For stability

Radioisotopes are used for a variety of diagnostic tests in medicine. Now D Murnick of Rutgers University, USA, and colleagues have pioneered the use of stable isotopes -- those that are not radioactive -- as a tracer in medicine. One application is the development of a fast, inexpensive and safe test for ulcer causing bacteria in the stomach. The patient is fed a small amount of urea that is labelled with carbon-13. The bacteria, if present, breaks the urea to ammonia and carbon dioxide, with the carbon dioxide containing carbon-13 together with the more common carbon-12 isotope. The patient's breath is then fed into a chamber where laser light, tuned specifically to a frequency which excites the carbon-13 to a higher state to shine. This changes the conductivity in the chamber and by monitoring the current, the researchers can get an idea of the amount of carbon-13 in the breath. With proper standardisation, this can then tell the physician about the presence of the ulcer causing bacteria in the stomach.