Development of an external beam nuclear microprobe on the Aglae facility of the Louvre museum

The external beam Line of our facility has been recently equipped with the focusing system previously mounted on a classical nuclear microprobe. When using a 0.1 mu m thick Si3N4 foil for the exit window and flowing helium on the sample under analysis, a beam spot as small as 10 mu m is attainable a t a distance of 3 mm from the window. Elemental micromapping is performed b y mechanical scanning. An electronic device has been designed which allows XY scanning by moving the sample under the beam by steps down to 0.1 mu m. Beam monitoring is carried out by means of the weak X-ray signal emitted by the exit foil and detected by a specially designed Si(Li) detector cooled by Peltier effect. The characteristics of external beams of protons and alp ha particles are evaluated by means of resonance scanning and elemental map ping of a grid. An example of application is presented, dealing with elemen tal micro-mapping of inclusions in gemstones. (C) 2000 Published by Elsevie r Science B.V. All rights reserved.