On-line gas-phase separation of short-lived bromine nuclides from precursor selenium

Short-lived bromine nuclides, available from thermal neutron induced nuclear fission of 235 U, may be useful tracers for laboratory studies in atmospheric chemistry. Short-lived fission products were delivered continuously to a laboratory with the gas-jet facility at the spallation neutron source SINQ. To increase the selectivity for the fission products from the light mass peak, the 235 U target was covered with a nickel foil to suppress the heavy fission products having lower recoil energies. In addition, carbon monoxide (CO) or propene (C 3 H 6 ) were added as reactive gases to the He carrier gas rather than aerosol particles. Besides isotopes from the noble gas krypton and its descendants, a selective transport of selenium isotopes was observed with each of these gases, though with higher yield using CO/He. Through β - -decay bromine isotopes are formed from selenium precursors. A bromine generator was established through controlled decomposition of the transported carbonyl selenide (OC 83-87 Se) and adsorption of the resulting elemental selenium on quartz. The addition of carrier bromine to the carrier gas led to a complete mobilisation of the bromine nuclides from the quartz surface while retaining selenium. With this procedure, a source of gaseous bromine species, presumably in the form of Br 2 with the isotopes 83-87 Br, could be established.