The Instrument in Frankfurt, Germany

Orginally, our collaboration with nuclear physicists began at Caltech, but the main development later moved to Frankfurt, Germany, where Professor Friedel Rauch and his students operated a linear accellerator at the Institut für Kernphysik and worked to bring detection limits down into the few ppm range.

The detector system, shown retracted from the vacuum chamber, is in a box of lead bricks that acts as a passive shield against external sources of gamma radiation. In the center is the front face of the BGO (bismuth germanium oxide) detector with the bore-hole. Anti-coincidence shielding consists of three plastic scintillation detectors in wooden cages, two on top and the other on the side. - This system was used for all mineral analyses.

Our original sample chamber, was used for early garnet analyses. The nose which fits in the bore-hole is seen on the left side. Samples were located in the nose or on a sample wheel close to the front face. Also seen are vacuum pumps, valves and other devices associated with the sample chamber.

A more sophisticated sample chamber was built by J. Maldener and used for more recent analyses. On top is the head of a goniometer used for positioning the samples, on the left a CCD camera for detecting the ionoluminescence to check the position. The movable sample holder was in the box-shaped annex to the front plate. Again, with vacuum pumps and other associated devices are associated with the sample chamber.

A view into the chamber with the front plate removed shows one of the important components of the sample chamber, a sputter source, dark, at the north-west side of the picture, used to clean the surface of the samples of adsorbed hydrogen.

When the sample and chamber are under high-vacuum, beam of 15N ions enters the chamber from behind after it is acceleratored to over 6 MeV by a linear accelerator in an adjacent room. These ions react with the hydrogen in the sample to produce the gamma rays detected by th BGO detector.

Here is the system as is appeared while in use.

In 2004, this linear acellerator facility and the associated sample chambers and detection systems were decomissioned and removed from the Frankfurt laboratory.

Reference:   Maldener, J., and F. Rauch, High energy ion-beam analysis in combination with keV sputtering, in Application of Accelerators in Research and Industry, edited by J. L. Duggan and I. L. Morgan, pp. 689– 692, AIP Press, New York, 1997.