Not quite six years have passed since the appearance of the first edition of this book. This is not a long period. Yet the rapid pace of scientific and technological development today is such that any book on experimental technique must be wary of becoming ob­ solete in some way or another even in such a short span of time. Thus, when the publisher Springer-Verlag informed me of the need for a new printing of this book, I decided it was an opportune moment to update some of the chapters as well as to include some new material. The result is this second edition. The most notable changes have been in Chapters 2 and 3. In the latter, which con­ cerns radiation protection, most of the sections have been rewritten to take into account the new recommendations from the International Commission on Radiation Protection, the most important of which are the new dose limits for exposure to ionizing radiation. In addition, emphasis has now been put on the use of SI units in dosimetry, i.e., the Gray and Sievert, which have now become standard.