Final answer:
The mass spectrometer is the preferred instrument for detecting very small leaks, particularly in sensitive research apparatus such as dilution refrigerators. It works by detecting ionized helium atoms evacuating through a leak, using helium as a tracer due to its inert nature and small atomic size. Ultrasonic technology is another tool that can detect changes indicating issues like leaks.
Step-by-step explanation:
The preferred instrument for detecting very small leaks, especially in sensitive environments such as low-temperature physics laboratories, is a mass spectrometer. This instrument is connected to a high-vacuum pump and used to detect ionized helium atoms, which signifies a leak between two compartments in a device like a dilution refrigerator. Helium is typically used in the leak detection process because it is inert and has small atoms that can easily pass through tiny openings, making it an effective tracer.
Another example of an instrument used to detect conditions or changes that may be analogous to small leaks is the use of ultrasonic technology. For instance, ultrasonic bolt elongation monitors can detect changes in tension and high-pressure loads on bolts, which could indicate issues similar to leaks in mechanical integrity. While this technology has been adapted for a variety of other applications, such as non-destructive evaluation and medical testing, its principle of detecting changes or anomalies can be similar to how small leaks are detected in other systems.