Preparation of drop-deposited quantitative uranium sources with low self-absorption

A source preparation procedure was optimised for 235U sources of about 1 mg or 100 Bq, to be standardised for their activity concentrations by α-particle counting at a defined solid angle. The aim was to obtain quantitative sources having a thin, homogeneous active layer with low self-absorption of the emitted α-particles. The procedure involves spraying the wetting and seeding agent in a circular shape onto a glass or stainless steel substrate, quantitative drop deposition of active solution onto the sprayed area by the pycnometer method and fast drying of the source on a heating plate. The fraction of heavily scattered and self-absorbed α-particles could be reduced to 0.05–0.1% for a majority of the sources.