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

Short-lived bromine nuclides, available from thermal neutron induced nuclear fission of235U, 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, the235U target was covered with a nickel foil to suppress the heavy fission products having lower recoil energies. In addition, carbon monoxide (CO) or propene (C3H6) 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 (OC83-87Se) 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 Br2with the isotopes83-87Br, could be established.