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melt sample. The location of the peaks and the
limited data on their decay rates indicate that these
activities can be attributed to various metubers of the
thorium decay series, such as 2rzPb, '"Bi, and
'"*Tl, although insufficient decay rate data were
obtained for conclusive identification. The lack of
233Pa activity on the cathode, coupled with almost
identical counts on samples OE melt taken below
and after electrolysis, indicated that deposition of
a significant amount of protactinium on the cathode
did not take place in this experiment.
The failure to reduce protactinium in this experi-
ment may be explained by its low concentration in
the melt. The amount added, 27 rng in 1556 g of
LiF-BeF2-ThF4, is approximately equal tu a mole
fraction of 2 x IOw5. If the protactinium is four-
valent in the melt, and if it is assumed that its
E, is close to that of thorium, that is, 1 v, the
potential required to reduce it at that concentra-
tion and at the HF-1-1, ratio used in the electrol-
ysis is 1.007 v. The very small denominator makes
the logarithm term positive, so that the reduction
potential is even more negative than E, in spite
of the low HF prt.: .\sure.
The same argument would deny that protactinium
can be reduced by thorium at this concentration,
which is contrary to fact. 'The nickel cathode did
not provide a low-activity alloy in this attempt.
This suggests the possibility of using a cathode
that would form a thorium alloy in which protactinium
dissolves at low enough activity to permit reaction.
For further experiments of this type we recommend
a potential of 1.1 v, at which thorium will be deposited,
hopefully, along with protactinium, and
stopping the experiment when five equivalents of
thorium have been deposited. This would give a
concentration of about 0.2 for protactinium in the
metal, and thus a low enough activity to permit
reduction of essentially all the protactinium.
12.4 PROTACTINIUM STUDIES IN THE HIGH-
ALPHA MOLTEN-SALT LABORATORY
C. J. Barton H. PI. Stone
In the previous progress report7 we mentioned the
possibility that icon coprecipitated with protacl inium,
when solid thorium was exposed to molten Li F-ThF,$,
might be carrying the reduced protactinium to the steel
wool surface in the Rrillo process. It was also
pointed out that variable iron analyses made it dif-
ficult to determine the role of iron in protactinium re-
duction experiments. We performed one reduction
experiment with 'Fe tracer dissolved in I,iF-ThF4
(73-27 mole %j in the absence of protactir~ium, and
the results are summarized below. Most of the
protactinium recovery experiments performed during
the current report period wetre thorium reduction tests.
An unsuccessful effort to deposit protactinium electrolytically
is discus:;ed in the preceding section of
this report.
Reduction of Iron Dissolved in Molten LiF-ThF,
We studied the reduction of iron dissolved in
molten LiF-ThF4 (73-27 mole %j by using hydrogen
and metallic thorium as the reducing agents. The
tracer iron results indicated that more than 40 hr
was required to reduce the iror? concentration from
330 to 2 ppm with hydrogen at a temperature of
6OOOC. During a 3-hr exposure to metallic thorium
at the same temperature, the iror! concentration in
filtered samples, caIculat.ed from tracer counts,
diminished from 550 to 13 ppm.
Colorimetric iron determinations performed by two
different laboratories agreed with the tracer iron data
for about half the samples. In general, agreement
was poorest for sarriplcs that gave "Fe counts indicating
an iron concentration less than 0.1 mg/g.
It appears that the colorimetric iron method tends
to give high results with samples having a low
iron concentration. This finding is in agreement
with results of earlier unpublished studies performed
by Reactor Chemistry Division personnel.
The results of this experiment will be discussed
in more detail in another report.
Thorium Reduction in the Presence of
an Iron Surface (Brill0 Process)
One Rrillo experiment of the type discussed in the
previous report' was performed during this report
period. A salt solvent, LiF-'ThF, (73-27 mole %),
containing initially 17 mg of 23 'Pa and 57 rrig of Fe
was exposed to thorium rods for two 1-hr petiods in
the presence of 4 g of steel wool (0.068 m2 per g of
surface area). The tracers 233Pa and 5gFe were
added to aid in following the behavior of these ele-
ments in the experiment. The first thorium exposure
removed 05% of the protactinium, as determined by
analysis of a filtered sample of salt, and almost all
the iron. The second thorium exposure resulted in
only a slight further decrease in protactinium con-