Mini-orange spectrometers for in- and off-beam observation of conversion electrons

Abstract

Orange-type configurations of permanent magnets around a central absorber serve with a Si solid-state detector as compact and versatile multi-channel spectrometers for conversion electrons. The spectrometers can separate electrons from dominating backgrounds of α, β +, γ and δ radiation with good filtering properties over broad and adjustable energy ranges from below 0.1 to above 2.5 MeV. Absolute detection efficiencies can be more than 7% at the lower and more than 3% at the higher energies. They allow decay studies with weak sources (nCi range) of short-lived activities. Energy resolutions of 2–3 keV (fwhm at 1 MeV) and time resolutions of 8 ns have been achieved. Overall dimensions of magnets plus source and detector are of the order of 10 cm. Examples of decay studies contain among others a weak E4 crossover transition and some recently discovered E0 transitions. In-beam measurements with cyclotron beams appear possible, though proper precautions against intense δ radiation are sometimes necessary. Modified for small angular acceptance, a mini-orange device has been used for in-beam observation of angular distributions of conversion electrons.