SCIENTIFIC IMPORTANCE OF X-RAYS—GARLAND 183 
2. The examination of castings and welds. 
8. The examination of packages and personnel for concealed materials. 
4, The examination of edible materials for defects or impurities (such as candy 
bars and oranges). 
5. The behavior of solids and liquids under projectile bombardment (such as 
high-speed roentgenography of bullets). 
The roentgenographic examination of metal parts in connection with 
the airplane industry is said to have used up more film per month dur- 
ing the last few months of the recent war than was used in all medical 
procedures in the United States during the same period. The im- 
portance of skilled interpretation of these roentgenograms and of 
adequate protection for the employees operating the X-ray equipment 
obviously is great. 
Since the early days of X-ray development, packages, clothing, and 
even personnel have been inspected for contraband and other illegally 
possessed materials. Packages and similar objects may be inspected 
without harm, provided they do not contain unprocessed film or other 
sensitized material. Individuals may be examined only under strin- 
gent conditions, as exposure of large amounts of the body to X-rays, 
especially if repeated, is fraught with ultimate danger to the indi- 
vidual; possibly resulting later in skin damage, anemia, or infertility. 
It is to be recollected that metals and other materials may be radio- 
graphed either with X-rays or radium rays. It is therefore appro- 
priate to consider a few aspects of radioactive substances, as many of 
them have properties analogous to those of X-rays. Radium rays are 
of three general types: 
1. Alpha rays, which are positively charged particles of very low penetrating 
power, being stopped by a sheet of ordinary paper. 
2. Beta rays, which are negative electrons, of moderate penetrating power, 
stopped by a thin metal filter (2 millimeters of brass or 0.5 millimeter plati- 
num or their equivalent). 
8. Gamma rays, which are electromagnetic radiations (photons) of considerable 
penetrating power, the hardest ones traversing several centimeters of lead. 
Because of their different charges, these three types of rays can be 
separated in a magnetic field. The alpha rays are deflected slightly 
in one direction, the beta more strongly in the opposite direction, and 
the gamma not at all. Radium disintegrates slowly, its half period 
being 1,590 years. For medical purposes it usually is kept in small 
containers in the form of a radium salt. Many of these containers 
can be placed together and the group then used like an X-ray tube. 
Since the work of Rutherford, in 1919, we have been able to produce 
artifically radioactive substances. One method of doing this is to use 
the cyclotron, by means of which the nuclei of atoms are transformed 
into new unstable substances. High-speed protons, deuterons, and 
neutrons have been used to transform most elements. The resultant 
