F. W. Lengemann

“ Several man-made radionuclides also have found their way into body tissues and organs in quantities that sometimes are large enough to be detected and counted.
Measurement of disintegrating potassium-40 atoms in the tissues of a human body can be used to determine the total amount of potassium (both radioactive and stable) in the body. It is known that potassium-40 makes up 0.0119% of all potassium and that 11% of all disintegrating potassium-40 atoms emit high-energy gamma rays that are measurable by the counter. ”

“ A scientist can thus identify the data delivered by a multichannel pulse-height analyzer as coming from potassium-40, zinc-65, or any other nuclide.
Counters using sodium iodide crystals intercept, and therefore count, a much smaller fraction of the gammas emitted by the subject’s body than liquid systems, but they also pick up a smaller amount of background. When speed is important, the liquid counter is more effective, but the crystal counter is preferred when radionuclides emitting gammas of nearly the same energies are to be separated and counted. ”

“ In contrast to devices that disclose concentrations of radioactivity in a small area or a particular organ, whole body counters usually are used to total up the burden of radioactivity in all parts of a human body. They also are distinguished from many radiation detecting instruments with the same general purpose by their large size, their heavy shielding, and their sensitivity to low levels of radioactivity. ”

“ Whole body counters are sensitive radiation detecting and measuring instruments that provide information not easily obtainable otherwise about that most important of all chemical systems, the human body. They can do this because, strange as it may seem, every person who ever lived is slightly radioactive.
Quickly, accurately, and painlessly, whole body counters reveal the kinds and amounts of radioactive substances that have accumulated in the body from natural sources, from man-made fallout, or from tracer isotopes given for medical purposes. ”

“ The number of light photons produced in the scintillation fluid is proportional to the energy transferred by the incoming gamma rays. For example, gamma rays emitted by potassium-40 have 1.46 million electron volts (Mev) energy; those of cesium-137 have 0.660 Mev energy. When both these radionuclides are producing flashes of light in the scintillation fluid at once, the photomultiplier tubes produce two different strengths of electrical pulses. Electronic devices called multichannel pulse-height analyzers sort and record the number of each. ”

“ Similar studies have been conducted by scientists of the Pacific Northwest Laboratory at Richland, Washington, who since 1959 have been measuring radioactivity of plants and animals in Alaska. When they found high levels of cesium-137 in lichens and caribou, they became interested in the body burdens of fallout isotopes in the Eskimos.
A portable crystal type of whole body counter was used to measure the cesium-137 content of Eskimos at five villages. The Eskimos cooperated willingly; in some communities nearly everyone accepted the invitation to be counted. ”

“ Figure 2 How a “walk-in” whole body counter, such as the one demonstrated at Geneva, works.
Shielding for the Geneva counter consisted of 3 inches of lead. Only the most energetic background gamma rays and 5 cosmic rays can penetrate this amount of shielding, and the number that do so remain almost constant during successive counting periods. This constant remaining “background” radiation level, once determined, could be subtracted from the recorded number of emissions to provide the correct radiation total from the body of each person examined. ”

“ More kinds of radionuclides were found than in the living babies, although the large counting time may have affected the results.
The same counting techniques were used with placental tissues from mothers of three of the stillborns. The placenta is the organ that nourishes an unborn child and through which substances from the mother’s bloodstream are exchanged with those in the baby’s blood. The graphs in Figure 17 show data from this experiment and illustrate the method of interpreting whole body counter data. ”

“ A visit to this type of counter recalls the first glimmers of scientific insight that the radiation in the human body could be counted. In the early 1950s, Frederick Reines and Clyde L. Cowan, two scientists at the Los Alamos Scientific Laboratory, Los Alamos, New Mexico, built a large liquid scintillation counter hoping to prove or disprove that neutrinos really existed. Neutrinos are elusive, uncharged particles with essentially no mass. ”

“ A reactor accident conceivably could add a unique hazard since neutron radiation might change the normally stable, nonradioactive atoms in the bodies of nearby workers into radioactive ones. Even gold or silver fillings in their teeth might become radioactive. ”

“ Investigation of the soil in northern Norway revealed that it averaged 20 nc of cesium-137 per square meter. Only 21 thin covers of lichens grow in this region, and reindeer must graze over large areas to obtain sufficient food. It was obvious that cesium-137 from fallout was collecting on lichens and then was being concentrated in the bodies of the reindeer before they were killed for meat. ”

“ The moving crystal makes it possible to use this whole body counter for scanning.
The role of iron in preventing one form of anemia has been clarified by using iron-59 as a tracer. Persons suffering from chronic infections or such blood diseases as leukemia and polycythemia vera have been checked for the amount of iron carried by their red blood cells. Cobalt-60 atoms have been substituted for stable cobalt in molecules of vitamin B-12 so that the way the body makes use of this vitamin can be studied. ”

“ Scanning devices are commonly used for noting the fate of tracer isotopes in medical diagnosis.
Two types of adaptations enable whole body counters to locate accumulations of radioactive materials in specific organs or small portions of the body. At the National Institutes of Health, Bethesda, Md., one counter is fitted with three rows of six 12-by-12-inch plastic blocks. Each block has four photomultiplier tubes to collect the scintillations from the crystal. The rows are curved so as to be equally distant from the patient’s body. ”

“ Data from whole body counters indicate that potassium-40 is the most abundant radionuclide in the human body. Our bodies also contain other naturally radioactive substances but the numbers of atoms usually present are so low (as with radium for instance) that they cannot be detected with whole body counters. ”

“ Radium-226 in the human body poses unique problems for whole body counters. People who have accumulated this nuclide only because of the minute amounts occurring naturally in food and water have counts of only two or three disintegrating atoms per second, and this amount cannot be distinguished from background radiation. Whole body counters are useful, however, in diagnosing effects in persons who have been overexposed to radium. These include 16 persons who formerly were employed to paint watch dials with a luminous paint containing radium. ”

“ For chemists or others working with arsenic, cyanide, or other chemical poisons, safety depends on recognizing the materials and keeping them where they belong. When accidents do happen and poisons are swallowed or breathed in, successful treatment requires that someone find out 22 exactly what and how much of the poisonous material was involved. ”

“ THE GENEVA COUNTER
In general, all whole body counters must have (1) a mechanism that reacts to the energy emitted by some kinds of disintegrating, or radioactive, atoms; (2) a device that displays or records these reactions; and (3) adequate shielding to exclude unwanted rays from other sources.
3 Figure 1 Types of whole body counters.
A The subject may be seated in a chair in an iron-shielded room and under a scintillation detecting crystal.
B The subject may lie in a bed that slides into the end of a hollow cylindrical tank filled with scintillation fluid. ”

“ Figure 20 Dogs about to be examined in a whole body counter.
How do dogs accumulate fallout isotopes in their bodies? This question was answered effectively by placing dogs in whole body counters and comparing the count from radioactive strontium-emitted gamma rays originating in their bodies with the count from a masonite phantom dog containing a known amount of radioactive strontium-85. It was found that female dogs increase their strontium retention while they are nursing newborn puppies. Strontium is much like calcium, which is a major component of milk. ”

“ Scientists at the Argonne National Laboratory, Argonne, Illinois, have attempted to improve crystal whole body counters so that they will be more useful in determining the amount of radium-226 in humans. Rolf Sievert at the Swedish Atomic Energy Commission also has studied the radium-226 detection. He devised a highly accurate whole body counter with 10 ion chambers arranged around a curved aluminum bed on which the subject rested. The instrument was installed below ground to reduce the interference of background radiation. ”

“ It is therefore apparent that potassium-40 determinations provide a way to indicate the amount of lean muscle in any individual, and indirectly the amount of fat. Estimates of the amount of fat based on the measurement of the specific gravity of the subject, often used in the past, have never been satisfactory. ”

“ This type of counter also uses a different detection device: a solid, rather than a liquid scintillator. A large crystal, usually of sodium iodide sensitized with thallium, is used to convert gamma rays to light photons.
Let us return to the shielding problem for a moment. Tanks of water, bricks, stone, and lead have been tried by scientists seeking effective, cheap, and convenient shielding. Some early counters were built deep underground in the hope of avoiding cosmic radiation. ”

“ Figure 22 shows how animals differ in their retention of orally administered zinc-65, as revealed by a whole body counter. It is apparent that counters can be used to determine the differences in the metabolism of different animal species used for research. ”

“ This film shows a method developed at LASL to monitor possible intake of radiation by personnel. The liquid scintillation counter is large enough to contain a man and sensitive enough to detect even the minute amounts of his natural gamma radioactivity. ”

“ Figure 13 A portable whole body counter used for research as well as routine monitoring of personnel in an atomic reactor installation. Usually gamma-emitting radionuclides can be detected in 10 minutes. This counter is in almost constant use at the AEC’s National Reactor Testing Station in Idaho.
When human tissue (for example, hair) is bombarded by fast neutrons, sulfur atoms in molecules of proteins are converted to the radionuclide phosphorus-32. ”