ORNL-1816 - the Molten Salt Energy Technologies Web Site

ANP QUARTERLY PROGRESS REPORT
For much cf the time during the last quarter the
Bulk Shielding Facility (BSF) was shut down for
modifications to the reactor pool. The modifi-
cations were being made to permit the use of
demineralized water in the reactor pool in order
to eliminate corrosion of the reactor fuel elements.
The set of highcpower fuel elements which had
iously been operating in process water that
had been treated by chromate addition had to be
discarded, even though burnup of the uranium in
these elements was negligible, because of the
extent of pitting of the aluminum cladding. In
order to utilize demineralized water, the pool was
cleaned and painted, and all steel was either
removed or sprayed with a stainless steel pro-
tective layer. A bypass demineralizer is being
installed to maintain the water purity. The
measurement reported below was made by members
of the BSF staff in other facilities.
A SEARCH FOR SHORT-HALF-LIFE NUCLEAR
ISOMERS IN K39, Rb85, Rb8’, AND Zr9’
R. W. Peelle
E. C. Campbell F. C. Maienschein
Rubidium, potassium, and zirconium are among
materials which have been considered as fuel
components for reactor systems in which the fuel
is circulated. Any short-period isomeric gamma-
ray transitions would complicate the shielding of
the external fuel loop, especially if the gamma
rays were of high energy. Rubidium was previ-
ously known to possess a low-energy isomeric
transition with a half life of about 1 min, but
measurements had not been made which would
reveal any shorter period that might be present.
Electromagnetically enriched K39, Rb85, and
Rb8’ in the form of nitrates were injected into
the ORNL Graphite Reactor by use of a fast
’ Part time.
1 56
14. BULK SHIELDING FACILITY
F. C. Maienschein
G. M. Estabrook E. B. Johnson
J. D. Flynn T. A. Love
M. P. Haydon’
R. W. Peelle
K. M. Henry W. Zobel
Physics Division
pneumatic probe assembly designed by E. C.
Campbell. Since the samples were ejected from
the center of the reactor within about 0.1 sec from
the end of the bombardment, it was possible to
make a search for very short-period activities.
The ejected sample was viewed by a thallium-
act i voted sodium iodide sc inti I lot ion-cry sta I
gamma-ray detector. The signal from the photo-
multiplier was transmitted by coaxial cables to
a multichannel differential pulse-height analyzer
located at the BSF. In addition, the counting rate
of any part of the spectrum could be measured as
a function of time with a linear count-rate meter
and a very fast Brown recorder. Thus both
spectral and time decay analyses of gamma radi-
ation emitted by the irradiated sample were ob-
tainable.
A study of K39 yielded no short-period activity.
In the rubidium isotopes the previously known
radiations were found, but no shorter period
isomers were discovered. Isomers with an ap-
preciable energy and cross section would‘ have
been detected if they had had a half life greater
than about 0.03 sec. A sample of Rb85 was found
to contain the known 550 k 6-kev transition, with
a 1.05 f 0.05-min period, and bombardment of
Rb8’ produced the known Rb88 activity.
The apparatus described above was also used
in the discovery of a number of new isomeric
transitions with half periods2 between 0.05 and
5 sec. One of these is Zr90m, which yields a
2.30 f 0.03-Mev gamma ray with a half life of
about 0.83 * 0.03 sec. This isomer is produced
by inelastic neutron ~cattering.~
2E. C. Campbell, R. W. Peelle, and F. C. Maienschein,
Phys. Semiann. Prog. Rep. Sept. 10, 1954 (unclassified),
ORNL-1798, p 36.
3E. C. Campbell, R. W. Peelle, F. C. Maienschein,
and P. H. Stelson, Decay and Fast-Neutron Excitation
of Zr90m, paper to be presented at the meeting of the
American Physical Society, New York, January 1955.
1-
* *