Archive for January, 2012

Radioactive Borders (part 2)

January 14, 2012

Tales from the Nuclear Age

Copyright © 2012 by Charles Glassmire

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Jan. 15, 2012

Radioactive Borders (part 2)

           On the morning of July 13, 2010, radiation inspector Enzo Montagna is summoned to the Voltri Terminal shipping dock near Genoa Italy. The dock manager has detected some suspicious cargo containers recently offloaded from cargo ships, and by Italian law, wants a radiation check of the containers before they may be opened. Enzo follows his normal routine and sets up a radiation counter some 60 feet from the stacked boxes. But he is surprised when the lo-range meter pegs off-scale. Then he quickly activates a high range meter which is able to detect dangerous amounts of gamma radiation, to find that it also alarms to the presence of high quantities of ionizing radiation bathing the dock, the surrounding area, and Enzo himself.

          Enzo knows we live in a radioactive world. Radiation is everywhere in the brick or stone walls of our homes, in our Truck being scannedbasements (Radon gas 222Ra), even in the bananas we eat for breakfast. It is not unusual for a truckload of bananas entering the U.S. from below the border to trigger radiation alarms as they cross the border, due to the radioactive Potassium 40 isotope in the fruit. We eat the bananas and the Potassium becomes part of our bodies, emitting small amounts of radiation to our cells.

          Cosmic radiation bombards the earth continuously from the Sun and outer space. These are extremely energetic particles (usually Protons) moving so energetically that some whiz right through the entire earth, passing through the spaces between atoms in our bodies and soil and doing no damage. Some cosmic rays collide with atoms in the upper Earth’s atmosphere, causing Radiation dose for U.S.showers of secondary particles to bombard the earth surface. The Earth’s atmosphere attenuates this radiation, protecting us living at the surface; but those radiations give someone living at a high mountain altitude many times the dose of someone living at sea level. Indeed, airline passengers traveling from New York to San Francisco at 35,000 feet can receive 60 times the dose to those living at the surface. These Cosmic radiations are probably also helpful to our evolution. During the millions of years of man’s evolutionary journey, they cause changes to individuals DNA, allowing the positive changes to survive, propagate and eventually to evolve into higher level life forms.  

          Do you smoke? The leaves of our Tobacco plants in the fields receive a light dusting of naturally occurring radioactive Lead 210 (210Pb). In the body, lead is deposited onto the surface of bones. It naturally decays to Polonium 210 (210Po), which is also radioactive and deposits in the liver, kidney and spleen(2). Smoking one-half pack a day can increase a smokers radiation dose by 44 percent over the annual dose received from natural background(1).

          Do you have a cat? The bags of kitty litter you have been emptying for years have trace quantities of active material which often set off the border inspection meters.

          Then there are our medical examinations, allowing early detection of cancers, tissue damage and other health threatening conditions. These systems use X-ray generators (similar to gamma rays) for things like chest X-rays, and high level isotopes like Cobalt 60 (60Co) encased in thick radiation absorbing containers, allowing release of small amounts only when an exposure is required for diagnosis. These medical exposures add about fifteen percent to our small annual dose (3).

          Do you watch television, or operate a computer with a CRT screen? These screens emit small amounts of X-rays into the bodies of those watching. Add about one percent to your annual background dose(4).

          So are we safe being exposed to background radiation? The table(1) shows some typical annual radiation doses to U.S. citizens. The unit is “mrem/year”. This unit, the rem, stands for “Roentgen equivalent mammal”. The mrem is a “millirem’. A millirem is one-thousandth of the rem unit. So how dangerous is a rem? U.S. radiation workers are limited by law to an exposure of 5 rem per year whole body exposure. This amount is deemed safe to show no medical effects even for someone exposed to radiation in his daily work. So the table tells us that the background dose to an average citizen is only 361/1000 of 1 rem, where 5 rem is still deemed a safe exposure.

          So Enzo knows that he can absorb a certain amount of this high radiation for a very short time, without showing ill effects. There are eleven cargo containers facing him on the dock. Which one can be the offender? More importantly, what contents could be causing this very high reading? The possibilities are ominous. Could it be a terrorist device – a nuclear weapon, or perhaps an RDD (Radiological Dispersion Device) – a “dirty bomb”? Whatever the contents, it is irradiating the surrounding area with a very dangerous gamma field. It must be dealt with as quickly as possible.

          Bravely, Enzo cranks the high range meter up to its maximum scale, and charges the stack of containers to get a closer reading, trying to locate the suspect container. Watching the meter dial he circles the stack of containers. He pauses beside a dirty rusty red container. Ominously, the meter is reading 50 rem per hour(5). This means, standing beside the container, in only 6 minutes he will receive the maximum allowable dose for a U.S. radiation worker for an entire year (5 rem). After 3 hours he would begin to vomit. If he stood there for 8 hours, the chances are 50/50 that he would die …

 (to be continued …)

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(1)   Background radiation”, Washington State Department of Health.

(2)   “Fact Sheet Backgground Radiation…”, U.S. Office of Radiation Protection. www.doh.wa.gov. Oct. 2010.

(3)   Washington State Department of Health.

(4)   “Radiation Dose Chart”, American Nuclear Society, www.new.ans.org.

(5)   “Mystery Box”, Andrew Curry, Wired magazine, Nov. 2011.

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