Artificial radioactive isotopes of polonium, bismuth, and lead

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Title:
Artificial radioactive isotopes of polonium, bismuth, and lead chapter IV : a new reaction with high energy deuterons
Series Title:
United States. Atomic Energy Commission. MDDC ;
Physical Description:
6 p. : ; 27 cm.
Language:
English
Creator:
Templeton, David Henry, 1920-
University of California
U.S. Atomic Energy Commission
Publisher:
Technical Information Division, Atomic Energy Commission
Place of Publication:
Oak Ridge, Tenn
Publication Date:

Subjects

Subjects / Keywords:
Radioisotopes   ( lcsh )
Polonium -- Isotopes   ( lcsh )
Lead -- Isotopes   ( lcsh )
Bismuth -- Isotopes   ( lcsh )
Radioactive substances   ( lcsh )
Genre:
federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Bibliography:
Bibliography: p. 6.
Restriction:
"Date Declassified: June 6, 1947"
Statement of Responsibility:
by David H. Templeton.
General Note:
Manhattan District Declassified Code
General Note:
"Date of Manuscript: Unknown"

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University of Florida
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 005023936
oclc - 277773234
System ID:
AA00009329:00001


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David H. Templeton


University of California


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US DEPOSITOORY


Published for use within the Atomic Energy Commisslon. Inquiries for
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Inasmuch as a declassified document may differ materially from the
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may bear the same title and authors.









Date of Manuscript: Unknown

Document Declassified: June 6, 1947

This document consists of 6 pages.


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MDDC 1069

UNITED STATES
ATOMIC ENERGY COMMISSION
OAK RIDGE
TENNESSEE





ARTIFICIAL RADIOACTIVE ISOTOPES OF POLOfIUM, BISMUTH, AND LEAD

Chapter IV: A New Reaction with High Energy Deuterons

by
































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
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issued in an attractive permanent form.




MDDC-1069


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

Chapter IV

A Ne* Reaction with High Energy Deuterons


211
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
211 (1)
At which is known to have these characteristic properties. No known reaction
211 209
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


-1-




xDDC-1069


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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

current.



Table 1

Yields of Astatine from Bismuth

Projectile Cross-section

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



211
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

em.ission.

A second hypothesis is that the compound nucleus emits a negative mesotron,
211
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






MDDC-1069


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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

necessary.

In order to obtain further evidence for or against a mechanism involving meso-

tron formation, lead was bombarded with 400 Mev helium ions.
207 211
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-

pletely rigorous.

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-

preciable concentration.

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

bombardments.





MDDC-1069
-4-

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
-25 2
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
-24 2
bismuth, which is of the order of 10 am .


Table 2
Cross-sections Required for Secondary Alpha Formation to Account for
the Astatino Formation

Projectile Cross-Section

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





m-- -10o69
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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.




DD-6-1069
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References

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.












































































































































































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