Gadolinium-148 and Other Spallation Production Cross Section Measurements for Accelerator Target Facilities
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Kelley, Karen Corzine
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Abstract
At the Los Alamos Neutron Science Center accelerator complex, protons are accelerated
to 800 MeV and directed to two tungsten targets, Target 4 at the Weapons Neutron Research
facility and the 1L target at the Lujan Center. The Department of Energy requires hazard
classification analyses to be performed on these targets and places limits on certain radionuclide
inventories in the targets to avoid characterizing the facilities as nuclear facilities.
Gadolinium-148 is a radionuclide created from the spallation of tungsten. Allowed isotopic
inventories are particularly low for this isotope because it is an alpha-particle emitter with
a 75-year half-life. The activity level of Gadolinium-148 is low, but it encompasses almost
two-thirds of the total dose burden for the two tungsten targets based on present yield estimates.
From a hazard classification standpoint, this severely limits the lifetime of these
tungsten targets. The cross section is not well-established experimentally and this is the
motivation for measuring the Gadolinium-148 production cross section from tungsten.
In a series of experiments at the Weapons Neutron Research facility, Gadolinium-148
production was measured for 600- and 800-MeV protons on tungsten, tantalum, and gold.
These experiments used 3 m thin tungsten, tantalum, and gold foils and 10 m thin aluminum
activation foils. In addition, spallation yields were determined for many short-lived
and long-lived spallation products with these foils using gamma and alpha spectroscopy and
compared with predictions of the Los Alamos National Laboratory codes CEM2k+GEM2
and MCNPX.
The cumulative Gadolinium-148 production cross section measured from tantalum, tungsten,
and gold for incident 600-MeV protons were 15.24.0, 8.310.92, and 0.5910.155,
respectively. The average production cross sections measured at 800 MeV were 28.63.5,
19.41.8, and 3.690.50 for tantalum, tungsten, and gold, respectively. These cumulative
measurements compared best with Bertini and were within a factor of two to three of
CEM2k+GEM2.
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Date
2004-03-31
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2277836 bytes
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Dissertation