Cosmic ray produced isotopes in terrestrial systems

Continuing improvements in the sensitivity of measurement of cosmic ray pro duced isotopes in environmental samples have progressively broadened the sc ope of their applications to characterise and quantify a wide variety of pr ocesses in earth and planetary sciences. In this article, I will concentrat e on the new developments in the field of nuclear geophysics, based on isot opic changes produced by cosmic rays in the terrestrial systems. This field , which is best described as cosmic ray geophysics, caught roots with the d iscovery of cosmogenic C-14 On the Earth by Willard Libby in 1948, and grew rapidly at first, but slowed down during the '60s and '70s. In the '80s, t here was a renaissance in cosmic ray produced isotope studies, thanks mainl y to the developments of the accelerator mass spectrometry technique capabl e of measuring minute amounts of radioactivity in terrestrial samples. This technological advance has considerably enhanced the applications of cosmic ray produced isotopes and today we find them being used to address diverse problems in earth and planetary sciences. I discuss the present scope of the field of cosmic ray geophysics with an e mphasis on geomorphology. I must stress here that this is the decade in whi ch this field, which has been studied passionately by geographers, geomorph ologists and geochemists for more than five decades, has at its service nuc lear methods to introduce numeric time controls in the range of centuries t o millions of years.