NUCLEAR IRRADIATION EFFECTS ON FERROMAGNETIC CORE MATERIALS
Effects of nuclear irradiation on the magnetic properties of 14 representative core materials were investigated. Measurements before, during, and after irradiation were made at a flux level of about 10/sup 12/ neutrons/ cm/ sup 2/ sec and for a total integrated neutron flux of ~ 10/sup 18/ nvt. The fast flux (E) 1 ev) was about 10/sup 11/ n/cm/sup 2/ sec and the gamma flux ~ 10/sup 11/ photons/cm/sup 2/ sec (E was 1 to 2 Mev). The temperature of the cores was 70 to 80 deg C with 10 to 20% of the total temperature attributed to gamma heating. The results of this work show: that the high nickel--iron alloys which have the highest permeabilities and lowest coercive forces showed the greatest changes in magnetic properties. Supermalloy, 4-79 Mo Permalloy, and Mumetal showed, respectively, increases of 515, 423, and 158% in coercive force and decreases of 93, 89, and 86% in their initial permeabilities. Changes in the corresponding properties in unoriented 48 nickel-- iron and oriented 50 nickel-- iron ranged from 30 to 100%. Grain oriented and unoriented 3 to 3.5 silicon-- irons and a 3-1 silicon--aluminum-iron (having square loop characteristics) showed small changes in their magnetic properties. The magnetic properties of a thermally ordered 18-aluminum--iron improvcd somewhat, while those of a thermaliy disordered material showed negligible changes. Although subject to limitations imposed by induced radioactivity, 2 V Permendur may be useful in some applications because it showed negligible changes due to irradiation and also operated successfuliy (in a saturable reactor circuit) up to 500 deg C. Four pressed powder cores and a nickel-ferrite core showed essentially no changes in their d-c magnetic properties and a-c permeabilities. Of these, two carbonyl- iron cores (one with a glass btader and the other with a plastic binder) showed negligible changes in their high-frequency loss characteristics. However, the loss factors of nickel-ferrite, 2-81 Mo Permalloy, and Sendust flake measured at 25 to 50 kc/s increased by 47, 94, and 93%, respectively. Structure-sensitive propcrties (such as permeability, coercive force, and remanence) changed significantly, suggesting changes in degree of order. Saturation induction, a structure insensitive property, was essentially unaffected by irradtation. Measurements made during the coarse of the irradiation showed progressive changes in properties with nvt. Some of the curves of initial permeability and coercive force as functions of nvt were found to be hyperbolic or exponential in form. Some of the hysteresis loops became highly distorted with irradiation and some materials showed a sataration of radiation damage effect. Reannealing of a 4-79 Mo Permalloy restored its pre-irradiation switching time characteristic, after irradiation had destroyed this property, indicating that transmutation effects were negligible. (auth)
- Research Organization:
- Naval Ordnance Lab., White OAk, Md.
- NSA Number:
- NSA-12-016803
- OSTI ID:
- 4307982
- Report Number(s):
- NAVORD-6127
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-58
- Country of Publication:
- United States
- Language:
- English
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