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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS – 1963
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ORNU-P-5N
LTE-A
OCT 30 1964
To be presented for publication in Journal of Applied Physics
Isotonic Contamination in Electromagnetic Separators
W. A. Bell
A. M. Veach
E. D. Saipley
L. T. Newman
0. C. Yonts
J. V. Lee
K. A. Spainhour
R. N. Goslin?
... Oak Ridge National Laboratory, Oak Ridge, Tennessee
ABSTRACT
The cross contamination of isotopes resulting in a calcium
separation carried out with a highly stabilized ion beam at an .
unusually low environmental gas pressure is reported. A segmented
boundary wall treatment contacting the beam was used to produce an un-
usually well focused stabilized beam. The degree of contamination pro-
duced in this separation is compared to that experienced in the conven-
tional calutron for many years experience with many elements. A
general procedure for graphing contamination data 18 used in making :
the comparison.
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Research sponsored by the U. S. Atomic Energy Commission under contract.
with the Unica Carbide Corporation.'
? Consultant, Oglethorpe University, Atlanta, Georgia

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This paper was submitted for publication
in the open literaturo at least months
prior to the issuance date of this Micro-
card. Since the U.S.A.E.C. has no ovi-
dence that it has been published, the pa-
per is being distributed in Microcard
form as a preprint.
V.
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Introduction
,
The demand by the scientific experimenter for an ever increasing
· purity of a given isotopic sample in larger and ever larger quantities
requires that the calutron (a large type of mass spectrograph) be con-
stantly improved. The contamination of the wanted species by other
isotopes of the given element has been the subject for many . .::
studies 1,2,3,4,57 and for many routine assays of separated material
at this laboratory. The contamination performance for a calcium
separation using a segmented boundary wall treatment, or BIN, in
contact with the beam as a calming device.rº) 18 compared to that
given by the conventional calutron.
Essentially all of the elements, not monoisotopic, have been pro-
cessed in the electromagnetic separators (the calutrons) since the
close of World War II. When the relative transmission of feed
isotopes into a reference position 18 plotted.on semilog scale against
the fourth root of difference between the reference mass and that of
the contaminant isotope a linear relationship 18 observed. (0) This
graphical procedure of depicting contamination 18 routinely used to
test the consistency of separations. An example of this type of
treatment of contamination data is shown in Fig. I. This graph shows
two lines in which the reference mass 18 normalized to 100% transmission
and the fractional part of other masses present either higher or lower--
· 18 graphed against the absolute value of the corresponding fourth root.
of the mass difference. Note the contamination of the adjacent mass
isotopes 18 greater than that for masses farther removed. If the
calutron achieved no enrichment of the feed material the lines would be
horizontal at the 100% level. If complete separation were to be achieved,
all contaminants would be on the 0% level. Any slope of either line 18 ..
indicative of contaminants exd.sting in ratios of altered .isotopic abundance.
Examination of this typical graph shows that contamination 18 not
basically a neutral gas condensation process since the line departs
from the horisontal. Also, the distribution noted 1. approximately
1
symmetrical relative to the reference mass. This indicates contaminat-
ing processes which almost equally distribute both high and low masses
Lato the reference pocket.
Several phenomena me;" impart particle motion which would serve to
contaminate the desired 1sotope. Table I shows a tabulation of some
contaminating processes grouped according to the direction in waich they
tend to shift a contaminating mass.
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::.. Some . Contamination Processes Encountered in Isotope Separation
II
III
High Side
Equal
"Lów. Side
Charge Exchange in Beam.
Regioa
Angular Scattering
Charge Exchange in
Electrode Region
Charge Exchange Involving
M in Source Region
High Voltage Sparking
M
Space Charge
blow-up
Reionization of Higa
Energy Neutrals
High Pressure
Blow-up
, Focusing Properties
..of Deflection Magnet
Low Pressure
• Blow-up
Fluctuation in
Accelerating potential
or Magnetic Field
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Neutral Gas Condensation
The listing is not all-inclusive and some of the effects could be
further subdivided. The possible contribution of each of these
processes to the net contamination at a given location does not
readily explain the amount of unwanted 18otope actually preseut. ...
Sepcifically, how does "Ca find its way into a **ca collector pocket
located some 6 inches away and on the high-energy side of the beam?
Experimental Procedure
To answer this question a special separation was made which would
minimize the effects of certain of the contaminating factors listed in
Columns I and II of Tabulation I. Particular emphasis was placed on
obtaining an operating pressure that was at least 50 to 100 times lower'
than usual. Segmented boundary wall treatment, ,or BIN, with the surface
in contact with the beam was utilized to ensure a high degree of beam
focus and stability. Ion outputs exceeded 120 ma. The exceptional
quality of beam focus and stability was confirmed by visual inspection,
.oscibus
oscilloscopic examination and rf spectrum. analysis.
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Experimental Results
The improvement in beam quality and the large reduction in pressure
(to ~ 2 x 10~Y torr )failed to reduce contamination in the foca or 48ca
reference positions. These results are shown in Figure 2. It will be
noted that the slope of the low pressure, high stability line is much
Žarger than that of the normal operation. The relative transmission of
feed contaminants .one mass unit from the reference 18 almost 10 times that
of normal operation. This difference becomes progressively less as the
mass difference increases. How 18 it possible for a well resolved and
stable beam to produce a sample of the quality indicated by figure 2 ..
Conclusions
1
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In allowing the segmented graphite boundary wall treatment, or BIN
surface to contact the primary ion beam, new phenomena may have been
introduced that increases the contamination. The isotopically well-separated
calcium ions in a given isotopic beam may be scattered by the boundary
wall treatment surface immediately in front of the receiver pocket. In
addition, neutral gaseous calcium particles condensed on cool surfaces
near the collector may be removed from the boundary wall treatment surface
to enter the reference pocket. The 40cat and 40cat lon beams are ~ 6
inches apart at the receiver. Thus, the contamination resulting from
the above postulated processes would be greater for adjacent masses than
for that of more distant masses.
It may well be thet the influence of the boundary wall is much more
subtle than indicated above. The boundary wall treatment alters the
potential distribution throughout the beam region and this laboratory 18
currently investigating these effects.
References
1.
W. A. Bell, Jr., A. M. Veach, E. D. Shipley, L. T. Newman and
J. V. Lee; Bu.?!. Am. Phys. Soc., Series II, Vol. 9 No. 5 (1964) p.537 .
J. H. Freeman, "The Relative Enhancement Factor in Electromagnetic
Separations" Electromagnetic Separation of Radioactive Isotopes
(Springer-Verlag, Vienna 1961, M. J. Higatsberger and F. P. Vienbock,
Eds., pp. 40-68 .
3.
R. Bernas, J. Compton, M. van Ments, and J. L. Sarrony, "Contribution
to the Study of Isotopic Contamination with a Double Magnetic
Deflection Isotope Separator," Ibid. Pp: 68-82.
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4.
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J. H. Freeman and W. A. Bell, "Factors Affecting Focus in Electromagnetic
Separators," AERE-R-4047 (May 1962).
5.
J. Koch, Ed., Electromagnetic Isotope Separators and Applications of
Electromagnetically Enriched Isotopes, (Interscience Publ..shers, Inc., ..
New York, 1958), Chap. XIV, pp. 275-300 .
6. E. D. Shipley, 0. C. Yonts, A. M. Veach, R. N. Goslin, W. A. Bell, Jr.,
..and G. E. Guest (submitted for publication in the Journal of Applied
: Physics).
.7.
i
Electromagnetic Isotopes Separations Department, Oak Ridge National
Laboratory. Electromagnetic Isotopes Separations (unpublished).
8.
L. .O. Love and W. "A. Bell, "Review of ORNL Electromagnetic Separations
Program January - December 1963,". ORNL-3606; May 1964, pp. 31-4.
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Figure Captions
Fig. 1
Relative Transmission of Feed Isotopes into Reference Position:
(Samarium Separations).
Fig. 2
Relative Transmission of Feed Isotopes into Reference Position (Calcium).
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% TRANSMISSION
LIITTTTTTITY
:.'.
4 3
2
1
1
2
3 4
MASS DIFFERENCE
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Fig. 1. Relative Transmission of Feed Isotopes into Reference Position:
(Samarium Separations).
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LOW PRESSURE
HIGH STABILITY
: OPERATION
i
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% TRANSMISSION
IT
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:
.:
".
— NORMAL OPERATION
ITTTTT
.001
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:
8
6 4 2 1
MASS DIFFERENCE
Fig. 2. Relative Transmission of Feed Isotopes into Reference Position (Calciun).
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END



DATE FILMED
10/11/65