Radiological Dosimetry

Radiological Dosimetry

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For the next week or so I am posting some articles on radiological preparedness. I have some knowledge of this, and worked for several years as a radiological preparedness trainer. This is one area of prepping that contains a lot of misconceptions and fear so I wanted to pass on a few simple things.

Today I am going to discuss Radiological Dosimetry. This is something that most preppers that are concerned with radiological issues are either ignorant of or do not feel is as important as meters or potassium iodide.

No matter how sensitive, expensive, or advanced your rad meter is, it is only designed to tell you how strong the field is that it is measuring. That makes it pretty similar to a car’s speedometer. Depending on what you are looking for it is generally measured in Cpm or counts per minute (which is a measurement of activity – being how many thousands of electrons strike the meter’s detector) or roentgen (Which measures the energy produced by gamma radiation in a cubic centimeter of air)

That tells us where something is, or how dangerous it is, but not how much radiation I have been exposed to over time. The measurements for that is either the Rad or the Rem. A Rad or Radiation Absorbed Dose recognizes that different materials that receive the same exposure may not absorb the same amount of energy. The Rem or Radiation Equivalent Man (or mammal depends on your teacher) relates your absorbed does to what biological effect that does will have on you.

I don’t care as much about roentgen as I do about my cumulative Rem. Even a little bit of exposure over time can have biological effects. Without knowing my Rem I may inadvertently receive too much over time.

That is where dosimeters come in. Dosimeters are like car ODOMETERS. They are useless for telling you how strong a field is, but they are great at telling you how much cumulative exposure they have over time.

The dosimeter in the video is pretty typical for the type you will encounter. It’s a pencil dosimeter and they are available commercially both new and from places like ebay. They all work in a similar manner.

Inside the tube body there is a crystal element with a filament attached. On one end of the tube there is a small metal charging tip, on the other a lens. When electricity is placed on the crystal it changes shape. If you are holding the charging tip up to the light at the same time you are looking into the lens you will see a chart and the filament. If the crystal is appropriately calibrated a full charge of electricity will have the filament aligned with the 0 on the chart. As the pencil dosimeter is exposed to ionizing radiation, the radiation knocks electrons off the crystal causing it to loose charge and move toward its original shape. This moves the filament and tells you how much CUMULATIVE exposure you have.

The EPA has come out with standards called protective action guides that tell what they feel is safe. The PAG guides have really low numbers for the general public and radiation workers, slightly higher permissible exposures for emergency workers, and much higher dose limits for military personnel in combat. I do not want to quote regulation as it is subject to change with administration, but as of this writing, the LIFETIME cumulative does for an emergency worker who is only receiving radiation exposure for immediate lifesaving activities is 75 REM. REACTS (Radiation Emergency Assistance Center/Training Site) which is a department of Energy radiological medicine specialty center says that the first noticeable health effects (under a microscope) is a slight change in red blood cell shape at 100 REM of acute dose. Draw your own conclusions but 75 Rem chronic is MUCH lower than 100 Rem acute.

The point is, it doesn’t matter how much you can safely be exposed to if you do not have some means of tracking your exposure. It does not matter to me what you feel you need to prep for. If rad/nuc is something that you want to prepare for, then do it. Just make sure your equipment is calibrated to read accurately, you know what you are reading, and you know what you are looking for.

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