The need for cross section measurements for neutron-induced reactions • If no cross section measurement exists, alternative strategies are: • The cross section for the corresponding proton-induced reaction is used. • Theoretical models are used to estimate the needed cross sections. • The cross section is inferred from analysis of the results from irradiating thick target stacks with protons. • None of these strategies is as good as an actual measurement!
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The need for cross section measurements for neutron- induced reactions If no cross section measurement exists, alternative strategies are: The cross section.
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The need for cross section measurements for neutron-induced reactions
• If no cross section measurement exists, alternative strategies are:
• The cross section for the corresponding proton-induced reaction is used.
• Theoretical models are used to estimate the needed cross sections.
• The cross section is inferred from analysis of the results from irradiating thick target stacks with protons.
• None of these strategies is as good as an actual measurement!
• To remedy this situation We are measuring cross sections for neutron induced reactions:
• LANSCE to make an energy integrated (average) cross section measurement using ‘white’ neutron beams 0 – 750 MeV.
• In the first year we will measure cross sections for the production of: 10Be, 14C, Ne, 26Al from
O and Si
The aim of the experiment in 20052 or 3 irradiations. These times are calculated assuming 1.8 microsec spacing and ~4-5 nA protons on the W target. 50 x 50 mm SiO2 and/or 50 mm diameter Si targets.
10 days using 3 mm thick targets: 1 day using 1 mm targets;SiO2(n,x)10Be SiO2(n,x)26Al or Si(n,x)26Al
Si or SiO2(n,x)20,21,22Ne SiO2(n,x)14C
1/2 day using 1 mm thick targets: SiO2(n,x)3He and Si(n,x)3He.
Total target irradiation time requested = 15 daysIn addition, we need ~4 days with a long micropulse spacing to characterize the low energy flux.
Experimental Procedure at LANSCE • Neutron beams cover the whole target stack.
• Total stack thickness is designed to attenuate <10% of the beam at all neutron energies.
• Irradiation times are designed to produce the optimum number of product atoms for determination using AMS or MS by appropriate collaborators.
• Short-lived radionuclides are measured using non-destructive gamma-ray spectroscopy.
• AMS and MS determinations will be made later.
Experiments at LANSCE
Target in target holder
LANSCE: 4FP15R 2002
• The energy spectrum ranges from 0.1 – 750 MeV.
• The neutron fluence is monitored directly using an uranium fission chamber.
Average cross sections measured at LANSCE 1998-2003 include:
natCu(p,x)60Co from S. J. Mills, G. F. Steyn and F. M. Nortier, Appl. Rad. Isot. 43, 1019, 1992
MC-ALICE calculations courtesy of Mark Chadwick.
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natCu(n,x)60Co
MC-ALICEThis workLANSCE average (1.25-750 MeV)KI99natCu(p,x)60Co MI92Other measurements
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ss s
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mb)
Incident neutron energy (MeV)
7-27-2004
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27Al(p,x)22Na and 27Al(n,x)22Na
27Al(p,x)22Naderived excitation functionImamura et al.27Al(n,x)22Na iTL
average 27Al(n,x)22Na LANSCE
Cro
ss s
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mb)
Neutron energy (MeV)
The excitation function was constructed from the measured values and the adopted values of W. S. Gilbert et al (1968) of 10 mb for En>60 MeV and ‘tweaked’ to get reasonable agreement with the average value measured at LANSCE..