Neutron Converter Layer Research Articles

Diamond Radiation Detector with Built‐In Boron‐Doped Neutron Converter Layer

Diamond Radiation Detector Neutron, a promising probe for bioimaging and non-destructive inspection, demands high efficiency flat-panel detector for imaging applications. Polycrystalline diamond is a material of choice, with built-in neutron converter formed by boron doping and scalability to wide-area image sensor. More information can be found in article number 2100315 by Tomoaki Masuzawa and co-workers.

Neutron-gamma dosimetry for BNCT using field oxide transistors with gadolinium oxide as neutron converter layer.

A new type of electronic dosimeter is presented, capable of discerning between the doses of gamma photons and neutrons in a mixed beam as found in boron neutron capture therapy (BNCT). We introduce a real-time dosimeter based on a thick gate field oxide field effect transistor (FOXFET) covered with a neutron converter layer containing gadolinium. To sensitize the FOXFET dosimeter to neutron fluxes, a converter layer containing gadolinium oxide particles embedded in photoresines was deposited over the sensor surface. Mixed neutron-gamma field configurations with different neutron energy spectra were used to assess the FOXFET response, considering different thicknesses of the neutron converter layer. The total gamma sensitivity of the devices resulted to be 43mV/Gy. The responses of sensors with different converter layer thicknesses irradiated with different neutron spectra are simulated using GEANT4 code. The response to photons is not significantly modified with thin conversion layers when used in water medium. A real-time dosimeter comprising a pair of FOXFET sensors-only one of them with a gadolinium neutron converter layer-allows the simultaneous measurement of gamma dose and neutron flux during BNCTirradiations.

Diamond Radiation Detector with Built‐In Boron‐Doped Neutron Converter Layer

Herein, a radiation detector made of polycrystalline diamond with a boron (B)‐doped neutron converter layer is presented. The detector is fabricated by the hot filament chemical vapor deposition technique, and consists of an undoped free‐standing polycrystalline diamond layer and a B‐doped polycrystalline diamond top layer that serves as an electrical contact and a converter for neutron‐alpha conversion. Characterization of the diamond films and detector operation is presented. The results indicate that the B‐doped layer acts as an effective neutron‐alpha converter, whereby neutron detection is demonstrated in particle‐counting mode using a multichannel analyzer.

Emerging Trends in Nano Structured Silicon Detectors for Neutron Spectroscopy

Neutron detectors are extensively used in numerous applications such as, in nuclear fuels plants, high energy accelerators, space explorations, imaging etc. Among the commercially available various detectors, 3D semiconductor detectors filled with an appropriate neutron converter layer were been studied over several years as they are highly sensitive small sensors and could provide high spectroscopic resolution and energy information with respect to the neutron spectrum of our interest. This paper reviews the current status of the nano structured silicon (Si) neutron detectors in consideration with their potential application in neutron spectroscopy. It includes a thorough review on simulation and experimental studies that were already reported in several literatures to analyse the primary radiation induced imperfections which can modify the response of a Si based detector.

Performance of 5-[formula omitted]m PIN diamond diodes as thermal neutron detectors

Diamond PIN diodes with an approximately 5-μm thick i-layer and coated with a thin boron nitride (BN) layer have been tested with a thermal neutron beam. For a flux of 4.4 × 106 n/s/cm2, count rates were on the order of 30–100 counts per second depending on the thickness of the BN neutron converter layer. Pulse height spectra showed features associated with α and 7Li fission products consistent with the thickness of the BN layer. An irradiation test with a 1 MeV neutron equivalent fluence of 1015 n/cm2 showed no significant alteration in the count rate of the tested detector.

Wavelength, fluence and substrate-dependent room temperature pulsed laser deposited B-enriched thick films

Boron carbide (B4C) has outstanding properties making it particularly interesting in the field of neutron detection. In this study we exploit nanosecond pulsed laser deposition (PLD) for the synthesis of B-enriched films with micrometer-scale thickness for future realization of a neutron converter layer. B-enriched B4C layers were deposited by PLD at room temperature under different wavelength conditions (λP = 266, 248,193 nm), fluence (from 2 to 10 J/cm2) and substrate (silica, Si (100), kapton (polyamide), PMMA and AZ 1512 resist).The measured elemental composition of boron (B), carbon (C) and oxygen (O) as well as the structural properties of the deposited films highlighted: i) wavelength- and fluence-dependent B sub-stoichiometry with respect to the ablated target, ii) formation of polycrystalline grains despite the room temperature growth in the case of λP = 266 nm, and iii) deposition rates higher for λP = 266 than for the other investigated wavelengths.The film deposited at a wavelength of λP = 266 nm and F = 2 J/cm2 yielded the best B/C ratio, negligible O-contaminations, and a very smooth surface with low density of surface particulates.Moreover, the possibility of depositing well adherent films on soft substrates with thicknesses > 1 μm is demonstrated, due to ability to accommodate tensile stress at the substrate-B4C film interface.

Large High-Efficiency Thermal Neutron Detectors Based on the Micromegas Technology

Due to the so-called 3He shortage crisis, many detection techniques for thermal neutrons are currently based on alternative converters. There are several possible ways of increasing the detection efficiency for thermal neutrons using the solid neutron-to-charge converters 10B or 10B4C. Here, we present an investigation of the Micromegas technology. The micro-pattern gaseous detector Micromegas was developed in the past years at Saclay and is now used in a wide variety of neutron experiments due to its combination of high accuracy, high rate capability, excellent timing properties, and robustness. A large high-efficiency Micromegas-based neutron detector is proposed for thermal neutron detection, containing several layers of 10B4C coatings that are mounted inside the gas volume. The principle and the fabrication of a single detector unit prototype with overall dimension of ~15 × 15 cm2 and its possibility to modify the number of 10B4C neutron converter layers are described. We also report results from measurements that are verified by simulations, demonstrating that typically five 10B4C layers of 1–2 μm thickness would lead to a detection efficiency of 20% for thermal neutrons and a spatial resolution of sub-mm. The high potential of this novel technique is given by the design being easily adapted to large sizes by constructing a mosaic of several such detector units, resulting in a large area coverage and high detection efficiencies. An alternative way of achieving this is to use a multi-layered Micromegas that is equipped with two-side 10B4C-coated gas electron multiplier (GEM)-type meshes, resulting in a robust and large surface detector. Another innovative and very promising concept for cost-effective, high-efficiency, large-scale neutron detectors is by stacking 10B4C-coated microbulk Micromegas. A prototype was designed and built, and the tests so far look very encouraging.

Boron-10 lined RPCs for sub-millimeter resolution thermal neutron detectors: conceptual design and performance considerations

A novel concept for position-sensitive thermal neutron detectors based on thin-gap Resistive Plate Chambers (RPC) lined with a neutron converter layer is presented and its feasibility is discussed. Several detector architectures implementing a stack of RPCs in multilayer and inclined geometries are introduced. The results of a Monte Carlo simulation study are presented demonstrating the effect of the main detector design parameters on the expected detection efficiency and spatial resolution.

Performance study of thin epitaxial silicon PIN detectors for thermal neutron measurements with reduced [formula omitted] sensitivity

A novel approach of using thin epitaxial silicon PIN detectors for thermal neutron measurements with reduced γ sensitivity has been presented. Monte Carlo simulations showed that there is a significant reduction in the gamma sensitivity for thin detectors with the thickness of 10–25μm compared to a detector of thickness of 300μm. Epitaxial PIN silicon detectors with the thickness of 10μm, 15μm and 25μm were fabricated using a custom process. The detectors exhibited low leakage currents of a few nano-amperes. The gamma sensitivity of the detectors was experimentally studied using a 33 μCi, 662 keV, 137Cs source. Considering the count rates, compared to a 300μm thick detector, the gamma sensitivity of the 10μm, 15μm and 25μm thick detectors was reduced by factors of 1874, 187 and 18 respectively. The detector performance for thermal neutrons was subsequently investigated with a thermal neutron beam using an enriched 10B film as a neutron converter layer. The thermal neutron spectra for all three detectors exhibited three distinct regions corresponding to the 4He and 7Li charge products released in the 10B-n reaction. With a 10B converter, the count rates were 1466 cps, 3170 cps and 2980 cps for the detectors of thicknesses of 10μm, 25μm and 300μm respectively. The thermal neutron response of thin detectors with 10μm and 25μm thickness showed significant reduction in the gamma sensitivity compared to that observed for the 300μm thick detector. Considering the total count rate obtained for thermal neutrons with a 10B converter film, the count rate without the converter layer were about 4%, 7% and 36% for detectors with thicknesses of 10μm, 25μm and 300μm respectively. The detector with 10μm thickness showed negligible gamma sensitivity of 4 cps, but higher electronic noise and reduced pulse heights. The detector with 25μm thickness demonstrated the best performance with respect to electronic noise, thermal neutron response and gamma sensitivity.

Neutron detection devices with 6LiF converter layers

The demand for new thermal neutron detectors as an alternative to 3He tubes in research, industrial, safety and homeland security applications, is growing. These needs have triggered research and development activities about new generations of thermal neutron detectors, characterized by reasonable efficiency and gamma rejection comparable to 3He tubes. In this paper we show the state of art of a promising lowcost technique, based on commercial solid state silicon detectors coupled with thin neutron converter layers of 6LiF deposited onto carbon fiber substrates. Several configurations were studied with the GEANT4 simulation code, and then calibrated at the PTB Thermal Neutron Calibration Facility. The results show that the measured detection efficiency is well reproduced by the simulations, therefore validating the simulation tool in view of new designs. These neutron detectors have also been tested at neutron beam facilities like ISIS (Rutherford Appleton Laboratory, UK) and n_TOF (CERN) where a few samples are already in operation for beam flux and 2D profile measurements. Forthcoming applications are foreseen for the online monitoring of spent nuclear fuel casks in interim storage sites.

Absolute efficiency calibration of 6LiF-based solid state thermal neutron detectors

The demand for new thermal neutron detectors as an alternative to 3He tubes in research, industrial, safety and homeland security applications, is growing. These needs have triggered research and development activities about new generations of thermal neutron detectors, characterized by reasonable efficiency and gamma rejection comparable to 3He tubes. In this paper we show the state of the art of a promising low-cost technique, based on commercial solid state silicon detectors coupled with thin neutron converter layers of 6LiF deposited onto carbon fiber substrates. A few configurations were studied with the GEANT4 simulation code, and the intrinsic efficiency of the corresponding detectors was calibrated at the PTB Thermal Neutron Calibration Facility. The results show that the measured intrinsic detection efficiency is well reproduced by the simulations, therefore validating the simulation tool in view of new designs. These neutron detectors have also been tested at neutron beam facilities like ISIS (Rutherford Appleton Laboratory, UK) and n_TOF (CERN) where a few samples are already in operation for beam flux and 2D profile measurements. Forthcoming applications are foreseen for the online monitoring of spent nuclear fuel casks in interim storage sites.

Study of silicon+6LiF thermal neutron detectors: GEANT4 simulations versus real data

Research and development on alternative thermal neutron detection technologies and methods are nowadays needed as a possible replacement of 3He-based ones. Commercial solid state silicon detectors, coupled with neutron converter layers containing 6Li, have been proved to represent a viable solution for several applications as present in the literature. In order to better understand the detailed operation and the response and efficiency of such detectors, a series of dedicated GEANT4 simulations were performed and compared with real data collected in a few different configurations. The results show an excellent agreement between data and simulations, indicating that the behavior of the detector is fully understood.

4H-SiC Neutron Sensors Based on Ion Implanted10B Neutron Converter Layer

In the framework of the I_SMART project the main aim is to develop an innovative complete radiation detection system based on silicon carbide technology in view to detect neutrons (thermal and fast) and photons for harsh environments. In the present work two geometries have been realized based on ion implantation of boron. In the first geometry, 10B ions have been implanted into the Al metallic contact of a p-n diode to create the neutron converter layer. In the second geometry one single process has been used to realize both the p+-layer and the neutron converter layer. The technological processes followed to fabricate these detectors, with a study of their electrical behavior and their responses under thermal neutron irradiations are addressed in this paper.

Improvements in Realizing 4H-SiC Thermal Neutron Detectors

In this work we presented two types of 4H-SiC semiconductor detectors (D1 and D2) both based on ion implantation of 10B inside the aluminum metallic contact. The first detector shows a high leakage current after the implantation and low signal to noise ratio. However, improvements concerning the implantation parameters and the distance between the implanted 10B thermal neutron converter layer and the active pn-junction have led to low leakage current and thus to higher signal to noise ratio. This proves the strength of this new method of realizing sensitive SiC-based thermal neutron detectors.

Characterization of the silicon+6LiF thermal neutron detection technique

The worldwide need to replace 3He for neutron detection has triggered research and development on new technologies and methods. A promising one is based on commercial solid state silicon detectors coupled with thin neutron converter layers containing 6Li. After proving the feasibility of this technique, we characterized the behavior of such a detector with different converter layer thicknesses. In this paper we also disentangle other contributions to the overall spectrum shape observed with this kind of detector, proving that its detection efficiency can be made reasonably high and that the gamma/neutron discrimination capability is comparable to that of 3He tubes.

Radiation Silicon Carbide Detectors Based on Ion Implantation of Boron

Radiation detectors based on radiation-hardened semiconductor such as silicon carbide (SiC), have received considerable attention in many applications such as in outer space, high energy physics experiments, gas and oil prospection, and nuclear reactors. In the frame work of the European project I_SMART (Innovative Sensor for Material Ageing and Radiation Testing), we demonstrated for the first time the reliability of thermal neutron detectors realized by standard ion implantation of boron atoms to form a neutron converter layer (NCL). Two types of detectors were realized; the first was implanted by aluminum to create the p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -layer, and then implanted by boron ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B) to realize the NCL. The second type was based on epitaxial p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> - layer, and was implanted by into the aluminum metallic contact in order to avoid implantation-related defect within the sensitive area. Both kinds of detectors reveal to respond to thermal neutrons and gamma rays, showing consistent counting rates as a function of bias voltages, radiation intensity and type of shielding.

Fabrication and nuclear reactor tests of ultra-thin 3D silicon neutron detectors with a boron carbide converter

We describe the design, fabrication process and characterization of a thermal neutron detector based on ultra-thin silicon PIN diodes with 3D electrodes and a 10B4C neutron converter layer. The sensors were fabricated on SOI silicon with an active thickness of 20 μm which allows for a low gamma sensitivity, while the 3D structure of the electrodes results in a lower capacitance that in the equivalent planar sensor. The 2.7 μm 10B4C converter layer was deposited through RF magnetron sputtering on a whole silicon wafer, opening the path for mass-production. The detectors were tested in a thermal neutron beam at the nuclear reactor at the Instituto Superior Técnico in Lisbon and their intrinsic detection efficiency for themal neutrons and the gamma sensitivity as a function of the energy threshold were obtained.

Thermal neutron detection enhancement by 10B implantation in silicon carbide sensor

ABSTRACT:The purpose of this paper is to propose the enhancement of device detectors based on p-n junction in 4H-SiC for nuclear instrumentation. Particular emphasis is placed on the interest on using Boron isotope 10 as a Neutron Converter Layer in order to detect thermal neutrons. Here, we present the main results obtained during several irradiation tests performed in the Belgian Reactor 1 (BR1). We show the capability of our detectors by means of first results of the detector response at different reverse voltage biases and at different reactor power.

Feasibility study of a SiC sandwich neutronspectrometer

Semiconductor sandwich neutron spectrometers are suitable for in-pile measurements of fast reactor spectra thanks to their compact and relatively simple design. We have assembled and tested a sandwich neutron spectrometer based on 4H-silicon carbide (4H-SiC) Schottky diodes. The SiC diodes detect neutrons via neutron-induced charged particles (tritons and alpha particles) produced by 6Li(n,α)3H reaction. 6LiF neutron converter layers are deposited on the front surface of Schottky diodes by magnetron sputtering. The responses of SiC diodes to charged particles were investigated with an 241Am alpha source. A sandwich neutron spectrometer was assembled with two SiC Schottky diodes selected based on the charged-particle-response experimental results. The low-energy neutron response of the sandwich spectrometer was measured in the neutron field of the Chinese Fast Burst Reactor-II (CFBR-II). Spectra of alpha particles and tritons from 6Li(n,α)3H reaction were obtained with two well-resolved peaks. The energy resolution of the sum spectrum was 8.8%. The primary experimental results confirmed the 4H-SiC sandwich neutron spectrometer's feasibility.

Silicon planar detectors adapted to slow neutron detection

AbstractMost neutron detectors use some type of conversion material to convert the incident neutrons into secondary charged particles, which can be detected inside the detector bulk afterwards. In these reactions, charged particles and recoil nuclei are emitted, with energies high enough to be distinguished from the gamma ray background. In this way, semiconductor detectors incorporating a layer of a neutron reactive material on top of the substrate can be used as neutron detectors. Based on their experience in the fabrication of radiation detectors, CNM‐IMB (National Center of Microelectronics in Barcelona, Spain) has started a new research line in solid‐state neutron detectors for imaging or dosimetry. The Geant4 Monte–Carlo simulation package has been used to predict the detection efficiency of planar silicon detectors with a neutron converter layer. At the same time, preliminary tests of silicon pad detectors covered with neutron converters have been carried out in the Autonomous University of Barcelona with a neutron source (241Am‐Be). Copyright © 2010 John Wiley &amp; Sons, Ltd.