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Friday, March 18, 2011

Ionizing Radiation & The Mind


On this day last week, northeastern Japan was hit by a magnitude 9.0 earthquake, the strongest recorded in history, triggering a tsunami with waves topping 30 feet in some locations. The impact of this catastrophe of epic proportions now known as Tōhoku Earthquake and Tsunami has been devastating. According to Fiona Ortiz's report with the title "Aid groups say most of Japan displaced have basics" published online on Reuters today, the death toll stands at 6,539, more than 10,000 are still missing. Entire coastal villages have disappeared. Hundreds of thousands have been displaced. Their basic needs have just been met.

On top of the wide-spread suffering, the disaster rendered the cooling systems of the nuclear power plant with six reactor blocs near the town of Fukushima 150 miles north of Tokyo dysfunctional (see Reuters summary entitled "Snapshot: Japan's nuclear crisis"). Uncovered by water, fuel rods in three reactor units and the spent fuel storage pool of a fourth have been heating up. Radiolysis of water and the oxidation of the bared rods' zirconium cladding has been producing hydrogen. Once a threshold concentration was reached, the hydrogen reacted with oxygen, triggering massive explosions that destroyed the reactor buildings. Reactor containments may have been compromised. Considerable amounts of ionizing radiation are being continuously released, exposing the direct surroundings of the reactors to highly dangerous levels.


Bird's eye view of reactors 4 and 3, published Apr. 14, 2011.

At this time, plant operators, first responders, and the Japanese military are still struggling to control the situation. The risk of radiation exposure at levels detrimental to health is considered minuscule outside the plant. Fallout reaching other countries in worrisome proportions has been ruled out, particularly in the continental U.S., which are 5000 miles removed from the plant in Japan. President Obama assured U.S. citizens that no radiation-related harm is expected to affect the nation (see Jeff Mason and Patricia Zengerle's report with the title "Obama requests nuclear review, sees risk in Japan" published online on Reuters yesterday).

However, prevailing winds have already driven air from the site to the West Coast. Iodine tablets have been sold out. People are worried, particularly because governments and agencies of various nations judge the threat in differing ways. Whereas U.S. expatriates in Japan are advised by their government to stay out of a 50-mile radius around the plant, the Japanese government believes that there is no  public health risk at roughly half that distance (see Shinichi Saoshiro and Chisa Fujioka's report with the title "WRAPUP 3-Japan scrambles to avert nuclear disaster, global fears mount" published online Mar. 16, 2011). The governments of the highly industrialized, energy-hungry nations commonly support nuclear power. Most experts tend to avoid alarming the public unnecessarily. Concerned citizens perceive great dangers. Opposing views result in diverse and opposing messages.

I worked in hot zones in the 1970s. Ionizing radiation seems sinister to us, because we cannot sense it and its deleterious effects cannot immediately be noticed, unless the levels are extremely high. Then, victims have reported that they could feel the radiation.

Chemical elements may vary in the composition of their nuclei. Whereas the number of protons remains the same for each element, defining the chemical properties and its name, the number of neutrons, and with that the atomic weight, may vary. The isotopes, as these variations are called, are distinguished by the sums of protons and neutrons called atomic mass numbers. For example, the isotopes of hydrogen, are labeled 1H (hydrogen: 1 proton) 2H (deuterium: 1 proton plus 1 neutron) and 3H (tritium: 1 proton plus 2 neutrons). Hydrogen is most prevalent, but the small amounts of deuterium and tritium naturally present are responsible for the fact that the chemical element hydrogen's atomic weight is listed in the periodic table of elements as slightly greater than 1.

Some isotopes, like tritium in the example above, are unstable. That is, their atomic nuclei decay at particular rates, transforming them into other elements. The rates are measured in half-lives, that is the discrete period of time in which half of the nuclei decay. The decaying nuclei emit ionizing radiation. Radioactivity represents the number of decays in a set window of time, e.g. one second, and is expressed in Becquerel [Bq] or Curie [Ci].
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Bidirectional Becquerel-Curie Converter
x 10 Bq = x 10 Ci
Insert your values in the appropriate boxes and push the button with the label of units you wish to convert to [femto - 10-15; pico - 10-12; nano - 10-9; micro - 10-6; milli - 10-3; kilo - 103; mega - 106; giga - 109; tera - 1012].

Ionizing radiation emitted during radioactive decay is mainly composed of three types which may occur in mixture:
  • α - large positively-charged particles composed of two protons and two neutrons (helium cations),
  • β - small negatively-charged particles (electrons), and
  • γ - high-energy electromagnetic rays.
The first type interacts with matter most dramatically, but is the least penetrating because the large α-particles come quickly to a halt owing to the multitude of interactions with the absorbing matter. β-particles travel further. Depending on their energy, they may travel meters in air, but are absorbed within millimeters in water or tissue. By contrast, γ-radiation interacts the least, but penetrates the deepest. Therefore, we suffer from the adverse effects of α- and β-radiation, only when we are in close proximity to the source or incorporate the source. Thin plastic foil may suffice to protect us. By contrast, lead bricks and distance may be necessary to shield us effectively from γ-radiation.The levels fall with the squared distance from the source following Newton's inverse square law. Ionactive Consulting provides an insightful demonstration of this law. Because γ-radiation dissipates in a sphere, the dose D at distance r can simply be calculated using:

D = dose at source / 4πr2

Electromagnetic rays of lower energy than that of γ-radiation, similar to X-rays, are also considered ionizing radiation and may be emitted during the decay of radioactive isotopes, but their effects do not seem to account for much. By contrast, fluxes of nuclear particles like neutrons and protons are highly ionizing.

The radioactive isotopes unleashed from the Japanese reactors emit α-, β- and γ-radiation. In addition, some neutrons have been detected near the plant and have been associated with fissible material from fuel rods scattered by the hydrogen explosions. The health hazard mounts with the duration of exposure, that is the doses of radiation absorbed by the whole body over time.

Two types of measurement are commonly used to express these doses. The radiation absorbed dose (expressed in Roentgen absorbed dose [rad] or Gray [Gy]) measures the amount of ionizing radiation absorbed regardless of its biological effect, while Roentgen equivalent man (expressed in rem or Sievert [Sv]) takes the biological impact of the type of radiation into account.

Ionizing radiation forms free radicals in the cells, particularly highly reactive species of oxygen, that can modify vital molecules. Theoretically, any particle of ionizing radiation, we may consider γ-rays particles, can damage DNA. The cells may not be able to repair the damage, leading to cancer. Therefore, a health risk-free level of radiation is impossible to determine, and the average naturally occurring radiation dose we are exposed to in every-day life is considered baseline. Multiples of this value are deemed permissible when unavoidable, e.g. in medical procedures or in professional settings like hot zones and nuclear facilities.

When I worked in this field, 0.125 rem per year were considered normal exposure. Workers in nuclear facilities were permitted 5 rem per year. Acute radiation syndrome, a potentially life-threatening illness, develops at 150 rem. Among other effects, the white blood cells drop to critically low levels, compromising the immune system. Half of the people exposed to 300 rem do not survive. Doses greater than 500 rem are instantly lethal.

1 Sv equals 100 rem.
Bidirectional Sievert-Rem Converter
x 10 Sv = x 10 Rem
Insert your values in the appropriate boxes and push the button with the label of units you wish to convert to [femto - 10-15; pico - 10-12; nano - 10-9; micro - 10-6; milli - 10-3; kilo - 103; mega - 106; giga - 109; tera - 1012].

In the current situation we find in Japan, such doses are only reached within the confines of the nuclear power plant. At the peak doses measured at the plant's gate during the past week, we would have been mildly sick in four hours. By contrast, levels recorded in the surrounding countryside away from the plant have been more than a thousand times lower. Therefore, the people at greatest risk at present are the personnel working inside the plant and the pilots flying helicopters low over the broken reactor buildings for water drops.

Here in the U.S., the situation is entirely different. By the time clouds from Japan reach the West Coast, α-emitting isotopes, like the highly toxic plutonium isotopes, have precipitated because of their sheer weight. Much of the radiation has been washed out by rain and scattered. Perhaps two γ-radiation emitting isotopes may drift our way that may potentially pose a health risk, known to cause cancer of the thyroid and the liver at high doses: 131I and 137Cs. However, they will arrive highly diluted, if at all. Contamination with significant amounts through direct ingestion or inhalation can be excluded.

Concentration in the food chain is the only imaginable path on which we might be exposed to trace amounts of these isotopes. For prudence's sake, we may wish to monitor radiation levels in fresh seafood, wild mushrooms and berries, venison, farm produce, as well as fresh dairy products and meats, more carefully during the coming months.

Addenda
  • According to William Broad's report with the title "Radiation Plume Reaches U.S., but Is Said to Pose No Risk" published online in The New York Times, plumes containing the two isotopes mentioned above have been detected over Sacramento, CA, yesterday. For the scientifically inclined, a suitable radiation detector like the RADIATION DETECTOR DOSIMETER TERRA-P FOR HOUSEHOLD USE !!!ENGLISH VERSION!!! can be acquired for a couple of hundred dollars. Unfortunately, this model was sold out on Amazon in one day. Fancier ones with digital data output cost twice as much; buyers must wait six weeks. Professional equipment like the Ludlum Geiger Counter Model-3_with-44-38 costs even more. The technically versed may wish to build a simple one themselves. Instructions can be found in Wenzel's post entitled "Cheap Sensitive Radiation Detector" published online on radiolocman.com Apr. 23, 2008. Care most be taken that the instrument remains properly calibrated over the duration of the study. Ideally, sample tests should be carried out in exact same location and geometry. Furthermore, we ought to ensure that we collect good background readings, before we check our samples. We must keep in mind that Geiger-Müller detectors are very sensitive for β- and γ-radiation, picking up the most minute amounts. Depending on amplification, the meter may rage in response to little (03/19/11).
  • As a rule of thumb in nuclear medicine, we considered a radioactive isotope decayed after ten half-lives. That is, at that time the radioactivity had diminished to one-thousandth of the initial amount. Applied to the present situation, a radiation exposure of milliSievert will have diminished to microSieverts within ten half-lives, and microSievert to nanoSievert. On the West Coast, we are looking at nano- and pico-levels to begin with. Iodine-131's half-live is 8 days. In three months, according to the above rule of thumb, the exposure from this isotope at the currently reported rates outside the plant will be entirely negligible, unless the source is replenished. Cesium-137 with a 30-year half-life poses a greater concern (03/19/11).
  • Targetmap.com provides regularly updated maps of radiation levels recorded in various prefectures of Japan. The levels are given in nGy/h. The conversion factor to Sievert can be assumed to be 1 because of the distance to the source which limits the effect to γ-radiation. More detailed information on conversion factors can be found on this page maintained by the Hiroshima International Council for Health Care of the Radiation-impaired. Interestingly, readings seem unavailable for Fukushima, where the plant is located. The prefecture is constantly considered “under survey”. However, Ibaraki Prefecture bordering south provides insight (03/20/11):
  • When the industrialized nations began to build civilian nuclear power plants for electricity generation four decades ago, the premise was a closed fuel cycle. That is, spent fuel was supposed to be reprocessed. Fissionable material was supposed to be extracted and used in fast breeder reactors. The breeders would produce fuel that could be reused in regular reactors. The most toxic and unusable remnants were to be embedded in molten glass and deposited in tectonically stable salt mines miles underground. This promise has not come to fruition to the day.
    Safe reprocessing became way more involved as initially believed. Fast breeder technology is wrought with technical challenges and was never developed to reach safe and stable operational levels on industrial scale. Sites for end storage proved difficult to find.
    The unclosed fuel cycle is the reason why so many spent-fuel rods have been piling up at the damaged plant in Japan as well as at other facilities around the globe. As the current crisis strikingly demonstrates, storage pools filled up to capacity with spent fuel appear to pose an equal, if not greater, risk as the reactors themselves.
    For nuclear power to remain a reasonable source of energy, safer reactor designs will not suffice. The fuel cycle must be safely and efficiently closed. How to achieve this not only technologically, but also in a socially and politically accepted manner, will eventually decide the future of nuclear power (03/22/11).
  • Since worries about radiation levels in drinking water are rising in Japan, recent high-end refrigerators use carbon block filters like UltraClarity for water filtration. This type is used in the nuclear industry and may remove iodine and cesium quite effectively. Perhaps it is best to change the filter every three months under the current circumstances instead of the recommended six. More effective are reverse osmosis filtration systems like the Watts Premier RO-Pure 4-Stage Reverse Osmosis System. Biomedical research laboratories are commonly equipped with separate systems that provide highly purified, deionized water
    (03/22/11).
  • Reuters maintained the most exhaustive ScribbleLive forum for current developments on the recovery from the quake and tsunami and, particularly, efforts at the crippled nuclear power plant with countless links to information of interest. Since its closure today, the lively discussion of cutting edge data at least two days ahead of the news has relocated to a new ScribbleLive forum independent from Reuters (03/25/11).
  • The expert presentation in the video below provides the clearest explanation of the events leading up to the nuclear accidents at the Fukushima power plant. The earthquake disrupted cooling water pipes feeding reactor vessels and a loss of coolant ensued. Loss of coolant accidents, or LOCAs for short, are unprecedented in the history of nuclear power generation and their possibility should pose great concern at reactors of similar design. Releases of radiation from the plant are not yet contained (03/29/11):
  • Evidence that fallout from the Japanese reactor accident has reached the SF bay area can be found in KFC's post with the title "Fukushima Fallout Reaches San Francisco" published today on the MIT technology review. The spectra warrant particularly close inspection (04/01/11).
  • Juergen Baetz reports in his post with the title "Germany's radioactive boars a legacy of Chernobyl" published online for AP on Apr. 1, 2011, that wild boars with concentrations of Cesium-137 greater than the recommended limit, that is more than 600 Bq/kg, can still be found in German forests 25 years after the reactor accident at Chernobyl in the Ukraine about 1,000 miles away. Mushroom lovers may find helpful advice on the species known to incorporate cesium-137 and other radioisotopes on HealWithFood.org. Below is the most recent google map of contamination in the surroundings of the Fukushima power plant Greenpeace established (04/11/&06/02/2011):
  • NHKWorld reports in a brief news clip with the title "Govt suspends shipment of Fukushima sand lances" published online today that “the [Japanese] government has instructed Fukushima Prefecture to suspend shipments of a small fish caught off its coasts found to have radioactive contamination, and to warn people not to eat them. The restrictions announced on Wednesday are being applied to marine products for the first time, amid ongoing troubles at the Fukushima Daiichi nuclear power plant. The instruction follows a health ministry report that the fish called sand lance caught on Monday near Iwaki city, south of the plant, was found to contain 14,400 Bq/kg of radioactive cesium. That's 29 times the safe limit. Ministry testing also found 3,900 Bq/kg, or twice the limit, of radioactive iodine in the fish. Excessive amounts of radioactive cesium were detected in sand lances caught in the same area on April the 7th and 13th. The government says the fish are not on the market, as fishery cooperatives in Fukushima are not operating” (04/20/11).
  • Live webcam view of the Fukushima nuclear power complex from inland (West) towards the sea (East). The superstructures of reactors #1 and #2 are visible on the left. Damage can be seen to the top floors of reactor #1. The remnants of reactors #3 and #4 are located on the right (05/07/11):
  • The U.S. Environmental Protection Agency regularly examines the regional concentrations of a number of radioisotopes including iodine-131 and cesium-137 in the air, rain and drinking water as well as milk. The agency provides a list of the latest results for your area in a table published by Socrata.com which can be best viewed best in full screen below (05/10/11):

Powered by Socrata
  • Last weekend's revelations by the Fukushima power plant operator TEPCO (press release of reactor #1 parameters immediately after the quake with the title "Reactor Core Status of Fukushima Daiichi Nuclear Power Station Unit 1" dated May 15, 2011) provide ample evidence that the incident was rather the result of aging reactors than the consequence of an unforeseeable event. We are left to live with the fallout, the full extent of which is not yet known and will affect us for years to come (05/16/11).
  • Yasaikensa provides comprehensive insight into the contamination level of foods in Japan (06/03/11).
  • According to Jbhealer's post with the title "Holistic Radioprotection: Fruit Pectin, A Gentle & Powerful Chelator", dated Jun. 22, 2011, pectins constitute formidable chelators for the detoxification of radionuclides like cesium-137 (07/09/11).
  • In his article with the title "Marginalization After the Fukushima Nuclear Meltdown" published online in the July issue of  The Asia-Pacific Journal, Robert Jacobs provides informative insights into the social impact of the Fukushima reactor accident on future life in Japan (07/12/2011).
  • Discoveries of cesium-137 contaminated beef sold for consumption in Japan have been increasing rapidly over the past week. This week, the Japanese government decided to suspend the sale of beef cattle from Miyagi Prefecture, in addition to the week-old ban of beef from Fukushima Prefecture, as Kyodo News reports today in their post with the title "Gov't bans all shipments of beef cattle from Miyagi Pref." Miyagi Prefecture ships roughly 30,000 heads of cattle a year. The cattle was fed contaminated straw harvested around the crippled Fukushima Daiichi nuclear power station. The Japanese government set the legal limit for cesium-137 in beef at 500 Bq/kg. Minoru Matsutani of The Japan Times noted in his online Q&A column on Jul. 22, 2011, that “the most highly contaminated beef found contained radioactive cesium of 4,350 becquerels per kilogram, according to the Health, Labor and Welfare Ministry.” The meat was confiscated. Reuters reports on the fallout:
  • I can only recommend "Ionizing radiation and life" by Victor Arena (Mosby, St Louis, 1971). Though a seemingly old text book, the contents remain pertinent today. The author concludes in his epilogue: “We also hope that radiobiologic knowledge will be a strong deterrent for man against unwise use of nuclear energy and against the temptation of deploying nuclear weapons for the "solution" of international conflicts. With the experience of Hiroshima and Nagasaki, we like to believe than man will have enough wisdom in the future to avoid the destruction of his own species in a nuclear holocaust.”
    According to pp. 239 of this book, measurements of chronic exposure doses across the 1960s US suggest 1.35 milliSv/y as a rough average for an effective absorbed dose from external natural sources. We must add about 0.8 milliSv/y from internal exposure. Individual doses may vary considerably with location (12/12/2011).

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Radiation dose meter at Fukushima Medical University 35 miles from the stricken nuclear power station. The readings are continuously updated. In the week after the quake, dosemeter readings in Fukushima City spiked above 20 microSv/h. At this dose, we are exposed to an effective absorbed dose of 175 milliSv in a year which corresponds to 17.5 rem; a dose that nuclear industry professionals perhaps accumulate over their entire career (03/09/2012).
  • According to Sarah Sheffer's video report with the title "Scientist fears radiation still leaking at Fukushima nuclear plant" published online on Reuters Nov. 19, 2012, Japan's contamination problems continue to mount one year and a half after the accident:

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4 comments:

  1. You write on page 1 "...Uncovered by water, the loaded fuel rods in four reactors...: I thought that reactor 4 was not loaded, and that units 5 and 6 are shut down, so this leaves 3 reactors with loaded fuel rods. am i wrong about this?
    billmcd.

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  2. Thank you! Here were a ot of useful information! Great site. :)
    Mona

    ReplyDelete
  3. Dear Mona:
    I am glad that the information was of use to you. Many thanks for your kind comment, :) Peter.

    ReplyDelete
  4. Dear William:

    Thanks for your kind admonition. You are cognizant reader, and you are correct. According to most accounts, reactor #4 had been shut down for service at the time of the quake, and its fuel had been entirely unloaded into the spent fuel pool under the same roof. However, there was a hydrogen explosion in the building in the week after the quake, and at the time of my writing the assumption was that the fuel in the pool had been exposed and might have partially molten. For simplicity's sake, I used Japanese conventions by which the term reactor refers to the whole unit. I corrected the text to “Uncovered by water, fuel rods in three reactor units and the spent fuel storage pool of a fourth…." to be more accurate. Moreover, your post sent me of to more research on the fate of reactor #4 and I uncovered some peculiarities, deserving a separate post: http://brainmindinst.blogspot.com/2011/05/enigma-of-1-fukushima-4.html

    ReplyDelete