AN INTEGRAL REACTOR PHYSICS EXPERIMENT TO INFER ACTINIDE CAPTURE CROSS-SECTIONS FROM THORIUM TO CALIFORNIUM WITH ACCELERATOR MASS SPECTROMETRY Page: 4 of 5
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G. YOUINOU et al., ND2010 Proceedings
respectively, 50 days, 100 days and 150 days.
Condition (2) is most readily satisfied when A is the
heavier long-lived isotope of an element because then the initial
A+1, A+2... impurities belong to another element and are
consequently easier to separate than when they belong to the
same element as A. This category of isotopes includes 232T,
238U, 237Np, 242Pu, 243Am and 248Cm and are given the highest
priority for the AMS analysis because its 2-3% precision should
be sufficient to infer cross-sections with an uncertainty of about
5%. The other isotopes, with a more important A+1, A+2...
contamination, will be analyzed with the less sensitive but more
precise methods available at INL (TIMS and ICP-MS), hence,
providing another set of data.
Table 1, 2 and 3 show the calculated actinide build-up in
238U, 242Pu and 248Cm samples (supposed to be 100% pure)
filtered with cadmium and boron. Since the AMS can detect
actinide abundances down to 10-2, these nuclides could
potentially be measured if the initial impurities are low enough
that they don't mask the actual build-up. The purity of the
samples will be essential for the success of the experiment.
Table 1. Example of actinides build-up in a U238 sample after 50
days with a cadmium filter and 200 days with a boron filter (U8
refers to 238U, with similar abbreviations elsewhere)
Cd 0.991 8E-03 2E-05 2E-06 2E-09 2E-11 1E-11
B 0.999 2E-04 7E-08 2E-11 - - -
Table 2. Example of actinides build-up in a 242Pu sample after 50
days with a cadmium filter and 200 days with a boron filter
Cd 0.964 3E-02 9E-04 6E-06 5E-09 4E-12
B 0.999 3E-04 1E-07 2E-11 - -
248
Table 3. Example of actinides build-up in a 2Cm sample after 50
days with a cadmium filter and 200 days with a boron filter
Cd 0.992 7E-03 4E-04 1E-04 8E-06 7E-08
B 0.999 1E-04 3E-05 2E-07 1E-10 -
4. EXPERIMENTAL DETERMINATION OF
THE ATOM DENSITIES
4.1 Accelerator Mass Spectrometry at ANL
The requirements placed on the AMS measurements to be
performed at ATLAS by this program are quite challenging.
Challenges to a successful program include high-precision
measurements, minimization of cross-talk between samples,
efficient use of milligram samples, and the processing of an
unprecedented number of samples for a facility as complex as
ATLAS. The measurement configuration for ATLAS will use
the Electron Cyclotron Resonance ion source, ECR-II,
significantly modified as discussed below, as the source of ions.After acceleration and deceleration in the ATLAS linac to
approximately 1 MeV/u, the actinide ions of interest will be
counted in the focal plane of the Fragment Mass Analyzer
(FMA). The major challenges are discussed in the succeeding
paragraphs.
Precision Requirements. Only 14C AMS has consistently
achieved precision levels in the <1% regime. This has been
achieved by use of dedicated facilities, automated sample
changes between unknown samples and absolute calibration
standards, and principally by the fast cycling of the accelerator
setup between the rare isotope (14C) and a normalizing abundant
isotope (13C). Generally, spectrum statistics are not the problem.
Knowing the transmission between the measurement point for
the stable reference and the detector of the AMS isotope is often
the limiting parameter for the final result uncertainty. This
problem will be tackled by developing an automated sample
changer to allow rapid, automatic changes between various
samples and improved automation of the accelerator scaling
required to measure the various isotopes required. In many cases
of interest, the measurement time for each sample will be only a
few minutes for adequate measurement statistics. But the lack of
known absolute standards, the possibility of cross-talk between
samples, and instabilities in the accelerator are the significant
problems that must be addressed to achieve the precision goals.
A recent AMS experiment on 146Sm [4] has required that
we develop an approach to measuring the absolute transmission
of the accelerator and detector system and has highlighted the
need to run ATLAS is an extremely stable mode. It has also
demonstrated that it is feasible to switch rapidly (by computer
control of the machine components' setup) between a rare and
abundant isotope (in a way similar to that used for 14C), thus
improving control over the accelerator transmission. Because of
this ongoing work and the additional techniques discussed here,
we believe we can achieve the required stability and
characterization of the transmission in order to enter this regime
of precision.
Small Sample Size and Cross-Talk Between Samples.
A major feature of AMS is the ability to analyze small samples.
At ATLAS the AMS activities always are focused on samples
of only a few milligrams. For this project, it is important that we
deal with many small samples. The smaller the samples, the less
are the radiological problems for ATLAS operation. The need to
measure many small samples as quickly as possible pushes us to
develop efficient sample feeding techniques for the ECR source.
We believe the best technique for this situation is to
develop laser ablation for the feeding of sample material into the
source. With laser ablation, a very small amount of sample
material can be introduced into the source without introduction
of extraneous material from the sample holder. Additionally, the
form of the sample material (metal, oxide, etc) is less critical
than with the sputtering or oven technique.
The ECR-II source will also be equipped with a quartz
liner. The quartz liner will keep the main body of the source
relatively clean of actinides, thus simplifying cleanup.
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Youinou, G.; Salvatores, M.; Paul, M.; Pardo, R.; Palmiotti, G.; Kondev, F. et al. AN INTEGRAL REACTOR PHYSICS EXPERIMENT TO INFER ACTINIDE CAPTURE CROSS-SECTIONS FROM THORIUM TO CALIFORNIUM WITH ACCELERATOR MASS SPECTROMETRY, article, April 1, 2010; Idaho. (https://digital.library.unt.edu/ark:/67531/metadc1012807/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.