Ph.D. Dissertation Defense by Karen C. Kelley
Wednesday, March 17, 2004
( Dr. Nolan Hertel, Chair)
"Gadolinium-148 Production Cross Section Measurements for Accelerator Target Facilities"
At the LANSCE accelerator complex, protons are accelerated to 800 MeV and
directed to two tungsten targets, Target 4 at the WNR facility and the 1L target
at the Lujan Center. DOE 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 Gd-148 is low, but it encompasses almost two-thirds of the total dose
burden for the two tungsten targets at LANSCE 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-measured and
this is the motivation for measuring the
W(p,x)Gd-148 production cross section.
In a series of experiments at LANSCE's WNR facility, Gd-148 production was measured for 600- and 800-MeV protons on tungsten, tantalum, and gold. These experiments used 3 um thin W, Ta, and Au foils and 10 um thin Al 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 LANL codes CEM2k+GEM2 and MCNPX.