John is exactly correct in his answer. Let me amplify a bit, though, and
by doing so present some practical information.
In situations like this one normally uses a Geiger-Müller tube as a
detector, which is connected to a power supply and counting circuit. The
readout is in number of events divided by time and the face of the meter
is normally marked to read out in milligrays or some multiple of that.
(The old U.S. Civil Defense meters read out in mrad/h.) This face plate
marking is calibrated to the particle and energy profile typical of
emissions by fissionable materials and by emissions of their fission
products. Commonly, a flip-up aluminum plate is available to filter out
most (~90 %) beta and alpha radiation. Differences in "open" and
"closed" window readings then indicate (roughly) alpha and beta
radiation intensity and the "closed" window reading indicates gamma
activity. G-M tube detectors do not detect neutron radiation.
So, the meter is actually detecting and tallying alpha, beta, and gamma
activity (measured in becquerels), but the faceplate calibration is set
to indicate human dosage in the detected emission field. John has again
given you the quality factors related to alpha and beta (QF=20) versus
gamma(QF=1) radiation.
Lets assume that we observe the following readings:
65 nGy/h with open window
58 nGy/h with closed window
The difference is 7 nGy/h, which is due to alpha and beta. those are
primarily hazards to skin and eyes due to their low penetrating
abilities. The QF for those is 20, giving us an effective alpha and beta
dose rate of 140 nSv/h. Add that to the gamma dose rate of 58 nSv/h
(since gamma QF=1) and we have a total effective dose rate of 198 nSv/h.
But in this example, it is important to know that most of that
calculated effective dose rate is the dose rate pertaining to the skin.
That can cause reddening (radiation burns) and eye problems (dried out
corneas and sclera). The whole body dose rate is the gamma dose rate of
58 nSv/h. That is the dose rate for which the limits I stated earlier
apply. Allowed skin and eye dosages are much higher.
It is common practice then, to do the surveys with the window closed on
the G-M tube. (That also helps protect the thin glass of the tube from
being poked and broken!) The working assumption used then is 1 nGy/h ~ 1
nSv/h.
Here is some useful information on your annual radiation dosage:
http://www.nrc.gov/about-nrc/radiation/around-us/doses-daily-lives.html#3
Remember that 100 mrem = 1 mSv = 1000 µSv when using their medical
procedures table. Their personal dose calculator is linked at the bottom
of that page, namely to
http://www.nrc.gov/about-nrc/radiation/around-us/calculator.html
for an online calculator or to
http://www.nrc.gov/reading-rm/basic-ref/teachers/average-dose-worksheet.pdf
for a worksheet. Note the annual radiation dosage that you receive from
your own body, 2.4 mSv. Note also that living near a coal-fired power
plant gives you a higher dosage than living near a nuclear power plant.
If coal ash had to be treated like any waste coming from a nuclear power
plant, power companies would be required to barrel it up and bury it in
restricted landfills.
I used the online calculator to find that my annual dosage was 326 mrem
which, in SI units, is 3.26 mSv or 3260 µSv.
Jim
On 2011-03-15 1447, John M. Steele wrote:
Pat,
Jim clearly understands doses of ionizing radiation better than I do.
Perhaps this will help until he answers.
Neither the gray or the sievert is a "space dose" like the watts per
square meter used for radio waves. The units are joules per kilogram and
represent energy absorption in a sensor that simulates a human. The
difference is that the gray measures the energy actually absorbed. The
sievert is an "equivalent dose" and uses quality factors to approximate
the damage done by the absorbed dose of different types of radiation.
Beta particles, x and gamma rays have QF of 1. Alpha particles (internal
only) have QF of 20. Random energy neutrons and protons have QF of 10,
(or neutrons can have differing QFs for different energies, if you have
the data)
--- On *Tue, 3/15/11, Pat Naughtin
/<[email protected]>/* wrote:
From: Pat Naughtin <[email protected]>
Subject: [USMA:50030] Re: Putting radiation levels in perspective
To: "U.S. Metric Association" <[email protected]>
Cc: "U.S. Metric Association" <[email protected]>
Date: Tuesday, March 15, 2011, 3:21 PM
Dear Jim,
At http://ireport.cnn.com/docs/DOC-572031?ref=feeds%2Flatest they
seem to measure "Rate of space dose" in "(nGy/h)". Could you explain
the quantity, "Rate of space dose", and the unit, "(nGy/h)", to me
please?
Thanks,
Pat Naughtin
Geelong, Australia
On 2011/03/16, at 02:54 , James R. Frysinger wrote:
> USMA Colleagues,
>
> I sent this out to my family and friends last night.
>
> Jim
>
> Folks,
>
> The reporters are going crazy and hyping the radiation from the
failing nuclear power plants in Japan. Meanwhile, coverage of the
shortages in food, water, fuel, shelter, and electricity and
coverage of the tremendous loss of life are being under-reported by
comparison. That's because the reporters do not understand
radioactivity, nuclear reactors, radiation limits, or radiation
calculations. It's not that hard to do and I'll show you here how to
do it.
>
> There are a lot of adjectives being used in the media. Hard data
is hard to find but I heard one value stated today on TV and this
site provides current hard data.
>
> Actual radiation levels in Japan:
> http://ireport.cnn.com/docs/DOC-572031?ref=feeds%2Flatest
>
> For your reference, the limits specified in the U.S. are listed
at the bottom of this email There are two groups presented here --
essentially for power plant workers and for the folks on the
streets. The latter is the one officials are concerned about, but
note that nuclear power plant workers are deemed safe at about 50
times those levels!
>
> Now you can do your own calculations. Note that 1 mSv = 1 000 µSv
= 1 000 000 nSv. So, assume a conservative QF of 20 and an exposure
limit of 0.02 mSv/h = 20 µSv/h. That limits you to 1 µGy/h since 20
× 1 µGy/h = 20 µSv/h. And 1 µGy/h = 1 000 nGy/h.
>
> From the data posted at the link above for 2011/03/15 03:20, it
appears that all the radiation levels are one-sixth or less of the
U.S. limit for exposure of members of the public to radiation from a
nuclear power plant. There may have been a brief spike near one
plant today, but I do not have that figure.
>
> Please keep these facts in mind:
> 1. Nuclear power plants are physically incapable of undergoing
nuclear explosion. The explosions you hear about are hydrogen
explosions, rather like natural gas explosions.
> 2. Radiation exists around you naturally.
> 3. Exposure limits are always much lower than natural radiation
levels to which you are exposed in your everyday lives.
> 4. Low level radiation is just that -- low level. If it's low
enough, there is nothing to be concerned about. You, the ground you
walk on, the banana in your breakfast cereal, and many other things
contain low level radiation. Yes, you yourself are a low level
radiation source!
> 5. Reactor plants generally are designed to contain reactor cores
even if the cores melt down. I do not know for a fact, but the
Japanese plants are probably designed for events like that, too. The
Russian nuclear reactor at Chernobyl definitely was an exception to
that rule, which is why nations kept after the Russians for years
not to operate plants of that design.
> 6. Airborne radiation is diluted as it spreads out. Our west
coast is in no grave danger!
>
> The largest problems facing the Japanese right now do not include
radiation, despite the hyperventilating you hear or read in the
news. The natural radiation levels there seem to be much larger than
those caused by the failure of those nuclear powered plants.
>
> Jim
>
> 10CFR20 radiation limits in the U.S.
> Exposure limits for occupational workers
> annual
> whole body 50 mSv (5 rem)
> lens 150 mSV
> skin 500 mSv
>
> Exposure limits for members of the public
> annual 1 mSv
> acute 0.02 mSv/h
>
> Multiply radiation levels in grays (Gy) by the appropriate
quality factor (QF) to determine estimated dosage in sieverts (Sv).
> QF exposure
> 1 x, gamma, or beta rays
> 20 fission products, alpha rays (internalized)
>
> --
> James R. Frysinger
> 632 Stony Point Mountain Road
> Doyle, TN 38559-3030
>
> (C) 931.212.0267
> (H) 931.657.3107
> (F) 931.657.3108
>
Pat Naughtin LCAMS
Author of the ebook, Metrication Leaders Guide, see
http://metricationmatters.com/MetricationLeadersGuideInfo.html
Hear Pat speak at: http://www.youtube.com/watch?v=_lshRAPvPZY
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has
helped thousands of people and hundreds of companies upgrade to the
modern metric system smoothly, quickly, and so economically that
they now save thousands each year when buying, processing, or
selling for their businesses. Pat provides services and resources
for many different trades, crafts, and professions for commercial,
industrial and government metrication leaders in Asia, Europe, and
in the USA. Pat's clients include the Australian Government, Google,
NASA, NIST, and the metric associations of Canada, the UK, and the
USA. See http://www.metricationmatters.com
<http://www.metricationmatters.com/> for more metrication
information, contact Pat at [email protected]
<http://us.mc824.mail.yahoo.com/mc/[email protected]>
or to get the free 'Metrication matters' newsletter go to:
http://www.metricationmatters.com/newsletter to subscribe.
--
James R. Frysinger
632 Stony Point Mountain Road
Doyle, TN 38559-3030
(C) 931.212.0267
(H) 931.657.3107
(F) 931.657.3108
