Initial Results with the Berkeley On-line Mass Separator - RAMA Page: 4 of 16
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LBL-7156
The capillary exit is aligned with a skimmer (1mm orifice) at a distance
of approximately 7 mm. This skimming removes most of the helium while allowing
a majority of the activity to pass through the skimmer undeflected. One series
of tests with 20Na activity demonstrated an opening angle of 2.80 for 55% of the
activity. (Many tests of the RAMA system have been performed with the S-delayed
alpha-emitter 20Na, produced via the 24Mg(p,tn) reaction at 38 MeV, due to its
easily identifiable alpha groups and its short half-life of 445 msec.)
As seen in Figure 1, the skimmed activity then enters the RAMA hollow-
cathode ion source. This ion source has been operated using both tantalum and
tungsten filaments, with the former lasting on the average % 50 hours at 1600 C.
Tungsten filaments have been tested for periods of up to 100 hours at temperatures
exceeding 2000 C. Under the arc conditions prevalent at these temperatures,
the species of interest is ionized primarily to +1 (recent tests indicate
40Ar+1 40+2 100 under normal arc conditions (Arc Current = 1.0 - 1.5A;
V = 180-250V).
ARC
In our setup, good ion source efficiency as well as optimal mass
resolution depend strongly upon the arc conditions. Different arc conditions
can change the emittance of the source, so that it is no longer well matched to
the acceptance of the spectrometer system. The arc conditions are governed by
three independently adjustable parameters: electron density (filament temperature),
electron temperature (arc voltage), and neutral gas density.
40 +1 20 +1
Internal beams of Ar and Ne ions from the RAMA ion source were
used to determine the effects of various optical devices in the mass analysis
system. The first device after the ion source is an Einzel lens; this electro-
static element is used to focus the beam into the Wien filter, a crude velocity
selector used to separate the large component of He+1 (arc support gas) produced
in the ion source from the nuclide of interest.-2-
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Cerny, J.; Moltz, D. M.; Evans, H. C.; Vieira, D. J.; Parry, R. F.; Wouters, J. M. et al. Initial Results with the Berkeley On-line Mass Separator - RAMA, article, November 1, 1977; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc831227/m1/4/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.