Assessment of neutron dosemeters around standard sources and nuclear fissile objects.

In order to evaluate the neutron doses around nuclear fissile objects, a comparative study has been made on several neutron dosemeters: bubble dosemeters, etched-track detectors (CR-39) and 3He-filled proportional counters used as dose-rate meters. The measurements were made on the ambient and the personal dose equivalents H*(10) and Hp(10). Results showed that several bubble dosemeters should have been used due to a low reproducibility in the measurements. A strong correlation with the neutron energy was also found, with about a 30% underestimation of Hp(10) for neutrons from the PuBe source, and about a 9% overestimation for neutrons from the 252Cf source. Measurements of the nuclear fissile objects were made using the CR-39 and the dose-rate meters. The CR-39 led to an underestimation of 30% with respect to the neutron dose-rate meter measurements. In addition, the MCNP calculation code was used in the different configurations.

Investigation of radiation damage in DNA by using atomic force microscopy.

The effect of radiations on supercoiled plasmid DNA has been investigated by using atomic force microscopy (AFM). The DNA molecules were deposited on a substrate and observed by AFM. Alternatively, DNA at different scavenger concentrations was initially exposed to different types of radiations (alpha and X rays) at various doses. After irradiation, fragments (open circular and linearised strands) were observed corresponding to single strand breaks and double strand breaks in DNA. This result indicates the capabilities of AFM for the qualitative detection of strand modifications due to irradiation. The amount of each class of topology enables a quantitative response to be determined for both types of radiation (alpha, X). A value of the radiosensitivity of DNA was obtained as a function of the scavenger concentration. Strong accordance was found between AFM results and those obtained by use of gel electrophoresis. The advantage of AFM in comparison with traditional techniques is the possibility of analysing the radiation effects on one molecule. Indeed, taking the example of alpha particles, it is shown that it is easy to measure the sizes of linear strands by AFM. Such additional or even precise results are difficult to obtain with gel electrophoresis since, in such a case, data are lost through smearing.

Chemical bonds broken in latent tracks of light ions in plastic track detectors.

When a swift ion is slowed down through a plastic detector it creates a latent track. In nuclear track detectors, this latent track can be specifically etched by an appropriate chemical solution. This enlargement process is due to a higher etch velocity (VT) along the ion's path than in the non-damaged part of the detector. The etched track velocity is definitely linked to the damage created by the incoming ion in the detector material. A relationship between the physical parameters of the energy deposition and the variation in this etched track velocity with the ion energy cannot easily be explained. We present here our study on the chemical damage created by several ions in a cellulose nitrate type detector and our first attempt to simulate them by the use of the hit theory.

Ultrastructural lesions induced by neptunium-237: apoptosis or necrosis?

In this study, we are concerned with the 237 isotope of neptunium (237Np), which is a by-product of uranium in nuclear reactors. To study ultrastructural lesions induced by this element, a group of rats were injected with a solution of 237Np-nitrate once a day for 14 weeks. Lesions observed in liver and kidney are described using electron microscopy. Ultrastructural alterations of cellular membranes and intracellular organelles demonstrated the existence of neptunium toxicity. This toxicity was characterized by various lesions, such as cytoplasmic clarification, disappearance of mitochondrial cristae, swollen mitochondria, abnormal condensation of nuclear chromatin, and nuclear fragmentations. This study demonstrated the probable induction of apoptosis by neptunium both in liver and kidneys.

The use of silicon photodiodes for radon and progeny measurements.

Reduced cost, high quantum efficiency and very good detection characteristics of PIN silicon photodiodes made possible their utilization for alpha particles detection. This paper presents different studies and applications of this type of detector for qualification and quantification of radon and its progeny in laboratory and in the field. Since photodiodes are sensitive to environmental electromagnetic fields, protecting cells were adapted for use around the detector. A small three-channel (2-5.5 MeV; 5.5-6.5 MeV; 6.5-8.2 MeV) portable alpha counter was developed that allows the determination of the radon concentration and the radon exhalation rate. Numerous field applications were conducted in different conditions (uranium waste storage, dwellings, etc.) where this simple and inexpensive instrumentation demonstrated very good performance, reliability, and easiness of operation while measuring radon concentrations from 50-100 Bq m(-3) to several MBq m(-3).

3-D confocal microscopy of etched nuclear tracks in CR-39.

Solid State Nuclear Track Detectors (SSNTD's) are used in a wide range of applications such as Geological Dating, Environmental Sciences (radon), life Sciences (Radiobiology, Dosimetry...), as well as Nuclear and Astro-Physics. In order to be observable under a microscope, the nanometric latent damaged trails due to the slowing down of charged particles into the SSNTD have to be specifically etched. In our laboratory, we are studying this chemical action and propose models that enable simulations to be performed. In the literature, the basic model uses two distinct etch-rates that are considered constant, VB; the Bulk and VT the Track etch-rate. A little bit more sophisticated and realistic, a model with a variable track etch-rate was established, taking into account the variation of energy deposition along the particle's trajectory. Up to now, the known methods used for determining the response function of CR-39 are very time consuming and strenuous. The method we present here is based on the use of the confocal microscope, which provides three-dimensional track images. The obtained set of 3-D co-ordinates can be treated mathematically, giving, in the framework of the two etch-velocity model, the response function. With this new approach, tracks are analysed one by one; response functions are obtained for each track and can be compared to fundamental characteristics of the charged Particle-Matter interactions. Moreover, the method we propose is applied semi-automatically and could easily be automated in the near future.

Ion-kill dosimetry.

Unanticipated late effects in neutron and heavy ion therapy, not attributable to overdose, imply a qualitative difference between low and high LET therapy. We identify that difference as 'ion kill', associated with the spectrum of z/beta in the radiation field, whose measurement we label 'ion-kill dosimetry'.