What follows is an excerpt from my book A Primer in the Art of Deception: The Cult of Nuclearists, Uranium Weapons and Fraudulent Science (www.du-deceptions.com). It provides background information that will allow the reader to follow what is to come in future postings. It is reproduced from the chapter entitled Radiation Safety in Its Infancy: 1895-1953.
In returning to the historical narrative, the discussion now arrives at a fateful moment in the history of radiation safety. The Manhattan Project was a gigantic experiment in applied physics. Physicists dominated all aspects of the science required to build the bomb. This included all aspects of the Health Division. When the Manhattan Project got under way, the only standards available to the Health Division were those established prior to the war by, respectively, the US Advisory and the International Committees on X-ray and Radium Protection. The complicated undertaking of building the bomb and having thousands work in close proximity to high levels of radioactivity and novel radioisotopes demanded a revolution in all aspects of radiation safety. Herbert M. Parker, a British radiological physicist, headed the Protection Measurements Group of the health physics section of the Health Division. Besides being responsible for designing a new generation of radiation detection equipment, Parker had to overcome the major obstacle that had confounded researchers and radiologists over the previous two decades: how to devise a meaningful way of relating x-ray exposure to biological effect. The exposure to x-rays impinging on the surface of the body from an outside source was quantified by so many roentgens — a measure of the amount of ionization that quantity of x-ray energy would produce in air. Once that x-ray energy passed into the body, it was traveling through a different, nonuniform medium and interacting with a variety of biologically significant molecular structures. Some means were necessary for quantifying the changes being induced within the biological system. Ionization of the air external to the body, or the gas within a radiation detector, was one phenomenon. Biological changes in an organism due to that radiation was another phenomenon. The problem was how to connect these two into a meaningful framework. A further problem also confronted Parker. The roentgen was a measurement for x-rays and gamma rays. People working in the Manhattan Project were potentially going to be exposed to additional radiation in such forms as alpha particles, beta particles, and neutrons. In order to effectively protect workers from the cumulative effects of different types of radiation, what was required was a method of quantifying the dosages from different types of radiation by a single unit of measurement. In this way, exposure to a combination of gamma rays and beta particles, for instance, could be combined in a meaningful way to denote the total dosage of radiation received.
Parker was a physicist. He brought a physicist’s mindset to the problem of how radiation impacted on biological systems. And the simple and practical solution he devised was a physicist’s solution. To Parker, when looked at abstractly, the essence of radiation’s interaction with matter was the transfer of energy. X-rays transfer electromagnetic energy from an x-ray machine to the human body. These x-ray photons, interacting with the atoms of the body, transfer their energy to orbital electrons. Alpha particles and beta particles, with the kinetic energy they derive from being ejected from an atom undergoing radioactive decay, transfer energy from the nucleus of atoms to the electrons of the atoms within the human body with which they collide. What these types of ionizing radiation have in common is this capacity to transfer their energy into the body where it is absorbed by electrons, thus exciting them in their orbits and/or ejecting them from the atoms to which they are bound. As the amount of energy absorbed by the body is increased, so greater is the amount of ionization and biochemical disturbance to the system. Sufficient disruption results in altered function which is manifested in various forms and degrees of injury. Thus, from this point of view, the extent of alteration to a biological system is directly related to the amount of energy absorbed. To quantify this phenomenon, Parker devised a new unit of measurement for absorbed dose. The rep (roentgen equivalent physical) measures dosage as the amount of energy in ergs deposited per gram of material. Undergoing slight modification, the rep evolved into the rad (radiation absorbed dose) which represents the absorption of 100 ergs per gram of material. The rad is a convenient unit of measure. It is used to describe the amount of energy absorbed by any type of material (be it wood, metal, bone, muscle, or whatever) from any type of radiation. [The roentgen was retained as a unit of measurement for exposure. In health physics it represented the amount of ionization in air caused by a quantity of radiation as measured from outside the body. The rad was the unit of absorbed dose measuring how much energy was absorbed by the material with which it interacted. Precise measurement determined that 1 roentgen corresponded to the absorption of 83 ergs per gram of air and the absorption of 93 ergs per gram of tissue at the body’s surface. So close were the two units of measurement that they began to be used interchangeably. This also permitted gas filled detectors, that measured ionization, to provide information about the absorbed dose at the surface of the body.]
To understand the impact that Parker’s mentality and mode of thinking had on the subsequent development of radiation safety, one point is essential to keep in mind: in Parker’s conceptual model, the quantity of energy absorbed is treated as if it is uniformly distributed throughout the mass that absorbs it, i.e., the energy is “averaged” over the entire mass. This is what the rad represents, ergs per gram. To do this makes perfect sense within the mathematically oriented discipline of physics. However, as we shall see later in the discussion, this model is woefully inadequate when transferred into the discipline of biology where averaging energy over a mass of living cellular material is, in many instances, a useless concept for determining biological effect.
Parker was aware that the model he was developing had to account for the fact that different types of radiation (x-rays, alpha particles, beta particles, etc.) differed in how effectively they induce change in a biological medium. Consequently, Parker devised a second unit of measure that took these differences into account. First, for each type of radiation, experimentation was conducted to determine its Relative Biological Effectiveness (RBE) — the relative damage each caused to living tissue. The biological dose delivered by a quantity of radiation was then determined by multiplying the amount of energy absorbed (measured in reps or roentgen equivalents physical) by the RBE of the type of radiation that delivered the dose. The unit of measure of the product of these two quantities was the rem (roentgen equivalent man). As a hypothetical example, suppose the health effect to a type of tissue created by 1 rep delivered by alpha particles is compared to the health effect delivered by 1 rep of gamma rays, and it is found that the alpha particles produce ten times as much health effect. Alpha particles would be assigned an RBE of 10. What would be said is that the alpha particles deliver 10 rem to the body while the gamma rays deliver 1 rem. Both forms of radiation deliver the same amount of energy to the body. The biological impact of the alpha particles, however, is ten times as great.
The quantitative model that Parker developed introduced clarity into people’s thinking about radiation’s interaction with matter. So successful was this approach that it influenced all future thinking on the subject of radiation protection. According to this model, the biological effects of radiation were proportional to the amount of energy absorbed by the target, whether this was a particular organ or the body as a whole. To determine the amount of energy transferred, all types of ionizing radiation were now quantifiable using a single unit of measure, and the varying capacity for different types of radiation to produce biological alterations could be accounted for mathematically. Scientific investigation could now proceed to build a body of knowledge comparing the quantities of radiation absorbed to the biological effects they produced in different types of cells, tissues, organs, systems, and the whole body. Radiation protection was given a scientific footing that would allow it to keep pace with the revolution that was taking place in nuclear physics and in the new world created by the Manhattan Project.
But a subtle flaw lay at the heart of Parker’s model. It was all built upon the unfounded assumption that biological effects of radiation depended solely on the amount of energy absorbed. What made perfect sense from the point of view of the physicist was not in harmony with basic biological realities. At first, this wasn’t apparent. Only in the latter part of the 1950s, after new fundamental discoveries were made in biology, did the major shortcomings to the model begin to intrude into what was already orthodoxy in radiation physics. Thus, the physics-based model — which was hugely successful in advancing radiation research — turned out in time to have been a conceptual blunder that blinded many to a true understanding of the biological effects of radiation. More significant is the fact that it continues to blind the understanding of people, even people who have spent years of study on the subject.