Liquid-scintillation spectroscopy of α-particle emitters and detection of spontaneous fission events for on-line studies of actinide and transactinide elements

A liquid-scintillation counting system has been developed for the internal measurement of α-particle energies and the detection of spontaneous fission events on-line in flowing organic solutions resulting from continuous rapid chemical separations by liquid-liquid extraction. The scintillator, dimethyl-POPOP and naphthalene dissolved in toluene, contains the extracting agent, di-(2-ethylhexyl-)-phosphoric acid or dibutylphosphate. An average α-energy resolution of 4.8% FWHM was measured in the energy range 4.78 to 7.69 MeV in stationary as well as flowing organic solutions. Additional features of the system are: (1) detection of spontaneous fission events by larger pulses than produced by α-particles; (2) suppression of interfering β- and γ-radiation by pulse shape discrimination and pile-up rejection; (3) identification of parent-daughter α-α- or α-fission-correlations in decay chains; (4) on-line α-energy calibration by spiking the organic phase with 3.96-s 219Rn-1.78-ms 215Po milked from a 227Ac source. In order to increase the detection efficiency, a unit with three detector cells in series was built and tested with 219Rn and 220Rn. An on-line model experiment for element 104 was carried out using the α-emitter 17-s 161Hf produced by nuclear fusion of samarium with neon and chemically separated by liquid-liquid extraction. (orig.)