Scintillation Detector System Research Articles

Simplified efficiency calibration methods for scintillation detectors used in nuclear remediation

Our study introduces innovative methods to address waste reduction and enhance resource efficiency in nuclear cleanup processes. We focus on sustainable nuclear technology, aligning with goals for cleaner production and environmental protection. We developed two novel methods, termed “oversimplified” and “simplified,” for easily determining the photopeak efficiency of NaI(Tl) scintillation detectors. These methods, along with a “general” solution method, were validated with calibrated radioactive sources such as 241Am, 57Co, 133Ba, 137Cs, and 60Co, and were used to commission a NaI(Tl) scintillation detector system at Chalk River Laboratories (CRL) for nuclear remediation. The system demonstrated high accuracy, making it suitable for screening unstable isotopes at contaminated sites. This screening tool significantly reduces the number of soil samples requiring detailed characterization, thereby lowering operational costs. The NaI(Tl) detector system was calibrated for near-contact geometry, which is commonly used at CRLs. Detection limits were established for this configuration. By improving the efficiency calibration of scintillation detectors, our study advances sustainable nuclear remediation practices, promoting environmental sustainability and cleaner production processes.

Cerenkov free micro-dosimetry in small-field radiation therapy technique

Objective. Optical fiber-based scintillating dosimetry is a recent promising technique owing to the miniature size dosimeter and quality measurement in modern radiation therapy treatment. Despite several advantages, the major issue of using scintillating dosimeters is the Cerenkov effect and predominantly requires extra measurement corrections. Therefore, this work highlighted a novel micro-dosimetry technique to ensure Cerenkov-free measurement in radiation therapy treatment protocol by investigating several dosimetric characteristics. Approach. A micro-dosimetry technique was proposed with the performance evaluation of a novel infrared inorganic scintillator detector (IR-ISD). The detector essentially consists of a micro-scintillating head based on IR-emitting micro-clusters with a sensitive volume of 1.5 × 10−6 mm3. The proposed system was evaluated under the 6 MV LINAC beam used in patient treatment. Overall measurements were performed using IBATM water tank phantoms by following TRS-398 protocol for radiotherapy. Cerenkov measurements were performed for different small fields from 0.5 × 0.5 cm2 to 10 × 10 cm2 under LINAC. In addition, several dosimetric parameters such as percentage depth dose (PDD), high lateral resolution beam profiling, dose linearity, dose rate linearity, repeatability, reproducibility, and field output factor were investigated to realize the performance of the novel detector. Main results. This study highlighted a complete removal of the Cerenkov effect using a point-like miniature detector, especially for small field radiation therapy treatment. Measurements demonstrated that IR-ISD has acceptable behavior with dose rate variability (maximum standard deviation ∼0.18%) for the dose rate of 20–1000 cGy s−1. An entire linear response (R 2 = 1) was obtained for the dose delivered within the range of 4–1000 cGy, using a selected field size of 1 × 1 cm2. Perfect repeatability (max 0.06% variation from average) with day-to-day reproducibility (0.10% average variation) was observed. PDD profiles obtained in the water tank present almost identical behavior to the reference dosimeter with a build-up maximum depth dose at 1.5 cm. The small field of 0.5 × 0.5 cm2 profiles have been characterized with a high lateral resolution of 100 µm. Significance. Unlike recent plastic scintillation detector systems, the proposed micro-dosimetry system in this study requires no Cerenkov corrections and showed efficient performance for several dosimetric parameters. Therefore, it is expected that considering the detector correction factors, the IR-ISD system can be a suitable dose measurement tool, such as in small-field dose measurements, high and low gradient dose verification, and, by extension, in microbeam radiation and FLASH radiation therapy.

Gross alpha/beta activity concentrations in imported bottled drinking water in Saudi Arabia

This research assessed the gross alpha and beta activity levels in bottled drinking water imported to Saudi Arabia, applying the evaluation process recommended by the World Health Organization (WHO). The WHO's approach for examining alpha and beta activity in drinking water consists of an initial phase of screening for gross alpha and beta levels to determine the need for further analysis. This is followed by a detailed assessment of specific radionuclide concentrations if initial screening levels are surpassed. The study utilized the evaporation method as a standard procedure to quantify the gross alpha and beta activity levels. Each water sample underwent evaporation, after which the activity levels of the residual matter were measured. Gross alpha activity was analyzed using a ZnS (Ag) scintillator detector system, while gross beta activity levels were gauged using a proportional counting system. The methodologies for determining gross alpha and beta activities align with the International Organization for Standardization (ISO) standards ISO 9696 and ISO 9697, respectively. The research identified the maximum alpha and beta activity levels to be 0.18 Bq/L and 0.34 Bq/L, respectively. These values were evaluated against the WHO guidance threshold values of 0.5 Bq/L for gross alpha and 1.0 Bq/L for gross beta activities, confirming that the exposure remains below the individual dose criterion of 0.1mSv/year. The estimated committed effective doses fell under the WHO's advised cap of 0.1 mSv annually, indicating the safety of the water samples for consumption. The study recommends the analysis of a larger set of samples over extended periods for increased assurance.

Characterisation of neutron fields at the n-lab, a fast neutron facility at the University of Cape Town

The n-lab is a fast neutron facility based in the Department of Physics, University of Cape Town, offering collimated neutron beams produced by an MP 320 deuterium–tritium sealed tube neutron generator, and a 220 GBq americium–beryllium radioisotopic source. Characterisations of the spatial and energy distributions of the fast neutron beams were performed using an EJ-301 organic liquid scintillator detector and digital data acquisition system. Neutron energy spectra were obtained through unfolding analyses with MAXED, and a Monte Carlo approach to the propagation of uncertainties was implemented. Measurements of fluence and neutron emission rates were determined through the neutron activation of copper foils and subsequently used to validate the scaling of the unfolded neutron energy spectra.

Characterization of a 0.8 mm3 Medscint plastic scintillator detector system for small field dosimetry

Objective. Plastic scintillator detectors (PSDs) have demonstrated ability to meet requirements of small field dosimetry. Medscint developed a 1 mm long, 1 mm diameter cylindrical PSD with effective volume of 0.8 mm3. Clinically relevant, small field dosimetric properties of this detector, combined with a novel scintillation dosimetry system—HYPERSCINT RP-200, and HYPERDOSE analysis software were evaluated in this study. Approach. This novel scintillator-based dosimetry system was characterized with 6 MV-WFF and 10 MV-FFF x-ray beams delivered by Varian TrueBeamTM linear accelerator. The detector was characterized for leakage, short-term repeatability, dose response linearity, angular response, dose rate response, and field size dependence for radiation field sizes of 0.25 × 0.25 to 10 × 10 cm2. Measured detector specific output ratios were compared with microDiamond output factors to determine small field output correction factors, Main results. The dosimetry system showed excellent short-term repeatability with standard deviation of only 0.04 ± 0.01%. It demonstrated good dose linearity with variations less than 1.0% for 14.4 cGy and above. The dosimetry system was found to be independent of dose rate and angle of irradiation, with deviations for both below 0.5%. Leakage was found to be comparable to background readings. For 6 MV-WFF energy beams, detector specific output ratios for field sizes down to 1 × 1 cm2 agreed with output factors measured with PTW TN60019 microDiamond, thus, equates to unity for these field sizes. For 10 MV-FFF energy beams, detector specific output ratios for field sizes down to 2 × 2 cm2 agreed with PTW TN60019 microDiamond output factors, thus, equates to unity for these field sizes. for field sizes down to 0.5 × 0.5 cm2 were determined to be within 6% of unity for both 6 MV-WFF and 10 MV-FFF energy beams. Significance. The HYPERSCINT RP-200 dosimetry system coupled with a 0.8 mm3 PSD showed excellent dosimetric properties and was found to be clinically relevant for relative dosimetry down to field sizes of 0.5 × 0.5 cm2 and potentially smaller.

Study on the application of SiPM to [formula omitted] ray and charged particle measurement using scintillation crystals

The characteristics of a Silicon Photo Multiplier (SiPM)-based scintillation detector system were studied. The influence of the bias voltage and the number of SiPMs on the energy resolution was identified. The single SiPM energy spectra in the multi-SiPM system showed their dependency on the position of the 60Co radiation source. The application of geometric mean on the multi-SiPM system was also considered to bypass single channel calibrations.Preliminary results on the performances of developing scintillation detectors with a CsI(Tl) crystal or a plastic scintillator are demonstrated. The capability of charged particle measurement for CsI(Tl) crystal and sub-nanosecond timing resolution of plastic scintillator were identified.

High-dose rate detection system for gamma and X radiation using scattered gamma rays

Recent developments in the field of ultra-high intensity gamma sources have led to a renewed interest in detection of pulsed gamma radiation. This paper thus proposed a scintillation detector system based on scattered gamma rays by using the tungsten target. System design parameters were investigated with Monte Carlo simulation and verified by 60Co/137Cs radiation experiments. The results showed that the system can raise the upper limit of gamma intensity detection by 4–5 orders. Signal-to-noise ratio of the system was studied in the 60Co radiation experiments. These findings suggested that this system is a suitable alternative for future needs for ultra-intense gamma-ray measurements.

Time-resolved dose rate measurements in pencil beam scanning proton FLASH therapy with a fiber-coupled scintillator detector system.

The spatial and temporal dose rate distribution of pencil beam scanning (PBS) proton therapy is important in ultra-high dose rate (UHDR) or FLASH irradiations. Validation of the temporal structure of the dose rate is crucial for quality assurance and may be performed using detectors with high temporal resolution and large dynamic range. To provide time-resolved in vivo dose rate measurements using a scintillator-based detector during proton PBS pre-clinical mouse experiments with dose rates ranging from conventional to UHDR. All irradiations were performed at the entrance plateau of a 250MeV PBS proton beam. A detector system with four fiber-coupled ZnSe:O inorganic scintillators and 20μs temporal resolution was used for dose rate measurements. The system was first characterized in terms of precision and stem signal. The detector precision was determined through repeated irradiations with the same field. The stem signal contribution was quantified by irradiating two of the detector probes alongside a bare fiber (fiber without a coupled scintillator). Next, the detector system was calibrated against an ionization chamber (IC) with all four detector probes and the IC placed in a water bath at 2cmdepth. A scan pattern covering 9.6×9.6cmwas used. Multiple irradiations with different requested nozzle currents provided instantaneous dose rates at the detector positions in the range of 7-1270Gy/s.The correspondence of the detector signal (in Volts) to the instantaneous dose rate (in Gy/s) was found. The instantaneous dose rate was calculated from the beam current and the spot-to-detector distance assuming a Gaussian beam profile at distances up to 8mmfrom the spot. Afterwards, the calibrated system was used in vivo, in mouse experiments, where mouse legs were irradiated with a constant dose and varying field dose rates of 0.7-87.5Gy/s.Theinstantaneous dose rate was measured for each delivered spot and the delivered dose was determined as the integrated instantaneous dose rate. The spot dose profile and PBS dose rate map were calculated. The dose contamination to neighbouring mice were measured together with the upper limit of the dose to the mouse body. The detectors showed high precision with ≤0.4% fluctuations in the measured dose. The stem signal exceeded 10% for spots <5mmfromthe optical fiber and >18mmfromthe scintillator. It contributed up to 0.2% to the total dose, which was considered negligible. All four detectors showed a non-linear relation between signal and instantaneous dose rate, which was modelled with a polynomial response function. In the mouse experiments, the measured scintillator dose showed 1.8% fluctuations, independent of the field dose rate. The in vivo measured spot dose profile had tails that deviated from a Gaussian profile with measurable dose contributions from spots up to 85mm from the detector. Neighbour mouse irradiation contributed ∼1% of the total mouse dose. The upper limit of the mouse body dose was 6% of the mouse leg dose. A fiber-coupled inorganic scintillator-based detector system can provide high precision in vivo measurements of the instantaneous dose rate if correction for the non-linear dose rate dependency is applied.

Initial operation of perpendicular line-of-sight compact neutron emission spectrometer in the large helical device.

The perpendicular line-of-sight compact neutron emission spectrometer (perpendicular CNES) was newly installed to understand the helically trapped fast-ion behavior through deuterium-deuterium (D-D) neutron energy spectrum measurement in the Large Helical Device (LHD). The energy calibration of the EJ-301 liquid scintillation detector system for perpendicular CNES was performed on an accelerator-based D-D neutron source. We installed two EJ-301 liquid scintillation detectors, which view the LHD plasma vertically from the lower side through the multichannel collimator. The D-D neutron energy spectrum was measured in a deuterium perpendicular-neutral-beam-heated deuterium plasma. By the derivative unfolding technique, it was found that the D-D neutron energy spectrum had a double-humped shape with peaks at ∼2.33 and ∼2.65MeV. D-D neutron energy spectrum was calculated based on the fast ion distribution function using guiding center orbit-following models considering the detector's energy resolution. The calculated peak energies in the D-D neutron energy spectrum almost match the experiment. In addition, a feasibility study toward the measurement of the energy distribution of ion-cyclotron-range-of-frequency-wave-accelerated beam ions was performed.

A large area efficient trigger scintillator with SiPM read out

A large area plastic scintillator detector system with SiPM read out has been prepared in order to improve the trigger selectivity for reaction studies induced by an intense proton beam with a beam momentum of several GeV/c. The system consists of six trapezoidal modules, each with three plastic scintillator elements that are each equipped with 12 SiPMs. The detection of a charged particle is based on registering coincident signals in several SiPMs. By requiring a signal on at least two of the SiPMs, the noise rate is negligible and a detection efficiency close to 100% is achieved.

Investigation of the gamma-ray efficiency for various scintillation detector systems

The calibrations of the full-energy peak efficiency, energy, and energy resolution are the main factors for successful quantitative gamma-ray analysis. The first purpose of this work is to present the calibration factors for 2"x2" ScintiPack Model 296 NaI(Tl). The detector was irradiated with radioactive sources ( 137 Cs, 60 Co, 152 Eu point sources, and 241 Am, 22 Na cylinder-shaped sources) that emit photons at different energies from 59 keV to 1408 keV. The detector efficiency was also evaluated using Geant4 based GATE simulation. The analytical equations for efficiency calibration were found out with their parameters. Since the results obtained from the experimental and simulation were compatible with each other and with literature results, then the simulation model was modified into the novel scintillation detector systems such as; LaBr3, GAGG(Ce), and SrI2 .

Time structure of pencil beam scanning proton FLASH beams measured with scintillator detectors and compared with log files.

Key factors in FLASH treatments are the ultra-high dose rate (UHDR) and the time structure of the beam delivery. Measurement of the time structure in pencil beam scanning (PBS) proton FLASH treatments is challenging for many types of detectors since high temporal resolution is needed. In this study, a fast scintillator detector system was developed and used to measure the individual spot durations as well as the time when the beam moves between two positions (transition duration) during PBS proton FLASH and UHDR treatments. The spot durations were compared with machine log-file recordings. A detector system based on inorganic scintillating crystals was developed. The system consisted of four detector probes made of a sub-millimeter ZnSe:O crystal that was coupled via an optical fiber to an optical reader with 50kHz sampling rate. The detector system was used in two experiments, both performed with a PBS proton beam with 250MeV beam energy and 215nA requested nozzle beam current. The sampling rate enabled multiple measurements during each spot delivery and during the beam transition between spots. First, the detector was tested in a phantom experiment, where a total of 305 scan sequences were delivered to the four detectors. The number of spots delivered without beam interruption in a single scan sequence ranged from one to 35. The spot duration and transition duration were measured for each individual spot. Secondly, the detector system was used in vivo in preclinical experiments with FLASH irradiation of mouse legs placed in the entrance plateau of the beam. A single detector was placed 1cm downstream of the irradiated mouse leg. The mouse dose ranged from 30.5 to 44.2Gy and the field consisted of 35 spots. The spot durations as well as the mean dose rate (field dose divided by the measured field duration) for each mouse were determined using the detector and then compared with the corresponding log files. The phantom experiment showed that the logged total duration of an uninterrupted spot sequence was consistently shorter than the measured duration with a difference of -0.252ms (95% confidence interval: [-0.255, -0.249ms]). This corresponded to 0.05%-0.07% of the spot sequence duration in the mice experiments. For individual spots, the mean±1SD difference between logged and measured spot duration was -0.39±0.05ms for the first spot in a sequence, 0.13±0.04ms for the last spot in a sequence, and -0.0017±0.09ms for the intermediate spots in a sequence. The measured spot transition durations were 0.20±0.04ms (5.1mm horizontal steps) and 0.50±0.04ms (5.0mm vertical steps). For the mouse experiments, the mean dose rate calculated from the measured field duration was 84.1-92.5Gy/s. It agreed with log files with a root mean square difference of 0.02Gy/s. Fiber-coupled scintillator detectors were designed with sufficient temporal resolution to measure the spot and transition duration during PBS proton UHDR deliveries. Their small volume makes them feasible for in vivo use in preclinical FLASH studies. The logged spot durations were in excellent agreement with measurements but showed small systematic errors in the logged duration for the first and last spot in a sequence.

A time resolved study of injection backgrounds during the first commissioning phase of SuperKEKB

We report on measurements of beam backgrounds during the first commissioning phase of the SuperKEKB collider in 2016, performed with the plastic scintillator and silicon photomultiplier-based CLAWS detector system. The sub-nanosecond time resolution and single particle detection capability of the sensors allow bunch-by-bunch measurements, enable CLAWS to perform a novel time resolved analysis of beam backgrounds, and make the system uniquely suited for the study of injection backgrounds. We present measurements of various aspects of regular beam background and injection backgrounds which include time structure and decay behavior of injection backgrounds, hit-energy spectra and overall background rates. These measurements show that the elevated background rates following an injection generally last for several milliseconds, with the majority of the background particles typically observed within the first {500}~upmu hbox {s}. The injection backgrounds exhibit pronounced patterns in time, connected to betatron and synchrotron oscillations in the accelerator rings. The frequencies of these patterns are determined from detector data.

A new dead-time determination method for gamma-ray detectors using attenuation law

This study presents a new dead-time measurement method using the gamma attenuation law and generalized dead-time models for nuclear gamma-ray detectors. The dead-time of the NaI(Tl) detection system was obtained to validate the new dead-time determination method using very thin lead and polyethylene absorbers. Non-paralyzing dead-time was found to be 8.39 μs, and paralyzing dead-time was found to be 8.35 μs using lead absorber for NaI(Tl) scintillator detection system. These dead-time values are consistent with the previously reported dead-time values for scintillator detection systems. The gamma build-up factor's contribution to the dead-time was neglected because a very thin material was used.

New discrimination algorithm for artificial [formula omitted] radiation sources based on average energy deposition in plastic scintillators

Plastic scintillators are characterized with high detection efficiency, high response speeds, uneven optical efficiency distributions, and poor energy resolution. In this work, we developed a new discrimination algorithm, namely, the average energy (AE) algorithm, for artificial γ radiation sources and implemented it in a hand-held plastic scintillator detector. The algorithm provided excellent discrimination capability of naturally occurring radiation materials (NORM) and artificial radiation Sources. The energy deposited by all radiation sources in small plastic scintillators, was simulated and analyzed using the Monte Carlo method. And all those radiation sources are categorized by the International Atomic Energy Agency. A plastic scintillator detector system was then constructed for proof of concept using 241Am, 137Cs, 60Co, radium-bearing ore, and thorium ore. A large-sized plastic scintillator detector was used for comparison, and the correctness of the AE algorithm was verified. The AEs of the NORM region ranged from 631.5 ± 13.3 keV to 783.6 ± 17.2 keV and 1173.6 keV or more, and the collection time of a single measurement was less than 3 s (5214 photons). Results showed that the AE algorithm could quickly and accurately identify γ artificial radiation sources from the background and NORM. The AE algorithm should always be used in conjunction with the energy window algorithm to avoid misjudgments.

OC-0110 Characterisation of an inorganic scintillation detector system for time resolved in vivo dosimetry

OC-0110 Characterisation of an inorganic scintillation detector system for time resolved in vivo dosimetry

Energy dependency of dose response function of a Gd2O2S scintillator detection system for spot-scanning carbon-ion and proton radiotherapy

To ensure quality assurance (QA) of scanning proton and carbon-ion therapy doses, an efficient and reliable method to measure the energy dependency of the dose response function (DRF) of an optical scintillator detection system (OSDS), is required. We present a calibration process that corrects the non-linear sensitivity of the imager's electronic readings into linear light intensities. After calibration, a digital readout of green colored stimulated-light emission (SLE) are converted to nominal SLE (N_SLE). The slope of N_SLE as a linear function of dose is labelled as K-factor. The K-factors for 7 energies of carbon-ion and proton have been measured. For the highest (424.89 MeV/u) and lowest (97.87 MeV/u) energies of carbon-ion, the K-factors are 0.96 and 0.76 N_SLE/Gy. For the highest (218.56 MeV) and lowest (53.04 MeV) energies of protons, the K-factors are 0.96 and 0.86 N_SLE/Gy. The variation of K-factor for its energy dependence are 18% and 11% between lowest and highest energies of carbon-ion and proton beam respectively. Similar trending of the K-factor was seen for the red and blue colors with respect to the green color channel, although the signal magnitude was lower for the red channel. The OSDS dose response is weakly dependent on the energy of the carbon-ion and proton beams regardless of color channel. The energy-dependency of DRF and interactive capability of OSDS can be used to create efficient dosimetry tools to measure data for spot-scanning carbon-ion and proton radiotherapy.

PO-1692: A novel approach to proton radiography and CT using a large-volume scintillator detector system

PO-1692: A novel approach to proton radiography and CT using a large-volume scintillator detector system

OC-0636: Highly spatially resolved 2D plastic scintillation detector system for small field real-time QA

OC-0636: Highly spatially resolved 2D plastic scintillation detector system for small field real-time QA

Neutron-neutron correlations in the photofission of U238

Background: In the fission of actinides, the nearly back-to-back motion of the fission fragments has a strong effect on the kinematics of fission neutrons. This leads to a favoring of opening angles near ${0}^{\ensuremath{\circ}}$ and ${180}^{\ensuremath{\circ}}$ in the neutron-neutron $(n\text{\ensuremath{-}}n)$ opening angle distribution of correlated neutron pairs from the same fission event.Purpose: To measure the $n\text{\ensuremath{-}}n$ opening angle and energy correlations in the photofission of $^{238}\mathrm{U}$. As of this writing, measurements of correlated $n\text{\ensuremath{-}}n$ opening angle distributions have been reported only for the spontaneous and neutron-induced fission of actinides. This work is the first to report such a measurement using photofission and will provide useful experimental input for photofission models used in codes such as Monte Carlo N-Particle (MCNP) and the Fission Reaction Event Yield Algorithm (FREYA).Methods: Fission is induced using bremsstrahlung photons produced via a low-duty-factor, pulsed, linear electron accelerator. The bremsstrahlung photon beam impinges on a $^{238}\mathrm{U}$ target that is surrounded by a large neutron scintillation detection system capable of measuring particle position and time of flight, from which the $n\text{\ensuremath{-}}n$ opening angle and energy are measured. Neutron-neutron angular correlations are determined by taking the ratio between a correlated $n\text{\ensuremath{-}}n$ distribution and an uncorrelated $n\text{\ensuremath{-}}n$ distribution formed by the pairing of neutrons produced during different beam pulses. This analysis technique greatly diminishes effects due to detector efficiencies, acceptance, and experimental drifts.Results: The angular correlation of neutrons from the photofission of $^{238}\mathrm{U}$ shows a high dependence on neutron energy as well as a dependence on the angle of the emitted neutrons with respect to the incoming photon beam. Angular correlations were also measured using neutrons from the spontaneous fission of $^{252}\mathrm{Cf}$, showing good agreement with past measurements.Conclusions: The measured angular correlations reflect the underlying back-to-back nature of the fission fragments. An anomalous decline in $n\text{\ensuremath{-}}n$ yield was observed for opening angles near ${180}^{\ensuremath{\circ}}$ for $^{238}\mathrm{U}$.