CPM Seminar

Recent Progress of Diamond Neutron Monochromator Development

Andreas Freund

ILL, Grenoble

It has been shown that single crystal diamond would be the most efficient monochromator material for thermal neutron beams (Freund, 2009). Thanks to the high reflecting power of diamond, important flux gains could be achieved in the thermal and higher energy range for neutron scattering instruments at continuous sources. The main obstacle for the application of single crystal diamond in neutron instrumentation had been the difficulty of producing large crystals with suitable mosaic spread at reasonable cost.

Nowadays chemical vapour deposition (CVD) techniques provide an alternative concept for the synthesis of diamond crystals that is not restricted to the size limitation of natural stones or the traditional high pressure high temperature (HPHT) technique. A hetero-epitaxial CVD technique of diamond on various single crystal substrates provides diamond layers with a mosaic spread of 0.2° - 0.3° on areas of at least several square centimetres (Gsell et al., 2004; Bauer et al., 2005). This method has a strong potential of scaling the substrate size up to several inches diameter and several mm thickness.

Before embarking on a large-scale diamond monochromator R&D programme, it was essential to characterize available samples with respect to their defect structure and to their neutron diffraction properties (Freund et al., 2010). The most recent results of extensive X-ray, gamma-ray and neutron diffraction studies of up to 2 mm thick and 2 cm² big samples will be presented. They show that there is a real chance to build highly efficient neutron monochromators made of diamond mosaic crystals in the near future.

References:
Bauer, T., Gsell, S., Schreck, M., Goldfu�, J., Lettieri, J., Schlom, D.G., Stritzker, B. (2005). Diamond Relat. Mater., 14, 314.
Freund, A.K. (2009). J. Appl. Cryst., 42, 36-42
Freund, A.K., Gsell, S., Fischer, M., Schreck, M., Andersen, K.H., Courtois, P., Borchert, G., Skoulatos, M. (2010). Nucl. Instrum. Meth. Phys. Res. A, in press.
Gsell, G., Bauer, T., Goldfuss, J., Schreck, M., Stritzker, B. (2004). Appl. Phys. Lett., 84, 4541-4543.