Guillaume H. V. Bertrand

Current Status on Plastic Scintillators Modifications

Recent developments of plastic scintillators are reviewed, from 2000 to March 2014, distributed in two different chapters. First chapter deals with the chemical modifications of the polymer backbone, whereas modifications of the fluorescent probe are presented in the second chapter. All examples are provided with the scope of detection of various radiation particles. The main characteristics of these newly created scintillators and their detection properties are given.

Understanding the behaviour of different metals in loaded scintillators: discrepancy between gadolinium and bismuth

Organometallic chemistry has recently gained a lot of attention in the domain of plastic scintillators. Homogenously dispersed metal complexes in a polymer matrix can afford plastic scintillators with unseen abilities. Heavy atom loading is very attractive as it gives access to plastics with increased sensitivity towards elusive radiations such as gamma and neutron. But this comes with a drawback, as heavy atoms tend to quench fluorescence, hence decreasing the scintillation yield. We present here a comprehensive study of this phenomenon with bismuth and gadolinium complexes. We investigate the influence of the ligand nature by varying organometallic and fluorophore concentration to probe their interaction. We also propose an explanation of the difference in behavior between these two metals. These results were applied to the fabrication of large volume loaded plastic scintillators (>100 cm3). Bismuth loaded scintillators displayed characteristics equivalent to lead loaded commercial materials, and gadolinium samples proved to be able to capture thermal neutrons and release gamma rays.

Thermo- and radioluminescent polystyrene based plastic scintillators doped with phosphorescent iridium(III) complexes

In this work, 29 iridium(III) heteroleptic organometallic complexes based on four cyclometalating and eight ancillary ligands were incorporated in a cross-linked copolymer. The photophysical properties of the complexes in chloroform solution and in the polymer matrix were studied. Preliminary scintillation behaviours of the samples, such as the influence of the iridium complex concentration within the matrix or the relative radioluminescence intensity of each sample are given. The scintillators showed promising scintillation yields (up to 1500 ph MeV−1) without the use of a primary fluorophore. Unexpectedly, one of the prepared scintillators exhibited thermoluminescence.

Influence of bismuth loading in polystyrene-based plastic scintillators for low energy gamma spectroscopy

This article presents the synthesis and the blend of bismuth complexes in polystyrene based plastic scintillators. A specific design has enabled the fabrication of a scintillator loaded with up to 17 wt% of bismuth. Tri-carboxylate and triaryl bismuth compounds were used to explore and understand the influence of bismuth loading on the two main criteria of plastic scintillation: light yield and detection efficiency of γ-rays. For gamma radiation with an energy <200 keV, bismuth loaded scintillators demonstrate the ability to produce a photoelectric peak (total absorption peak) in pulse height spectra. The increase of interactions due to bismuth doping was quantified and fitted with standard models. Finally the performance of our bismuth loaded scintillators was evaluated to be better than that of a commercial lead loaded counterpart.

Gadolinium-loaded Plastic Scintillators for Thermal Neutron Detection using Compensation

Plastic scintillator loading with gadolinium-rich organometallic complexes shows a high potential for the deployment of efficient and cost-effective neutron detectors. Due to the low-energy photon and electron signature of thermal neutron capture by Gd-155 and Gd-157, alternative treatment to pulse-shape discrimination has to be proposed in order to display a count rate. This paper discloses the principle of a compensation method applied to a two-scintillator system: a detection scintillator interacts with photon and fast neutron radiation and is loaded with gadolinium organometallic compound to become a thermal neutron absorber, while a not-gadolinium loaded compensation scintillator solely interacts with the fast neutron and photon part of incident radiation. After the nonlinear smoothing of the counting signals, a hypothesis test determines whether the resulting count rate post-background response compensation falls into statistical fluctuations or provides a robust indication of neutron activity. Laboratory samples are tested under both photon and neutron irradiations, allowing the authors to investigate the performance of the overall detection system in terms of sensitivity and detection limits, especially with regards to a similar-active volume He-3 based commercial counter. The study reveals satisfactory figures of merit in terms of sensitivity and directs future investigation toward promising paths.

N-(2-Ethylhexyl)carbazole: A New Fluorophore Highly Suitable as a Monomolecular Liquid Scintillator.

The synthesis, photophysical properties, and applications in scintillation counting of N-(2-ethylhexyl)carbazole (EHCz) are reported. This molecule displays all of the required characteristics for an efficient liquid scintillator (emission wavelength, scintillation yield), and can be used without any extra fluorophores. Thus, its scintillation properties are discussed, as well as its fast neutron/gamma discrimination. For the latter application, the material is compared with the traditional liquid scintillator BC-501 A, and other liquid fluorescent molecules classically used as scintillation solvents, such as xylene, pseudocumene (PC), linear alkylbenzenes (LAB), diisopropylnaphthalene (DIN), 1-methylnaphthalene (1-MeNapht), and 4-isopropylbiphenyl (iPrBiph). For the first time, an excimeric form of a molecule has been advantageously used in scintillation counting. A moderate discrimination between fast neutrons and gamma rays was observed in bulk EHCz, with an apparent neutron/gamma discrimination potential half of that of BC-501 A.

Compensated gadolinium-loaded plastic scintillators for thermal neutron detection and counting

Plastic, scintillator loading with gadolinium-rich organometallic complexes shows a high potential for the deployment of efficient and cost-effective neutron detectors. Due to the low-energy photon and electron signature of thermal neutron capture by gadolinium-155 and gadolinium-157, alternative treatment to Pulse Shape Discrimination has to be proposed in order to display a trustable count rate. This paper discloses the principle of a compensation method applied to a two-scintillator system: a detection scintillator interacts with photon radiation and is loaded with gadolinium organometallic compound to become a thermal neutron absorber, while a non-gadolinium loaded compensation scintillator solely interacts with the photon part of the incident radiation. Posterior to the nonlinear smoothing of the counting signals, a hypothesis test determines whether the resulting count rate after photon response compensation falls into statistical fluctuations or provides a robust image of neutron activity. A laboratory prototype is tested under both photon and neutron irradiations, allowing us to investigate the performance of the overall compensation system in terms of neutron detection, especially with regards to a commercial helium-3 counter. The study reveals satisfactory results in terms of sensitivity and orientates future investigation toward promising axes.

X-ray detection capability of bismuth-loaded plastic scintillators

We evaluated the high-energy X-ray detection capabilities of Bi-loaded plastic scintillators. The detection efficiency for 67.4 keV X-rays was successfully increased by increasing the Bi concentration. The detection efficiency of a plastic scintillator loaded with 10 wt % Bi was comparable to that of a commercially available plastic scintillator loaded with 5 wt % Pb, NE-142. A subnanosecond time resolution was achieved, and no long scintillation component appeared with Bi loading. These results indicate that Bi loading is an effective method of enhancing the detection efficiency for high-energy X-rays while preserving the timing properties of plastic scintillators.

Plastic scintillators modifications for a selective radiation detection

Recent developments of plastic scintillators are reviewed, from January 2000 to June 2015. All examples are distributed into the main application, i.e. how the plastic scintillator was modified to enhance the detection towards a given radiation particle. The main characteristics of these newly created scintillators and their detection properties are given.

Implementation of gadolinium for neutron measurement systems based on plastic scintillators and semiconductors

CEA LIST has investigated different schemes enabling neutron detection thanks to the implementation of gadolinium converters. The fine analysis of the prompt gamma ray signature has permitted us to propose and test dedicated designs such as Gd-doped plastic scintillator, large spherical scintillators or compensated CdZnTe diodes.