Response Of Plastic Scintillator Research Articles

Lineshape response of plastic scintillator to pair production of 4.44 MeV [formula omitted]’s

We measure the distribution of energy deposited in a 40 × 88 mm plastic scintillator by e+e− pair production of 4.44 MeV γ-rays. We observe the double-escape peak of 3.42 MeV from pair production by tagging 511 keV annihilation radiation in two high-Z scintillators. The source is a standard commercial neutron source using α-emitting 241Am encapsulated with 9Be, which has a reaction branch feeding the first Iπ=2+ state of 12C making the 4.44 MeV γ-rays. We demonstrate the extraction of the double-escape peak from the large neutron-produced backgound, and explore some of the features and difficulties of this technique with our apparatus.

Light-transport incorporated plastic scintillator response to prompt gamma-rays for use in range verification of proton therapy

In this study, the prompt gamma-rays (PGs) produced during the interactions of proton beams of various energies have been investigated using the MCNPX2.6 Monte Carlo code. Having considered a detection setup consisting of a thick lead collimator and a commercial plastic scintillator, the event-by-event data, generated by the PTRAC card of the MCNPX code, when the scintillator is exposed to PGs have been extracted before they are used in a dedicated light transport code, PHOTRACK. The plastic scintillator response when it is moved along the phantom axis determines the flux variation of proton-induced PGs which can be further related to the longitudinal deposition energy profile of protons, i.e., the Bragg curve. The present study shows that the Bragg peak location is ∼3.7 cm after the PG peak for different proton energies of interest. The uncertainty in the Bragg peak location data is about 0.02 cm which can be improved by taking into account the precise electron-transport simulation details.

Technical note: Characterization and practical applications of a novel plastic scintillator for online dosimetry for an ultrahigh dose rate (FLASH).

Although flash radiation therapy (FLASH-RT) is a promising novel technique that has the potential to achieve a better therapeutic ratio between tumor control and normal tissue complications, the ultrahigh pulsed dose rates (UHPDR) mean that experimental dosimetry is very challenging. There is a need for real-time dosimeters in the development and implementation of FLASH-RT. In this work, we characterize a novel plastic scintillator capable of temporal resolution short enough (2.5ms) to resolve individual pulses. We characterized a novel plastic dosimeter for use in a linac converter to deliver 16-MeV electrons at 100-Gy/s UHPDR average dose rates. The linearity and reproducibility were established by comparing relative measurements with a pinpoint ionization chamber placed at 10-cm water-equivalent depth where the electrometer is not saturated by the high dose per pulse. The accuracy was established by comparing the plastic scintillator dose measurements with EBT-XD Gafchromic radiochromic films, the current reference dosimeter for UHPDR. Finally, the plastic scintillator was compared against EBT-XD films for online dosimetry of two in vitro experiments performed at UHPDR. Relative ion chamber measurements were linear with plastic scintillator response within ≤1% over 4-20Gy and pulse frequencies (18-180Hz). When characterized under reference conditions with NIST-traceability, the plastic scintillator maintained its dose response under UHPDR conditions and agreed with EBT-XD film dose measurements within 4% under reference conditions and 6% for experimental online dosimetry. The plastic scintillator shows a linear and reproducible response and is able to accurately measure the radiation absorbed dose delivered by 16-MeV electrons at UHPDR. The dose is measured accurately in real time with a greater level of precision than that achieved with a radiochromic film.

TENIS — ThErmal Neutron Imaging System for use in BNCT

A thermal neutron flux measurement tool with two perpendicular sets of plastic scintillator arrays was designed and simulated (Ghal-Eh and Green, 2016) with the MCNPX code (Version 2.6.0, with ENDF/B-VII cross section library (ENDF, 2011)). The proposed system aimed to provide a thermal neutron map based on the detection of 2.22 MeV gamma-rays resulting from 1H(nth, γ)2D reactions. In the present work, using Monte Carlo code FLUKA and its scintillation light transport capability, several important upgrades were carried out to include the light transport modeling in the response of plastic scintillators, analyze the cross-talk phenomenon, optimize the system geometry, and also provide a new approach in thermal neutron image reconstruction. The results showed that the last two cases played a significant role in improving the longitudinal profile of thermal neutron flux.

Assessing the suitability of three proxy sources for the development of detectors of special nuclear materials

Numerous techniques and equipment have been developed to provide a capability for the detection of special nuclear materials (SNM), but due to the necessary security measures surrounding these materials alternate, or proxy, neutron sources are often utilised in their stead. In this paper we report the neutron and gamma pulse shape discrimination response of plastic scintillator to mixed neutron/gamma beams produced from two radionuclide neutron sources, and also from an SNM source of weapons-grade plutonium. We discuss the suitability of using radionuclide sources, with appropriate shielding configurations as proxy sources for SNM.A 3σnth-γ discrimination level has been achieved for an SNM source at a low-level energy threshold of ∼220 keVee when a shielding configuration of 5 cm of lead was implemented. Varying amounts of lead and high-density polyethylene (HDPE) shielding were also investigated with the 3σ limit being reached by ∼240 keVee.This work shows that an AmBe neutron source serves as an appropriate SNM proxy achieving a comparable value for figure of merit above ∼1 MeVee. For energies below 1 MeVee down to ∼100 keVee a closer approximation of the expected FoM for SNM can be attained when using 252Cf as a proxy source or by utilising an ‘enhanced’ AmBe source with the addition of a further low energy γ ray source.

Response of plastic scintillator to gamma sources

In this study, we developed a method for directly determining the energy deposited over the entire energy range by monitoring the light output from a plastic scintillator under gamma irradiation. The relative light output was analyzed based on Birks’ semi-empirical formula for ionization to obtain the quenching parameter as kB = 0.016 ± 0.0004 g cm−2 MeV−1. Comparisons of experimental and calculated results for the light output spectra showed that considering the quenching effect, background subtraction, source casing, and energy sampling were essential for achieving good agreement.

Quantifying the impact of lead doping on plastic scintillator response to radiation.

Through the addition of high-Z dopants, the sensitivity of plastic scintillators to low-energy radiation can be increased. This study quantifies this change in sensitivity as a function of dopant concentration. Measurements were conducted using four different lead-doped scintillators (0%, 1%, 1.5%, and 5% Pb) in high-energy electrons (6 to 15MeV) and low-energy photon (100 to 300kVp) radiation fields. High-energy and low-energy irradiations were done using a clinical linear accelerator and an orthovoltage unit, respectively. Light emitted by the scintillator was quantified using a photosensor module. The experimental setup was replicated in Geant4.10.3 Monte Carlo and scintillator parameters (Quenching parameter: kB and the light yield: L0 ) were varied until agreement between measured and simulated results was reached. Monoenergetic electrons were used to simulate the high-energy electron beam while a spectrum generated using SpekCalc® software was used in the low-energy simulations. Light produced by the scintillator was quantified using a flux scorer sensitive only to photons in the visible wavelength range. In order to compare measured and simulated results, the light produced by the scintillator was normalized to the absorbed dose-to-water at the point of measurement. At high lead dopant concentrations, the scintillator's sensitivity to the 100kVp beam increased by 474% relative to the 15MeV electron beam; the scintillator's kB parameter increased from 0.126 to 0.27mm/MeV. A model quantifying the change in kB and L0 as a function of Zeff was derived; presenting a modified Birks' Law for metal-doped plastic scintillators. The impact of high-Z doping on plastic scintillator response was quantified; this can allow for the controlled induction of energy dependence in plastic scintillator detectors.

Experimental study of a large plastic scintillator response with different reflective coverings based on digital pulse processing method

Digital pulse processing methods have various applications in radiation spectroscopy due to their unique properties. Here, the effect of light reflector on the response of a large plastic scintillator with different reflective coverings (Teflon tape, aluminum foil and black tape) coupled to a fast photomultiplier tube is investigated based on some extracted anode pulse features. Results showed that the pulse features were changed according to the reflection coefficient of the covering. For instance, the fall time of the average anode pulse shape for Teflon tape, aluminum foil and black tape coverings are 10.46, 6.88 and 3.65 ns, respectively.

Time Over Threshold as a measure of energy response of plastic scintillators used in the J-PET detector

The Jagiellonian Positron Emission Tomograph (J-PET) is a multipurpose detector being developed to provide an economical alternative of commercially available PETs as well as to perform the tests on the discrete symmetries and entanglement. It is composed of 192 plastic scintillators axially arranged in three cylindrical layers. In the framework of J-PET detector, Time-Over-Threshold (TOT) approach is adopted for the signal readouts in order to utilize the excellent time resolution of the plastic scintillators. In this paper, we present a method elaborated for establishing a relation between TOT and energy loss.

Sci‐Sat AM: Radiation Dosimetry and Practical Therapy Solutions ‐ 10: Towards LET detection: A study on the effects of scintillator doping

Purpose:In radiotherapy, the amount of radiation delivered is determined by optimizing the amount of absorbed dose to the tumor. Dose does not always correlate well with the actual biological effects of radiation. This work seeks to validate the LET‐dependence of doped plastic scintillators for use in a radiation beam quality (LET) detector.Methods:The LET spectrum ([Φ]) can be resolved knowing the measured signals of uniquely LET‐dependent detectors, [S], and the response of each LET‐dependent detector to specific LETs ([R]), through the relation [Φ]=[S][R]−1. Plastic scintillator response is intrinsically LET dependent and can be varied via doping. Initial prototype consists of plastic scintillator and glass taper coupled to an optical fiber; components are housed in black acrylic, reducing effect of ambient light. In order to determine [R], the light response matrix, GEANT4.10.1 Monte Carlo (MC) was used. To validate MC, measurements were done using high energy electrons (9,12,15MeV) and orthovoltage x‐rays (100,250kV); scintillator signal was normalized to dose measured simultaneously.Results:Stopping power was varied by changing particle type/energy; measurements indicated that as stopping power increased from 1.9 to 6.6MeV/cm, detector response increased by 263% (+/−29.2%) for 5%Pb‐doped scintillator (155% in MC); 52% (+/−7.8%) increase observed when undoped scintillator was used (49% in MC). 5%Pb‐doped discrepancy (100kV x‐rays) is being investigated.Conclusions:This work validates that doping effects LET/energy response of scintillators; an effect that can be utilized for construction of an LET detector.

Counting of ultraintense laser-driven neutrons from the pulse height of time-of-flight detector includes ultrafast timing plastic scintillator

The scintillation process is one of the most important methods available for neutron detection and spectroscopy. The radioactive isotopes used in calibration of the scintillators cannot provide the required accurate measurement of their response. Here, a comprehensive study including a simple model to calculate the scintillation response of plastic scintillators to high fluxes of neutrons produced by the ultraintense lasers is presented. The number of recoiled protons due to elastic scattering by the neutrons incident on a plastic scintillator is calculated at any neutron energy over the energy range 0.3 < E < 30 MeV. The specific energy loss, the light energy, and the range of the recoiled protons are calculated over the same energy range. As well, the current peak of the electrical signal produced by a photomultiplier tube coupled to the scintillator is given as a function of the neutron energy. Counting of the neutrons incident on the scintillator from the current peak is computed depending on the neutron energy over the energy range 0.3 < E < 30 MeV. The calculated spectra are compared with those obtained from calibration for the available experimental data.

Study of non-linear energy response of POLAR plastic scintillators to electrons

The POLAR experiment is a joint Chinese-European project conceived for a precise measurement of gamma ray polarization and optimized for the detection of the prompt emission of Gamma-Ray Bursts (GRBs) in the energy range 50–500keV. POLAR is a novel compact space-borne Compton polarimeter consisting of 1600 low-Z plastic scintillator bars (EJ-248M), read out by 25 flat-panel multi-anode photomultiplier tubes. In the paper, we first present a dedicated experiment to study the non-linear energy response of EJ-248M plastic scintillator bars to electrons and the detailed data analysis. Second we obtained the Birks’ constant of EJ-248M plastic scintillator as kB=0.143mm/MeV by least squares fitting. Finally we used Geant4 simulation to study the influence of non-linear energy response on the performance of POLAR, through which it was found that non-linear energy response will lead to a significant decrease in statistics and result in larger uncertainty in polarization measurement. The paper presents a general solution to the study of non-linear energy response of plastic scintillators to electrons.

Comparison of light transport-incorporated MCNPX and FLUKA codes in generating organic scintillators responses to neutrons and gamma rays

The NE102 plastic scintillator response to 137Cs gamma rays and NE213 liquid scintillator response to both mono-energetic and 241Am–Be neutrons have been modeled using FLUKA׳s EVENTBIN and MCNPX׳s PTRAC cards. The comparison made in different energy regions confirms that the overall difference is less than 6%.

Response of plastic scintillators to low-energy photons

Diagnostic radiology typically uses x-ray beams between 25 and 150 kVp. Plastic scintillation detectors (PSDs) are potentially successful candidates as field dosimeters but careful selection of the scintillator is crucial. It has been demonstrated that they can suffer from energy dependence in the low-energy region, an undesirable dosimeter characteristic. This dependence is partially due to the nonlinear light yield of the scintillator to the low-energy electrons set in motion by the photon beam. In this work, PSDs made of PMMA, PVT or polystyrene were studied for the x-ray beam range 25 to 100 kVp. For each kVp data has been acquired for additional aluminium filtrations of 0.5, 1.0, 2.0 and 4.0 mm. Absolute dose in the point of measurement was obtained with an ionization chamber calibrated to dose in water. From the collected data, detector sensitivities were obtained as function of the beam kVp and additional filtration. Using Monte Carlo simulations relative scintillator sensitivities were computed. For some of the scintillators these sensitivities show strong energy-dependence for beam average energy below 35 keV for each additional filtration but fair constancy above. One of the scintillators (BC-404) has smaller energy-dependence at low photon average energy and could be considered a candidate for applications (like mammography) where beam energy has small span.

On possible temperature dependence of plastic scintillator response

On possible temperature dependence of plastic scintillator response

An experimental study of the relative response of plastic scintillators to photons and beta particles

Abstract A scintillation counting system has been constructed with the use of BC-400 and EJ-212 series plastic scintillators along with a subminiature photomultiplier tube to investigate the effect of increasing plastic scintillator thickness on system-integrated counts. Measurements have been carried out using four different gamma sources with different energies ranging from 6 keV to 1.332 MeV and a Ni-63 beta source with a maximum energy of 66 keV. Scintillator thicknesses ranged from 10 μm to 2500 μm. The response of the system was determined by measuring the integrated counts as a function of scintillator thickness. These experimental findings were used to empirically determine the optimum thickness of scintillator material with which to build a low energy beta detector which discriminates against high energy gamma photons in a mixed radiation field environment.

Modelling plastic scintillator response to gamma rays using light transport incorporated FLUKA code

The response function of NE102 plastic scintillator to gamma rays has been simulated using a joint FLUKA+PHOTRACK Monte Carlo code. The multi-purpose particle transport code, FLUKA, has been responsible for gamma transport whilst the light transport code, PHOTRACK, has simulated the transport of scintillation photons through scintillator and lightguide. The simulation results of plastic scintillator with/without light guides of different surface coverings have been successfully verified with experiments.

A Monte Carlo method for calculating the energy response of plastic scintillators to polarized photons below 100 keV

The energy response of plastic scintillators (Eljen Technology EJ-204) to polarized soft gamma-ray photons below 100 keV has been studied, primarily for the balloon-borne polarimeter, PoGOLite. The response calculation includes quenching effects due to low-energy recoil electrons and the position dependence of the light collection efficiency in a 20 cm long scintillator rod. The broadening of the pulse-height spectrum, presumably caused by light transportation processes inside the scintillator, as well as the generation and multiplication of photoelectrons in the photomultiplier tube, were studied experimentally and have also been taken into account. A Monte Carlo simulation based on the Geant4 toolkit was used to model photon interactions in the scintillators. When using the polarized Compton/Rayleigh scattering processes previously corrected by the authors, scintillator spectra and angular distributions of scattered polarized photons could clearly be reproduced, in agreement with the results obtained at a synchrotron beam test conducted at the KEK Photon Factory. Our simulation successfully reproduces the modulation factor, defined as the ratio of the amplitude to the mean of the distribution of the azimuthal scattering angles, within ∼ 5 % (relative). Although primarily developed for the PoGOLite mission, the method presented here is also relevant for other missions aiming to measure polarization from astronomical objects using plastic scintillator scatterers.

Spatial and spectral gamma-ray response of plastic scintillators used in portal radiation detectors; comparison of measurements and simulations

Portal radiation detectors are commonly used by steel industries in the probing and detection of radioactivity contamination in scrap metal. Furthermore, a large number of portal monitors are installed at the border crossings to prevent illegal radioactive material trafficking. These portal detectors typically consist of either PS (polystyrene) or PVT (polyvinyltoluene) plastic scintillating detectors. Through the electronic circuit of the detector, an energy region-of-interest window can be determined in order to focus on the detection of certain radionuclides. In this study, the spatial response of a portal's PS scintillator to a Cs-137 and a Co-60 source for various energy region-of-interest windows is presented. Furthermore, a number of measured spectra for different source positions on the surface of the scintillating detector are shown. The measured spatial response showed a quantitative and qualitative dependence on the energy window used each time. In addition, measured spectra showed energy shifts for different positions of the two sources on the detector surface. The aforementioned phenomena could not be adequately explained and modelled using gamma-particle transport Monte Carlo simulation tools, such as the MCNP4C2 code. In order to fully explain these phenomena, we performed optical simulations, modelling the transport of the light yield within the detector, using Gate v3.0.0 with Geant 4.8.0p01 of CERN. The results of those simulations are presented and compared to the measured ones.

Monte Carlo simulation of a plastic scintillator response function in β–γ coincidence measurement

A β–γ coincidence spectrometer consisting of a 2π plastic beta detector and a NaI(Tl) detector, is described. In order to evaluate performance of the spectrometer, Monte Carlo simulation of the plastic and NaI(Tl) scintillators responses has been performed using GEANT4 code. This study reveals the possible efficiency loss of the system and enables us to calculate gamma detection efficiency of the system for different source-detector geometries.