IEEE Ttnwactionz on NucteaA
Science, VotZNS-23, No,2, Aptik 1976
IONS IN COLLISIONS OF 60-250
HELIUM
BEAMS
TRAVERSING CARBON FOILS*
KEV
A.J. Kestelman, E. Alonso and R.A. Baragiola
Centro At6mico Bariloche
Comisi6n Nacional de Ener4ga At6mica
8400 Bariloche, ARGENTINA
FORMATION OF He
Summary
A grounded shield(9) surrounds the detector
assembly. The whole experimental set-up is
inside a chamber which was held at 2 to
5 x 106 Torr during the experiment. The detector moving system is mechanically connected to a potentiometer whose signal is sent to
the X axis of an X-Y recorder, the Y axis receiving a signal proportional to the ion current as measured by an electrometer connected
to the movable detector.
Because of experimental reasons we have
not measured the He+ and He" components (except to check that the measuring system was
working properly) but to get Fj,,we have used
measuinstead, the values of Fo previously
prvosymau
16
red in our laboratory . A typical spectrum
of components He0 and He (where component
He+ is also seen) is shown in Fig. 2. The double peaks observed for each component are due
to a backlash effect in the gear train mechanism of the detector moving system, and the
different position of the peaks depends on
whether the detector is moving CW or CCW.
The measured equilibrium fractions FTO
for He in carbon are shown with its statistical errors in Fig. 3 as a function of beam
energy.
Preliminary measurements of the charge
equilibrium fraction FT,,for the negative com
ponent are presented for a He + beam traversing a 2 pg/cm 2 carbon foil. This fraction
decreases with energy with a value of about
2.5 x 10i4 at 60 keV and about 1 x 10 4 at
250 keV.
Introduction
Dukel'skii et al. first reported the
formation of He ions from He beams traversing different noble gases. Since then various authors have studied the process of He
formation from He traversing different gases
2-10 and metal vapors
However to our
knowledge, the formation of He in solids has
not been studied so far.
11-13.
Experimental Arrangement and Results
To study the formation of He
ions from a
He+ beam traversing carbon foils, the equipment previously used in this laboratory to
measure He formation in gases 10 was modified as sketched in Fig. 1.
The magnetically separated He+ beam from
a 300 keV Cockcroft-Walton type accelerator
is collimated by diaphragm (2) before traversing a carbon foil(3)l4which is about 2 pg/cm2
thick, enough to charge equilibrate the beam
without causing too much energy degradation
(not more than - 5% at the lowest energies).
The charge equilibrated beam passes through
collimators (4) and (5) and the different
charge components are separated by electrostatic deflector (6) and collected by a movable secondary emission detector (7) after
having traversed a positively polarized diaphragm covered by a thin (rv10pg/cm2 ) carbon
foil (8) thus ensuring the same detection efficiency for ions and neutral atoms 15.
*Work supported in part by the Organization
of American States Multinational Program in
Physics.
Acknowledgements
We wish to thank Messrs. C. Lulich and F.
Tutzauer for their fine machine work.
References
1. V.M. Dukel'skii, V.V. Afrosimov, and N.V.
Fedorenko, Sov. Phys., JETP 3, 764 (1956).
2. P.M. Windham, P.J. Joseph, and J.A. Weinman, Phys. Rev. 109, 1193 (1958).
3. Ya.M. Fogel', V.A. Ankudinov, and D.V. Pilipenko, Sov. Phys., JETP 11, 18 (1960).
4. T. Jorgensen, Jr., C.E. Kuyatt, W.M. Lang,
D.C. Lorentz, and C.A. Sautter, Phys. Rev.
140, A 1481 (1965).
S. A. Papkov and G.J. Steiger, Z. Naturforschg.
21a, 1048 (1966).
6. L.E. Collins and P.T. Stroud, Proc. Phys.
Soc. 90, 641 (1967).
7. H.B. lilbody, R. Browning, K.F. Dunn, and
1143
Authorized licensed use limited to: University of Virginia Libraries. Downloaded on January 31, 2010 at 14:44 from IEEE Xplore. Restrictions apply.
A.I. McIntosh, J. Phys. B (Atom. Molec.
Phys.) 2, 465 (1969).
8. H.B. Gilbody, K.F. Dunn, and R. Browning,
J. Phys. B (Atom. Molec. Phys.) 3, L19
(1970).
15. S.K. Allison, Rev. Mod. Phys. 30, 1143
(1958)_
9. K.F. Dunn and H.B. Gilbody, Proc. VII Intl.
Conf. on Physics of Electronic and Atomic
Collisions, 1085, Amsterdam (1971).
10. A.J. Kestelman and R.A. Baragiola, Proc.
VIII Intl. Conf. on Physics of Electronic
and Atomic Collisions, 825, Belgrad (1973);
A.J. Kestelman, R.A. Baragiola, and J.
Bratina, Comunicaciones Asociacion Fisica
Argentina (AFA), 1, 12 (1973); A.J. Kestelman and R. Baragiola, Comunicaciones AFA,
2, 83 (1974) and 60th Meeting AFA Paper L.3,
Tucuman, May 1974 (unpublished).
11. B.L. Donnally and G. Thoeming, Phys. Rev.
159, 87 (1967).
12. R.A. Baragiola, E.R. Salvatelli, and G.
Lantschner, Proc. VII Intl. Conf. on Physics
of Electronic and Atomic Collisions, 788,
Amsterdam (1971); R.A. Baragiola and E.R.
Salvatelli, J. Phys. B (Atom. Molec. Phys.)
8, 382 (1975).
13. R.N. Il'in, V.A. Oparin, I.T. Serenkov,
E.S. Solov'yov, and N.V. Fedorenko, Proc.
VII Intl. Conf. on Physics of Electronic
and Atomic Collisions, 793, Amsterdam
(1971).
14. Supplied by Yissum Research Development
Company, Hebrew University, Jerusalem,
Israel.
16. A.J. Kestelman, W. Meckbach, and J.I. Cisneros, 57th Meeting AFA, Paper D.3.1, Cordoba, May 1972 and Final Scientific Report
Grant AFOSR-69-1802, August 1972 (unpublished).
124 keV
He'+ Carbon
lOOmV-10 Qt
He
I
Iv-lofI
I
Fig. 2
Typical spectrum of the He-, He0 and He+ peaks
taken at 124 keV. Figures at the top of each
peak indicate sensitivity settings for the
electrometer. Arrows point at changes in these
settings while peaks are being recorded. For
explanation of double peaks see text.
3
I
2
0
0
2
1W
3
4 cm
Fig. 1
1) He' beam; 2) Diaphragms; 3) 2 p/cm2 carbon
foil; 4 and 5) Collimators (the configuration
shown was designed for a different experiment
which is now being performed); 6) Electrostatic plates; 7) Movable detector; 8) Diaphragm
with charge equilibrating carbon foil; 9)
Shielding. Insert shows movable detector in
better detail.
He +Carbon
-~~~~~~~~~~~5
n
50
100
_
200
150
BEAM ENERGY (keV)
250
Fig. 3
Charge equilibrium fraction for He- in carbon
vs. He+ beam energy.
1144
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