Single Crystal Diamond Detector Research Articles

Analysis of laser-generated plasma ionizing radiation by synthetic single crystal diamond detectors

Diamond based detectors have been used in order to analyze the ionizing radiation emitted from the laser-generated plasma. High energy proton/ion beams were generated at Prague Asterix Laser System (PALS) Centre by the sub-nanosecond kJ-class laser at intensities above 1016W/cm2.The tested detectors consisted of a photoconductive device based on high quality chemical vapor deposition (CVD) single crystal diamond, produced at Rome “Tor Vergata” University. They have been operated in planar configuration, having inter-digitized electrodes.The proposed diamond detectors were able to measure UV, X-rays, electrons and ions. They have been employed in time-of-flight (TOF) configuration and their reliability was checked by comparison with standard ion collectors (mostly used at PALS). Both the forward and backward expanding plasma was characterized in the experiment. The results indicate that diamond detectors are very promising for the characterization of fast proton and ion beams produced by high power laser systems.

Diamond detectors for fast neutron measurements at pulsed spallation sources

The performance of a single crystal diamond (4.7x4.7x0.5mm3 active volume) detector was tested in the ISIS pulsed neutron beam using biparametric (time of flight and pulse height) data acquisition. Three characteristic regions in the biparametric spectra are observed: i) low pulse height events with very short time of flight induced by γ-rays; ii) low pulse height events at longer flight times (i.e. neutron energies En > 3.5–6 MeV), possibly due to neutron elastic scattering off 12C; iii) events with large pulse height and flight times corresponding to En > 6 MeV mainly due to inelastic reactions such as 12C(n,α)9Be and 12C(n,n')3α. The potential use of this detector is discussed in relation to the ChipIr neutron beam line for fast neutron irradiation of electronic components at the ISIS spallation source.

Thermal and fast neutron dosimetry using artificial single crystal diamond detectors

Abstract In this work we propose the artificial Single Crystal Diamond (SCD) detector covered with a thin layer (0.5 μm/4 μm) of 6 LiF as a simultaneous thermal and fast neutron fluence monitor. Some interesting properties of the diamond response versus the neutron energy are evidenced thanks to Monte Carlo simulation using the MCNPX code which allows to propose the diamond detector also as an ambient dose equivalent (H∗(10)) monitor (REM counter).

Diamond detectors for fast neutron irradiation experiments

Single-crystal diamond detectors (SDD) were tested in view of their use as neutron beam monitors at fast neutron irradiation facilities. First results on time of flight (ToF) and energy resolution obtained at the ISIS pulsed neutron source and at the Physikalisch-Technische Bundesanstalt (PTB) with SDD of different thicknesses are presented. The peculiar double pulse structure of the ISIS proton beam does not seem to prevent SDD to be used for deriving the neutron energy spectrum from the measured ToF in the energy range up to 20 MeV. Further developments aimed at full exploitation of the biparametric (time and pulse height) output of the device are discussed.

Development of On-Line Tritium Monitor Based Upon Artificial Diamond for Fusion Applications

In this paper a novel on-line tritium monitor is presented. It is made with a single crystal diamond detector (SCD) covered with a thin layer of LiF 95% enriched in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li. Thermal neutrons impinging on the LiF layer produce α and T ions which are detected by the active diamond. The pulse height spectrum shows two separated peaks due to α and T ions respectively. By a proper calibration in a reference thermal flux the number of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li atoms and thus the absolute n+ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li→α+T reaction rate per unitary flux can be established. Once calibrated the detector can be used to measure the tritium production. Due to the many outstanding properties of diamond this detector could operate in the harsh working conditions of a fusion breeding blanket. A test of this detector was performed at the 14 MeV Frascati Neutron Generator (FNG). The detector was inserted inside a mock-up of the European Helium Cooled Lithium Lead (HCLL) Tritium Blanket Module (TBM), designed to validate the neutronic database for fusion application. The mock-up of the TBM was designed to perform a full set of experiments to validate tritium production code prediction comparing the experimental results with calculations. The measured tritium rates with the Li-Diamond detector are described in this paper. Comparison with calculations is in progress and will be reported in a future paper.

Full characterization of laser-accelerated ion beams using Faraday cup, silicon carbide, and single-crystal diamond detectors

Multi-MeV beams of light ions have been produced using the 300 picosecond, kJ-class iodine laser, operating at the Prague Asterix Laser System facility in Prague. Real-time ion diagnostics have been performed by the use of various time-of-flight (TOF) detectors: ion collectors (ICs) with and without absorber thin films, new prototypes of single-crystal diamond and silicon carbide detectors, and an electrostatic ion mass spectrometer (IEA). In order to suppress the long photopeak induced by soft X-rays and to avoid the overlap with the signal from ultrafast particles, the ICs have been shielded with Al foil filters. The application of large-bandgap semiconductor detectors (&amp;gt;3 eV) ensured cutting of the plasma-emitted visible and soft-UV radiation and enhancing the sensitivity to the very fast proton/ion beams. Employing the IEA spectrometer, various ion species and charge states in the expanding laser-plasma have been determined. Processing of the experimental data based on the TOF technique, including estimation of the plasma fast proton maximum and peak energy, ion beam currents and total charge, total number of fast protons, as well as deconvolution processes, ion stopping power, and ion/photon transmission calculations for the different metallic filters used, are reported.

Time structure of ns duration bunches with single crystal diamond detector

A single crystal diamond detector (SC-DD) has been used to obtain the time structure of bunches with lengths between 4 and 88 ns. This was achieved by setting an electronic chain based on a time-to-amplitude converter (TAC), which used the output of the diamond detector as the start of the time interval, and the accelerator RF as the stop. Moreover, the SC-DD not only provided the time information, but also the energy of the beam.

Experimental response functions of a single-crystal diamond detector for 5–20.5 MeV neutrons

A single crystal diamond detector was exposed to quasi mono-energetic neutron fields in the energy range from 5 to 20.5 MeV. Response functions of such a detector were measured for the first time for neutron energies above 14 MeV. The pulse height spectra showed sharp peaks at specific energies. These peaks result from neutron induced charged particle reactions occurring in carbon at different neutron energies. The centroid of the peaks due to the 12C(n,α) 9Be reaction permitted, by means of the reaction Q-values, to point out a good linearity of the detector response versus neutron energy and a good intrinsic energy resolution of about 56 keV at full width at half maximum. The results reveal that single crystal diamond detectors are good candidates as high resolution fast neutron spectrometers for nuclear fusion applications and for systematic studies of beam and target characteristics for neutron-producing reactions.

Lateral IBIC characterization of single crystal synthetic diamond detectors

AbstractIn order to evaluate the charge collection efficiency (CCE) profile of single‐crystal diamond devices based on a p‐type/intrinsic/metal configuration, a lateral Ion Beam Induced Charge (IBIC) analysis was performed over their cleaved cross sections using a 2 MeV proton microbeam. CCE profiles in the depth direction were extracted from the cross‐sectional maps at variable bias voltage. IBIC spectra relevant to the depletion region extending beneath the frontal Schottky electrode show a 100% CCE, with a spectral resolution of about 1.5%. The dependence of the width of the high efficiency region from applied bias voltage allows the constant residual doping concentration of the active region to be evaluated. The region where the electric field is absent shows an exponentially decreasing CCE profile, from which it is possible to estimate the diffusion length of the minority carriers by means of a drift–diffusion model. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Neutron Spectroscopy by Means of Artificial Diamond Detectors Using a Remote Read Out Scheme

Artificial crystal diamond neutron detectors are under test at JET tokamak since 2003 and they have demonstrated to be reliable and stable as well as to withstand the harsh working condition available in a large tokamak. Up to now they were used to measure the total and time dependent neutron emission while neutron spectroscopy was never attempted. On the other hand neutron spectrometry con yields important information on the burning plasma and it is requested for future experiments that will use DT plasmas so producing 14 MeV neutrons. Neutron spectrometry can only be attempted by using single crystal diamond (SCD) which, as it has been demonstrated, can show an energy resolution (FWHM) as low as 0.5%. However, in a future fusion reactor such as ITER, the huge neutron and gamma fluxes as well as the high temperature will not allow the electronics to be located close to the detector measuring point and near the plasma. For this reason it is necessary to develop a new approach in which new detectors able to withstand harsh environments and the electronics are far apart. This is a very challenging task if it is devoted to perform signal Pulse Height Analyses (PHS) with high energy resolution. To exploit this concept a SCD detector covered with a thin layer of 6LiF was installed at JET during the 2008 experimental campaigns and equipped with a remote read-out scheme located about 100 m away from the detector. The detector's signal was transported up to a conceptually new fast charge amplifier (FCA) developed to fulfil the task by means of a high frequency, single, low attenuation, super-screened cable. This FCA is able to read, stretch (up to 100 ns) and amplify the small (some μV) and ultra fast (<; 100 ps wide) signal produced by the radiation in the diamond detector. The signal amplified by the FCA was then processed through a commercial fast digitizer (NI-5114) 250 Ms/sec, 200 MHz equipped with 64 MB ram memory. Both signal amplitude and area can be used to get a PHS spectrum demonstrating the unique performances of the FCA. In the present paper the results obtained at JET are reported as well as the first attempt to get 14 MeV neutron spectrometry using the 14 MeV Frascati Neutron Generator.

Development of diamond-based X-ray detection for high-flux beamline diagnostics

High-quality single-crystal and polycrystalline chemical-vapor-deposition diamond detectors with platinum contacts have been tested at the white-beam X28C beamline at the National Synchrotron Light Source under high-flux conditions. The voltage dependence of these devices has been measured under both DC and pulsed-bias conditions, establishing the presence or absence of photoconductive gain in each device. Linear response consistent with the theoretically determined ionization energy has been achieved over eleven orders of magnitude when combined with previous low-flux studies. Temporal measurements with single-crystal diamond detectors have resolved the nanosecond-scale pulse structures of both the NSLS and the APS. Prototype single-crystal quadrant detectors have provided the ability to simultaneously resolve the X-ray beam position and obtain a quantitative measurement of theflux.

Single crystal artificial diamond detectors for VUV and soft X-rays measurements on JET thermonuclear fusion plasma

Diamond appears to be a promising material for VUV and soft X-ray radiation detection. Its wide band-gap (5.5 eV) results in a very low leakage current (it can operate above room temperature) and its electronic properties (high carrier mobility) allow a fast time response. More importantly, it is optimally suited for harsh environment applications, like those in the JET Tokamak located at the Culham laboratory (UK). Its extreme radiation hardness is well known and another interesting feature, again related to the wide band-gap, is its selective sensitivity to radiation with wavelengths shorter than 225 nm (visible-blind detectors).We report on the performances of two photodetectors based on Chemical Vapor Deposition (CVD) single crystal diamonds, one optimized for extreme UV detection, the other for soft X-ray radiation detection in the 0.8–8 keV range. These detectors have been fabricated at Roma “Tor Vergata” University using a p-type/intrinsic/metal configuration and they behave like photodiodes allowing operation with no external applied voltage. They have been installed on JET inside a vacuum chamber with a direct horizontal view of JET plasma without any wavelength selection. Their low thickness, low sensitivity to gamma ray and the unbiased operation mode make both detectors ideal for a Tokamak environment. The measurements routinely performed at JET show a low intrinsic dark current (∼0.01 pA) and very high signal to noise ratio (50 dB). Both detectors show a fast response and their signals are acquired using an electronic chain and ADC able to operate at 200 kHz, providing very interesting results for MHD and Edge Localized Modes (ELMs) instability studies on fusion plasmas.

Single crystal CVD diamond detector for high resolution dose measurement for IMRT and novel radiation therapy needs

One of the main aims for the improvement of the metrology during cancer treatment is the development of new tools for the real time measurement of the dose delivered to the patient. In the frame of The MAESTRO project ( Methods and Advanced Equipment for Simulation and Treatment in Radio-Oncology, 6th FP) CEA-LIST in collaboration with the Gustave Roussy Institute (IGR in France) and the Institute of Nuclear Physics (IFJ in Poland) have realised clinical tests towards the use of single crystal diamond detectors (SCDD) for dose measurements for Intensity Modulated Radiation Therapy (IMRT). We present here a summary of the most significant steps realised with our dosimeter for the evaluation of IMRT clinical tests. After a brief presentation of the optimised single crystal diamond growth performed at CEA, we probed the performances of the SCDD with conventional radiotherapy fields. Performance evaluated in agreement with IAEA 398 Code of practise allows the dosimeter to be tested in IMRT beams. The evaluation of the doses measured with our 0.534 mm 3 SCDD is compared respectively to that obtained with the 0.125 cm 3 air ionisation chamber (IC) and with the TPS (Treatment Planning System) calculations respectively. The results exhibit a good agreement between the doses evaluated with the SCDD, the IC and TPS calculations. These very promising results show the potentiality of diamond for such a use and open up the field towards novel applications such as for very small beam dosimetry. For this specific topic a new miniaturised dosimeter is currently being developed at CEA and is briefly presented here.

Light intensity dependence of photocurrent gain in single-crystal diamond detectors

The authors report on the photocurrent gain in a diamond photodetector that has two nonohmic contacts connected back-to-back. This photocurrent gain strongly depends on both the deep-ultraviolet (DUV) light intensity and the applied voltage. In addition, the gain is accompanied by a slow response. The gain is observed to originate from a metal/diamond interface trap center. Numerical analysis discloses that the photocurrent-voltage characteristics follow thermionic-field emission tunneling at low DUV light intensity and field-emission tunneling at high DUV light intensity. The deep traps are thought to produce a thin interface barrier layer at the metal/diamond interface under DUV illumination, which is responsible for the tunneling processes.

Single crystal chemical vapor deposited diamond detectors for intensity-modulated radiation therapy applications

We report here on first intensity-modulated radiation therapy (IMRT) clinical tests performed at the Gustave Roussy Institute in France using one small (0.117 mm3) synthetic single crystal diamond detector (SCDD). We report the comparison between the point doses evaluated with our detector, with a PTW semiflex air ionization chamber (0.125 cm3) and calculated with the treatment planning system (TPS), respectively. The obtained results show a maximum difference of 2.3% for the diamond detector and of 4.6% for the ionization chamber, as compared with the TPS calculations. These very promising results show the potentiality of chemical vapor deposited SCDD for dosimetry of IMRT fields and opens up the field for diamond dosimeters toward novel applications such as very small beam monitoring.

A single-crystal diamond-based thermal neutron beam monitor for instruments at pulsed neutron sources

Single-crystal diamond detectors manufactured through a Chemical Vapour Deposition (CVD) technique are recent technology devices that have been employed in reactor and Tokamak environments in order to detect both thermal and almost monochromatic 14 MeV neutrons produced in deuterium–tritium ( d–t) nuclear fusion reactions. Their robustness and compactness are the key features that can be exploited for different applications as well. Aim of the present experimental investigation is the assessment of the performance of a diamond detector as a thermal neutron beam monitor at pulsed neutron sources. To this aim, a test measurement was carried out on the Italian Neutron Experimental Station (INES) beam line at the ISIS spallation neutron source (Great Britain). The experiment has shown the capability of these devices to work at a pulsed neutron source for beam monitoring purposes. Other interesting possible applications are also suggested.

Neutron Detectors Based Upon Artificial Single Crystal Diamond

This paper reports about state-of-the-art artificial Single Crystal Diamond (SCD) neutron detectors based on a multilayered structure and grown by chemical vapour deposition (CVD) technique. Multilayered SCD detectors covered with a thin layer of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> LiF allow the simultaneous detection of both slow and fast neutrons and can operate in pulse and current mode. These detectors can also be produced with a thin layer of Boron. Application of SCD detectors to neutron detection around fusion tokamak is reported. Some problems related to the processing of the very fast electrical pulse produced by diamond are addressed and the achieved and foreseen development of the processing electronics is reported as well.

Thermal neutron dosimeter by synthetic single crystal diamond devices

We report on a new solid state dosimeter based on chemical vapor deposition (CVD) single crystal diamond fabricated at Roma “Tor Vergata” University laboratories. The dosimeter has been specifically designed for direct neutron dose measurements in boron neutron capture therapy (BNCT). The response to thermal neutrons of the proposed diamond dosimeter is directly due to 10B and, therefore, the dosimeter response is directly proportional to the boron absorbed doses in BNCT. Two single crystal diamond detectors are fabricated in a p-type/intrinsic/metal configuration and are sandwiched together with a boron containing layer in between the metallic contacts (see Fig.1). Neutron irradiations were performed at the Frascati Neutron Generator (FNG) using the 2.5 MeV neutrons produced through the D(d,n) 3He fusion reaction. Thermal neutrons were then produced by slowing down the 2.5 MeV neutrons using a cylindrical polymethylmethacrylate (PMMA) moderator. The diamond dosimeter was placed in the center of the moderator. The products of 10B(n,α)Li nuclear reaction were collected simultaneously giving rise to a single peak. Stable performance, high reproducibility, high efficiency and good linearity were observed.

Single crystal CVD diamonds as neutron detectors at JET

This paper reports on the three new Single Crystal Diamond (SCD) detectors installed at JET for the 2008 Restart campaign. The yields of total neutrons produced during DD plasma pulses as well as the time dependent neutron emission have been measured. The three detectors present some main new developments as for their fabrication characteristics, embeddings and electronic chains. The first detector is 200 μm thick and is embedded in paraffin. The second detector is 104 μm thick and is covered by a thermally evaporated 3 μm thick 6LiF film in order to detect the total and the 14-MeV neutrons. In addition, it is surrounded by a 2.5-cm thick polyethylene shield to enhance its thermal neutron response. The third detector is operated in an innovative way that is with a single low capacitance super-screened cable and its whole electronic chain put outside the JET Torus Hall. Furthermore it uses fast electronics, suitable to the fast diamond response pulse (<1 ns). It is 75 μm thick, covered by a 3 μm thick 6LiF film and surrounded by a 2.5-cm-thick layer of polyethylene. All the detectors have been previously tested and qualified at the ENEA-FNG with 2.5 and 14.7 MeV neutron beams. After the description of their main features, the results of the measurements, so far performed, are reported showing a very good matching with other standard detectors, such as fission chambers, routinely used at JET.

Development of Diamond-Based X-ray Detection for High Flux Beamline Diagnostics

AbstractHigh quality single crystal and polycrystalline CVD diamond detectors with platinum contacts have been tested at the white beam X28C beamline at the National Synchrotron Light Source under high-flux conditions. The voltage dependence of these devices has been measured under DC and pulsed-bias conditions, establishing the presence or absence of photoconductive gain in each device. Linear response has been achieved over eleven orders of magnitude when combined with previous low flux studies. Temporal measurements with single crystal diamond detectors have resolved the ns scale pulse structure of the NSLS.