may be sensitive to asymmetrical photopeaks of CZT detectors. In this paper we conduct a performance assessment of a 500 mm3 CZT detector of a quasi-hemispherical design and a 2 × 2 inch LaBr 3 (Ce) scintillator with the enrichment-meter method using a set of certified uranium standards with enrichment degrees from 0.31% to 4.46% of 235U atomic abundance. We investigate the impact of different methods used for net peak area determination, statistical quality of acquired spectra and size of region-of-interest boundaries on accuracy and uncertainty. We propose an algorithm for symmetrical/asymmetrical region-of-interest boundaries determination and make recommendations on the best combinations of the region-of-interest size and method used for the net peak area determination for each of the detectors. The underlying routines of the algorithm and analysis procedures are described in detail and results are presented. • Determination of the uranium enrichment is important in safeguards applications. • Room temperature medium resolution CdZnTe and LaBr 3 (Ce) detectors are studied. • A comprehensive performance assessment of the enrichment-meter method is conducted. • Spectra statistical quality, peak shapes, type of analysis tool impact performance. • A ROI selection algorithm for symmetrical/asymmetrical peak boundaries is proposed. [ABSTRACT FROM AUTHOR]

In this study, we investigated the performance of two cuboid scintillation detectors: thallium-activated cesium iodide [CsI(Tl)] and cerium-doped lutetium yttrium orthosilicate [LYSO(Ce)]. The CsI and LYSO crystals were 5 mm thick with an active area of 10 mm × 10 mm. The LYSO scintillator is characterized by its high stopping power and non-hygroscopicity (neither packaging nor light guide are required). Nevertheless, the main disadvantages of LYSO detectors are a lower light output (32 photons/keV) and an intrinsic radioactivity caused by the β− decay of 176Lu (half-life 3.78 × 1010 years). In contrast, CsI crystals present a relatively high light output (54 photons/keV) allowing better energy resolution; however, the drawback of a CsI detector is low detection efficiency. First, we measured the photon detection efficiency of each scintillator in the photon energy range of 60–1332 keV using radioactive sources. Second, we computed detector efficiencies using the Monte Carlo codes MCNP and Geant4. A comparison between simulated and measured efficiencies showed a good agreement. This comparison confirmed the validity of the mathematical models developed for the two scintillation detectors CsI(Tl) and LYSO(Ce) under investigation. • CsI(Tl) and LYSO(Ce) scintillator detectors (10 × 10 × 5 mm) characterized experimentally. • Energy resolution and detection efficiency measured in photon energy range 60–1332 keV. • Detector efficiencies computed using Monte Carlo codes MCNPX and Geant4. • Mathematical models developed for the CsI(Tl) and LYSO(Ce) detectors validated. [ABSTRACT FROM AUTHOR]