Radiation Exposure Readiness: Part 2, When Your Health Is At Risk
How do scientists determine when your health is at risk due to the amount of radiation in the air? First they measure the amounts and translate those measurements into levels that they know have caused biological harm in the past. They have learned from longitudinal studies of people in the paths of Hiroshima, Chernobyl, Three Mile Island, and many smaller-scale, but serious, incidents of radiation exposure. Here is a look at the basic radiation measuring scheme and how other variables can affect biological dangers from radiation.
The concepts of time, distance, and shielding are those that govern radiation measurement: the longer one stays (time) in the vicinity (distance) of the source, and the amount of shielding the source contains to protect individuals from radioactivity all figure into the danger estimates.
The exposure pathways can also determine the extent of danger. Inhalation, ingestion and external or direct exposure are three pathways radiation can affect us. You can inhale radiation, which tends to have the largest impact on the thyroid gland and the lungs; you can ingest radiation through milk and food sources, which has gastrointestinal impact, but can affect the nervous system, as well; and radiation can have direct contact with the skin, causing burns to the skin and eyes. Generally, the most dangerous kinds of radiation are inhaled and ingested radiation.
There are also different types of radiation....
"Four types of radiation may be found at a nuclear plant ; alpha, beta, gamma, and neutrons. Gammas and neutrons are the more highly penetrating as illustrated by the figure to the left. Neutrons are typically only found near the reactor during operation. Alpha is found near new or exposed fuel. Betas and Gammas are found when systems are opened." Source: Nuclear Tourist
While the amount of radiation absorbed by humans or by materials is expressed in rad, what's called the 'dose equivalent,' includes not just the amount of radiation absorbed, but the medical effects of that radiation, which takes into account the variables such as the type of radiation and the typical pathways of exposure. So when we get the measurement of radiation in rem or millirem (mrem), we are getting measurements that our very specific to what are our danger levels.
The Nuclear Regulatory Commission (NRC) considers up to 10,000 mrem radiation exposure to be a low level, and it says most of us are exposed to around 360 mrem in a whole year. You can actually estimate your own yearly radiation dose on this EPA calculator.
The National Academy of Sciences estimates that for every 1,000 mrem of short term exposure greater than 10,000 mrem, there is only 1/20 of one percent greater risk of developing radiation-induced cancer. "In other words, if you were to receive a short term exposure of 11,000 mrem, your estimated risk of developing some type of cancer would increase by .05 percent." (source: San Luis Obispo County Online)
Personally, I would not be too glib about .05 percent. Ten thousand mrems of radiation exposure in a short period of time is much more serious than the same dose over, say, a year. When you begin to add up the extra short term mrem and the long term mrem, the nature of your exposure, your genetic makeup, your overall health, your age, and many other factors, who really knows what that extra .05 percent might mean? And will today's exposure be back again tomorrow?
In the next section, we'll look at ways we can protect ourselves and families from increased 'short term' radiation exposure.