Beam-induced back-streaming electron suppression analysis for an accelerator type neutron generator designed for 40Ar/39Ar geochronology. (July 2017)

• Record Type: Journal Article
• Authors: Waltz, Cory; Ayllon, Mauricio; Becker, Tim; Bernstein, Lee; Leung, Ka-Ngo; Kirsch, Leo; Renne, Paul; Bibber, Karl Van
• Is Part Of: Applied radiation and isotopes. Volume 125(2017:Jul.)
• Page Start: 124
• Page End: 128
• Publication Date: 2017-07
• Subjects: Neutron generator -- Backstreaming electrons -- Electron suppression -- Electrostatic shroud -- Geochronology; Radiology -- Periodicals; Radiation -- Industrial applications -- Periodicals; Nuclear chemistry -- Periodicals; Internet resource; Periodical; 660.298
• DOI: 10.1016/j.apradiso.2017.04.017
• Languages: English
• ISSNs: 0969-8043

Abstract

Abstract: A facility based on a next-generation, high-flux D-D neutron generator has been commissioned and it is now operational at the University of California, Berkeley. The current generator designed for 40 Ar / 39 Ar dating of geological materials produces nearly monoenergetic 2.45 MeV neutrons at outputs of 10 8 n/s. The narrow energy range is advantageous relative to the 235 U fission spectrum neutrons due to (i) reduced 39 Ar recoil energy, (ii) minimized production of interfering argon isotopes from K, Ca, and Cl, and (iii) reduced total activity for radiological safety and waste generation. Calculations provided show that future conditioning at higher currents and voltages will allow for a neutron output of over 10 10 n/s, which is a necessary requirement for production of measurable quantities of 39 Ar through the reaction 39 K ( n, p ) 39 Ar . A significant problem encountered with increasing deuteron current was beam-induced electron backstreaming. Two methods of suppressing secondary electrons resulting from the deuterium beam striking the target were tested: the application of static electric and magnetic fields. Computational simulations of both techniques were done using a finite element analysis in COMSOL Multiphysics ® . Experimental tests verified these simulations. The most reliable suppression was achieved via the implementation of an electrostatic shroud with a voltage offset of −800 V relative to the target. Abstract : Highlights: Two methods of electron suppression were analyzed using a finite element computer code (COMSOL Multiphysics). An electrostatic shroud with a voltage offset of −800 V was built and tested. Experimental tests showed that successful electron suppression was achieved.