Feasibility of photodetachment isobar suppression of WF5− with respect to HfF5−

Abstract The feasibility of using laser photodetachment as a means for isobar suppression in accelerator mass spectrometry has been investigated for the special case of HfF 5 − /WF 5 − . A method for absolute photodetachment cross section measurements was applied and the cross sections of tungsten pentafluoride and hafnium pentafluoride negative ions were measured. The measurements indicate that the photodetachment cross section for WF 5 − is at least 100 times larger than for HfF 5 − at the wavelength of the fourth harmonic of the Nd:YAG laser at 266 nm. The absolute cross section for WF 5 − at this photon energy was found to be (2.8 ± 0.3) × 10 −18  cm 2 , while an upper limit of 2 × 10 −20  cm 2 was obtained for the HfF 5 − cross section. The measured cross sections indicate that an optical filtering scheme for isobar suppression in accelerator mass spectrometry for the case of Hf 182 should be feasible.