Study of laser interaction with negative ions

Negative ions can be neutralized by detaching their additional electron through interaction with a laser beam. By properly choosing the laser wavelength, the process is highly selective; it can in principle enhance the discrimination power of an accelerator mass spectrometry system for ions of different elements (e.g. isobaric background) by allowing their separation prior to their injection into a tandem accelerator. We demonstrate this process in the case of the ⁵⁹Ni- ⁵⁹Co pair with the AMS system based on the Rehovot 14UD Pelletron accelerator and a pulsed Nd-YAG laser at the fundamental wavelength (1064 nm). A photodetachment cross section of (0.6 ± 0.3) × 10^-17 cm² was measured for ⁵⁹Co^- and a suppression factor of 125 for the ⁵⁹Co isobaric background was achieved in a ⁵⁹Ni AMS measurement. The duty factor due to the pulsed laser was about ^10-4. The laser-AMS system was also applied to the study of rare negative ions in the actinide region. Preliminary results on the laser interaction with uranium negative ions are reported.