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.
Total-Ionizing-Dose Effects on Piezoelectric Micromachined Ultrasonic Transducers
Total-ionizing-dose (TID) effects on piezoelectric micromachined ultrasonic transducers (pMUTs) are investigated using 10-keV X-rays under different bias conditions. The corresponding changes in resonant frequency and quality factor are evaluated using impedance analysis methods. Radiation-generated electrons or holes are trapped in the pre-existing defects of piezoelectric materials. Therefore, the sensitivity of pMUTs to X-ray irradiation depends strongly on the device bias during irradiation. The trapped charges change stress and strain in the materials due to the inverse piezoelectric effect, resulting in resonant frequency shifts and quality factor variation.
Impurity-Movement Problems in Analysis Methods Using Particle Bombardment
Most of the analysis methods described in this book rely upon the use of charged-particle beams of either ions or electrons to produce secondary species or radiation which on detection reveals the constituents of the materials under analysis. Two generic types of analysis may be distinguished: (1) those in which the bulk is analyzed directly, and (2) those in which the surface is analyzed directly and the bulk characteristics are determined by profiling either by the use of the analyzing beam or by the use of an auxiliary sputtering beam. Typical of the first type would be electron probe microanalysis (see Chapter 18), in which an electron beam of energy of the order of 20 keV is used to excite fluorescent x rays from the solid under analysis. The range of such electrons is of the order of a few micrometers. Analysis methods of the second type include ion microprobe microanalysis (see Chapter 21), ion-scattering spectrometry,(1) Auger electron spectroscopy (see Chapter 20), and SCANIIR (see Chapter 23). The assumption made in many of these analysis methods is that the beam does not disturb the distribution of elements in the solid which is being analyzed. For many methods which use charged-particle beams, this is not, in fact, the case. In this chapter we will discuss the ion-migration problems which may occur in all these methods of surface analysis.