THE PHYSICS OF HIGH RESOLUTION GAMMA-SPECTROSCOPY AND EXPERIIYIENTAL RESULTS WITH A SEMI-CONDUCTOR COIYIPTON-SPECTROMETER FOR NONDESTRUCTIVE BURN-UP DETERMINATION OF NUCLEAR FUEL

摘要

In June 1962 the author suggested in a report on nuclear materials control to the International Atomic Energy Agency in Vienna to employ high resolution gamma spectroscopy for determining by nondestructive means total fuel burn-up and burn-up history in nuclear reactors. Most of the fission products both for uranium and plutoniumnfissions ranging from 30 Zn 72 up to 66Dy 161 were known then already fair enough with respect to their yields, their characteristic gamma emission energies and decay schemes as well as their decay constants. Because also the fission to capture cross section values for neutrons of different energies are well enough in hand, it is possible to calculate the amount of fissionable atoms spent for a thin foil, when measuring the intensity of a given gamma emitting radioactive isotope. Only one further constant is required for practical nondestructive testing nf solid samples or fuel elements, namely the selfabsorption coefficient for the gamma quanta emitted therefrom. Conventional gamma spectroscopic methods lack two important requirements. First the resolution of scintillation crystals used in a routine manner is not good enough to resolve characteristic energies and second also the response function, i.e. the number of counts ir a peak compared with the low energetic continuum is very poor. For comparative relative abundance measurements, however, the ratio of tail to peak should be less than 5 percent.