Scanners
Many of the applications described in this booklet require accurate knowledge of the exact location of the radioactive source within the body. Commonly a detecting tube is used having a collimating shield so that it accepts only that radiation that strikes it head-on. A motor-driven carrier moves the counter linearly at a slow rate. Radiation is counted and whenever the count reaches the predetermined amount—from one count to many—an electric impulse causes a synchronously moving pen to make a dot on a chart. The scanner, upon reaching the end of a line moves down to the next line and starts over, eventually producing a complete record of the radiation sources it has passed over.