Analysis of U/Th spiked Sample UA30, activated at MIT 3/21/2001 22:26 for 5 hours
Zelimir Djurcic and Andreas Piepke
University of Alabama
Two of the Packard PPO samples (batch 21-634) have been spiked by Bryan Tipton at Caltech with organic
U and Th compounds. These samples CIT30 and UA30 have been activated at the MIT reactor together with
the other samples. UA30 has been activated for 5 hours ending 3/21/2001 22:26 (CST).
It was used to determine the retention of 233Pa and 239Np in
ion exchange extraction. We used small (2 ml) Eichrom TRU Resin ion exchange columns, supplied by
David Glasgow of
Oak Ridge National Laboratory. David had worked out a procedure to dissolve Np in 8 normal
HNO3. He then demonstrated, using alpha counting, that the Np is retained with more
than 95% efficiency in these columns. In our experiments, described below, we followed the procedures
outlined by David.
The 233Pa and 239Np activities were determined by means of gamma ray counting after
receipt of the samples. All activities reported are corrected to 3/24/2001 10:28 (CST), the time
of our first measurement. According to Bryan Tipton sample UA30 contained:
0.438 g of Packard PPO
The following activities were determined for sample UA30 before it
was subjected to any chemical treatment. This measurement can hence serve
as the normalization of the efficiencies to be determined. All sample vials were externally cleaned by
etching after receipt.The sample vials were packed in secondary containment bags to avoid direct
handling at the reactor.
2.7 µg of Th
6.4 µg of U
On 3/25/2001 we extracted the Pa/Np activity from the sample using the following procedure:
for the extraction of the PPO, contained in a sealed plastic container (which was cut open
to perform the extraction), we used 15 ml 8 molar HNO3,
pre-heated to 68-75 deg Celsius. At these temperatures the PPO melts and is miscible with the acid.
The mixture was kept for 30 min at this temperature on a hot plate. The mixture was then allowed
to cool down. As soon as the temperature of the mixture goes below the PPO melting point it
precipitates. The liquid was then poured into the ion exchange column, which had been activated
with 10 ml of high purity 8 molar HNO3. The remaining PPO slurry was collected and
counted to determine the effectiveness of the first acid wash. It was determined (by counting) that
approximately 550 Bq of 233Pa (or 28%) and 2500 Bq (or 10%) of 239Np was
still left. A second extraction was then performed.
A total of 20 ml of acid was poured through the ion exchange column. This acid was collected
in small plastic vials and the amount of 233Pa and 239Np contained in
the discarded acid was again determined by counting to provide a consistency check of the
In a last step the column was flushed with de-ionized water in an attempt to elute the target
activity from the column. David had found quantitative transfer of Np into the water. However,
this was not observed here. After three washes we found only (in the
following only statistical errors are quoted. We estimate the systematic error
to be on the order of ±10%)
224±9.2 Bq of 233Pa and
10135±44 Bq of 239Np in the water.
Counting of the ion exchange column alone yielded 1260±5 Bq
and 13800±30 Bq
of 239Np in the columns.
Counting of the columns together with the water (as done for the PPO sample)
yielded 1440±13 Bq of
22640±27 Bq of
239Np. Note that
the activities measured in the water and in the columns separately add up reasonably well to the numbers
obtained counting water and columns together.
This finding of a high retention efficiency is confirmed by the activities measured for the
discarded acid after it went through the column. This data gives us
a direct cross check on the inefficiency of the column itself.
We measured 20±23 Bq of 233Pa and
629±27 Bq of 239Np in the acid plus
352±14 Bq of 233Pa and
3130±26 Bq of
239Np in the PPO left after the second acid digestion.
Using above data we determine the following efficiencies and in inefficiencies for the
extraction by ion exchange itself:
The measurements of the initial activity and the inefficiency involved the
same counting geometry. We hence consider the inefficiency to be the better quantity to deal with.
The Spread of above efficiencies are understood on the basis of the systematic errors quoted.
These are mainly caused by the fact that the counting geometries do slightly vary from run
As we filled the PPO-acid mixture into the column without prior filtering we removed the PPO
residue left in the neck of the column. All data shown above was obtained with this residue present
in the neck. However, as it was removed for the real PPO sample we need to quantify its
contribution to the inefficiency. Counting of the residue (removed) alone yielded:
11.8±1.3 Bq of 233Pa and
142.4±12.6 Bq of 239Np.
Before removal of the PPO residue we found the following activities left in the column (without
the wash water):
1260±6.1 Bq of 233Pa and
15140±40 Bq of 239Np.
Counting the column after removal of the PPO yielded
1186±14 Bq of 233Pa and
14090±200 Bq of 239Np.
The retention efficiency is derived from the ratio of column activities after PPO removal divided
by that determined before removal, it is: 0.94±0.01 for 233Pa and
0.93±0.01 for 239Np.
The inefficiency as determined from the measurement of the discarded PPO is:
0.01±0.001 for both 233Pa and 239Np.
As identical counting geometries could be used in the measurement of the efficiency
will be used to quantify the removal of the PPO residue from the column.
Retention of 233Pa and 239Np in ion exchange:
In view of the similar inefficiencies measured for the ion exchange itself we will use
one unified efficiency for both species. Based on the analysis presented here we derive the
This page is maintained by A. Piepke
Last update April 27, 2001