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A numerical example for tutorial and possibly design exercise use is described which is concerned with the performance of household waste as a fuel in power generation.

A design exercise in chemical engineering is described which is concerned with thermocouples. Physics is the relevant discipline, a point that was made to the students doing the exercise, and accordingly an account of the exercise for the guidance of teachers and lecturers is presented as a contribution to Physics Education.

The photon flux spectra from two 6 MeV Linear Accelerators and a 2 MeV Van de Graaff Generator which are in normal use for radiotherapy, have been measured using a 7·5 × 7·5 cm NaI (Tl) crystal spectrometer. The X-ray beam was scattered by aluminium sheets to reduce the intensity and energy range, and the primary spectra calculated from the measured scattered spectra using the Klein-Nishina formula. The crystal spectrometer was calibrated from theoretical Monte Carlo calculations which were compared with experimentally obtained isotope spectra. The measured pulse height spectra were converted to photon flux spectra by a digital computer. Photon flux spectra were obtained for different field sizes and under different operating conditions, and the variation in the spectra over the X-ray field was investigated. The results were compared with theoretically calculated thick target spectra using published formulae for the bremsstrahlung cross-sections.

A semiempirical pseudopotential for crystalline mercury has been determined using a fitting procedure to experimental dimensions of the Fermi surface. Three separate classes of pseudopotential were found to be consistent with measured calipers of the Fermi surface. One pseudopotential is equivalent to the Evans's pseudopotential used for liquid mercury.