Negative-Ion Formation Processes and Sources

Alton, G. D.

doi:10.1007/3-540-27095-7_20

Cited by 14 publications

(19 citation statements)

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“…(iii) The surface-plasma negative ion sources are based on positive ion bombardment of an emitter surface. 13,14 Here the main mechanism of negative ion formation is the secondary emission of sputtered and scattered particles accompanied by the capture of electrons from the electrodes.…”

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confidence: 99%

Charge steering of laser plasma accelerated fast ions in a liquid spray — creation of MeV negative ion and neutral atom beams

et al. 2013

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Charge steering of laser plasma accelerated fast ions in a liquid spray — creation of MeV negative ion and neutral atom beams

et al. 2013

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“…To our knowledge, there have been no published data on the charge-exchange efficiencies of U and Th positive ions. It is well known that the charge exchange is a two-step process and the yield of negative ions depends primarily on the collision energy, the electron affinity (EA) of the projectile element, and the IP and density of the exchange vapor [34]. It is generally true that higher charge-exchange efficiencies can be expected for higher projectile EA values.…”

Section: Discussionmentioning

confidence: 98%

Ion source development for ultratrace detection of uranium and thorium

Liu

Batchelder

Galindo-Uribarri

et al. 2015

Nuclear Instruments and Methods in Physics Research Section B:

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a b s t r a c tEfficient ion sources are needed for detecting ultratrace U and Th impurities in a copper matrix by mass spectrometry techniques such as accelerator mass spectrometry (AMS). Two positive ion sources, a hot-cavity surface ionization source and a resonant ionization laser ion source, are evaluated in terms of ionization efficiencies for generating ion beams of U and Th. The performances of the ion sources are characterized using uranyl nitrate and thorium nitrate sample materials with sample sizes between 20 and 40 lg of U or Th. For the surface ion source, the dominant ion beams observed are UO + or ThO + and ionization efficiencies of 2-4% have been obtained with W and Re cavities. With the laser ion source, three-step resonant photoionization of U atoms has been studied and only atomic U ions are observed. An ionization efficiency of about 9% has been demonstrated. The performances of both ion sources are expected to be further improved.

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“…Negative atomic ions were not as well known as positive ions in 1939 and their use for nuclear physics had to await the development of suitable high current negative ion sources by Whittier (1954) at McGill University and by Weinman and Cameron (1956) for use with tandem accelerators and nuclear physics. The development of such sources has continued since then for both AMS and nuclear physics (Alton, 2005).…”

Section: Negative Ions the Tandem Accelerator And The Rapid Growtmentioning

confidence: 99%

“…Negative ion sources are required for electrostatic tandem acceleration and their development has taken place almost continuously for nuclear physics and for AMS (Alton, 2005). For the early work in nuclear physics the ion sources were based upon charge changing collisions in gases from cations to anions at many keV energy.…”

Section: A Ion Sources Used In Tandem Amsmentioning

confidence: 99%

“…The negative ion sputter source was first introduced with Kr þ ions sputtering surfaces coated with near monolayers of Cs atoms (Müller & Hortig, 1969;Alton, 2005). The cesium was used to lower the surface work function to increase the ion currents of the low electron affinity atomic anions such as C À (electron affinity of 1.26 eV).…”

Section: The Versatile Cs þ Sputter Ion Sourcementioning

confidence: 99%

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Mass spectrometry with accelerators

2010

Mass Spectrometry Reviews

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As one in a series of articles on Canadian contributions to mass spectrometry, this review begins with an outline of the history of accelerator mass spectrometry (AMS), noting roles played by researchers at three Canadian AMS laboratories. After a description of the unique features of AMS, three examples, (14)C, (10)Be, and (129)I are given to illustrate the methods. The capabilities of mass spectrometry have been extended by the addition of atomic isobar selection, molecular isobar attenuation, further ion acceleration, followed by ion detection and ion identification at essentially zero dark current or ion flux. This has been accomplished by exploiting the techniques and accelerators of atomic and nuclear physics. In 1939, the first principles of AMS were established using a cyclotron. In 1977 the selection of isobars in the ion source was established when it was shown that the (14)N(-) ion was very unstable, or extremely difficult to create, making a tandem electrostatic accelerator highly suitable for assisting the mass spectrometric measurement of the rare long-lived radioactive isotope (14)C in the environment. This observation, together with the large attenuation of the molecular isobars (13)CH(-) and (12)CH 2(-) during tandem acceleration and the observed very low background contamination from the ion source, was found to facilitate the mass spectrometry of (14)C to at least a level of (14)C/C ~ 6 × 10(-16), the equivalent of a radiocarbon age of 60,000 years. Tandem Accelerator Mass Spectrometry, or AMS, has now made possible the accurate radiocarbon dating of milligram-sized carbon samples by ion counting as well as dating and tracing with many other long-lived radioactive isotopes such as (10)Be, (26)Al, (36)Cl, and (129)I. The difficulty of obtaining large anion currents with low electron affinities and the difficulties of isobar separation, especially for the heavier mass ions, has prompted the use of molecular anions and the search for alternative methods of isobar separation. These techniques are discussed in the latter part of the review.

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Negative-Ion Formation Processes and Sources

Cited by 14 publications

References 90 publications

Charge steering of laser plasma accelerated fast ions in a liquid spray — creation of MeV negative ion and neutral atom beams

Charge steering of laser plasma accelerated fast ions in a liquid spray — creation of MeV negative ion and neutral atom beams

Ion source development for ultratrace detection of uranium and thorium

Mass spectrometry with accelerators

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