TheMossbauerEffectScientificAmerican
The Mossbauer EFfect https://www.scientificamerican.com/issue/sa/1960/04-01/
- A good pendulum is the heart of a good clock, but it is not the clock itself. There must also be a device, such as a dial with hands, that counts the swings of the pendulum and thus allows us to read the time. We cannot directly count the oscillations of a vibrating nucleus. What we can do, however, is to compare with great accuracy the frequencies of two nuclear pendulums.
- The method is based on the familiar observation that sound waves from a vi brating piano-string induce resonant vi brations in another string, initially at rest but tuned to the same note. In the same manner gamma rays emitted by an os cillating nucleus are absorbed by another nucleus of the same kind, and set it into vibration. ' When we observe this, we know that tIre two nuclei must have the same vibration rate, within very narrow limits of error.
- One starts with a radioactive source of the isotope cobalt 57, which is commercially avail able and has a convenient half-life of 280 days. As the cobalt-57 nuclei decay at this leisurely rate, they change into excited nuclei of iron 57. The iron nuclei vibrate at a frequency of 3 X 10)8 oscillations per second, with a half-life of 10-7 second (a 10th of a millionth of a second). Thus an iron-57 nucleus emits roughly 1e12 waves.
- The theory of nuclear resonance goes back several years, and, as we have re marked, the crucial experiment is a com paratively easy one. Why was it not done earlier? The reason is that certain secondary effects made it quite difficult to observe nuclear resonance before the work of Mossbauer.