<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">A fair report by William Broad on the dangers of radioactivity from the severely damaged Japanese reactor. We don't yet know the intensity of its radiations, and so we don't know if they are a serious problem. We are constantly exposed to nuclear radiations, and the safety limits imposed by the responsible agencies are considered super safe; there could be very high multiples of those limits and yet have no observed effects on human health (despite the claims of someone like Wasserman). <div><br></div><div><a href="http://www.nytimes.com/2011/03/13/science/13radiation.html?hp">http://www.nytimes.com/2011/03/13/science/13radiation.html?hp</a></div><div><br></div><div><div class="articleBody"><nyt_text><p> The different forms of radioactivity being reported at the nuclear accidents in <a href="http://topics.nytimes.com/top/news/international/countriesandterritories/japan/index.html?inline=nyt-geo" title="More news and information about Japan." class="meta-loc">Japan</a> range from relatively benign to extremely worrisome.</p></nyt_text></div><div class="articleInline runaroundLeft">
<div class="doubleRule"><h3 class="sectionHeader"><span class="Apple-style-span" style="font-weight: normal; font-size: medium; ">The central problem in assessing the degree of danger is that the
amounts of various radioactive releases into the environment are now
unknown, as are the winds and other atmospheric factors that determine
how radioactivity will disperse around the stricken plants.</span></h3></div></div><div class="articleBody"><p>
Still, the properties of the materials and their typical interactions
with the human body give some indication of the threat. </p><p>
“The situation is pretty bad,” said Frank N. von Hippel, a nuclear
physicist who advised the Clinton White House and now teaches
international affairs at Princeton. “But it could get a lot worse.”
</p><p>
In Vienna on Saturday, the <a href="http://www.iaea.org/">International Atomic Energy Agency</a>
said Japanese authorities had informed it that iodine pills would be
distributed to residents around the Fukushima Daiichi and Daini plants
in northeast Japan. Both have experienced multiple failures in the wake
of the huge earthquake and tsunami that struck Friday. </p><p>
In the types of reactors involved, water is used to cool the reactor
core and produce steam to turn the turbines that make electricity. The
water contains two of the least dangerous forms of radioactivity now in
the news — radioactive nitrogen and tritium. Normal plant operations
produce both of them in the cooling water, and they are even released
routinely in small amounts into the environment, usually through tall
chimneys. </p><p>
Nitrogen is the most common gas in the earth’s atmosphere, and at a
nuclear plant the main radioactive form is known as nitrogen-16. It is
made when speeding neutrons from the reactor’s core hit oxygen in the
surrounding cooling water. This radioactive form of nitrogen does not
occur in nature. </p><p>
The danger of nitrogen-16 is an issue only for plant workers and
operators because its half-life is only seven seconds, after which it
decays back into natural oxygen. A half-life is the time it takes half
the atoms of a radioactive substance to disintegrate. </p><p>
The other form of radioactivity often in the cooling water of a nuclear
reactor is tritium. It is a naturally occurring radioactive form of
hydrogen, sometimes known as heavy hydrogen. It is found in trace
amounts in groundwater throughout the world. Tritium emits a weak form
of radiation that does not travel very far in the air and cannot
penetrate the skin. </p><p>
It accumulates in the cooling water of nuclear reactors and is often
vented in small amounts to the environment. Its half-life is 12 years.
</p><p>
The big worries on the reported radiation releases in Japan center on radioactive iodine and cesium. </p><p>
“They imply some kind of core problem,” said Thomas B. Cochran, a senior scientist in the nuclear program of the <a href="http://www.nrdc.org/">Natural Resources Defense Council</a>, a private group in Washington. </p><p>
The active core of a nuclear reactor splits atoms in two to produce
bursts of energy and, as a byproduct, large masses of highly radioactive
particles. The many safety mechanisms of a nuclear plant focus mainly
on keeping these so-called fission products out of the environment.
</p><p>
Iodine-131 has a half-life of eight days and is quite dangerous to human
health. If absorbed through contaminated food, especially milk and milk
products, it will accumulate in the thyroid and cause cancer. Located
near the base of the neck, the thyroid is a large endocrine gland that
produces hormones that help control growth and metabolism. </p><p>
Dr. von Hippel of Princeton said the thyroid danger was gravest in
children. “The thyroid is more sensitive to damage when the cells are
dividing and the gland is growing,” he said. </p><p>
Fortunately, an easy form of protection is potassium iodide, a simple
compound typically added to table salt to prevent goiter and a form of
mental retardation caused by a dietary lack of iodine. </p><p>
If ingested promptly after a nuclear accident, potassium iodide, in
concentrated form, can help reduce the dose of radiation to the thyroid
and thus the risk of cancer. In the United States, the <a href="http://topics.nytimes.com/top/reference/timestopics/organizations/n/nuclear_regulatory_commission/index.html?inline=nyt-org" title="More articles about Nuclear Regulatory Commission" class="meta-org">Nuclear Regulatory Commission</a>
recommends that people living within a 10-mile emergency planning zone
around a nuclear plant have access to potassium iodide tablets. </p><p>
Over the long term, the big threat to human health is cesium-137, which has a half-life of 30 years. </p><p>
At that rate of disintegration, John Emsley wrote in “Nature’s Building
Blocks” (Oxford, 2001), “it takes over 200 years to reduce it to 1
percent of its former level.” </p><p>
It is cesium-137 that still contaminates much land in Ukraine around the
Chernobyl reactor. In 1986, the plant suffered what is considered the
worst nuclear power plant accident in history. </p><p>
Cesium-137 mixes easily with water and is chemically similar to
potassium. It thus mimics how potassium gets metabolized in the body and
can enter through many foods, including milk. After entering, cesium
gets widely distributed, its concentrations said to be higher in muscle
tissues and lower in bones. </p><p>
The radiation from cesium-137 can throw cellular machinery out of order,
including the chromosomes, leading to an increased risk of cancer.
</p><p>
The <a href="http://topics.nytimes.com/top/reference/timestopics/organizations/e/environmental_protection_agency/index.html?inline=nyt-org" title="More articles about the Environmental Protection Agency." class="meta-org">Environmental Protection Agency</a>
says that everyone in the United States is exposed to very small
amounts of cesium-137 in soil and water because of atmospheric fallout
from the nuclear detonations of the cold war. </p><p>
The agency says that very high exposures can result in serious burns and
even death, but that such cases are extremely rare. Once dispersed in
the environment, it says, cesium-137 “is impossible to avoid.” </p></div><div><div><br></div></div></div></body></html>