Using optical correlation to measure leak rates in sealed packages.
An optical correlation technique has been shown to accurately measure leak conduction rates from 10(-1) to 10(-6) atm cc/sec. Using hybrid microcircuit packages with glass capillary leakers, dimensional changes were detected as the packages were exposed to a small increase in external pressure. The rate at which the package returns to its original dimensions is measured and used, along with the internal free volume, to compute the leak rate. Because of its several advantages, the technique has the potential to become a useful nondestructive quality-control technique.
Van der Lugt optical correlation for the measurement of leak rates of hermetically sealed packages
Van der Lugt optical correlation, involving Fourier transform holography, has been shown to be successful in detecting and accurately measuring leak rates in hermetically sealed packages in the range of 10' to iO6 atm cc/sec. The technique depends on the measurement of the relaxation time of sealed packages under vacuum conditions, from which leak rates can be calculated. This technique has the advantage over conventional 'leak testing, in that it requires no backfilling with tracer gas, and therefore is more cost effective and faster. Also, packages such as pacemakers can be examined at the end of the manufacturing process, after the polymer neck has been inserted, eliminating any absorption of the helium or radioactive tracer gas that normally reduces the accuracy of conventional methods. Furthermore, this new technique can be used to rapidly test packages with large internal free volumes, in that it requires only a small differential pressure across the walls of the package, and avoids measurements depending on slowly changing internal helium or tracer gas concentrations. A comparison will be made between this HNDT technique and other leak testing methods commonly used in the packaging industry, in terms of cost and time factors, and range of accuracy.
Within and Inter-Institutional Differences Between Death Certifiers on Autopsy Conclusions
This study seeks to establish whether medico-legal practitioners differ in their autopsy conclusions within and across medico-legal institutions. Data include 459 violent deaths (homicides, suicides, and accidents) autopsy reports written by more than 20 death certifiers from four medico-legal institutions in two countries (France and the United States). Multinomial models show that compared with accidental deaths, weapon use and decedents’ characteristics both influence a homicide verdict, but not a suicide one. In addition, French practitioners are more likely than Americans to reach a conclusion of homicide or suicide compared with accident, and homicides are more likely to be certified by male practitioners.