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I am rather baffled to see how terms of radiation, effective doses, absorbed doses are mixed up in the Sievert terminology. I see a sloppy scientific standard there.

Firstly, Sievert is a unit of dose, so it is questionable to use it to measure background radiation. If there are no living creatures to absorb any dose, whom are we kidding? When they use microsieverts in medical applications, they indeed talk about dose.

Secondly, Sievert is weighted both over radiation type and tissue. And obviously, when organs are hit randomly by background radiation, weighting by tissue makes no sense. You just get some average number, under conservative assumptions.

So I see quite several loopholes to obfuscate and abuse results of Sievert measurements. The weights are politically influenced by IAEA preferences, you can be sure. Here is an example how these Sieverts can lie: they say full-body scans give 5-8 milisieverts - but here the weighting factor is probably high. So saying "ah, this radiation is just a CT scan per day" can be badly misleading. (And besides, the two weightings need not be "multiplicative". Say, beta radiation may affect organs in different proportions than gamma.)

The term "effecive dose" as it is measured captures only very approximately that difference between outside and inside radiation. It does differ much whether a particle splits at your nose tip or in your lungs. So I share Giambrone's sentiment of "effective" unscientific bias. Weighting just by radiation type is ok - but that "measurement" should be distinguished from supposed weighting by tissues as well. And it would be great if the distinction between radiation and radioactivity would be reflected in terminology (and technically possible) - but sure, fast measurements of heavy particle concentrations must be tricky.

by das monde on Mon Apr 4th, 2011 at 05:24:49 AM EST
[ Parent ]
You have made this point before, and it is correct. One of the problems with this is that there isn't a single measure that captures the risks from radiation exposure.

The health effects of radiation depend on the kind of radiation (alpha, beta, gamma), its energy (kinetic), its intensity (time rate of emission), and the tissue affected. And then different kinds of tissues respond differently.

The way "effective dose" is defined is reminiscent of Drake's formula where, just because you have separated a factor (tissue sensitivity) and given it a multiplicative weight doesn't make the method "scientific". It also doesn't make it "unscientific", may be just cargo cult science.

In any case, the evil IAEA and WHO already incorporate the risk from radiation inside the body in their assessments. Otherwise, nobody would care much about plutonium contamination, since for all intents and purposes the health effects of plutonium come from ingested/inhaled plutonium, not from its contribution to "background radiation". None of this is controversial:

Plutonium - Wikipedia, the free encyclopedia

Isotopes and compounds of plutonium are radioactive poisons that accumulate in bone marrow. ...

...

Even though alpha radiation does not penetrate the skin, it does irradiate internal organs if plutonium is inhaled or ingested.[33] The skeleton, where plutonium is absorbed by the bone surface, and the liver, where it collects and becomes concentrated, are at risk. ...

and making it sound like one side or the other of a debate is ignoring such things is less than helpful.

Maybe the "really scientific" way to give the data is to break it down by isotope, but then what does it mean?

Economics is politics by other means

by Migeru (migeru at eurotrib dot com) on Mon Apr 4th, 2011 at 05:41:57 AM EST
[ Parent ]
Can the whole weighting be explained and justified in a few lines?
by das monde on Mon Apr 4th, 2011 at 05:51:15 AM EST
[ Parent ]
What do you mean?

Economics is politics by other means
by Migeru (migeru at eurotrib dot com) on Mon Apr 4th, 2011 at 05:56:15 AM EST
[ Parent ]
What do I have to know (and have) to measure the "effective dose" on the street, without a custom ready shiny instrument?
by das monde on Mon Apr 4th, 2011 at 06:13:44 AM EST
[ Parent ]
At a minimum you need to be able to measure ambient radiation by type:

Sievert - Wikipedia, the free encyclopedia

Equivalency Weighting Factors[1] Radiation type and energy range Factor
electrons, positrons, muons, or photons (gamma, X-ray) 1
neutrons <10 keV 5
neutrons 10-100 keV 10
neutrons 100 keV - 2 MeV 20
neutrons 2 MeV - 20 MeV 10
neutrons >20 MeV 5
protons other than recoil protons and energy >2 MeV 2
alpha particles, fission fragments, nonrelativistic heavy nuclei 20
 
How are you going to do that "without a custom ready shiny instrument"?

Economics is politics by other means
by Migeru (migeru at eurotrib dot com) on Mon Apr 4th, 2011 at 06:25:41 AM EST
[ Parent ]
So the Sievert is an estimate of the damage done by some combination of radioactivity present in an environment, and the accuracy of this estimate depends strongly on the degree to which various sources of that radiation is incopropated INTO living organisims?

"It is not necessary to have hope in order to persevere."
by ARGeezer (ARGeezer a in a circle eurotrib daught com) on Mon Apr 4th, 2011 at 11:05:37 AM EST
[ Parent ]
Yes here they're telling you that the cross-section of interaction of neutrons with living tissue is largest between 100 keV and 2 MeV.
neutrons 10-100 keV 10
neutrons 100 keV - 2 MeV 20
neutrons 2 MeV - 20 MeV 10
Which sort of makes sense: extremely energetic neutrons, being neutral particles, will just whizz past living matter having a shorter time to interact with atomic nuclei, while low-energy neutrons will have a low penetration depth.

But the specific numerical factors must have been determined empirically though who knows what procedures.

Rolf Maximilian Sievert - Wikipedia, the free encyclopedia

Professor Sievert (Swedish pronunciation: [ˈsiːvəʈ]) was born in Stockholm, Sweden. He served as head of the physics laboratory at Sweden's Radiumhemmet from 1924 to 1937, when he became head of the department of radiation physics at the Karolinska Institute. He played a pioneering role in the measurement of doses of radiation especially in its use in the diagnosis and treatment of cancer. In later years, he focused his research on the biological effects of repeated exposure to low doses of radiation. In 1964, he founded the International Radiation Protection Association, serving for a time as its chairman. He also chaired the United Nations Scientific Committee on the Effects of Atomic Radiation.

He invented a number of instruments for measuring radiation doses, the most widely known being the Sievert chamber.



Economics is politics by other means
by Migeru (migeru at eurotrib dot com) on Mon Apr 4th, 2011 at 11:10:36 AM EST
[ Parent ]
How are you going to do that "without a custom ready shiny instrument"?

To put it in other way, how can you verify what the "custom ready shiny instrument" is saying with more basic means? Do you know other measurements that are comparatively hard to replicate independently?  

by das monde on Mon Apr 4th, 2011 at 10:43:44 PM EST
[ Parent ]
To put it in other way, how can you verify what the "custom ready shiny instrument" is saying with more basic means?

If you trust that the manufacturer is not completely full of shit, you can read the specifications to see whether it is capable of doing what you want it to do.

If you're just looking at one on TV, you have no way to reassure yourself that it does what the newsies claim it does. Even if the manufacturer is honest (which he usually is), and even if the newsie understands the difference between a dosimeter a Geiger counter (which he usually doesn't), the TV format is not conducive to providing verifiable facts.

When I see something measuring radiation on TV, I tend to assume that it's a Geiger counter, because those are sufficiently useful that you want them around and sufficiently simple (and cheap) that they can be issued in bulk. They also make better TV than dosimeters, because Geiger counters go click-click-click, while dosimeters are quiet until they tell you to haul ass (and a newsie won't be allowed to come along if there's even a remote chance that the dosimeter will tell him to haul ass at some point during the show). Geiger counters measure Becquerel, however, and any conversion from Bq to Sv/h must necessarily rely on some pre-set assumptions about the distribution of radioactive atoms and the ratio between ambient and internal exposure.

As a practical matter, you use the Geiger counter to tell whether you are in one of four kinds of situation:

  1. Safe, so far.

  2. Leave as soon as practical.

  3. OMFG GTFO NOW!

  4. You'll be dead within the hour anyway. Might as well get the job done while you're here.

You don't need three significant figures to make that distinction.

Do you know other measurements that are comparatively hard to replicate independently?

Oh, lots. Particulate pollution levels and pollen readings, just off the top of my head.

What I can not recall off the top of my head is one that combines this level of obscurity with quite so strong vested interests.

- Jake

Friends come and go. Enemies accumulate.

by JakeS (JangoSierra 'at' gmail 'dot' com) on Mon Apr 4th, 2011 at 11:46:23 PM EST
[ Parent ]
Let's deconstruct this example: Polonium - Wikipedia, the free encyclopedia
Alpha particles emitted by polonium will damage organic tissue easily if polonium is ingested, inhaled, or absorbed, although they do not penetrate the epidermis and hence are not hazardous if the polonium is outside the body. [edit] Acute effects

The median lethal dose (LD50) for acute radiation exposure is generally about 4.5 Sv.[36] The committed effective dose equivalent 210Po is 0.51 µSv/Bq if ingested, and 2.5 µSv/Bq if inhaled.

So, are we to understand that the effective dose for Polonium-210 is
  • 0 (negligible) if outside the body
  • 0.51 µSv/Bq if ingested
  • 2.5 µSv/Bq if inhaled


Economics is politics by other means
by Migeru (migeru at eurotrib dot com) on Mon Apr 4th, 2011 at 06:07:02 AM EST
[ Parent ]
The greater weight assigned to alpha emissions is justified by the fact that alpha particles are really, really messy - they have both higher charge and higher momentum than beta, by a couple of orders of magnitude.

I don't know how the dose weighing by body part is done, but if I were doing it I would base it partly on the sensitivity of the tissue type hit, partly on how much I'd like to keep the organ in question and partly on how much any future kids would like me to keep the organ in question (so reproductive organs would get a comparatively higher weight due to the risk of germ line mutations).

External sources would be expected to hit salvage workers equally, while inhaled and ingested pollution hits your stomach, gut, lungs and chest first, then probably your liver and kidneys.

As an aside, I would not find "one extra CT scan a day" at all reassuring. CT scans are not harmless - they're just a lot less harmful than the stuff they are used to find.

- Jake

Friends come and go. Enemies accumulate.

by JakeS (JangoSierra 'at' gmail 'dot' com) on Mon Apr 4th, 2011 at 06:07:39 AM EST
[ Parent ]
JakeS:
I don't know how the dose weighing by body part is done, but if I were doing it I would base it partly on the sensitivity of the tissue type hit, partly on how much I'd like to keep the organ in question and partly on how much any future kids would like me to keep the organ in question (so reproductive organs would get a comparatively higher weight due to the risk of germ line mutations).
In addition, different cell types are more or less differentiated and therefore at different risk of cancer and mutation.

Very undifferentiated cells (stem cells) are the most sensitive to genetic damage and the most able to mutate into cancerous cells. This is why the bone marrow is so sensitive and low radiation to it causes leukemia (high radiation simply destroys the tissue). The same gows for the gonads. Highly differentiated cells are less susceptible to mutating into cancer cells - they are more likely to just die because of mutations than to survive as a cancer cell. Also, the ability to metasthasize is linked to how undifferentiated a cancer cell is, because a cell cannot just migrate and survive in the midst of another tissue. The closer a cell is to a stem cell, the easier it is.

Whether this can be captured by a multiplicative factor for committed equivalent dose is a different question...

Economics is politics by other means

by Migeru (migeru at eurotrib dot com) on Mon Apr 4th, 2011 at 06:13:10 AM EST
[ Parent ]
Sievert - Wikipedia, the free encyclopedia
Tissue type Factor
 
bone surface, skin 0.01
bladder, breast, liver, esophagus, thyroid, other 0.05
bone marrow, colon, lung, stomach 0.12
gonads 0.20


Economics is politics by other means
by Migeru (migeru at eurotrib dot com) on Mon Apr 4th, 2011 at 06:29:45 AM EST
[ Parent ]
Before we write off the IAEA, this presentation Biological effects of ionizing radiation at molecular and cellular levels (PowerPoint) seems quite good, and it explains the efect of what they call "indirect" effect of ionizing radiation, where radiation ionizes some atom or molecule and the products of this ionization are the ones that act on the DNA. There's in particular a slide where it is argued that because of the lifetime of OH- radicals in water, there is a tube around DNA where ionizing radiation can have an indirect effect on the DNA by ionizing the water.

Economics is politics by other means
by Migeru (migeru at eurotrib dot com) on Tue Apr 5th, 2011 at 01:03:26 PM EST
[ Parent ]

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