An epitaxial diamond detector obtained by CVD (Chemical Vapor Deposition) has been used in order to monitor
X-ray pulses from a radiological portable X-ray generator commonly used in hospitals. X-ray maximum energies
varied from 50 to 120 KeV, while (electron anodic current)x(time duration) products were in the range from 20 to
100 mAs. Current pulses were recorded and from their shapes the timing and the collected charge were calculated
and compared with those obtained by standard 6 cm3 ionization chambers and by a silicon diode arrays used in
quality assurance programs for radiological X-ray apparatuses. Both diamond detector and silicon array display a
standard deviation in time recording of 0.3% in the time range from 0.15 up to 2.5 s. The integrated current recorded
from diamond is linear with respect the dose recorded by the ionization chamber from 5 up to 125 mGy, with a
standard deviation on single points of the order of 0.5%. The stability of the detector is very good even without a
priming treatment generally used in order to stabilize diamond dosimeters. Homogeneity of the detector in terms of
its response was tested by means of alpha particles, which indicate an energy resolution of 0.7%, quite close to that
of a standard surface barrier silicon detector. These results indicate that epitaxial diamond could be considered ready
to be used in standard quality control procedures concerning radiological X-ray apparatuses.
We present a systematic study of the growth of polycrystalline diamond thin films on W wires and tips by hot filament assisted chemical vapor deposition for x-ray detection purposes. We carry out correlations between scanning electron microscopy (SEM) observations and micro- Raman spectra, while varying different growth parameters. SEM observations show a uniform covering of the substrate, with growth rates ranging from 0.5 to 1.5 micrometers /h. All (mu) - R spectra show a well defined diamond peak at 1330.8-1333.7 cm-1 together with abroad structure at 1400-1600 cm-1 and a luminescence background extending over the whole scanned range. A close analysis shows that best quality is obtained with the lowest diameter substrates, at the lowest CH4 concentration and at a low pressure. Some depositions have been studied as x-ray detectors and their sensitivity at low energy and 6 MeV beam evaluated, showing a good response with respect to standard ionization chambers.
This paper deals with the evaluation of neutron spectra in a wide energy range by unfolding the responses of different passive detectors. The unfolding method is based on the BUNKI code which has been optimized for this application. The major goal of this investigation is to obtain a better evaluation of the neutron dose equivalent both in accelerator environments and cosmic ray fields. This unfolding method has been tested in the neutron field at the CERN SPS facility, which is characterized by a neutron spectrum similar to that of cosmic rays. Finally the same procedure has been applied to evaluate the neutron cosmic ray spectrum on the mountain of Matterhorn at an altitude of 3500 m. In particular the high energy region of the neutron spectrum has been obtained taking into account the difference between the proton and neutron cross sections of bismuth, as recently proposed by one of the authors on the basis of theoretical and experimental data re-examination.
In the electron linear accelerators used for radiotherapy by high energy electrons or gamma rays, there is a non negligible production of neutrons by photodisintegration or electrodisintegration reactions on the high Z components of the head machine (target, flattening filter, collimators). At the Experimental Physics Department of Torino University, Torino, Italy an experimental and theoretical evaluation has been performed on the undesired neutron production in the MD Class Mevatron Siemens accelerator used at the Radiotherapy Department of S. Giovanni Battista A.S. Hospital for cancer therapy by a 15 MV gamma ray beam. A simulation of the total process has been carried out, using EGS4 MonteCarlo computer code for the evaluation of photoneutron spectra and MCNP code for the neutron transport in the patient's body. The geometrical description both of the accelerator head in EGS4 and of the anthropomorphous phantom in MCNP have been highly optimized. Experimental measurements have been carried out by bubble detectors BD 100R appropriately allocated inside a new phantom in polyetylene and plexiglass, especially designed for this purpose.
KEYWORDS: Sensors, Electrons, Spectroscopy, Monte Carlo methods, Electric field sensors, Gamma radiation, Sensor performance, Computer programming, Picosecond phenomena, Computer simulations
Simulations of spectroscopic performances of CdTe detectors by means of a Monte Carlo code have been recently reported. The computer code was demonstrated to be an extremely useful tool in simulating the spectral response of CdTe to gamma rays and in understanding the detailed effects of physical and electronic parameters on the experimental performances. In the present work, the attention is focused on the various aspects of the CdTe response to Co gamma rays, in an energy range which is extremely interesting for practical applications of CdTe spectroscopy. Spectra are presented for different experimental conditions particularly in connection with the rise time distributions and with the spatial distribution of the electric field in the detector. A precise correlation is established between the energy distribution and the pulse rise time distribution: the spectra obtained by a selection of a particular rise time interval are presented and discussed, and the conditions for reaching the best energy resolution are indicated. These conditions depend on the material quality and on the electrical field distribution.
A study concerning the use of a 1 cm2 p-i-n (alpha) -Si:H structure coupled to a 1 cm3 CsI(Tl) scintillator is presented and discussed as a survey meter in the range from 20 to 125 keV x ray peak energy. A particular mesa etch, coupled with standard photolithography, lowers dark current in the pA region, allowing the use of the detector in the photovoltaic mode. In this work, we describe the details of detector fabrication, the various steps of detector simulation in order to look for detector performance improvements, and the different stages of detector testing in the reported energy range. For each energy, the linearity of the detector response as a function of the dose rate has been accurately measured and compared with standard ionization chambers of different volumes. Finally, the effective energy reconstruction and the instrument calibration is presented and discussed. Wearing-on applications, similar to film badges, are envisaged and possible solutions are introduced and discussed.
Photostable hydrogenated amorphous-silicon films have been deposited by disilane decomposition in a quartz reactor 2 m in length and 5 in. in diameter. A deposition temperature of around 420 degree(s)C, pressure in the interval of 5 to 10 Torr, and gas holding time around 250 sec are the most appropriate parameters to deposit fairly good quality films having density states ranging from 1016 to 1017 cm-3 eV-1 and Urbach's tail from 70 meV to 100 meV.
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