M. Jung

Feasibility of a semiconductor dosimeter to monitor skin dose in interventional radiology.

The design and preliminary test results of a semiconductor silicon dosimeter are presented in this article. Use of this dosimeter is foreseen for real-time skin dose control in interventional radiology. The strong energy dependence of this kind of radiation detector is well overcome by filtering the silicon diode. Here, the optimal filter features have been calculated by numerical Monte Carlo simulations. A prototype has been built and tested in a radiological facility. The first experimental results show a good match between the filtered semiconductor diode response and an ionization chamber response, within 2% fluctuation in a 2.2 to 4.1 mm Al half-value layer (HVL) energy range. Moreover, the semiconductor sensor response is linear from 0.02 Gy/min to at least 6.5 Gy/min, covering the whole dose rate range found in interventional radiology. The results show that a semiconductor dosimeter could be used to monitor skin dose during the majority of procedures using x-rays below 150 keV. The use of this device may assist in avoiding radiation-induced skin injuries and lower radiation levels during interventional procedures.

A new method for evaluation of transport properties in CdTe and CZT detectors

Abstract The precise evaluation of transport properties of both electrons and holes in compound semiconductor detectors, like CdTe or CZT, is of great interest for the development of these devices. Although the electron behaviour can be measured in most cases, that of holes is much more difficult. Both alpha or gamma radiations, as well as conventional computer simulations, have shown their limits. In this paper, we present a new approach based on computer simulations, which are performed at various energies. This model will be applied on various kinds of materials. The results will be discussed in terms of sensitivity of the method, electronic noise level as well as electric field distribution within the detector.

Diamond X-ray personal dosimetry. Numerical evaluation against silicon response

Abstract The performances achieved by diamond planar detectors are presented in comparison with high-sensitive personal silicon semiconductor dosimetric responses. Numerical simulation results are discussed in terms of diode signal pulse height analysis. The study already allows the proposition of thin layers of diamond for personal dosimetry of X-rays ranging between 20 and 660 keV .

Thermalization patterns for broad neutron energy range real-time semiconductor personal dosimetry

This paper concerns neutron detection below 500-keV energies. The paper studies numerically simulated responses from thermalized neutrons. These neutrons are induced by monoenergetic dose equivalent neutron beams ranging between 14 MeV and 1 eV. Results are first discussed against several moderating stack efficiencies. The discussion analyzes the lowest standard deviation relative to the mean thermalized flux calculated over several incident neutron energy bands of which upper values decrease from 14 MeV to 100 keV. The simulated responses show near 50% response accuracy if monitoring neutrons in the range 1 eV to 100 keV with a small 1.5-cm radius 5-cm thick polyethylene cylinder. Adding neutron converter foils, the efficiency is then calculated against secondary photon detection. An overlap between fast neutron detection efficiencies and those at lower energies is found to be possible, so that similar diodes can be used for both recoil protons and radiative photon detection.

Gamma-rays and fast neutron responses calculations for personal electronic dosimetry purpose

Abstract Real-time dosimeters with small size N-type silicon diodes are proposed here for low-dose rate controls. Numerical simulations are used to predict the responses of various associated filters, neutron converters and sensors. The monitor is foreseen to work as a counter with acceptance cut-offs set on each individual pulse height. Discussions are undertaken against the minimal outline necessary to reach convenient measurement accuracies in unknown gamma–neutron fields.

Fast-neutron personal real-time dosemeter for mixed neutron and gamma fields

In recent years silicon detectors have nearly replaced Geiger-Muller tubes in personal dosemeters for gamma and X- rays. Several tentatives have been undertaken to extend these dosemeters to fast neutrons, but problems arose since in the generally present mixed fields it appeared difficult to separate the effect of both kind of radiations. In this paper, a method for fast neutron monitoring is investigated. It results from a computer simulation analysis of fast neutrons and gamma-ray interactions in silicon detectors. For neutron energies between 0.75 and 15 MeV, it proposes a real time personal dosemeter, with a response accuracy better than 30% in a mixed neutron and gamma-ray field.

Theoretical 137Cs γ-ray detection sensitivity curves calculated for silicon sensor devices

Abstract There are two different domains of using silicon semiconductors as gamma-ray dosimeters which are widely separated if one considers the dose-rate sensitivity levels which can be reached, namely the low-dose-rate region which is that of the personal monitoring and the high-level one corresponding mainly to area survey or catastrophic flash accidents (for example). Such sensitivities depend strongly on the properties of the detector (surface, carrier lifetime) as well as on the working conditions (applied bias, integration time) and on detector mounting (shielding). All these points are discussed here with the help of the theoretical sensitivity curves we calculated for a 7.6 mm 2 n-type silicon detector mounted behind Sn and Al γ-ray moderators. These calculations are done for the 662 keV 137 Cs γ-rays which are used in our studies mostly as the normalization point of all of our graphs.