[en] Many outstanding properties of diamond can, in principle, lead to the development of radiation detectors with interesting capabilities. In particular, diamond-based nuclear particle detectors are good candidates to replace silicon-based detectors in several fields, e.g. in high-flux applications such as next generation particle-accelerator experiments or beam monitoring. However, the high concentration of defects (grain boundaries, impurities) in synthetic diamond films can strongly limit the detector's performance. A significant increase in the efficiency of CVD diamond detectors is achieved by means of pre-irradiation (pumping) with β particles. We report here on a systematic study of the effects of pumping in high-quality microwave CVD diamond films. The efficiency (η) and charge collection distance (CCD) of nuclear particle detectors based on these films depend on the methane content in the growth gas mixture and on the film thickness. Both efficiency and CCD behave in a markedly different way in the as-grown and pumped states. Experimental data are found to agree with a recently proposed model (Appl. Phys. Lett. 75 (1999) 3216) discussing how in-grain defects and grain boundaries affect the charge collection spectra of CVD diamond detectors, before and after pumping. The dependence of pumping effects at different operating temperatures of the detector is also reported

[en] Purpose: Small field output correction factors have been studied by several research groups for the PTW 60019 microDiamond (MD) dosimeter, by comparing the response of such a device with both reference dosimeters and Monte Carlo simulations. A general good agreement is observed for field sizes down to about 1 cm. However, evident inconsistencies can be noticed when comparing some experimental results and Monte Carlo simulations obtained for smaller irradiation fields. This issue was tentatively attributed by some authors to unintentional large variations of the MD active surface area. The aim of the present study is a nondestructive experimental determination of the MD active surface area and active volume. Methods: Ten MD dosimeters, one MD prototype, and three synthetic diamond samples were investigated in the present work. 2D maps of the MD response were recorded under scanned soft x-ray microbeam irradiation, leading to an experimental determination of the device active surface area. Profiles of the device responses were measured as well. In order to evaluate the MD active volume, the thickness of the diamond sensing layer was independently evaluated by capacitance measurements and alpha particle detection experiments. The MD sensitivity, measured at the PTW calibration laboratory, was also used to calculate the device active volume thickness. Results: An average active surface area diameter of (2.19 ± 0.02) mm was evaluated by 2D maps and response profiles of all the MDs. Average active volume thicknesses of (1.01 ± 0.13) μm and (0.97 ± 0.14) μm were derived by capacitance and sensitivity measurements, respectively. The obtained results are well in agreement with the nominal values reported in the manufacturer dosimeter specifications. A homogeneous response was observed over the whole device active area. Besides the one from the device active volume, no contributions from other components of the housing nor from encapsulation materials were observed in the 2D response maps. Conclusions: The obtained results demonstrate the high reproducibility of the MD fabrication process. The observed discrepancies among the output correction factors reported by several authors for MD response in very small fields are very unlikely to be ascribed to unintentional variations of the device active surface area and volume. It is the opinion of the authors that the role of the volume averaging as well as of other perturbation effects should be separately investigated instead, both experimentally and by Monte Carlo simulations, in order to better clarify the behaviour of the MD response in very small fields.

[en] Pulsed x-ray dose measurements have been carried at maximum x-ray energies from 40 to 120 KeV out by using a single crystal epitaxial diamond sample grown by chemical vapor deposition (CVD). Delivered doses were between 0.1 and 10 mGy and pulse duration times between 0.01 and 0.5 s. Values of dose linearity index very close to 1 (between 1.02 and 1.07) at increasing x-ray energies and pulse decay times between 15 and 20 ms were obtained. The reproducibility was very good with no memory effects. CVD homoepitaxial diamond results to be very promising for x-ray diagnostic applications

[en] Carrier free paths in Chemical Vapour Deposition (CVD) diamond films depend on the presence of traps, which therefore strongly affect the performance of those CVD diamond based devices which rely on the electronic properties of the material, like radiation detectors. For the same reason, these devices can in turn be used as tools to study carrier dynamics. It is well known that some traps may be saturated by pre-irradiation with ionizing radiation (e.g. β-particles), a process called ''pumping'' or ''priming''. Not all traps behave in the same way. Due to the large bandgap of diamond, both shallow (not affected by pumping) and deep traps for electrons and holes may exist. We measured, using 5.5 MeV ²⁴¹Am α-particles, the response of high quality CVD diamond based detectors after successive annealing steps performed at selected temperatures. The analysis of the decay of the detector efficiency with annealing time at several temperatures allows a quantitative evaluation of the activation energy of these defects. Two main trapping centres connected to the pumping process were found, both related to holes, having activation energies of about 1.6 eV and 1.3 eV respectively. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] 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.

[en] A simple technique for measuring the electron and hole mean drift distance in chemical vapor deposition polycrystalline diamond in the as-grown and in the so-called pumped state obtained by ⁹⁰Sr β-particle irradiation is presented. To this purpose, the efficiency η of a diamond-based particle detector was measured using a 5.5-MeV ²⁴¹Am α-particle source. In particular, two different experimental setups were specifically designed and realized in order to perform a systematic study of the device efficiency as a function of the α-particle penetration depth, both in the positive and negative bias polarization. In the first setup, air is used as an absorbing layer in order to change the energy of the impinging α particles, while in the second one, the measurements were performed in vacuum and the incidence angle was varied in the 0 deg. -80 deg. range. The advantages of the latter setup are evidenced. The theoretical formula for the mean drift distances of carriers is derived using a properly modified Hecht model, and fitted to the data, allowing a separate evaluation of the charge collection distances of each carrier type (λ_e=μ_eτ_e sansser-tag(E) and λ_h=μ_hτ_h sansser-tag(E)). The obtained results unambiguously show that the pumping process is much more effective on hole conduction, λ_h being much greater than λ_e in the pumped state

[en] CVD diamond is an interesting material for radiation detection, its atomic number (Z = 6) is close to that of soft tissues (Z = 7.1) and it can also work in harsh environments. Since many years CVD diamond films have been grown at the Faculty of Engineering, Rome 'Tor Vergata' Univ., and in 1998 a collaboration with ENEA Fusion Div. was established to develop fast neutron monitors to be used in fusion tokamak environment. In this paper the first test of a 120 μm thick polycrystalline CVD diamond detector used for monitoring 14.7 MeV neutrons emission produced with the Frascati Neutron Generator (FNG) is reported. The detector operates in air and in pulse mode. The time irradiation profiles recorded with the CVD diamond detector were compared with those recorded by the standard monitors available at FNG (SSD, fission chamber, NE-213). Good stability and capability to operate in neutron flux up to 1.5 x 10⁸ n cm^-2 s^-1 was observed. The radiation hardness property was also investigated using a 460 μm thick film and these results are also reported. (authors)

[en] We report on a comparative study of transfer doping of hydrogenated single crystal diamond surface by insulators featured by high electron affinity, such as Nb_2O_5, WO_3, V_2O_5, and MoO_3. The low electron affinity Al_2O_3 was also investigated for comparison. Hole transport properties were evaluated in the passivated hydrogenated diamond films by Hall effect measurements, and were compared to un-passivated diamond films (air-induced doping). A drastic improvement was observed in passivated samples in terms of conductivity, stability with time, and resistance to high temperatures. The efficiency of the investigated insulators, as electron accepting materials in hydrogenated diamond surface, is consistent with their electronic structure. These surface acceptor materials generate a higher hole sheet concentration, up to 6.5 × 10"1"3 cm"−"2, and a lower sheet resistance, down to 2.6 kΩ/sq, in comparison to the atmosphere-induced values of about 1 × 10"1"3 cm"−"2 and 10 kΩ/sq, respectively. On the other hand, hole mobilities were reduced by using high electron affinity insulator dopants. Hole mobility as a function of hole concentration in a hydrogenated diamond layer was also investigated, showing a well-defined monotonically decreasing trend.

[en] The paper reports about the use of single-crystal Chemical Vapour Deposited (CVD) diamonds as radiation detectors in laser-matter interaction experiments on the ABC laser in ENEA – Frascati. The detectors have been designed and realized by University of Tor Vergata – Rome. The interdigital configuration and the new design of the bias-tee voltage supply units guarantee a fast time response. The detectors are sensitive to soft-X photons and to particles. A remarkable immunity to electromagnetic noise, associated with the laser-target interaction, makes them especially useful for the measurements of the time of flight of fast particles. A novel diamond assembly has been tested in plasmas generated by the ABC laser in the nanosecond regime at intensities I =10^13÷ 14 W/cm², where contributions from X rays, fast electrons and ions could be observed.

[en] In the present paper, the performances of single crystal diamond detectors 'ad hoc' designed to operate at high temperature are reported. The detectors were realized using commercial CVD single crystal diamond films, 500 micron thick with metal contacts deposited by sputtering method on each side. The new detector layout is based upon mechanical contacts between the diamond film and the electric ground. The detector was first characterized by measuring the leakage current as function of temperature and applied biasing voltage (I-V characteristics). The results obtained using two different metal contacts, Pt and Ag respectively, while irradiated with 14 MeV neutrons at the Frascati neutron generator (FNG) are reported and compared. It is shown that diamond detectors with Ag metal contacts can be properly operated in spectrometric mode up to 240^oC with energy resolution (FWHM) of about 3.5%.