Progress of laser photo detachment experiment at MALT

Full text: A laser photo detachment (LPD) method for Accelerator Mass Spectrometry (AMS) systems is developing at Micro Analysis Laboratory Tandem accelerator, The University of Tokyo (MALT). LPD is a method of neutralizing negative ions by interacting with a laser and a negative ion beam. Neutralization of negative ions occurs when the electron affinity (EA) of the atoms in the negative ion is lower than the energy of the laser photon. Therefore, if the laser energy is appropriately selected, only the targeted ions can be separated. For example, the isobaric compound of ³⁶Cl (T1/2 = 3.01×10⁵ y) is a stable nuclide ³⁶S. The EA of Cl is 3.61 eV, while the EA of S is 2.08 eV. Thus, if a laser with a wavelength of 532 nm (hν = 2.33 eV) is used, only S can be selectively neutralized and separated from Cl. The test bench beamline for the LPD experiment at MALT was constructed, which consists of a negative ion source, an analyzing magnet, a negative ion cooler, an electrostatic deflector, a laser system, and a detection system such as a FC. The negative ion beam produced by the ion source with the energy of 22 keV is mass analyzed and then interacts with the laser in the ion cooler. The laser is a 20 W continuous wave laser ,and its wavelength is 532 nm. After passing through the ion cooler, negative ions are deflected and measured as current by the FC. On the other hand, neutralized particles are separated without being deflected. In this study, we report recent progress of the LPD experiment of Cl and S, the change in the suppression of S by the laser when He is introduced as a buffer gas, and the change in the transmission efficiency.