Application of Monte Carlo calculations to calibration of anthropomorphic phantoms used for activity assessment of actinides in lungs.

This paper reports on a new utility for development of computational phantoms for Monte Carlo calculations and data analysis for in vivo measurements of radionuclides deposited in tissues. The individual parameters of each worker can be acquired for an exact geometric representation of his or her anatomy, which is particularly important for low-energy gamma ray emitting sources such as thorium, uranium, plutonium and other actinides. The software discussed here enables automatic creation of an MCNP input data file based on computed tomography (CT) scanning data. The utility was first tested for low- and medium-energy actinide emitters on Livermore phantoms, the mannequins generally used for lung counting, in order to compare the results of simulation and measurement. From these results, the utility's ability to study uncertainties in in vivo calibration were investigated. Calculations and comparison with the experimental data are presented and discussed in this paper.

The reduction of limits of detection in in vivo counting of low-energy photon emitters by optimising the shape and size of detectors.

This paper compares three ways to reduce the detection limits of in vivo measurements by using passive techniques: the use of shielded rooms, the use of underground laboratories and the adjustment of the detector's dimensions to the examined energy. This study indicates that the efficiency of the detector is not the critical parameter for achieving sensitive measurements in the low-energy range and is secondary to optimisation of the background level. However, reduction of the background has a limited impact on the sensitivity of counting due to 40K in the body. This study also shows that the advantage of using deep underground laboratories could be replaced by detectors with properly designed shape and size and used at ground level in normally shielded rooms to reach the necessary limits of detection for in vivo assessment of low-energy photon emitters.

The in vivo assessment of thorium body burden by gamma ray sepctrometry.

Thorium is used in many different industrial technologies and is widely found in nature. Internal contamination with thorium is considered as highly hazardous because of its radiological and chemical toxicities, which depend on the chemical form in which thorium appears. The assessment of the thorium body burden is then of primary importance in detecting the risks of personal contamination, and for appropriate counteractions when contamination is detected. The in vivo assessment of the thorium lung burden is commonly achieved by gamma ray spectrometry of its progeny. Three methods for the assessment of thorium in the lungs are compared. In the first method, the radionuclide examined is 208Tl, measured with a Nal(TI) detector. This simple method can be affected by systematic errors due to 220Rn exhalation and because of the assumption of equilibrium between 232Th and 228Th. The second method, based on the measurement of the gamma rays emitted by 228Ac, requires the use of high-resolution gamma spectrometry (HPGe detectors). The accuracy of the thorium quantification is better with this technique. The third method is based on the measurement of exhaled 220Rn.

In-vivo measurement of low energy photon emitters: room-temperature semiconductor diodes vs. large scintillators and germanium crystals.

The in-vivo monitoring of low energy x- and gamma-ray emitters gained importance with the increasing use of these radionuclides in nuclear medicine and nuclear energy production. The main problems encountered are the lack of accuracy in the measurement and the high detection limits obtained with the classical techniques [proportional counters, thin NaI(TI) or phoswich scintillators]. The best technique available today is the array of planar germanium detectors. The purpose of this paper is to analyze specific problems in the assessment of low energy photon emitters in the body and to describe applications of room-temperature diodes (silicon and CdZnTe) using a new technique involving a portable jacket. In certain cases, the device can be used outside a shielded room, making possible an immediate long counting, reducing the psychological stress, and optimizing the medical treatment and the intervention. By considering the attenuation effect, this work shows that an optimized volume of the diodes reduces the detection limits of the counting. The developed methodology offers new possibilities in the assessment of radioactive deposition in the body and in the long term follow-up of the metabolism of radionuclides in small quantities.

New technique using room temperature diodes for the direct assessment of internal contamination by low energy gamma-ray emitters.

Silicon PIN diodes were tested as direct detection elements for in vivo counting. They have a low sensitivity to background radiation in the energy range below 80 keV so that they can be used outside a shielding room for the measurement of weakly absorbing organs or tissues in cases of incorporation of fuel particles and medical radionuclides. Results are reported on the spectral characteristics of these detectors. Comparison with other techniques is examined. This paper describes a novel technique of in vivo counting which needs no shielded room and which is applicable to other types of room temperature detectors. The concept of wearable counting devices is presented with description of their design.

Room-temperature semiconductor detectors for in vivo monitoring of internal contamination.

In vivo monitoring of low-energy X-ray and gamma-ray emitters has always been a difficult task, primarily because of lack of accuracy and the high detection limits of classical techniques. Various types of PIN diodes (diodes with a large intrinsic zone) were tested in the Radiation Protection Department of the Studie Centrum voor Kernenergie, Centre d'étude de l'Energie Nucléaire (Mol, Belgium) in the measurement of radioactive body burden by direct methods. Current research is oriented toward the use of room-temperature diodes for the detection of low-energy photons escaping the body. In this paper, a new counting technique that involves a portable jacket containing the diodes is described. The system uses silicon diodes and is used out of shielding room in order to be near the contamination. With this method rapid analysis and long counting times are possible, stress is reduced, and medical treatment can be optimized. CdZnTe detectors were also evaluated for this measurement technique but this type of detector is better adapted for counting inside a shielding room. The improvement of the accuracy of the measurement, taking into account the effect of the ribs, is described here, as well the associated electronics necessary for this type of counting.

The assessment of plutonium and americium in contaminated wounds with high energy resolution semiconductor detectors.

A simple to use method was installed for the measurement of wounds contaminated with plutonium and americium by using a semiconductor detector. This technique does not explicitly require the knowledge of the detector efficiency but uses a plant 241Am calibration source. A computer programme has also been developed for the quantification of the contamination according to the shape and the depth of the contaminant in the wound.