Ultrasonic NDE in a reactor core
We have irradiated bulk single crystal piezoelectric AlN operating as an ultrasonic transducer up to a fast and thermal neutron fluence of 1.85×1018 n/cm2 and 5.8×1018 n/cm2 respectively along with a gamma dose of 26.8 MGy. Our primary interest was in the radiation effects on the piezoelectric performance of the AlN crystal. Ideally standard procedures for extracting material properties from the impedance spectra would have been applied. However, this procedure was anticipated to be very error prone due the effects of radiation on passive components, such as electrodes and cabling. As a result the transducer was coupled to an aluminum cylinder and operated in pulse echo mode throughout the irradiation. In addition to the pulse echo testing impedance data were obtained. Although, material parameters such as d33 could not be measured in-situ during irradiation with our procedure, our work is the only publication, to the author's knowledge, showing the operation of an ultrasonic transducer in a reactor core. Further, the piezoelectric coefficient was measured prior to irradiation and found to be 5.5 pC/N which is unchanged from as-grown samples, and in fact higher than the measured d33 for many as-grown samples. Further proof of the viability of utilizing ultrasonic transducers in a reactor core is provided by means of successful time of flight (TOF) measurements throughout the irradiation. The TOF data was used to measure the gamma heating of an aluminum cylinder. The heating due to short lived isotopes in the Al was also detected via TOF.
Metamictization of lithium niobate by thermal neutrons
Lithium niobate plates intended for application as sensors for acoustical monitoring of reactors were subjected to thermal-neutron irradiation near room temperature. By 8 x 10$sup 19$n/cm$sup 2$, a crystal had become highly disordered, as shown by the back-reflection Laue picture, by loss of piezoelectric response, and by loss of optical birefringence. This transformation appears to be a metamictization. Changes in optical absorption, tritium loss, postirradiation lithium migration, surface crazing, and effects of postirradiation storage at room temperature and of heating to 140$sup 0$C are also observed. (auth)
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.