Abstract
The efficiency of the NPL magnetic β-ray spectrometer has been increased by a factor ∼ 240 so that the decay of long-lived actinide nuclei may be studied. This large increase in efficiency was achieved by the use of a large area multistrip source in the manner of Bergkvist, together with the development of a sixteen element proportional counter. These modifications to the β-ray spectrometer have permitted the study of internal conversion following the decay of
237Np. The low-energy scheme of
233Pa has been determined on the basis of these measurements and the results of complementary singles and coincidence γ-ray studies.