Instruments for Observations of Radioactivities

Abstract

This chapter describes key tools used to observe cosmic radioactivity including astronomical methods, laboratory measurements of meteorites and detection of Galactic cosmic rays. Cosmic nucleosynthesis, that is, the creation of new elements including radioactive isotopes, occurs in the most energetic, often explosive, sites in the universe. To observe these targets and processes in the light of high-energy photons, which are emitted in nuclear transitions and particle interactions, sensors for photon energies from around 100 keV to more than 10 MeV have been developed and employed on satellites and balloon platforms, outside the Earth’s atmosphere, which is opaque to this radiation. The basic interactions for such photons are the photoelectric effect, Compton scattering, and pair creation. Typical examples for instrument designs are described in the first section of this chapter, followed by a presentation of successful missions since the 1980s (SMM, Compton Gamma-Ray Observatory CGRO), then currently operational missions (INTEGRAL, NuStar, Fermi), and perspectives for future telescopes with advances in technology. The second section addresses radioactivities in meteorite samples, which are generally measured by means of mass spectrometry. The most widely used methods are thermal ionisation (TIMS), multi-collector inductively-coupled-plasma (MC-ICPMS), secondary ion- (SIMS), and resonance ionisation mass spectrometry (RIMS). Parent and daughter nuclides can be measured on a variety of sample sizes, with precision depending on the size of the sample and concentrations of the elements of interest. The ultimate attainable precision is generally limited by the number of atoms in a given sample. New developments in RIMS, accelerator-based SIMS, and laser-assisted atom-probe tomography all hold promise for pushing meteoritic measurements to higher sensitivity and smaller spatial scales. Galactic cosmic rays are addressed in a third section. These are analysed by a variety of instruments from the ground, on high altitude balloons, or on spacecraft. Basic principles are discussed as well as specific experiments, including the Pierre Auger Observatory, the Cosmic Ray Isotope Spectrometer on the ACE spacecraft, TIGER, and PAMELA.