KIP publications

Absolute activity measurements of alpha, beta and gamma emitting radioactive
sources are important in numerous fields such as therapeutic radiology and
the characterization of nuclear waste. Conventional ionization and liquid scintillation
detectors, which are commonly used for these applications, have an energy dependent
quantum efficiency and severe limitations in energy resolution. As a novel alternative
we have developed a detector based on a metallic magnetic calorimeter (MMC)
with a gold absorber that covers the full solid angle of 4π around the radioactive
source. Deposition of energy in the absorber causes a temperature rise and results in
a change of magnetization of a parametric Au:Er sensor, which can be measured by
a low-noise high-bandwidth dc-SQUID. The detector has equal sensitivity for beta
and gamma radiation. In this paper we describe a detector which has a deviation from
linear behavior for energies up to 700 keV of smaller than 0.5% and an overall quantum
efficiency for beta particles in this energy range close to unity. We show the data
of our experiments measuring the decay of 36Cl and compare the results to the theoretically
expected spectrum for this second order forbidden non-unique β-decay. We
discuss the observed contributions to noise, the quantum efficiency and the achieved
energy resolution.