Sunday, August 14, 2011

GUEST POST: On the Effects of Radiation


Before posting Sickputer's comments, let me provide some background.

Sickputer is clarifying radiation forms and suggesting strategies for approximating knowledge about their biological effects.

One of the biggest challenges for those of us trying to measure Fukushima's effects is understanding the relationship between
beta and gamma levels (quantitative measures of ionizing radiation)
and
sieverts (measures of biological effects).

This radiation monitoring website suggests that many Geiger counters are calibrated so that
120 Counts Per Minute (CPM) of Cesium-137 = 1 microsievert of radiation (a measure of its biological effects). http://www.blackcatsystems.com/GM/converting_CPM_mRhr.html

120 CPM CESIUM-137 = 1 microsievert

However, I have heard from individuals who say that not all machines are calibrated in this way and that it is difficult to presume this relationship is always constant. I need more information on how to establish relationships between CPM and sieverts (please post your ideas if you have any)

Aside from the problem of the relationship between CPM and sievert dose, Sickputer provides considerable helpful information about the distinct measures of radiation.

SICKPUTER'S GUEST POST

Let us examine some of the confusing terms: curies, becquerels, Roentgens,grays, rads, rems, sieverts,

The first two are older units measuring "activity" of radiation and the modern usage of curie is archaic. A curie is a very large amount of radioactivity.

Becquerels refers to decay per unit of time and is somewhat less archaic and used infrequently by older radiation industry scientists.

A Roentgen (R) is a unit of exposure from the old U.S. customary system and sometimes used by older scientists.

1 Roentgen equals 0.877 rad, and 1 Roentgen equals 0.877 rem and 1 Roentgen = .00877 Sieverts

Grays and rads are also infrequently used and both refer to an absorbed dose (of ionizing radiation).

Rems and sieverts are the terms we read about most frequently and of course we know from recent Fukushima reports that a large Sievert emission is very dangerous. So let's take a close look at them:

Rems and sieverts are special dosimetric units to help limit radiation exposure of nuclear workers and the public. They apply to single and mixed radiations and measure the harm to humans.

One rem of alpha radiation presents the same risk to warm-blooded organisms as 1 rem of gamma rays or as 1 rem of combined exposure to neutrons and gamma rays.

The rem and Sv were developed to account for different efficiencies of different types of radiation in producing harm. These units apply to single and mixed radiations including alpha, neutrons, and gamma rays.

1 rem of alpha radiation = 1 rem of gamma rays.

1 rem of gamma rays = 1 rem of neutrons + gamma rays.

1 sievert (Sv) = 100 rem. (An important ratio!)


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Now let's see how the NRC explains gray, rad, and sievert:

"Gray (Gy) is the SI unit of absorbed dose. One gray is equal to an absorbed dose of 1 Joule/kilogram (100 rads).

Rad is the special unit of absorbed dose. One rad is equal to an absorbed dose of 100 ergs/gram or 0.01 joule/kilogram (0.01 gray).

Rem is the special unit of any of the quantities expressed as dose equivalent. The dose equivalent in rems is equal to the absorbed dose in rads multiplied by the quality factor (1 rem=0.01 sievert).

Sievert is the SI unit of any of the quantities expressed as dose equivalent. The dose equivalent in sieverts is equal to the absorbed dose in grays multiplied by the quality factor (1 Sv=100 rems)."


SP: Got that down pat? *;-) The last dozen letters make sense to me!

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Nuclear industry worker annual dose limit "Annual limit on intake (ALI) means the derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year. ALI is the smaller value of intake of a given radionuclide in a year by the reference man that would result in a committed effective dose equivalent of 5 rems (0.05 Sv) or a committed dose equivalent of 50 rems (0.5 Sv) to any individual organ or tissue."

NRC regulations:
http://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020-1003.html

Translation: workers allowed 5 rems of exposure per year.

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Individual members of the public annual dose limit "The total effective dose equivalent to individual members of the public from the licensed operation does not exceed 0.1 rem (1 mSv) in a year,"


Translation: public allowed 1/10th of a rem per year or 100 millirems.

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Converting From CPM (Counts Per Minute) to mR/hr (millirems per hour) (Now we are getting somewhere useful!)

"Many radiation survey meters are calibrated to Cs137 or Co60. 1080 CPM is about equal to 1 mR/hr for Co60. For Cs137, it is closer to 1200 CPM for 1 mR/hr. For those who prefer to use Sieverts, 108 CPM is about 1 uSv/hr for C060, and for Cs137 it is around 120 CPM per 1 uSv/hr."



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SP: So to sum up and use some of the RadNet data from today: Amarillo had an average CPM of nearly 400. So if the conversion factor as shown above is about 1 millirem per 100 to 120 CPM then in an hour the RadNet monitor in Amarillo is absorbing around 3 millirems per hour and 72 millirems a day.

Every 14 days at 400 CPM the monitor receives 1 rem of exposure. Over a year about 25 rems. That is 5 times the nuclear worker recommended dosage for a year and 250 times the recommended dosage for a member of the public.

If the rate per hour at a monitor is 2,000 CPM like Alaskan officials tell us is the worrying level..then you multiply those yearly numbers by fivefold.100 rems of exposure per year for John Q. RadNet Monitoring Post.

Probably RadNet is a monitor mounted up on a pole, or on a building roof and people and animals are getting shielding at times by building materials, their cars, and other barriers. Who can estimate the amount people on the ground will receive? Less, but by how much? 30% less, 50% less?

For POYA (Pull Out of your A**) estimation values let's estimate 75% of the CPM rates at the monitor reaches humans on the ground. Thus Amarillo becomes 18.75 rems per year and Alaska becomes 93.75 rems.

At 18.75 rems real data (Amarillo) and 93.75 rems Alaskan proposed high level. the dangers may be explained as this for radiation poisoning using our Geiger counter guy blog:



1. Earliest onset of radiation sickness is estimated at 75 Rem

Earliest onset of radiation sickness would be 4 years at Amarillo 400 CPM (75% human absorption)

Earliest onset of radiation sickness would be 1.2 years at Alaskan 2000 CPM (75% human absorption)


2. Onset of radiation poisoning is estimated at 300 Rem

Earliest onset of radiation poisoning would be 16 years at Amarillo 400 CPM (75% human absorption)


Earliest onset of radiation poisoning would be 3.2 years at Alaskan 2000 CPM (75% human absorption)

3. Expected 50% death from radiation is 400 Rem (SP: Many might argue a much lower Rem dose for 50%, but let's examine it)

Expected 50% death from radiation would be 21.3 years at Amarillo 400 CPM (75% human absorption)


Expected 50% death from radiation would be 4.27 years at Alaskan 2000 CPM (75% human absorption)

I am going to run these numbers by some employees I know at one of the largest Geiger counter manufacturer in the world and I'll get back to you when I get those comments. I also will appreciate any comments by readers

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