This item is only available as the following downloads:
grs~;%8~ '86 Y
David H. Templeton
University of California
SS DEP, TR
Published for use within the Atomic Energy Commisslon. Inquiries for
additional copies and any questions regarding reproduction by recipients
of this document may be referred to the Technical Information Division,
Atomic Energy Commission, P. 0. Box E, Oak Ridge, Tennessee.
Inasmuch as a declassified document may differ materially from the
original classified document by reason of deletions necessary to
accomplish declassification, this copy does not constitute authority
for declassification of classified copies of a similar document which
may bear the same title and authors.
Date of Manuscript: Unknown
Document Declassified: June 6, 1947
This document consists of 6 pages.
ATOMIC ENERGY COMMISSION
ARTIFICIAL RADIOACTIVE ISOTOPES OF POLOfIUM, BISMUTH, AND LEAD
Chapter IV: A New Reaction with High Energy Deuterons
This document is a direct reproduction, by photo offset, of the copy in
the files of the Technical Information Division. This method of repro-
duction is being used temporarily as an emergency expedient in order
to effect earliest possible distribution of the information contained
therein. As soon as the expansion of the TID composing unit and of the
Oak Ridge printing plant, now under way, is completed, MDDC's will be
issued in an attractive permanent form.
AWIICIAL RAlIQACTIEx ISOYPEIVS P H LODIOM, BISMUTH, AND LEAD
Dissertation for the Degree of Doctor of Philosophy
David H. Temple ton
University of California, Berkeley, California
A Ne* Reaction with High Energy Deuterons
The formation of At has been observed when bismuth was bombarded with high
energy deuterons. This cannot be explained by impurities in the target or helium in
the ion source. A reaction of the type (d,p') is unreasonable for theoretical
reasons. A reaction of the type (d,pf) where p represents a negative mesotron,
cannot explain the phenomenon in every case. An explanation which is consistent with
the observed facts assumes that secondary alpha particles produced by the incident
deuterons in turn muse the Bi0 (a,2n)At211 reaction. Reasonable cross sections for
the two steps in this mechanism account for the observed yield.
When bismuth was bombarded with 200 Mev deuterons the polonium fraction, sepa-
rated by distillation, contained a strong alnha activity of 7.5 hours half-life.
Alpha-pulse analysis showed two groups of alpha particles at about 5.9 and 7.4 Mev.
lhis activity carried on tellurium when reduced with sulfur dioxide, while Po210
under the same conditions did not carry. It was concluded that the activity was
At which is known to have these characteristic properties. No known reaction
of deuterons can produce At from Bi This same tvpe of reaction has, however,
teen confirmed in other parts of the periodic table by noting the formation of iodirc
activities from antimony,(2) tellurium from tin,() and gallium from copper.()
Bombardments were made with various ener-ies of deuterons by setting the probe
t different radii in the cyclotron, and astatine was separated from a portion of
Lech target. The deuteron energies were estimated from magnetic field measurements.
The yields of astatine from these bombardments are listed in Table 1 as calculated
assuming a current of 0.3 microampere of deuterons. Ihe yield from a 400 IMv helir
ion bombardment, assuming 0.015 microampere, is also listed. These values 4re only
approximate because of large uncertainties in the chemical yield, in the geometrical
distribution of the beam on the target, and especially in the values of the beam
Yields of Astatine from Bismuth
400 Mev a 2 x 102 am2
200 Mev d 1 x 10-
150 Mev d 4 x 10-
90 Mev d 6 x 10-31
70 Mev d 6 x 10"31
50 Mev d 4 x 10-31
30 Mev d 7 x 10"31
If the compound nucleus P211 were to decay by emitting a negative beta par-
ciole of very hirh energy, leaving insufficient energy for any other particle to be
ejected, At211 would result. If one csloulates the time required for this process
by extrapolation of the known half-life vs energy relationship for beta emitters,
the resulting half-life is many powers of ten longer than the expected lifetime of
an excited nucleus. As the excitation energy is increased, the time required for
;.eav particle emission decreases much faster than that required for beta-particle
A second hypothesis is that the compound nucleus emits a negative mesotron,
forming At 2 his mechanism should be possible only at high energies, because
about 100 Mev must be supplied for the mass of the mesotron. Considering the
binding energy of the deuteron and the uncertainty in the value of the mass of the
mesotron, 90 Mev deuterons mirht have just enough energy for this reaction. The
small but finite yields at 70, 50, and 50 Mev show that some other explanation is
In order to obtain further evidence for or against a mechanism involving meso-
tron formation, lead was bombarded with 400 Mev helium ions.
Pb plus a helium ion forms the same compound nucleus, Po21 as deuterons
on bismuth. When lead was bombarded with 400 Mev helium ions, very little if any
astatine was formed. Thus the formation of the astatine by mesotron formation or by
any other mechanism involving this compound nucleus is very improbable. In the case
of the helium bombardment of lead the excitation of the compound nucleus was much
greater than for deuteron bombardments of bismuth, so that the argument is not com-
The astatine was not formed from thorium or uranium impurities in the target,
because of the absence of short-lived radium isotones known to be formed from these
materials under these conditions.(5) There is no known isotope between thorium and
bismuth of long enou-h life to have been present undetected in the target in ap-
Helium ion contamination in the ion source is not a possible explanation for
the astatine at high energies. When the target is at radius 81 inches, the yield
of astatine per unit time is about the same with deuterium as with helium in the ion
source, even when the tank had been pumped out repeatedly to remove helium. The
higher cross-section for formation by helium ions is compensated by the lower ef-
ficiency of the ion source to produce helium ions. Since the cross-section for for-
ration of astatine by helium ions is much greater at lower enerries, helium contam-
nation may have contributed to the observed yields in the lower energy deuteron
Ihe only single mechanism which is fairly consistent with all the facts is
that the astatine is produced by secondary alpha particles. It is likely that these
alpha particles would be expelled from the heavy element nuclei with about 30-40 MbT
energy. It is known experimentally that the a,2n cross-section for alpha particles
of this energy range is about 5 x 10 am If it is assumed that this cross-sectia
is effective, on t;.e average, over the first 0.025 cm of the alpha particle path in
bismuth, one such alpha particle in 3000 w 11 produce At211. Usinp this figure and
the observed yields of At211, the cross-section for formation of the secondary alpha
particles was calculated. These cross-sections are listed in Table 2. 4erefore if
the cross-sections for formation of secondary alpha particles are as high as the
values listed in Thble 2, the phenomenon is explained. It should be noted that most
of these cross-sections are but small fractions of the geometrical cross-section for
bismuth, which is of the order of 10 am .
Cross-sections Required for Secondary Alpha Formation to Account for
the Astatino Formation
400 Mev a 6 x 1025
200 M-ev d 3 x 10-26
150 Mev d 1 x 10-26
90 Mev d 2 x 10-27
70 Mev d 2 x 10-27
50 Mev d 1 x 10-27
30 Mev d 2 x 10-27
It may be possible to verify this su-rested mechanism in a number of ways. If
several very thin foils of different thicknesses (much less than the range of a 30
Mav alpha particle) are bombarded with deuterons, the observed overall cross-section
should be a function (approximately linear) of the thickness of the foil. For a
one-step mechanism, the orosa-seotion should be independent of target thickness.
Alternate approaches are to try to observe the secondary alpha particles by cloud
chamber or photographic emulsion tracks, or by inducing reactions in secondary tar-
gets outside of the incident deuteron beam, but within the range of secondary alpha
particles. None of these experiments has yet been attempted.
1) D. R. Corson, K. R. bacKenzie, and E. Sepre, Phys. Rev. 58, 672 (1940).
2) R. H. Goeokermann, private communication.
3) M. Lindne-, private cobnsunioation.
4) D. R. Miller, private communication.
5) P. R. O'Connor, private communication.
UNIVERSITY OF FLORIDA
3 1262 08909 7876
xml version 1.0 encoding UTF-8
REPORT xmlns http:www.fcla.edudlsmddaitss xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.fcla.edudlsmddaitssdaitssReport.xsd
INGEST IEID E1OJPEN9S_0IKGSU INGEST_TIME 2012-02-29T18:28:35Z PACKAGE AA00009329_00001
AGREEMENT_INFO ACCOUNT UF PROJECT UFDC