Some RAD Information
The "international" standard for radiation measurement is the "Sievert", which is a metric standard. One thousandth of a Sievert is a "millisievert", which is what the news media has been using to report the levels of radiation in Japan: "Dose rates of up to 400 millisievert per hour (mSv/hr) have been reported at the site."
Here in the USA, we have for decades used Rems and Rads, which are based upon an English standard. The differences are somewhat confusing, so I am going to break this down to more easily understood measurements.
If you have old surplus Civil Defense dosimeters or Radiation Survey Meters (also inaccurately called "Gieger Counters"), these will be in measurements of Roentgens or Rads, not millisieverts, so knowing how to convert between the two standards will become important very shortly.
No, the following conversion is not scientifically precise, but it is close enough for our purposes on the ground. Nuclear physicists may split hairs as often as they split atoms, but that does not mean that we, as the people who actually have our lives on the line, cannot come up with a more useful way of measuring our own level of risk.
A "Rem" and a "Rad" are virtually interchangeable for field measurements.
True, they are not exactly equal, but they are close enough.One thousandth of a Rad is called a "millirad".One thousandth of a Rem is called a "millirem".
One "Rad" is roughly equivalent to .876 Rem, more than close enough for me to calculate them as equal. By the time you worked out the exact conversion, you might be cooked, so don't worry about the fine differences when you are trying to calculate whether you should close the door to your underground shelter.
1 millisievert (mSv) = 100 Millirems (or Millirads)10 millisieverts
= 1000 Millirads = 1 Rad
So, roughly speaking, you need 10 Millisieverts to equal one Rad.
Looking at news reports from the BBC, we see that today the Japanese were admitting to 400 Millisieverts per hour of radiation on the ground within 20 miles of their former nuclear reactor complex. That roughly equates to about 40 Rads per hour.
The effects of radiation are cumulative, so 40 Rads per hour will result in a total of 80 Rads of exposure in two hours, 120 Rads of exposure in three hours, and so on.
100 Rads, or about 1000 Millisieverts, will result in the symptoms commonly referred to as "radiation sickness". 200 Rads, or about 2000 Millisieverts, will make you as sicker than the proverbial dog.
Considering that 400 Rads would definitely put you in a hospital, and 600 would absolutely, positively kill you dead, 40 per hour is bad news, folks.
After about ten hours of exposure at that rate you would definitely wind up deathly ill and would have a 50-50 chance of winding up dead. IF you survived, you would also have about a 50 percent chance of developing some form of malignant cancer.
After about 15 hours of exposure at that rate, you would not have to worry about ever getting cancer, because you would be dead in a few weeks to a
month. 600 rads of exposure will be 100 percent fatal. 40 rads per hour will definitely ruin your day. The level at what used to be the Fukushima Daiichi nuclear complex has apparently risen a LOT higherhttp://grendelreport.posterous.com/radiation-risks-read-carefullyhttp://www.mun.ca/biology/scarr/Radiation_definitions.htmlHigh-level waste
Nuclear waste is divided into several categories. High-level waste consists mostly of spent nuclear reactor fuel from both commerical power plants and military facilities, as well as reprocessed materials which can emit large amounts of radiation for hundreds of thousands of years. Commercial nuclear power plants in the U.S. alone produce 3,000 tons of high-level waste each year. The amount of spent fuel removed annually from the approximately 100 reactors in the U.S. would fill a football field to a depth of one foot. When spent fuel is removed from a reactor core, it still emits millions of rems of radiation. For more information on units of measurement (such as the rem), see the radiation effects page.
In the absence of high-level waste repositories, nuclear power plants genearlly store their spent fuel rods in lead-lined conceete pools of water. These pools somewhat contain the spread of gamma radiation by keeping the rods relatively cool. They also help prevent fission. The average commercial power plant puts 60 used assemblies into temporary storage each year and will probably continue to do so until the year 2000, when responsibility for spent fuel will be transferred to the Department of Energy. Space is running out at many plants though. The plants have another option of storing their spent fuel at other plants still under construction. It is theoretically possible to reduce the amount of storage space that spent fuel rods require by removing them from their assemblies, bundling them tightly, and then packing them into heavily shielded dry storage, but repacking these highly radioactive rods may present too much of a challenge.
For long-term storage of high-level waste, a waterproof, geologically stable repository and leak-proof waste container is required. Packaging has to be tailored to the volume of the waste, the actual radioactive isotopes of elements it contains, how radioactive it is, its isotopes' half-lives, and how much heat it still generates. One technique for packaging high-level wastes involves melting them with glass and pouring the molten material into impermeable containers. The containers could be buried in soil or in a rock pile and surrounded by fill material and a barrier wall. From the 1940s through the 1960s, barrels of radioactive waste were frequently dumped in oceans. This ended in 1970 when the EPA (Energy Protection Agency) determined that at least one-fourth of these barrels were leaking. A new, possibly safer proposal under consideration for long-term ocean storage includes offshore drilling and a procedure known as self-burial. In offshore drilling, holes would be drilled into the seabed and filled with barrels of waste. In self-burial, specially shaped barrels would be dumped and left to sink to the ocean floor.
Geologic disposal is currently the most popular solution for waste disposal. During the 1980s, the U.S. government invested more than $2 billion into geologic disposal. In this form of disposal, mined tunnels with deep holes for waste canisters would be built using conventional mining techniques. Monitoring and waste retrieval would be relatively easy. In 1987, a site was chosen for the first permanent high-level commercial nuclear waste storage repository in the United States--Yucca Mountain, 100 miles northwest of Las Vegas, Nevada. Expected to cost up to $15 billion, this repository is scheduled to go into operation by the year 2010.
Over the years, a number of other ideas for high-level waste disposal have been proposed and, at least temporarily, abandoned. One was disposal in space, in which sealed containers of radioactive material would be sent up into distant orbits. This would be an expensive and risky operation, as problems on the launchpad or in space could expose the earth and atmostphere to an enormous amount of radiation. Another suggestion was burying waste under the Antarctic ice sheets. However, this would risk irradiating that area and the surrounding sea. A much safer idea, which would render disposal unnecessary, is to bombard radioactive waste with subatomic particles to transform it into less harmful isotopes. Unfortunately, this attractive proposal awaits still unrealized technology.Mill TailingsMill tailings, left over when ore is refined and processed is the largest by volume of any form of radioactive waste. Only 1% of uranium ore contains uranium--the rest is left on-site as sandlike residue. These tailings are generally left outdoors in huge piles, where they blow around, releasing radioactive materials into the surrounding air and water. By 1989, some 140 million tons of mill tailings had accumulated in the United States alone, with 10 to 15 million tons added each year. Although their radiation is generally less concentrated than other types of waste, some of the isotopes in these tailings are long-lived and can be hazardous for many thousands of years.
Until their radioactive risk was known, mill tailings were sometimes used as foundation and building materials, especially in western states. When their risk was discovered, these materials in the buildings had to be monitored. These monitored sites are generally safer, although some groundwater contamination still occurs at them. It has been recommended that tailings be stored underground in clay pits, far from population centers.Low-Level Waste
Low-level wastes are usually defined in terms of what they are not. They are not spent fuel, milling tailings, reprocessed materials, or transuranic materials. Low-level waste includes the remainder of radioactive wastes and materials generated in power plants, such as contaminated reactor water, plus those wastes created in medical laboratories, hospitals, and industry. Wastes in this category usually, although not always, release smaller amounts of radiation for a shorter amount of time. "Low level" does not mean "not dangerous," though. Although its radioactivity is usually less concentrated than that of high-level waste, low-level waste can be dangerous for up to tens of thousands of years.
Most low-level wastes come from reactors. These wastes can be divided up into two categories:
o Fuel wastes are fission products that leak out of fuel rods and into cooling water.
o Nonfuel wastes result when stray neutrons bombard anything in the core other than fuel--such as the reactor vessel itself--and cause them to become radioactive.
The remainder of low-level wastes comes from industry and institutional sources, including pharmaceutical plants, universities, and medical facilities. Instead of going to low-level waste dumps, these wastes are often kept on-site for the short time it takes for them to decay to safe levels. Then they are deposited into sanitary landsfills. However, it is likely that liquid wastes are literally poured down the drain, whether or not they are still radioactive.
Low-level waste landfills were first built in the 1960s. In near-surface land burial, containers of waste fill a trench and are covered and surrounded by compacted earth. There are currently a few burial grounds in the U.S. to which most commercial low-level waste materials emitting detectable amounts of radiation are sent. A few other landfills are currenly inactive due to severe waste-containment problems and radioactive leakage. Waste containers in near-surface landfills are prone to corrosion, particularly in moist climates. Landfills provide a false sense of comfort because they are "out of sight, out of mind." More worthwhile alternatives include above-ground landfills and to store waste at existing nuclear plant sites.
There are a number of unresolved issues regarding disposal of low-level wastes. The current institution control period (the amount of time a waste site must remain under guard after it has been filled and closed) is only 100 years. Yet the hazards presented by some low-level wastes can continue for thousands of years. What will keep future generations from uncovering and being contaminated by these substances?http://library.thinkquest.org/3471/nuclear_waste.htmlZeolite ClayThe unique structure of clays gives them unusual filtering capabilities for absorbing toxic wastes, including radioactive contaminants.
In just one gram of zeolite clay, for instance, the three dimensional structure of the channels in its crystalline structure provide up to several hundred square meters of surface area on which absorption (and channel reactions) can take place. The zeolites are particularly useful for removing heavy metals and radioactive species from water.
While you can take an Epson salt or Clorox bath, you can also take a radiation detox bath of zeolite clay that’s formulated with special herbs for the process.
Zeolites are natural, inert, non-toxic, environmentally friendly substances that are known to remove toxic metals from waste water, land, septic systems and the air. Zeolites can adsorb huge amounts of materials such as ions or gas molecules. Zeolite clay has an unusual crystalline structure and is tetrahedral in shape, similar to a honeycomb appearance. The channels and holes in the sponge-like structure of zeolite have a uniform shape and size. It is this unique crystalline structure that gives zeolite clay such unusual capabilities of filtering, mineralizing, and absorbing toxic wastes. In one gram of zeolite, the channels in its structure provide up to several hundred square meters of surface area on which adsorption and chemical reactions can take place. Its unique structure acts like sieves, or “shape-selective catalyst,” catching only molecules small enough to fit into the cavities, while excluding larger molecules.
There are around 50 different kinds of natural zeolites and about 150 synthetic versions with varying physical and chemical properties. Natural zeolites were discovered as major constituents of numerous volcanic tuffs in saline-like deposits. Zeolite contains the minerals potassium, calcium, silicon, hydrogen, oxygen, aluminum and sodium. Zeolite clay has been beneficial in remineralizing and re-establishing pollution control in the soil and for use in hydroponic plant growth. The high purity of the natural deposits has aroused considerable commercial interest in the United States and abroad. The name “zeolite” literally means “boiling stones.”
Zeolite clay has been a medium for air filters, water filters, and odor control. It is environmentally friendly for waste dump sites and has been used as a filter medium for the removal of radioactive wastes and for the removal of heavy chemical toxins and heavy metals such as iron, zinc, cadmium, lead, and copper, deemed hazardous by the government, from individuals as well as from mining and water waste sites. Zeolite clay has been used successfully for the extraction of radionuclides from human beings and animals.
The natural zeolites can absorb up to 30% of their dry weight of gases, such as nitrogen or ammonia. Toxic gases, chemicals, mold, mildew, formaldehyde, and other toxins are drawn by the natural negative electrical charge into the crystal micro pores of the clay. The odors and gases are removed, not merely covered up. Research is now being done by several companies for its use as an absorbent of excess moisture, molds, and fungi. “Pouches” of zeolite clay are now available for, not only odor control, but the elimination of toxic gases and chemicals, smoke, and radioactive gases. These “pouches” are placed in a room, and act like a magnetic sponge.The British Nuclear Fuels (BNF) uses this specific type of zeolite to remove radioactive strontium and cesium
and, therefore, reduces the radioactivity of liquid waste discharged into the Irish Sea . The Hanford , Washington nuclear weapons facility, uses this same kind of zeolite to prevent contamination. This type of zeolite also had a role in the cleanup after the atomic energy plant accident at Three Mile Island . A Swedish study showed another kind of zeolite could decontaminate live animals and meat affected by the Chernobyl disaster.http://www.tuberose.com/Radiation.html
Units of measurementrad
The rad represents a certain dose of energy absorbed by 1 gram of tissue. It is a unit of concentration. So if we could uniformly expose the entire body to radiation, the number of rads received would be the same whether we were speaking of a single cell, an organ (e.g., an ovary) or the entire body (just as the concentration of salt in sea water is the same whether we consider a cupful or an entire ocean).rem
Some forms of radiation are more efficient than others transferring their energy to the cell. To have a level playing field, it is convenient to multiply the dose in rads by a quality factor (Q) for each type of radiation. The resulting unit is the rem ("roentgen-equivalent man"). Thus, rem = rad x Q. X rays and gamma rays have a Q about 1, so the absorbed dose in rads is the same number in rems. Neutrons have a Q of about 5 and alpha particles have a Q of about 20. An absorbed dose of, say, 1 rad of these is equivalent to 5 rem and 20 rem respectively.The sievert
(Sv) and gray
Despite the years of high-quality research reported in rems and millirems (mrem, 10-3 rem), the International Commission on Radiation Units and Measurements wants us to give up the rad in favor of the gray (Gy), a unit 100 times larger. Similarly, the rem is to be replaced by the sievert (Sv), again so that 100 rem = 1 Sv. So I will try to express all radiation doses in a single unit, the millisievert (mSv).
|Estimated average annual radiation exposure from various sources (in millisieverts) of an inhabitant of the United States (total = 5.86 mSv). Individual exposures, especially to radon and medical sources, vary widely from these average values. The use of medical imaging in the United States (some 67 million CT scans were performed here in 2006) has increased greatly in recent years. As for radon, only the lungs are exposed as the alpha particles emitted by radon cannot penetrate other tissues. (Data from the National Council on Radiation Protection and Measurements, Bethesda, MD.) |
About 27% of our annual exposure to radiation is from background radiation:
- cosmic radiation (0.27 mSv). The value increases with altitude, so the dose for people in Denver, Colorado is about 0.50 mSv.
- rocks and soil (0.28 mSv). This value varies with the geology of a region: people in Louisiana get as little as 0.15 mSv/yr; people on the Colorado plateau (incl. Denver!) get 1.4 mSv/yr.
- from within the body (0.4 mSv). Most of this comes from potassium-40. About 0.02% of the potassium in nature is in the form of the radioactive isotope 40K. Living tissue cannot discriminate between radioactive and nonradioactive versions, so the same 0.02% of the total potassium in the body (about 1.7 g in a 70-kg person) is radioactive.