S. Almaviva

Chemical vapor deposition diamond based multilayered radiation detector: Physical analysis of detection properties

Recently, solid state photovoltaic Schottky diodes, able to detect ionizing radiation, in particular, x-ray and ultraviolet radiation, have been developed at the University of Rome “Tor Vergata.” We report on a physical and electrical properties analysis of the device and a detailed study of its detection capabilities as determined by its electrical properties. The design of the device is based on a metal/nominally intrinsic/p-type diamond layered structure obtained by microwave plasma chemical vapor deposition of homoepitaxial single crystal diamond followed by thermal evaporation of a metallic contact. The device can operate in an unbiased mode by using the built-in potential arising from the electrode-diamond junction. We compare the expected response of the device to photons of various energies calculated through Monte Carlo simulation with experimental data collected in a well controlled experimental setup i.e., monochromatic high flux x-ray beams from 6 to 20 keV, available at the Diamond Light Sour...

Thermal and fast neutron detection in chemical vapor deposition single-crystal diamond detectors

Recently, a compact solid-state neutron detector capable of simultaneously detecting thermal and fast neutrons was proposed [M. Marinelli et al., Appl. Phys. Lett. 89, 143509 (2006)]. Its design is based on a p-type/intrinsic/metal layered structure obtained by Microwave Plasma Chemical Vapor Deposition (CVD) of homoepitaxial diamond followed by thermal evaporation of an Al contact and a L6iF converting layer. Fast neutrons are directly detected in the CVD diamond bulk, since they have enough energy to produce the C12(n,α)B9e reaction in diamond. Thermal neutrons are instead converted into charged particles in the L6iF layer through the L6i(n,α)T nuclear reaction. These charged particles are then detected in the diamond layer. The thickness of the L6iF converting layer and the CVD diamond sensing layer affect the counting efficiency and energy resolution of the detector both for low- (thermal) and high-energy neutrons. An analysis is carried out on the dynamics of the L6i(n,α)T and the C12(n,α)B9e reactio...

Radiation tolerance of a high quality synthetic single crystal chemical vapor deposition diamond detector irradiated by 14.8 MeV neutrons

Diamond exhibits many properties such as an outstanding radiation hardness and fast response time both important to design detectors working in extremely radioactive environments. Among the many applications these devices can be used for, there is the development of a fast and radiation hard neutron detector for the next generation of fusion reactors, such as the International Thermonuclear Experimental Reactor project, under construction at Cadarache in France. A technology to routinely produce electronic grade synthetic single crystal diamond detectors was recently developed by our group. One of such detectors, with an energy resolution of 0.9% as measured using an A241m α particle source, has been heavily irradiated with 14.8 MeV neutrons produced by the Frascati Neutron Generator. The modifications of its spectroscopic properties have been studied as a function of the neutron fluence up to 2.0×1014u2002n/cm2. In the early stage of the irradiation procedure an improvement in the spectroscopic performance o...

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 6LiF 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.

Characterization of damage induced by heavy neutron irradiation on multilayered L6iF-single crystal chemical vapor deposition diamond detectors

High performance neutron detectors sensitive to both thermal and fast neutrons are of great interest to monitor the high neutron flux produced, e.g., by fission and fusion reactors. An obvious requirement for such an application is neutron irradiation hardness. This is why diamond based neutron detectors are currently under test in some of these facilities. In this paper the damaging effects induced in chemical vapor deposition (CVD) diamond based detectors by a neutron fluence of ∼2×1016u2002neutrons/cm2 have been studied and significant changes in spectroscopic, electrical, and optical properties have been observed. The detectors are fabricated using high quality synthetic CVD single crystal diamond using the p-type/intrinsic/Schottky metal/L6iF layered structure recently proposed by Marinelli et al. [Appl. Phys. Lett. 89, 143509 (2006)], which allows simultaneous detection of thermal and fast neutrons. Neutron radiation hardness up to at least 2×1014u2002n/cm2 fast (14 MeV) neutron fluence has been confirmed s...

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 detectors 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.

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 (10)B 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)(3)He 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 (10)B(n,alpha)Li nuclear reaction were collected simultaneously giving rise to a single peak. Stable performance, high reproducibility, high efficiency and good linearity were observed.

X-Ray Detection by Using CVD Single Crystal Diamond Detector

A number of diamond detectors, obtained by a two-step growing procedure by chemical vapour deposition (CVD) technique, have been grown on a low cost commercial high temperature high pressure (HTHP) Ib single crystal diamond. The first diamond layer is 15 mu m thick and heavily doped by boron. A 35 mum thick layer of intrinsic high purity and high quality CVD diamond is then grown on top of the doped diamond. A metal contact (aluminium 100 nm thick) is deposited on top of the intrinsic diamond. One of these devices has been placed in the beam of the station 9.1 of Synchrotron Radiation Source at Daresbury laboratory (UK) and several tests have been performed to assess the linearity of responsivity as a function of the photon flux, the long term stability, and the response to the sudden onset of radiation. The device shows an excellent linearity and long term stability (tested in the order of hours), while the response to the onset of radiation have still to be understood. The results obtained can open up the path to the construction of extremely radiation hard devices to be exploited as X-ray beam monitor.

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 6Li. 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 6Li atoms and thus the absolute n+6Li→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.

High-resolved fluorescence imaging of x-ray micro-radiographies on novel lif detectors

A novel X-ray imaging detector based on optical reading of photoluminescent color centers in lithium fluoride, LiF, is presented. Its main characteristics – i.e. high spatial resolution on a large field of view, wide dynamic range, versatility and simplicity of use – make it a high performance imaging detector for applications in X-ray microscopy, photonic devices, Extreme UltraViolet (EUV) lithography, and materials science, as well as in the characterization of intense X-ray sources, including Free Electron Laser (FEL). nThe peculiarities of the LiF imaging detector overcome some of the limitations of other commonly used ones, and can be exploited for X-ray microscopy in very simple configurations, such as lensless techniques, even for in vivo investigations of biological samples. nAdvanced optical microscopy techniques have been used to obtain highly–resolved microradiographies of biological specimens, performed in absorption contrast mode. Its peculiarities seem suitable also for use in phase-contrast experiments. The LiF-based detector versatility allows improvements in order to optimize its response and sensitivity.