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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 ]

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