Neutron Activation Analysis of Packard Batch 21-634
Zelimir Djurcic1, Andreas Piepke1 and Bryan Tipton2
University of Alabama1
Caltech2
(Status 4/28/2001)
(Updated 5/15/2001)
In this note we discuss the results obtained by neutron activation analysis of
Packard PPO batch 21-634. This is the first production lot to be used in KamLAND.
An extended irradition, lasting for 5 hours at the research reactor of MIT, was
performed. After irradiation side activities were seprated from the PPO by
means of ion exchange columns. This analysis was optimized for U and Th detection.
In parallel part of the sample were just extracted by HNO3 and then counted
without ion exchange. The analysis of this sample serves to study the chemical
purity of the PPO. An extensive set of blank samples was prepared to determine
the background. A PPO sample spiked with organic U and Th solutions,
of known mass, was used to demonstrate the efficiency of the ion exchange.
As in the previous irradiations the sample preparation was performed in the
UA cleanroom.
The activity of the activation products was determined by gamma ray counting.
At UA both the existing and our new low background detectors were used.
In the following we will discuss the details of this work. Click on the
appropriate subject.
Sample preparation.
Initial counting results
after receipt of the samples.
New low background
counting set up.
Determination of
the neutron flux.
Determination of the retention efficiency for U/Th
in ion exchange and description of the sample preparation procedure
used for the PPO samples.
Analysis of the U/Th concentration of the PPO after
inon exchange.
Analysis of activated PPO samples without ion exchange,
used to determine the chemical impurities.
The same batch of PPO has been analyzed at
Caltech.
Their results are also available on the web.
Conclusion for Packard batch 21-634 based on the UA analysis
Analysis of the chemical contaminations in Packard PPO 21-634 showed an improved purity compared to the pre-production
batches 21-0113, 21-1011 and 21-1012. It is noted that the large Br concentration found in some of those samples
is no longer observed. This helps to achieve better sensitivities with regards to U/Th detection.
Using both the sample conditioned by ion exchange after irradiation, and the original PPO, allows us to determine the
following limits for the
concentrations of U/Th and K, respectively:
K: 300±100 ppb or <464stat ppb
<600total ppb
Th: 2.5±0.85 ppt
U : 0.15±0.93 ppt or <1.7stat ppt
<2.2total ppt
KamLAND scintillator will have a PPO concentration of 1.5 g/l. The corresponding mass dilution factor is 520.
Using above data we estimate the effective U/Th concentration of KamLAND scintillator due to Packard PPO
batch 21-634:
K: <1.2·10-9 g/g
Th: (4.8±1.6)·10-15 g/g
U : <4.2·10-15 g/g
Conclusion for Packard batch 21-634 based on the
Caltech analysis
Above results are compared to the results obtained at Caltech in a parallel analysis of the same PPO batch.
K: <72total ppb
Th: <28total ppt
U : <11total ppt
Again using the same factor 520 dilution PPO of above purity would result in the following concentrations
in KamLAND scintillator:
K: <1.4·10-10 g/g
Th: <5.4·10-14 g/g
U : <2.1·10-14 g/g
Conclusion for Packard batch 21-634
Even without further purification Packard PPO batch 21-634 would be marginally suited for use in KamLAND. If we use the
purification factors found by Borexino
for K, Th and U (500, >160 and 70) we would arrive at a scintillator
purity (due to PPO only) of:
K: <2.8·10-13 g/g
Th: <3.0·10-17 g/g
U : <6.0·10-17 g/g
In case the same purification factors apply here the PPO should definitely be suitable for KamLAND.
This page is maintained by A. Piepke
Last update June 11, 2001