Program - Brookhaven National Laboratory

DA 3 4:20 PM
Characterization and Preparation of Multi-Isotope Actinide Sources and Targets: The
Fission Time Projection Chamber
W. Loveland
Oregon State University
The preparation and characterization of actinide sources and targets for use if nuclear data elated projects
involves special challenges. These challenges involve securing sufficiently pure materials for target preparation,
characterizing those materials, preparing the usually thin sources and targets and characterizing
the resulting sources and targets. No where are these challenges more evident than in the fabrication of
sources and targets for the Fission Time Projection Chamber (TPC) where the announced goal is to make
precise, accurate cross section measurements of fission cross sections with uncertainties of less than one
percent. The challenges/opportunities of the TPC are in the plan to measure the ratios of cross sections
235 U(n,f)/ 238 U(n,f)/ 239 Pu(n,f)/ 1 H(n,p)) by simultaneously measuring all these reactions using a single
target. This requires multi-isotopic targets where all the different target nuclei are separated spatially.
The TPC, a tracking device, has to be able to track a given reaction product to a specific point on the
multi-isotopic target. Unusual “pointing resolution” sources are needed to characterize the TPC resolution.
Inherent in all the measurements is the need to have thin uniform actinide deposits/foils whose chemical
and isotopic composition is well-known. We present the results of the use of AFM, XRD, XRF and SEM
to obtain this information for actinide targets prepared by vacuum volatilization and molecular plating
DA 4 4:40 PM
Commissioning the NIFFTE Time Projection Chamber: the 238 U/ 235 U (n,f) Cross-Section
Ratio
Rhiannon Meharchand, on behalf of the NIFFTE collaboration
Los Alamos National Laboratory
Nuclear data play a fundamental role in reactor and weapons calculations, and the uncertainties in nuclear
data propagate into other calculated quantities. Therefore, it is imperative that data uncertainties are
minimized and well understood. To this end, the Neutron Induced Fission Fragment Tracking Experiment
(NIFFTE) collaboration is developing a Time Projection Chamber (TPC) to measure fission cross sections
with unprecedented accuracy. The NIFFTE TPC marks the first application of TPC technology in fission
research. The miniaturization and modification of existing technologies — as well as the development of
new systems for this specific application — is a challenging endeavor. Frequent evaluation is required
as new hardware and software capabilities are implemented. To evaluate progress, the TPC is tested in
beam at the Los Alamos Neutron Science Center (LANSCE) Weapons Neutron Research (WNR) facility.
LANSCE-WNR, a spallation neutron source, provides a white neutron spectrum ranging from hundreds of
keV to hundreds of MeV. Since 2010, the TPC has been loaded with actinide samples and blank backings
and has collected in-beam engineering data while readout capabilities were gradually increased. In 2010,
data were collected on 238 U and natural C samples, with 64 then 192 active channels (1/93 and 1/31 of the
fully instrumented TPC, respectively). In late 2011 and early 2012, data were collected on 238 U, 235 U,
239 Pu, and natural Al samples, with 496 active channels (1/12 full TPC). In late 2012, data will be collected
on 238 U, 235 U, 239 Pu, and plastic samples, with 2976 active channels (1/2 full TPC). An overview of
the NIFFTE TPC experiments performed at LANSCE and preliminary results for the 238 U/ 235 U neutroninduced
fission cross section ratio will be presented. This work was performed under the auspices of the U.S.
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