Ph. Renaud

A new cytological tool, based on the microCoulter particle counter (microCPC) principle, aimed at diagnostic applications for cell counting and separation in haematology, oncology or toxicology is described. The device measures the spectral impedance of individual cells or particles and allows screening rates over 100 samples s(-1) on a single-cell basis. This analyzer is intended to drive a sorting actuator producing a subsequent cell separation. Size reduction and integration of functions are essential in achieving precise measurements and high throughput. 3D finite element simulations are presented to compare various electrode geometries and their influence on cell parameters estimation. The device is based on a glass-polyimide microfluidic chip with integrated channels and electrodes microfabricated at the length scale of the particles to be investigated (1-20 microm). A laminar liquid flow carries the suspended particles through the measurement area. Each particle's impedance signal is recorded by a differential pair of microelectrodes using the cell surrounding media as a reference. The micromachined chip and processing electronic circuit allow simultaneous impedance measurements at multiple frequencies, ranging from 100 kHz to 15 MHz. In this paper, we describe the microfabrication and characterisation of an on-chip flow-cytometer as the first building block of a complete cell-sorting device. We then discuss the signal conditioning technique and finally impedance measurements of cells and particles of different sizes and types to demonstrate the differentiation of subpopulations in a mixed sample.

Iodine-131 and various other radionuclides were released into the atmosphere from the damaged Japanese reactors of Fukushima Dai-ichi from 12 to 22 March 2011. The contaminated air mass was detected in France after 24 March; samples of grass, vegetables, and milk have been analyzed for (131)I by the IRSN, considering the fact that few values of iodine-131 transfer parameters have been directly measured in situ, due to the radioactive decay of this isotope. Data are compared with calculated values according to the air iodine concentration. The apparent dry deposition velocity of iodine on grass is therefore estimated to range between 1 × 10(-3) and 5 × 10(-3) m s(-1) from site to site. In addition, the grass to milk transfer factors are 2.8 × 10(-2) and 3.6 × 10(-3) d L(-1) for goat's and cow's milk respectively. These parameters fit well with the current values usually considered for radioecological assessment.

In 2011 the IRSN conducted several assessments of atmospheric radioactive releases due to the Fukushima Daiichi NPP accident (March 11, 2011) and of their impact on Japan’s terrestrial environment. They were based on the IRSN’s emergency management tools and on the abundant information and technical data gradually published in Japan. According to these assessments, the main release phase lasted from March 12 to 25, 2011 and impacted Japanese land in two events, the first on 15 and 16 March, in which the main radioactive deposits were formed, and the second from March 20 to 23, which was less significant. The highest amounts of radioactive deposits were found in an area extending upwards of several tens of kilometers northwest of the plant. Lower amounts were discontinuously scattered in an area extending up to over 250 km away. Initially composed mainly of short-lived radionuclides, the deposits’ activity sharply decreased in the subsequent weeks. Since the summer of 2011, cesium-134 and cesium-137 have become the residual deposits’ main components. According to IRSN estimates, in the absence of protection, the doses due to exposure to the radioactive plume during the atmospheric release phase may have been potentially higher for people who remained in coastal areas up to several tens of kilometers north and south of the damaged plant. Thereafter, people living up to 50 km northwest of the plant, outside the 20-km emergency evacuation zone, were potentially most vulnerable to residual radioactive deposits over time.

Geological and climatic diversity leads to significant spatial variability of naturally occurring radioactivity levels, whether in soils, sediments or natural waters. The activity level of Rhône sediments is estimated at 1450 Bq/kg, between the levels observed in the Loire (1925 Bq/kg) and Seine (730 Bq/kg). The largest amounts of radioactive effluent from nuclear facilities concern tritium, for which activity levels are currently 1000 times higher than the sum of artificial gamma emitters discharged. The proportions of naturally occurring 14C and 3H in the lower reaches of the River Rhône are estimated at 50 to 70% and <5%, respectively, with the remaining amount coming from nuclear facilities. Long-term records from River Rhône monitoring show that the level of radioactive contamination from artificial sources declined sharply starting in the early 90s, with the level divided by 10 to 100 depending on the element. Radioactivity of natural origin remained unchanged as expected.