time that these crystals would fluoresce in the presence of a vacuum tube activated by
high voltage, but it occurred to Roentgen that the fluorescence of the crystals was due
to some type of ray that could pass through the black paper around the tube. When he
picked up the chemically coated cardboard, his fingers came between it and the tube,
and he saw the bones of his hand. He realized that he had discovered the presence of
a ray that would penetrate solid matter. By replacing the chemically coated cardboard
with a photographic plate, he was able to record an image of the internal structure of his
wife's hand. He also noted that the rays could not be reflected or refracted by the usual
means and that they were not affected by electrical and magnetic fields as were the
cathode rays, which he was studying. Because he did not know the nature of these
rays, he called them x-rays. Others have called them roentgen rays.
d. Following the discovery of x-rays, man was not long in learning about both the
harmful and useful characteristics of this new energy source. E. H. Grubbe, a
manufacturer of Crookes' tubes in Chicago, Illinois, suffered severe hand injuries by
exposing his hands to x-rays. Realizing from his own experience the destructive power
of x-rays, Grubbe, on January 29, 1896, treated a patient for carcinoma of the breast
with his Crookes tube. Numerous applications of the x-ray for medical purposes
followed Grubbe's procedure and today x-ray machines are among the most valuable
therapeutic and diagnostic tools available to the clinician.
e. The year following the discovery of x-rays, Henri Becquerel observed that
crystals of a uranium salt emitted rays which were similar to x-rays in that they were
invisible, were highly penetrating, and could affect a photographic plate. Becquerel's
discovery was followed by the identification of other "radioactive" elements and further
investigation showed that there were actually three different kinds of radiation from
naturally occurring radioactive substances. These three types of radiation were called
alpha (α), beta (β) and gamma (ϒ) from the first three letters of the Greek alphabet.
f. It has been shown that all three radiations are not emitted simultaneously by
all radioactive substances. Some elements emit α-rays, others emit β-rays, while γ-rays
sometimes accompany one and sometimes the other. To date, numerous radioactive
elements have been identified or artificially produced. As with x-rays, radioactive
elements are used quite extensively for medical purposes for the diagnosis and
treatment of a variety of diseases.
a. Since 1895, the number of uses of radioactive materials and radiation-
producing devices has continued to increase without bound. Indeed, the lot of mankind
has been altered as a result of the discovery of radiation. This is demonstrated by the
fact that the utilization of radiation affects just about every field of endeavor imaginable,
to include research, industry, agriculture, teaching, and, of course, medicine.
b. To this extent, the preventive medicine specialist must be able to identify the
sources of radiation within his facility, to evaluate the hazards associated with these