Stored Energy Release in Graphite Irradiated at Low Temperatures

Technical Report · Mon Oct 01 04:00:00 EDT 1956

DOI:https://doi.org/10.2172/4339833· OSTI ID:4339833

Austerman, S. B. ^[1]

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1. North American Aviation, Inc., Canoga Park, CA (United States). Atomics International Div.

Previous measurements of electrical and thermal resistivities and paramagnetic resonance have shown that graphite, when irradiated at or near liquid nitrogen temperatures, retains considerable damage which anneals out at below room temperatures. This report deals with the release of stored energy associated with this damage. To compute stored energy release, the relative specific heat of an irradiated specimen is compared with that of the specimen after annealing. Various types of artificial and natural graphite were irradiated in the liquid nitrogen facility of the Brookhaven reactor. The stored energy release spectrum during steady temperature rise shows a peak at 215° K for graphite o having large crystallities i.e., 3,000 Å length and about 185° K for fine-crystallite graphite i. e., 300 Å length. If it is assumed that the defects diffuse out of the crystallites on heating, the dependence of the annealing behavior on crystallite size can be be accounted for with an activation energy of approximately 0.4 ev. The total stored energy releasable at below 275° K accumulates linearly with neutron exposure at a rate of 1.4 cal/gm per 10¹⁸ nvt. By estimating the number of responsible defects from neutron scattering data, the stored energy per atomic displacement is found to be in the order of 3 to 6 ev. An apparent increase in specific heat appears at low temperatures and can be qualitatively accounted for on the basis of isolated interstitial atoms behaving as Einstein oscillators.

• Research Organization: North American Aviation, Inc., Canoga Park, CA (United States). Atomics International Div.
• Sponsoring Organization: US Atomic Energy Commission (AEC)
• DOE Contract Number: AT(11-1)-GEN-8
• NSA Number: NSA-10-011736
• OSTI ID: 4339833
• Report Number(s): NAA-SR--1564
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ANNEALING
CRYSTALS
DEFECTS
ELECTRIC CONDUCTIVITY
ENERGY
EXCITATION
GRAIN SIZE
GRAPHITE
HIGH TEMPERATURE
IRRADIATION
LATTICES
LOW TEMPERATURE
MAGNETIC RESONANCE
MAGNETISM
MEASURED VALUES
NEUTRON BEAMS
OSCILLATIONS
PARAMAGNETISM
RADIATION EFFECTS
REACTORS
SPECIFIC HEAT
THERMAL CONDUCTIVITY