Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Neutron Irradiation to Increase the C-Axis Compressive Strength of Sapphire at Elevated Temperature



T M. Regan, D C. Harris, D W. Blodgett, K C. Baldwin, J A. Miragliotta, M E. Thomas, M J. Linevsky, J W. Giles, R M. Stroud, T A. Kennedy, M Fatemi, David R. Black


Neutron irradiation of sapphire with 1 x 1018 neutrons (≥ 1 MeV)/cm2 increases the c-axis compressive strength by a factor of 3 at 600 C. The mechanism of strength enhancement is the retardation of r-plane twin propagation by radiation-induced defects. 10B and Cd shielding was employed during irradiation to filter out thermal neutrons (less than or equal to} 1 eV), thereby reducing residual radioactivity in the sapphire to background levels in a month. Yellow-brown irradiated sapphire is nearly decolorized to pale yellow by annealing at 600 C with no loss of mechanical strength. Annealing at sufficiently high temperature (such as 1200 C for 24h) reduces the compressive strength back to its baseline value. Neutron irradiation decreases the flexure strength of sapphire at 600 C by 0-20% in some experiments. However, the c-plane ring-on-ring flexure strength at 600 C is doubled by irradiation. The principal elastic constants of irradiated sapphire are not significantly affected by irradiation, but the off-diagonal elastic constants are slightly changed. High temperature infrared absorption and emission and thermal conductivity of sapphire are not affected by irradiation at the neutron fluence used in this study. Defects that might be correlated with strengthening were characterized by electron paramagnetic resonance spectroscopy. Color centers observed in the ultraviolet absorption spectrum were not clearly correlated with mechanical response. No radiation-induced changes could be detected by x-ray topography or x-ray diffraction.
Proceedings Title
Proceedings of the 8th DoD Electromagnetric Windows Conference
Conference Dates
April 24-28, 2000
Conference Location
Conference Title
DOD Electromagnetric Windows Conference


compressive strength, defects, neutron irradiation, sapphire, twins


Regan, T. , Harris, D. , Blodgett, D. , Baldwin, K. , Miragliotta, J. , Thomas, M. , Linevsky, M. , Giles, J. , Stroud, R. , Kennedy, T. , Fatemi, M. and Black, D. (2000), Neutron Irradiation to Increase the C-Axis Compressive Strength of Sapphire at Elevated Temperature, Proceedings of the 8th DoD Electromagnetric Windows Conference, Undefined (Accessed July 15, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created February 28, 2000, Updated October 12, 2021