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BackgroundDetectors based on the third-generation semiconductor material silicon carbide (SiC) offer several important advantages, such as compactness, faster charge-collection times, and easier n/γ identification, and they are widely used in reactor core dose monitoring.PurposeIn this study, the n/γ signal amplitude, neutron fluence rate, and linear response calibration performances were tested systematically for a self-developed third-generation SiC semiconductor detector.MethodsFirstly, the neutron conversion layer material 6LiF (with a 95% abundance of 6Li) was sprayed onto a SiC substrate using electron beam evaporation vacuum coating technology to achieve the optimized thickness of 25 μm for the self-developed third-generation SiC semiconductor detector. Then, 241Am α radioactive source (activity 9.37×103 Bq) was used to observe α particle response signal amplitude, and γ response testing of radiation was conducted in the 137Cs γ source (activity 6.23×107 Bq) environment. In addition, the SiC detector's neutron flux response linearity, γ dose rate response linearity and calibration of neutron fluence rate response linearity were measured in the standard radiation field systems.ResultsThe measurement results show that the SiC semiconductor detector has a linear fit of R² = 0.996 9 in the neutron fluence rate range of 1×103~1×106 cm-2∙s-1, with a good linear response, and the response range of the neutron/gamma dose is 0.005~20 Gy∙h-1.ConclusionThe SiC detectors with such good n/γ performance can be used for real-time and accurate monitoring of neutron and gamma doses in nuclear power field reactors.

Advanced targets based on thin foils of graphene oxide (GO) covered by metallic layers show many advantages with respect to others because permit high proton and light ion acceleration using high intensity pulsed lasers in Target‐Normal Sheath‐Acceleration (TNSA) regime. GO foils contain parallel micrometric graphene sheets, have low density, show high penetration, and low scattering by energetic electrons accelerated by laser, inducing electron channelling effects. They contain high concentrations of hydrogen, water, and functional oxygen groups, can be realized as thin films with high mechanical resistance, and show high photon absorbance for laser beams. In this work, we present experimental results obtained by our research group using thin GO targets covered by thin gold films, prepared in our laboratories. Advanced targets have been irradiated in TNSA regime with 40 fs laser pulses at the intensity of the order of 1019 W/cm2, using a laser spot of about 10 microns diameter, permitting to accelerate ions at energies of the order of 6 MeV per charge state. The electric field of ion acceleration can be increased by optimizing the irradiation conditions and the GO and Au film thicknesses. The novel findings of this work concern the high forward ion acceleration obtained using thin targets containing GO which induces the effect of electron channelling and production of high‐density forward plasma. The plasma diagnostics are developed with fast SiC semiconductor detectors connected in time‐of‐flight (TOF) configuration. The fast semiconductor detector response permits to optimize the ion acceleration conditions by changing the distance of the laser focus with respect to the target surface, the incidence angle and the laser parameters. [ABSTRACT FROM AUTHOR]

Proton acceleration can be induced by non‐equilibrium plasma developed by high‐intensity laser pulses, at 1016 W/cm2, irradiating different types of thin polyethylene targets. The process of proton acceleration and directive yield emission was investigated, optimizing the laser parameters, the irradiation conditions, and the target properties. The use of 600 J pulse energy, a laser focalization inducing self‐focusing effects and advanced targets with embedded nanoparticles and optimal thicknesses, has permitted to accelerate forward protons up to the energies of about 6 MeV and amount of the order of 1015 H+/pulse. High proton energy is obtained using thin foils enriched with gold nanoparticles, whereas high proton yield is obtained using targets with a thickness of about 10 μm. The plasma diagnostics using SiC semiconductor detectors in time‐of‐flight configuration was fundamental to monitor the optimal conditions to improve the plasma processes concerning the ion acceleration and the X‐ray and relativistic electron emission. [ABSTRACT FROM AUTHOR]

Proton acceleration using high‐intensity laser pulses, at 1016 W/cm2 was studied irradiating different types of thin metal and plastic targets having 1‐micron thickness. The maximization of the proton energy process was investigated optimizing the laser parameters, the irradiation conditions and the target properties. Employing 600–700 J laser pulse energy, a focalization inducing self‐focusing effects and using targets with optimized thickness, it was possible to accelerate protons up to energies of above 8 MeV. The time‐of‐flight diagnostics has allowed to monitor the plasma properties and to control the ion acceleration process. [ABSTRACT FROM AUTHOR]

The nonequilibrium plasma generated by nanosecond laser pulse is characterized using a SiC detector connected in time‐of‐flight configuration to measure the radiations emitted from the plasma. Different metallic targets were irradiated by the pulsed laser at an intensity of 1010 W/cm2 and 200 mJ pulse energy. The SiC allows detecting ultraviolet radiations and soft X‐rays, electrons, and ions. The obtained plasma has a temperature of the order of tens to hundreds eV depending on the atomic number of the irradiated target and ion accelerations of the order of 100 eV per charge state. [ABSTRACT FROM AUTHOR]

Non‐equilibrium plasma was obtained by irradiating Al foils in vacuum with a femtosecond (fs) laser at intensities of the order of 1018 W/cm2. Protons and other light ions were accelerated in the forward direction by using the target‐normal‐sheath acceleration regime. Time‐of‐flight technique was employed to measure the ions' kinetic energy using SiC detectors placed at known distances and angles. The ion acceleration was monitored under different conditions of laser focal position, laser pulse energy, and laser contrast. The target was irradiated using different thicknesses and anti‐reflecting graphene films. By optimizing the laser parameters, irradiation conditions, and target properties, it was possible to accelerate up to 2.3 MeV per charge state, as will be presented and discussed. [ABSTRACT FROM AUTHOR]

Abstract A neutron beam monitor was developed for the time-of-flight neutron reflectometer (NR) instrument at the China Mianyang Research Reactor (CMRR). The SiC neutron monitor employs a wide-bandgap silicon carbide (SiC) semiconductor detector coated with a 6LiF neutron converter film evaporated on a thin ceramic sheet. Given the relatively large active area [(10 × 10) mm2] and sufficiently thick epitaxial layer (30 μ m), the monitor can discriminate the gamma background from the signals. Prior to assembling the monitor, the I–V characteristics and alpha responses of the SiC detector were measured. Next, the SiC detector and 6LiF neutron converter were installed in a small aluminum shielding box, and the neutron and gamma responses were measured with an Am–Li neutron source and a 137Cs plus 60Co gamma source, respectively. The fabricated SiC neutron monitor was mounted inside the slit of the NR instrument (after the focusing neutron guide), and the intensity of the transmitted neutron beam was measured. To measure the incident neutron flux, the distinct triton peaks from the 6Li (n, α) T reaction were counted as normalized data for the NR instrument. This paper describes the fabrication details of the SiC neutron monitor, and discusses the preliminary measurements. Highlights • A neutron beam monitor based on a 6LiF-coated SiC detector is proposed. • Neutron beam intensity is accurately monitored with the triton peak. • The compact size is suitable for NR instrument measurement with a reasonable efficiency of 0.28%. • This SiC neutron monitor has the remarkable gamma discrimination ability. [ABSTRACT FROM AUTHOR]

In order to improve the temporal response of SiC-HPMTs, a new SiC detector with a faster time response (leading edge 1.5 ns, FWHM 4 ns) was developed for constructing an improved SiC-HPMT. Then the properties of the improved SiC-HPMT were studied in detail. Compared with those of the previous SiC-HPMT, the temporal response of the improved SiC-HPMT, with a leading edge of about 2 ns and a FWHM of less than 5ns was effectively improved. The maximum linear current that exceeded 630 mA depends on both the accelerating and focusing voltage (V a) and the bias voltage (V SiC) of the SiC detector, but has a strong dependence on V a. The scintillation detector comprised of the improved SiC-HPMT and an EJ228 scintillator can accurately obtain the multiple peaks characteristic of the pulsed X-ray source, which indicates that the improved SiC-HPMT can well satisfy the requirements for measuring the time information of fast pulsed radiation fields. In addition, the SiC-HPMT should be placed at the position that deviates from the radiation beam to avoid the direct irradiation on the SiC detector. The improved SiC-HPMT will further expand its application in pulsed radiation field measurements and become a supplement for existing photoelectric detectors. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the performance of a 4H–SiC radiation sensor in the temperature range from 25 °C to 450 °C to explore its compatibility as detector of fast ion losses in plasma diagnostic of future nuclear fusion reactors. To simulate the escape of fusion-born alpha particles in D-T (deuterium-tritium) fusion plasmas, spectroscopic measurements were carried out in a vacuum chamber by irradiating the detector with a 3.5 MeV alpha beam from a Tandem accelerator. The detector was found to have an energy resolution ≤2% over the entire temperature range analyzed. Relevantly, the excellent spectrometric capabilities of the device have allowed us to calculate from experimental data, with unprecedented accuracy, the average energy required to create a single electron-hole pair in 4H–SiC as a function of temperature. • Novel 4H–SiC radiation detector for the next generation of nuclear fusion reactors. • Excellent spectroscopic response up to 450°C, with resolutions below 2%. • Best accuracy values for the average electron-hole pair creation energy reported. [ABSTRACT FROM AUTHOR]

An Nd:YAG pulsed laser was employed to irradiate a nitrogen gas-puff target. The interaction gives rise to the emission of soft X-ray (SXR) radiation in the ‘water window’ spectral range (λ= 2.3÷4.4 nm). This source was already successfully employed to perform the SXR microscopy. In this work, a Silicon Carbide (SiC) detector was used to characterize the nitrogen plasma emission in terms of gas-puff target parameters. The measurements show applicability of SiC detectors for SXR plasma characterization.

The paper presents a study of the performance of some selected UV detectors. Unlike many similar works, the obtained data refer to commercial photodiodes (not only to detector materials). The main task of the research was to determine the influence of the operating temperature and annealing on the detector spectral responsiveness. A comparison of the results obtained for the photodiodes made of GaN and SiC was also performed. Although both kinds of detectors can work at high temperatures for a long time, some modification of their properties was observed. However, for GaN and SiC photodiodes, this modification has a substantially different nature. It is very important for some applications, e.g. fire alarms and a military equipment.

Abstract SiC Schottky detectors, having a superficial active zone up to 80 micron depths and a thin surface metallization, are adapt to detect high energetic ions. In order to demonstrate their detection ability with high-energy resolution, a helium Rutherford backscattering spectroscopy (RBS) was employed to evaluate their detection efficiency, energy resolution in the region 1.0 – 6.0 MeV alpha ions, depth resolution and dependence on the ion beam current. The detector parameters dependencies on the surface passivation layers, ion energy and current are presented. The comparison of RBS analysis using a traditional barrier silicon detector is investigated, and the differences with SiC detector is presented and discussed. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) detectors based on Schottky diodes were used to monitor low and high fluxes of photons and ions. An appropriate choice of the epilayer thickness and geometry of the surface Schottky contact allows the tailoring and optimizing the detector efficiency. SiC detectors with a continuous front electrode were employed to monitor alpha particles in a low-flux regime emitted by a radioactive source with high energy (>5.0 MeV) or generated in an ion implanter with sub-MeV energy. An energy resolution value of 0.5% was measured in the high energy range, while, at energy below 1.0 MeV, the resolution becomes 10%; these values are close to those measured with a traditional silicon detector. The same SiC devices were used in a high-flux regime to monitor high-energy ions, x-rays and electrons of the plasma generated by a high-intensity (10 W/cm) pulsed laser. Furthermore, SiC devices with an interdigit Schottky front electrode were proposed and studied to overcome the limits of the such SiC detectors in the detection of low-energy (∼1.0 keV) ions and photons of the plasmas generated by a low-intensity (10 W/cm) pulsed laser. SiC detectors are expected to be a powerful tool for the monitoring of radioactive sources and ion beams produced by accelerators, for a complete characterization of radiations emitted from laser-generated plasmas at high and low temperatures, and for dosimetry in a radioprotection field. [ABSTRACT FROM AUTHOR]

The elemental analysis method, with fast neutron associated particle imaging, holds immense potential in identifying concealed explosives, nuclear materials, and container security inspection, owing to its superior sensitivity and three-dimensional analysis capability compared to traditional neutron activation analysis technology. However, the temperature and irradiation fragility of the traditional associated particle detector curtails its usage in harsh environments such as space missions. The adoption of wide-bandgap semiconductor detectors, such as SiC, is expected to address this constraint. In this work, an associated particle imaging system based on a 4 × 4 SiC pixel detector was designed, built, and tested. The SiC detector exhibited consistent energy resolution and time performance between 25–150 °C. The built API system achieved an intrinsic time resolution of 1.8 ns and spatial resolution of at least 10 cm in the neutron flight direction. By utilizing the coincidence time spectrum and pixel SiC detector, the built system can provide the element content distribution in three-dimensional space. The results demonstrate the feasibility of employing SiC detectors in associated particle imaging systems and pave the way for developing a new type of sealed neutron tube with a prolonged lifetime and high environmental adaptability. [ABSTRACT FROM AUTHOR]

SiC detectors for charged particle identification can be assembled as a “telescope” device. It represents a powerful detector showing some advantages with respect to the traditional silicon ones. Their high gap energy, high density, high sensitivity, and high radiation resistance confer indisputable advantages with respect to silicon. A special geometry for this telescope is proposed and discussed in order to detect ions from low kiloelectron-volts energy up to energies of 100 MeV using different fluence. An active depth of 100~\mu \textm is employed for the ion stopper detector and an active superficial layer of 4- \mu \textm depth for the energy loss detector. Applications to low fluence use radioactive sources, while short plasma pulses generated by high intensity lasers are used at high fluence. [ABSTRACT FROM AUTHOR]

The transport properties of a series of Si and SiC diodes have been studied using the Ion Beam Induced Charge (IBIC) technique. Structural defects were induced into the samples during the irradiation with 17 MeV protons. The experimental values of the charge collection efficiency (CCE) vs bias voltages have been analyzed using a modified drift-diffusion model, which takes into account the recombination of carriers in the neutral and depletion regions. From these simulations, we have obtained the values of the carrier’s lifetime for pristine and irradiated diodes, which are found to degrade faster in the case of the SiC samples. However, the decrease of the CCE at high bias voltages is more important for the Si detectors, indicative of the lower radiation hardness of this material compared to SiC. The nature of the proton-induced defects on Si wafers has been studied by Positron Annihilation Spectroscopy (PAS) and Doppler Broadening Spectroscopy (DBS). The results suggest that the main defect detected by the positrons in p-type samples is the divacancy while for n-type at least a fraction of the positron annihilate in another defect. The concentration of defects is much lower than the number of vacancies predicted by SRIM. [ABSTRACT FROM AUTHOR]

fs pulsed lasers at an intensity of the order of 1018 W/cm2, with a contrast of 10−5, were employed to irradiate thin foils to study the target‐normal‐sheath‐acceleration (TNSA) regime. The forward ion acceleration was investigated using 1/11 µm thickness foils composed of a metallic sheet on which a thin reduced graphene oxide film with 10 nm thickness was deposited by single or both faces. The forward‐accelerated ions were detected using SiC semiconductors connected in time‐of‐flight configuration. The use of intense and long pre‐pulse generating the low contrast does not permit to accelerate protons above 1 MeV because it produces a pre‐plasma destroying the foil, and the successive main laser pulse interacts with the expanding plasma and not with the overdense solid surface. Experimental results demonstrated that the maximum proton energies of about 700 keV and of 4.2 MeV carbon ions and higher were obtained under the condition of the optimal acceleration procedure. The measurements of ion energy and charge states confirm that the acceleration per charge state is measurable from the proton energy, confirming the Coulomb–Boltzmann‐shifted theoretical model. However, heavy ions cannot be accelerated due to their mass and low velocity, which does not permit them to be subjected to the fast and high developed electric field driving the light‐ion acceleration. The ion acceleration can be optimized based on the laser focal positioning and on the foil thickness, composition, and structure, as it will be presented and discussed. [ABSTRACT FROM AUTHOR]

The laser irradiation of tantalum targets is presented for different pulsed laser intensities ranging from 1010 up to about 1018 W/cm2 and pulse durations from 9 ns up to 40 fs. The results show that the produced non‐equilibrium plasma accelerates Ta ions in the backward direction from values of the order of keV up to values of about 5 MeV. In thin foils, the forward plasma, developed behind the target along the direction of incoming laser, at intensities of about 1016 W/cm2 and 300 ps pulse duration, accelerates Ta ions at energies of the order of 4.6 MeV and produces charge states up to about 40+. For fs lasers at intensities of the order of 1018 W/cm2, only proton acceleration occurs up to 2.1 MeV while no Ta ions are accelerated, due to the reduced duration of the electric field and to the too high inertial mass of the Ta ions. [ABSTRACT FROM AUTHOR]

Measurements of ion acceleration in polymethylmethacrylate foils covered by a thin copper film irradiated by fs laser in target normal sheath acceleration regime are presented. The ion acceleration depends on the laser parameters, such as the pulse energy; depends on the irradiation conditions, such as the focal point position of the laser with respect to the target surface; and depends on the target properties, such as the metallic film thickness. The proton acceleration increases in the presence of the metallic film enhancing the plasma electron density, reaching about 1.6 MeV energy for a focal position on the target surface. The plasma diagnostics uses SiC detectors, absorber foils, Faraday cups, and gafchromic films. Employing p‐polarized laser light and a suitable oblique incidence, it is possible to increase the proton acceleration up to about 2.0 MeV thanks to the effects of laser absorption resonance due to plasma waves excitation. [ABSTRACT FROM AUTHOR]

Advanced targets based on graphene oxide and gold thin film were irradiated at high laser intensity (1018–1019 W/cm2) with 50‐fs laser pulses and high contrast (108) to investigate ion acceleration in the target‐normal‐sheath‐acceleration regime. Time‐of‐flight technique was employed with SiC semiconductor detectors and ion collectors in order to measure the ion kinetic energy and to control the properties of the generated plasma. It was found that, at the optimized laser focus position with respect to the target, maximum proton acceleration up to about 3 MeV energy and low angular divergence could be generated. The high proton energy is explained as due to the high electrical and thermal conductivity of the reduced graphene oxide structure. Dependence of the maximum proton energy on the target focal position and thickness is presented and discussed. [ABSTRACT FROM AUTHOR]