Spectrometer for measuring total beta decay energies

A spectrometer for Qsub(β)-determinations has been constructed. It consists of a coincidence - anti-coincidence arrangement recording those β-pulses in a Si(Li)-detector which are coincident with a chosen γ-gate as measured by two NaI-detectors and anti-coincident with pulses from a set of three Si(Li)-detectors surrounding the main β-detector. In addition, the γ-gate pulses have to be anti-coincident with γ-pulses from four large plastic detectors (for Compton- and background reduction). The total decay energy is determined by measuring the β branch to an excited state of the daughter nucleus. The spectrometer has been carefully calibrated with respect to energy, response and efficiency. The calibration technique and the possibility for extrapolations to higher energies are described. (Auth.)