A hyperpure germanium detector for precise beta endpoint energy determinations

A hyperpure germanium detector of 300 mm2 area and 10 mm thickness was used to measure energies of β-rays up to 10.5 MeV. Extensive tests with the conversion electron spectrometer BILL at the Institute Laue-Langevin in Grenoble showed that the pulse height spectrum generated by the impact of monoenergetic electrons on the detector resulted in a response function which consists of a peak at the full electron energy of about 15 keV full width at half maximum and a structured tail towards lower energies. The position of this peak increases linearly within 2 x 10-4 up to an electron energy of 11.3 MeV. The gamma sensitivity of the detector allowed an easy calibration up to about 6 MeV. The response function was parameterised (12 energy dependent parameters) and a computer program was developed to fit the measured beta-spectra of short lived fission products delivered by the on-line separator OSTIS at the ILL. Results of beta-endpoint energies of 28Al, 20F, 38Cl and 88Rb are reported. (orig.)