The media coverage of the Fukushima nuclear emergency has naturally caused a lot of concern. For some reason the words nuclear and radiation used together cause reason to fly out the window. It is still the case that only a handfull of people have been killed directly by the nuclear power industry in over 50 years. During the same period many tens of thousands have been killed producing or using fossil fuels, and even wind power has killed 35 people erecting the turbines.
Radiation is a much misused word since it covers both electromagnetic radiation like light and wireless as well as “ionising radiation” from X-rays and radioactive decay. When people get scared about “radiation” it is just ionising radiation from nuclear decay of radioactive isotopes that concerns them. We cannot escape an environment full of ionising radiation since most of it is natural. There is also no difference between any man-made radiation and that emitted by the environment. One particle of “ionising radiation” must have enough energy to knock at least one electron out of an atom in the human body. If one particle hits the body then it “absorbs” this energy. The total energy absorbed by the body is called the “dose”. If one kilogram of your body absorbs 1 joule of energy of ionising particles then it has had a dose of 1 Sievert (100 rads in CGS units). (I joule is about the the same energy as the body heat we emit from each kilogram through metabolism each second). If we take an electron of say 500keV then a dose of 1 Sievert would mean that a kilogram of body being hit by about 2*10**13 electrons. Electrons are the most common form of particle from beta decay of fission products.
Radioactivity of a sample is measured in Bequerel which is simply 1 bequerel = one particle emitted per second. You can think of this as being a geiger counter which clicks once a second. Therefore to receive a whole body dose of 1 rem in one year you would need to ingest and retain in your body 6500000 Becquerel of radioactive material for the whole year. Our bodies actually flush out elements like Caesium every 20 days so the effective ingestion would need to be over a regular extended period – so probably a much larger Becquerel. In the summer of 1964 a couple of individuals in New Mexico following the Nevada Bomb testing were found to have ingested the equivalent of 100 million Becquerel of Caesium. They were unaware of this and in good health. To get the risk of man induced radiation in perspective you have to consider natural radiation in the environment which we cannot avoid.
Natural Radiation
Naturally occuring radon gas is produced by the decay of Uranium in rocks and we all breathe it in to some extent. When this is combined with cosmic radiation from space everyone on earth receives an average annual dose of about 0.4 rem per year or 0.004 gray. This dose however actually varies enormously depending on the geology of different parts of the world. In some parts of India it reaches as high as 3 rem per year (0.01 gray). Houses with poor ventilation in granite regions can accumulate radon gas so it is best to avoid living in the basement. Radon is a potential cause of lung cancer.
Potassium 40 is present naturally in many foodstuffs which we eat and gives each of us an equivalent dose is about 30 mrem/year. This is internal exposure.
Average Natural Radiation Dose of 0.4rem/year
Medical Exposure
All of us get regular X-rays at the dentist etc. and clearly this varies enormously depending on the individual (see below). The pie chart summarises normal exposure levels for a US citizen. The “Other” column includes nuclear fallout from bomb tests and nuclear power and is insignificant. If you smoke then the dose increases by about 280 mrem because tobacco contains radioactive lead and is drawn into the lungs.
Nuclear Accidents
Fallout from Chernobyll added significant quantities of caesium 137 to the environment especially over certain parts of Europe. One of the worst affected areas was Sweden where measurements estimate a total average dose of 50 mrem over a 50 year period. Clearly some people will have had much more. In 1988 I started work at the JRC Ispra which is in the northern lake area of Italy. That area had a large rainfall following Chernobyll and consequently Caesium fallout was quite high. As a result of this everyone in that area as well as other hot spots consumed food containing Caesium. I had a whole body scan a couple of years later and a “chernobyll” signal of Caesium 132 was apparent in the spectrum although smaller than the potassium 40 signal. Probably many millions of Europeans had similar signals of which they were blissfully unaware. Today the signal has essentially disappeared.
The U.S. tested nuclear weapons in the Nevada desert from 1951 to 1962. Some people living downwind of the site received doses of about 400 rem (4 sievert) from iodine and elsewhere in the US typical doses were typically a few (5) rem.
The Centers for Disease Control reported that they expected to see eventually perhaps 200,000 additional cases of thyroid cancers from fallout caused by nuclear tests in Nevada. The worst fallout from a single test was the first Fusion bomb test Bravo at Bikini Atol showering some Marshal Islanders with about 150 rad of fallout, and seriously exposing 23 Japanese fishermen, 40 miles downwind of the bomb, who suffered radiation sickness, one of whom died in hospital. Nuclear testing was banned above ground in 1963. Today the residual doses from nuclear testing worldwide is of the order of 1 mrem per year per person. http://www.senes.com/Thyroid.Doses.Final.Report.pdf
Nevada Tests – Iodine 131 doses
Extreme Medical Exposure.
1. In 1960 my mother was diagnosed with thyrotoxicosis and was treated with radioactive iodine to destroy the thyroid gland. This technique is known as thyroid ablation. Iodine 131 taken in a drink is taken up mostly by the thyroid gland and the intense beta radiation destroys the cells. The dose taken was about 18,000 rem (180 gray) which is huge but localised. She was kept in an isolation ward with no direct contact for 10 days or so. Her food was delivered through a trapdoor so nurses would not need to come into contact with her. I remember as a small boy eventually being able to visit her in hospital a few weeks later. She was fine afterwards and lived another 40 years.
2. In 2000 I discovered a small lump in my salivary gland which turned out to be malignant, which was a bolt out of the blue. I had an operation to remove the whole salivery gland which was followed by radiotherapy. The radiotherapy was personally a nightmare which I had to endure. A steel mask was made to target the area affected on the right side of my face from just below the eye to the lower neck and I was placed in a shielded room below an electron accelerator delivering essentially beta rays (electrons) at 100 KeV and sometimes gamma/X-rays. It is a nerve racking experience as the operator closes the 12 inch thick steel shielding door and you are left alone waiting for the machine to hum. In my case with eyes shut I could see a light show of Cherenkov raditaion as the high energy electrons passed through the liquid surface of my right eye – a very unnerving experience. I had 30 sessions over 6 weeks each delivering a dose of 2 gray – 60 gray in total. Radiation burns eventually caused the external skin of my face to scale like leather. I had blisters inside my cheeks plus scarring down my throat. Luckily I have a very good dentist to thank for protecting my gums and for preventing bad damage to my tongue. He made a special protective shield which I could wear with air holes for breathing. This saved my sense of taste and my gums. It then took me about 6 months to a year to return to a more or less normal life. However I have permanent hair loss on the right side of my face, a permanent numbness and occasional throbbing, plus loss of feeling in my right ear. Other than that – 11 years later I feel great !
The two workers sent to hospital last Thursday from the Fukushima nuclear plant after standing in radioactive water containing Iodine 131 also received similar beta burns to their feet. Each received about 4 grays to their feet – roughly what I received in 2 of my 30 sessions to a similar area. They should be fine after a week with no long term side effects, because the exposure was external and not internal. The real worry is the dispersal of Iodine and Caesium in the air, since these can enter the food chain and are retained in the body for 1 or more days. Although they give no noticeable effect at all Iodine increases the risk, especially in children, of developing thyroid cancer, and it is suspected that caesium may also increase risk of cancer. Iodine decays naturally in a few weeks while the body will eventually excrete the caesium over periods of 20-40 days. Ironically the best treatment for thyroid cancer is to take massive doses of Iodine 131 to kill the thyroid tissue as happened to my mother.
Fukushima effects.
Today the level of Iodine 131 found in tap water in Tokyo was 34 becquerels per litre/kg. To receive the same dose from Iodine as you receive anyway just from natural radon, I calculate that you would have to drink 100 litres of tap water per day. However, since Iodine 131 has a half life of 8 days you would need to double your intake every 8 days. Therefore by monitoring caesium and iodine in food it should be possible to limit greatly any potential yet small risk to people, especially children, over the coming few weeks. My gut feeling is that the plant is now getting under control and hopefully no further large emissions widespread will occur.
