Indoor radon in the region of Brussels.

The indoor radon (222Rn) concentration has been measured by charcoal detectors in 278 buildings in the region of Brussels, Belgium. The correlation with the nature of the subsoil can be studied in detail thanks to the available geotechnical map. With a geometrical mean indoor radon concentration of 19 Bq m(-3), Brussels can be considered as generally unaffected by the radon problem. No value higher than 400 Bq m(-3) (the EU reference level for existing houses) was measured in an occupied room. However, two factors that may enhance the risk are identified: the absence of a basement or a ventilated crawl space, and the presence of loess, under the house. About one third of the houses without basements or ventilated crawl spaces built on loess show an indoor radon concentration above 200 Bq m(-3) (the EU reference level for new houses).

Improvement of a p(65)+Be neutron beam for therapy at Cyclone, Louvain-la-Neuve.

The variable energy cyclotron of the Catholic University of Louvain is used to produce intense neutron beams for neutron therapy purposes. As a first step, neutrons were produced by bombarding a Be target with 50 MeV deuterons; at present they are produced by 65 MeV protons. This paper describes the improvements to the target system. A new (17 mm) Be target together with the old (10 mm) Be target are inserted in a movable support which allows the production of neutrons either by 65 MeV protons or by 50 MeV deuterons. Both targets can be removed for proton beam therapy. The dosimetric characteristics of the p(65)+Be and d(50)+Be neutron beams are compared: dose rate, gamma-contribution, depth dose and room activation.