alpha, Becquerel, beta, Chavara, Curt Stern, Ernst Caspari, gamma, Gray, Guarapari, hormesis, ICRP, International Commission on Radiological Protection, Linear No Threshold, LNT, nuclear, radiation, Ramsar, röntgen equivalent in man, röntgen equivalent physical, Sievert, Warren Spencer, Yangjiang
One of the greatest fears surrounding nuclear energy is radiation. Critics maintain that if an accident were to occur and radiation were to escape the facility, the impact of such an event upon the environment and the population around the plant as well as globally could be catastrophic. Such doomsday scenarios are frequently conjured up to fuel opposition to the expansion of nuclear energy. Unfortunately, most fear of nuclear technology is based on an ignorance of basic science which is then played upon by interest groups using risk aversion, negativity bias, the framing effects of risk, and an echo chamber to amplify it all.
The argument – condemnation – that is most often repeated by anti-nuclear groups is that radiation is harmful to life. Unfortunately for them, they have a most intractable opponent on this point – Mother Nature. Radiation is prevalent everywhere; there is no such thing as zero radiation. Life on earth is constantly exposed to radiation from dozens of sources, from the building materials they surround themselves with, the earth they walk on, some of the technology they use, to even the food and water they consume. If you had a banana for breakfast this morning, you have ingested a source of radiation and it may be wise to keep away from the rajma chawal or aloo gobi during lunch. Ironically, nuclear power stations contribute the least radiation to the average dosage a person receives.
Before moving further, a little refresher course on radiation physics for those whom high school physics is a distant memory 🙂 In the context of nuclear phenomena, radiation means ionising radiation: when larger atoms, usually of the actinide series, disintegrate due to neutron bombardment or naturally, there are the various fragments of decay or fission and a release of energy. This energy – radiation – can be released in three forms: alpha particles, beta particles, and gamma rays.
To understand the impact of radiation on humans, there are a few variables that need to be ascertained: first, how much of radiation was there?; second, for how long did the radiation last?; third, what kind of radiation was it?; fourth, what is the mass of the person exposed?; fifth, and finally, what part of the body was exposed?
Radiation and its effects are measured in several units and can be confusing to laypeople. So how does on go about making sense of röntgen equivalent in man, Grays, röntgen equivalent physical, and Sieverts? These different units measure different effects of radiation. For example, the absorbed dose – the amount of radiation per kilogramme that a body is exposed to – is usually measured in gray. This means that if X joules of radiation energy were to hit Person A who weighs 55 kgs and Person B who weighs 80 kgs, the absorbed dose for the two would be X/50 and X/80 respectively.
What makes radiation harmful? When a particle or ray collides with tissue, it can knock an electron off an atom that forms any of the various larger biological systems such as bone, muscle, or even DNA. Such a collision forms an ion, a charged particle that does not behave in the same manner as its more stable cousin and may lead to tumours, cancers, and other ailments. However, as penetrating ability increases, ionising ability decreases and this is why the absorbed dose alone does not paint a complete picture.
It matters what sort of radiation A and B have been exposed to. Alpha particles cause the most damage but are thankfully the easiest to shield, stopped by a thin sheet of paper or even a few centimetres of air. Beta particles are smaller and can therefore penetrate more than alpha particles but are also easily stopped by a few millimetres of aluminium. Gamma rays are massless and need several metres of concrete to stop. The equivalent dose is a measurement of the effect of radiation on tissue after factoring in its type; usually measured in Sieverts, it is equal to the absorbed dose weighted for the degree of effect of different radiations. one Gray of alpha particles can cause 20 times the biological damage one Gray of gamma or beta radiation does.
The matter does not end here – certain parts of the body are more susceptible to damage by radiation than others, just as blunt force trauma can cause greater damage to the skull, eye, or trachea than to the back or thigh. For radiation, this is measured by introducing another weight factor for the different tissues of the body and adjusting the equivalent dose by that factor. The result is called the effective dose. For example, the same amount of the same type of radiation will potentially cause more damage to the testes and ovaries than in would to the bladder or breasts; the colon and lungs are more susceptible to radiation damage than the skin.
Another unit of radiation measurement is the Becquerel. It indicates the amount of radioactivity present in an item but makes no observations about impact on flora and fauna. One Becquerel of a material is the amount of that material in which the disintegration of one nucleus occurs every second. An average human being will give a reading of 65 Bq/kg, so approximately 4,600 Bq. A kilogramme of coffee will read 1,000 Bq; breast milk comes in at 70 Bq, and a banana at 15 Bq. For comparison, a radioisotope for cancer therapy is 100 milion Bq.
Radiation is ubiquitous and yet there persists a fear that even the slightest exposure to it is harmful. The source of this idea was Hermann Joseph Muller, recipient of the 1946 Nobel Prize in Physiology or Medicine. Muller’s work showed that radiation, x-rays specifically, could cause genetic mutations. It must be remembered that the field of genetics and radiology were in their nascent stages and little was known about either or how they interacted. Indeed, it was not until seven years later that the double helix structure of deoxyribonucleic acid was discovered by James Watson and Francis Crick (and Rosalind Franklin and Maurice Wilkins). In his acceptance speech in Oslo, however, Muller declared that his research offered “no escape from the conclusion that there is no threshold dose.”
Muller’s utterance has become the basis of what is now called the linear no threshold (LNT) theory, the gist of which is that there is no dose of radiation small enough to not cause damage to living tissue. This has proven to be a controversial claim not just today with greater scientific advancement but even in its own time. Methodologically, the doses Muller used in his study were massive. The lower end of his radiation dosage was as high as 400 R total and rates of 0.01 R/minute – the recommended maximum dosage by the International Commission on Radiological Protection (ICRP) for the general public is 1 mSv and 20 mSv for nuclear industry workers (400 R is 3,732 mSv).
There is evidence to believe that this oversight was known to Muller even at the time of receiving his Nobel. Two research papers, one by Warren Spencer and Curt Stern and another by Ernst Caspari and Curt Stern, were sent to Muller five weeks before the prize-giving ceremony. Muller’s response was that the findings were interesting yet required additional testing. Caspari, a research associate of Muller, experimented with 50,000 fruit flies and showed that below a certain dose and dose rate, irradiated flies had no more mutations than the control group; at an even lower level, the irradiated flies actually had fewer mutations than the control group!
Rather than harm living tissue, a level of radiation marginally above background radiation was shown to actually be beneficial. This is known as radiation hormesis and is easily as controversial as the LNT theory. This is not as outlandish as it may seem at first. Hiroshima and Nagasaki have indelibly imprinted our minds with an association between death and radiation yet there are plenty of places around the world where people are subjected to levels of radiation several times higher than the dose deemed acceptable by the ICRP. The average dose of absorbed radiation in Lakshadweep, Bombay, Delhi, Madras, Bangalore, and Hyderabad, are 0.026, 0.484, 0.7, 0.81, 0.825, and 1.278 mGy/yr respectively. Some spots such as Yangjiang, Guarapari, Chavara, and Ramsar measure significantly higher readings of 5.4, 35, 110, and 260 mGy/yr. Interestingly, there has been no higher incidence of stochastic health risk at these or the many other similar sites. At Chavara and Guarapari, locals freely lie on the radioactive beach sands without fear of consequence.
There is a lot of interesting biology that can be discussed here but suffice it to say that the ability of cells to repair themselves seems to be amplified with exposure to low doses of radiation. However, to put this into context, spontaneous DNA damage occurs at the rate of approximately 200,000 events per cell per day. The approved radiation dose of 1 mSv from nuclear power plants results in natural cell damage at a rate of 0.03 events per cell per day.
The phenomenon of something being beneficial to humans in small doses and harmful in higher doses is not restricted to nuclear reactions alone – the same effect is seen in curcumin, the active ingredient of turmeric. While its antiseptic and anti-microbial properties have been known to Indians for centuries, the same substance is carcinogenic in higher doses.
Even regarding long-term impact of radiation, Hiroshima provides some interesting scientific data. Studies done in the early 1990s made a startling revelation: below a radiation threshold of approximately 100 cSv, the health of the survivors of the nuclear attacks on Hiroshima and Nagasaki may have actually improved! Untoward pregnancy outcomes in the control group were at 4.99% and for the exposed group 5.00%; deaths of live-born children stood at 7.35% and 7.08%; stable chromosomal aberrations at 0.31% and 0.22%; aneuploidy at 0.3% and 0.23%; mutations in blood proteins at 6.4 x 10-8 and 4.5 x 10-8; and leukaemia at 0.05% in both groups. In several indicators, the genetic effects of radiation in the children of the survivors of Hiroshima and Nagasaki were insignificant to slightly better than the general population!
What exactly constitutes a low dose of radiation is difficult to tell. In 1958, the ICRP set the tolerance dose limit of 50 mSv for nuclear workers and 5 mSv for the general public; before then, it was 680 mSv. In 1991, the limits were brought down to 20 mSv and 1 mSv. It is difficult to ascertain why the dosage limit was reduced for there is no scientific reason beyond the dubious LNT theory. The paranoia about radiation and the “no threshold” position is unfortunate for it prevents genuine research on the effects of low dose radiation on flora and fauna.
Nuclear advocates face a Sisyphean task in trying to allay the fear of nuclear energy. This has little to do with the risks inherent in technology and much more to do with human psychology and neuroscience. First, the effect of framing: the way a situation is presented elicits different responses from people. For example, a scenario was presented wherein 600 people have been infected by a deadly disease; Solution A will save 200 people, while Solution B has a 33% chance that all 600 people live and a 67% chance that there are no survivors. About 72% of subjects preferred A over B. Another group of people were offered the same choices worded differently: would they pick Solution C which will result in the deaths of 400 people, or Solution D in which there was a 33% chance that nobody will die and 67% chance that everyone will die? An overwhelming 78% of the people chose D over C. The acceptability of an option, it was shown, can depend on whether a negative outcome is evaluated as a cost or as an uncompensated loss.
Psychology also shows that people do not necessarily evaluate risks on an empirical or rational basis but emotions also play a great role in decision-making. Ignorance and fear of the unknown will, therefore, influence their position on an issue. Furthermore, the human brain has a natural tendency towards negativity: people remember things that went dreadfully wrong for them more easily than their happier moments. The reptilian brain is likelier to devote more attention to negative stimuli because of an evolutionary survival coping mechanism.
Given the biological barriers against risk and ignorance of the subject matter, no amount of scientific reaching out is going to help the pro-nuclear crowd make their case persuasive. As Roy Durstine wrote in 1945 (and several people since), “Don’t confuse me with facts!” Durstine, who has summed up the problem so wonderfully, was in the advertising industry and the solution may also lie there. As David Ogilvy always tried to teach his staff, good advertising is not an intellectual debate but about positioning a product to meet the audience’s needs – emotional, psychological, or material. Perhaps this is the lesson the nuclear industry needs to take to heart.