Details of the confinement of primary ionizing electrons and plasma by multidipole fields are given. It is shown that primary electrons are very efficiently confined by the cusps, with leakage half-widths given by the electron gyroradii. Plasma is confined much more weakly. Leakage half-widths of helium, argon, and xenon plasmas are found to be twice the hydrid gyroradii. Plasma noise in the neighborhood of the hybrid frequency is observed in the cusp regions.
H− ions formed by volume processes are extracted from a multicusp ion source. It is shown that a permanent magnet filter together with a small positive bias voltage on the plasma grid can produce a very significant reduction in electron drain as well as a sizable increase in H− ions available for extraction. A further reduction in electron current is achieved by installing a pair of ceramic magnets at the extraction aperture. The combined arrangement improves the ratio of extracted H− ion current to electron current to about unity.
Neutron irradiation of samples for 40 Ar/ 39 Ar dating in a 235 U fission reactor requires error-producing corrections for the argon isotopes created from Ca, K, and, to a lesser extent, Cl. The fission spectrum includes neutrons with energies above 2-3 MeV, which are not optimal for the 39 K(n,p) 39 Ar reaction. These higher-energy neutrons are responsible for the largest recoil displacements, which may introduce age artifacts in the case of fine-grained samples. Both interference corrections and recoil displacements would be significantly reduced by irradiation with 2.45 MeV neutrons, which are produced by the deuteron-deuteron (D-D) fusion reaction 2 H(d,n) 3 He. A new generation of D-D reactors should yield sufficiently high neutron fluxes (>10 12 n cm À2 s À1 ) to be useful for 40 Ar/ 39 Ar dating. Modeling indicates that irradiation with D-D neutrons would result in scientific benefits of improved accuracy and broader applicability to fine-grained materials. In addition, radiological safety would be improved, while both maintenance and operational costs would be reduced. Thus, development of high-flux D-D fusion reactors is a worthy goal for 40 Ar/ 39 Ar geochronology. r
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.