ABSTRACT
Flux monitoring is of great interest for experimental studies in material testing reactors. Nowadays, only the thermal neutron flux can be monitored on line, e.g., using fission chambers or self-powered neutron detectors. In the framework of the Joint Instrumentation Laboratory between SCK-CEN and CEA, we have developed a fast neutron detector system (FNDS) capable of measuring on line the local high-energy neutron flux in fission reactor core and reflector locations. FNDS is based on fission chambers measurements in Campbelling mode. The system consists of two detectors, one detector being mainly sensitive to fast neutrons and the other one to thermal neutrons. On line data processing uses the CEA depletion code DARWIN in order to disentangle fast and thermal neutrons components, taking into account the isotopic evolution of the fissile deposit. The first results of FNDS experimental test in the BR2 reactor are presented in this paper. Several fission chambers have been irradiated up to a fluence of about 7 × 10(20) n∕cm(2). A good agreement (less than 10% discrepancy) was observed between FNDS fast flux estimation and reference flux measurement.
ABSTRACT
Eyes with corneal disease receiving transplants from premature, full gestational newborns or postnatal donors yield refractive results with a myopic shift. When the donor cornea is from a newborn (40-41 week gestation) this myopic shift was sufficient to correct 5 of 7 aphakic eyes to an average postsurgical refraction of -1.0 diopter (spher equiv). One premature cornea gave -6.0 diopters while six postnatal infant corneas gave an average correction of +8.6 diopters (spher equiv). The steep corneal curvature resulting from surgery explains the additional refractive power noted. The surgical difficulties encountered and the unknown long-term results auger for a slow and controlled introduction of this concept into our everyday practices.
