M. Angelone

The 14 MeV Frascati neutron generator

Abstract The 14-MeV Frascati neutron generator (FNG) uses the T(d, n)α fusion reaction to produce 5.0 × 10 11 n/s. In FNG a beam of deuterons is accelerated up to 300 keV by means of a linear electrostatic tube and directed onto a tritiated-titanium target containing 37 × 10 10 Bq of tritium. This paper describes the FNG facility and its auxiliary apparatus as well as the neutron source calibration performed using the associated α-particle method.

Extreme ultraviolet single-crystal diamond detectors by chemical vapor deposition

High-quality single-crystal diamond films, homoepitaxially grown by microwave chemical vapor deposition, have been used to produce diamond-based photodetectors. Such devices were tested over a very wide spectral range, from the extreme ultraviolet (UV) (20 nm) up to the near IR region (2400 nm). An optical parametric oscillator tunable laser was used to investigate the 210–2400 nm spectral range in pulse mode. In this region, the spectral response shows a UV to visible contrast of about 6 orders of magnitude. A time response shorter than 5 ns, i.e., the laser pulse duration, was observed. By integrating the pulse shape, a minor slow component was evidenced, which can be explained in terms of trapping–detrapping effects. Extreme UV gas sources and a toroidal grating vacuum monochromator were used to measure the device response down to 20 nm in continuous mode. In particular, the extreme UV He spectrum was measured and the He II m, 30.4 nmand He I 58.4 nm emission lines were clearly detected. The measured t...

High-quality diamond grown by chemical-vapor deposition: Improved collection efficiency in α-particle detection

Diamond films were grown on silicon by microwave chemical-vapor deposition using a CH4–H2 gas mixture. The crystalline quality of the films was assessed through their α-particle detection performance, a property highly sensitive to film quality, by using a 5.5 MeV 241Am source. A maximum collection efficiency η of 70%, 50% being the average value, was obtained in a 115-μm-thick sample after β-particle irradiation (“priming effect”). Unprimed efficiency η=50% maximum, 30% average, was also obtained on other samples. The dependence of the efficiency and the resolving power on the external electric field was studied as well. The results are interpreted by means of a Monte Carlo analysis of the α-particle detection process. It is concluded that, in the priming process, a saturation occurs of deep defects limiting the as-grown detector performance, and charge collection distance is only limited by grain boundaries located close to the substrate side. Therefore, there is indication that further improvement can ...

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...

High performance Li6F-diamond thermal neutron detectors

Fabrication reproducibility and high performance reliability were obtained in fissile-material-free thermal neutron detectors based on chemical vapor deposited diamond in a multilayered p-type/intrinsic/metal design. Under α particle irradiation, all the detectors (more than ten) have shown 100% charge collection efficiency and approximately 1.5% energy resolution. A Li6F layer was deposited on the detector surface as converting material for thermal neutrons through the Li6(n,α)T nuclear reaction. Both the 2.73MeV tritium and the 2.06MeV α peaks are detected and clearly resolved. Stable performance and excellent linear behavior of the count rate versus the incident neutron flux were observed.

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...

Absolute experimental and numerical calibration of the 14 MeV neutron source at the Frascati neutron generator

The absolute neutron yield of the 14 MeV Frascati neutron generator (FNG) is routinely measured by means of the associated alpha‐particle method with a silicon surface barrier detector (SSD). This paper describes the work carried out to characterize the neutron source in terms of absolute intensity and angle‐energy distribution of the emitted neutrons. The development of the measuring setup and the assessment of the measurement results are also reported. A complementary calibration procedure for validating the SSD results, based on the use of fission chambers and the activation technique, is also reported. An accurate analysis of the system has been performed via the Monte Carlo neutron and photon MCNP transport code. A detailed model of the neutron source that includes ion slowing down has been inserted into the MCNP code to permit a numerical calibration of the neutron source for comparison with the experimental results. The resulting agreement among the various methods is very good considering the unce...

Synthesis and characterization of a single-crystal chemical-vapor-deposition diamond particle detector

The growth conditions and the detection properties of a homoepitaxial diamond film, deposited in Roma “Tor Vergata” University Laboratories by microwave chemical vapor deposition on a high-pressure high-temperature single-crystal substrate are reported. An energy resolution as low as 1.1% was achieved when irradiating the device with 5.5 MeV Am241 α-particles. The dependence of the charge collection efficiency and the energy resolution on the applied voltage are reported as well. A clear saturation plateau was observed in both curves. Preliminary results with 14.8 MeV neutron irradiation are reported, showing a well separated C12(n,α0)Be9 reaction peak.

Systematic study of the normal and pumped state of high efficiency diamond particle detectors grown by chemical vapor deposition

The efficiency and charge collection distance (CCD) of nuclear particle detectors based on high quality diamond films grown by chemical vapor deposition (CVD) have been systematically studied as a function of the methane content in the growth gas mixture and for varying film thickness. The effects of preirradiation with β particles (pumping) have been thoroughly studied. The results fully support a recently proposed model [Marinelli et al., Appl. Phys. Lett. 75, 3216 (1999)] discussing the role of in-grain defects and grain boundaries in determining the charge collection spectra of CVD diamond films both in the normal and in the pumped state. The model allows us to quantitatively explain the dependence of CCD and efficiency on film thickness, giving a microscopic picture of the effects of preirradiation with ionizing radiation in CVD diamond films. The highest average CCD obtained is 145 μm in a 160 μm thick detector (corresponding to about 50% average efficiency), while the maximum value (about 70% effic...

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 2.0×1014 n/cm2. In the early stage of the irradiation procedure an improvement in the spectroscopic performance o...