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w
the
to, any information pursuant to his employ-
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1
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اسکو 3 م ا
CONF-650706-6
JUN 24 1965
bonis
On Radiative Transitions in culpb and wºPb Folloring Resonance Neutron
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Capture on 206p6 and 20700*
r. .........
.::-Inne
:..; Hermio
J. A. Biggerstaff, J. R. Bird, ^^ J. H. Gibbons, W. M. Good, and R. L. Macklin
Oak Ridge National Laboratory
Oak Ridge, Tennessee
LEGAL NOTICE -

The report no prepared u ua account of Government sponsored work. Mollber the Vallad
Suta, cor e Coomooloa, bor my person ucun oa behall of Coduloo:
A. Meker way writy or ropnenautoa, exproud or laplied, with respect to the accu-
racy, completeness, or wretulness of the information coaleload a report, or that the we
of way laformasuon, appenatus, Rathod, or procuro di lorod la o report may not latring
prinuly oned righus; or
B. Asmod. v. llabillues will respect to the wool, or for damagu rusulung Irom the
ume of way lalorostioa, appuntu, bulbod, or procon discloud la the report.
As und la tbe above, "parko etag on behalf of the Commission" lacludes may on-
pregn or contractor ol le Commission, or employee of such contractor, to the isnt that
much wapioya or coatrictor of the Commission, or ouploys al auch matractor propurus,
disumiall, or provider access to, may for a lon purnt to Mi caploganat or coatrict
with the Communion, or Mo imploywear with sucb cools actor.
The spectrum of gama rays emitted in resonant radiative neutron capture
permits the study of states which are related to each other by electric or
.
magnetic dipole transitions. It is expected therefore that levels either bound
.
or unbound can, appear prominently in resonant radiative capture, which are not
readily observable in other reactions. Such resonant capture can be studied
in light nuclei and in closed shell regions by means of a pulsed van de Creaft
as neutron spectrometer and a large (9" x 12") NaI crystal as gamma-ray
spectrometer. The time resolution at the present state of the art 18 30 to 100
ns/meter wbich, with the Van de Graaff, permits the study of nuclides for which
the level spacing is a few kilovolts.
Figures 1, 2, and 6 show preliminary results of a study of 20° PO and
207 Po. Neutron resonances in 20 Po, first observed in capture gamma studies,
are barely resolved (1488. 1 and 2) but later transmission measurements,
capable of much better resolution, gave precise values of resonance energies
* Research sponsored by the U. S. Atomic Energy Commission under contract
with the Union Carbide Corporation.
** Visiting scientist from AERE, Harwell, England.
PATENT CLEARANCE OBTAINEL. RELEASE TO
THE PUBLIC IS APPROVED. PROCEDURES
BRE ON FILE IN THE REALI!G SECTION,
together with widths and probable parities
.
-
-
(F48. 3). In Fig. 1 the multichannel analyzer
was used to examine gamma pulse heights in de-
tail, whereas in Fig. 2 the yield of a given

-
·
gamma ray was observed as a function of neutron
energy.
The yield of the 7.4 MEV ground state
cu FU(,7) ine gave evidence for resonances in
addition to the known one at 42 kev. This was
a
Fig. 1. Pulse spectrum of ima rays
versus neutron flight time 206 Pb(a,y).
confirmed with separated isotope transmission
studies (Fig. 4) in which parities and widths
were obtained. ?

a sitio
1
now orang Mom what were buena
on mone more band w
e
canneth
In spite of the relatively crude nature
of these results we submit the following:
(a) The scheme of levels with parities and
angular momenta shown in Fig. 5, if used with
E1, M reduced widths in the general range given
3 .account for the observed spectra,
by Bartholomew,"/() in addition to the unbound
levels summarized in Fig. 5, two new bound levels
Fig. 2. Yield of gamma rays witb.
were discovered whose exact positions are ambigu neutron energy versus gamma-pulse-
ous because the sequence of gamma rays is not sample.
yet known, (c) the 207pbla,y) 8-Wave resonance
capture at 42 keV 18 a candidate for direct cap-
ture for which no evidence (e.gi asymmetry in
the ground state transition due to direct and
compound interference offerts) was observed.
12:

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19:12 PARASH
FONDO IN RERIH MOTO
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THIETENIMI?
il
Mg. 3.
Total cross section of
206 pts
The 1sotopic sample of Zul Pb was too small
Ej,
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to obtain data corresponding to Fig. 1. How-
ever, the results of a similar experiment with
poor resolution 18 shown in Fig. 6. The transi-
tions through the 3° state at 2.61 MeV in 20° Pb
become relatively more intense at lower neutron
energy which suggests but does not prove the
interpretation of Fig. 7. .
.
نليللنلل
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Little
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Mg. 4. Neutron total cross section
of 20770.
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Fig. 5. Partial energy.
level diagram 201Pb show-
ing observed levels.
its ...
Fig. 6. Pulse spectrum of gamma
rays versus neutron flight time
207p0(0,7).
Fig. 7. Partial energy level
diagram 200 pb showing observed
levels.
References
1. J. R. Bird, J. H. Gibbons, and W. M. Good, Bull. Am. Phys. Soc. Z 552 (1962).
2. R. L. Macklin, P. Jo Pasma, and J. H. Gibbons, Phys. Rev. 136, B695 (1964).
3. Go A. Bartholomew, Electromagnetic Hetimes and Properties of nuclear States,
Nuclear Science Series Report No. 37 (RAS-NRC publication 974), p. 213 (1962).
ack
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22
9 / 16 / 65
DATE FILMED
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