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Author Topic: does a picture say more than a thousand words?  (Read 86208 times)

Offline CliffordK

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Re: does a picture say more than a thousand words?
« Reply #275 on: 20/12/2014 09:52:47 »
- 1950’s, average background radiation went > 1 mSv (max. public limit for radiation exposure)
- 1960's, Due to 2,400 open air atomic bomb tests radioactive fallout, > 2 mSv
- 1994, average background radiation, Chernobyl, TMI, other accidents and dumping; > 3 mSv
- 2002, average background radiation, more accidents, spills, ocean/air dumping > 3.6 mSv
- 2014, average background radiation, Fukushima mega disaster and more dumping > 6.2 mSv (max. limit for public has been raised 600%)
…the average annual radiation dose per person in the U.S. is 620 millirem (6.2 milliSieverts)."

I think it is time to start studying Radiation Hormesis

I suppose this is a good point.  One should just consider the local effects of individual nuclear reactors, but consider their global impacts too.
 

Offline yor_on

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Re: does a picture say more than a thousand words?
« Reply #276 on: 20/12/2014 10:02:02 »
Yes Clifford. Some types of radiation clings for a very long time, and if it is correct, then how we decide today will have a impact on, I don't know how many generations? But I dearly would like to know. I would hate to live in a high tech society where we for example find the average IQ (whatever that now 'is':) getting lowered, as I've seen described as one possible outcome of radiation on fetus. It doesn't sound as a good proposition to me. Actually I think that one has been lying dormant for me, until I saw that flawed presentation. That made it much more current, sort of.
« Last Edit: 20/12/2014 10:04:09 by yor_on »
 

Offline yor_on

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Re: does a picture say more than a thousand words?
« Reply #277 on: 20/12/2014 11:16:44 »
Seems I still can't find one? 1987 is the only (pie) chart I find, and that one has apparently been cited in publications since then? I got to admit to finding that slightly weird? As if we stopped measuring the natural background radiation, deciding that 1987 should be the year we hereafter would use as the correct reference? In it the 'man made contribution' is defined as 18 % though. And in it it seems as if 79 % of that percentage is defined as belonging to x-rays of different kinds. It's an American survey though, and as such reflect the use of medical imagining done there.

So, does anyone on TNS have a link, measuring the natural background radiation on a annual basis? Because that is what I would like to see. Not a link to specific countries use of x rays, absorbed by a human in some medical facility, but to the type of radiation we meet naturally, without such imagining. It should be possible to find?
 

Offline alancalverd

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Re: does a picture say more than a thousand words?
« Reply #278 on: 21/12/2014 20:57:36 »
Depression of fetal IQ is a known effect of very large doses of radiation delivered between the 8th and 15th week of conception. The effect is possibly as high as 0.04% per milligray, so the effect might be detectable if the fetal dose exceeds about 200 mGy during the critical period. A human fetus receives about 1 mGy from natural radiation from its mother's bones, or from a maternal lumbar spine x-ray series, so we don't get too excited about such things, but CT, radionuclide imaging, or radiotherapy, do require very careful consideration in pregnancy.

There is no point on measuring natural background on an annual basis as it is entirely predictable, being the natural consequence of events that have been going on for billions of years. The local variation is between 1.5 mSv/yr in parts of Japan and over 40 mSv/yr in Kerala and Iran, but the reference level is taken as the US population average of 3 mSv/yr, because we have good historical epidemiology for that population. We can estimate the manmade addition quite accurately and this is done routinely in areas of known or potential contamination, but as with medical radiation, the notion of an average is meaningless.

The real threat to a fetus is, I think, alpha emitters. Plutonium and to a lesser extent (natural) thorium have a nasty habit of attaching to the blood-forming organs and inducing leukemia. Problem is that these particular stinkers are very hard to detect.

Bit short of time right now but I'll happily come back to the subject in a couple of days - I'm off to measure medical radiation in various places around the UK for the next two days!
« Last Edit: 21/12/2014 22:20:56 by alancalverd »
 

Offline alancalverd

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Re: does a picture say more than a thousand words?
« Reply #279 on: 21/12/2014 20:59:00 »
Clifford: please read my reply # 271 to see why the figures are bullshit.
 

Offline CliffordK

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Re: does a picture say more than a thousand words?
« Reply #280 on: 29/12/2014 21:38:44 »
Ahhh...
I see the difference between "exposure" and "background", and confusion between the two.

So, one might consider the number of miles an average person flew in airplanes pre 1940's up till today.  The more miles and higher altitudes, the greater the cosmic radiation exposure.

As I understand it, the power of the average medical X-Ray has been decreasing a lot over time, although perhaps it is being offset by ordering more of them.  But, as you point out, X-Rays aren't ordered just in the last year, but more in the older patients than the younger ones (except for dental X-Rays).

One could probably get a good estimate of background radiation by observing the steel in ships (or even cars) built in the early 1900's, WWII, then in each decade since then, especially if one could control for the iron/steel source. 
 

Offline demografx

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Re: does a picture say more than a thousand words?
« Reply #281 on: 30/12/2014 02:44:03 »
 

Offline alancalverd

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Re: does a picture say more than a thousand words?
« Reply #282 on: 31/12/2014 07:34:32 »
One could probably get a good estimate of background radiation by observing the steel in ships (or even cars) built in the early 1900's, WWII, then in each decade since then, especially if one could control for the iron/steel source. 

Doesn't really define "background"!

There are two aspects to consider: natural and man-made (or man-enhanced). The natural background comes from rocks, natural radioactive gases, and cosmic radiation. These are hugely variable, from (reportedly, though I don't believe it) 1.5 mSv/yr in parts of Japan to around 100 mSv/yr in areas of thorium sand. The most useful figure is a population-weighted average, and it happens that most  areas where the background exceeds 5 mSv/yr are quite thinly populated. A convenient and well-researched baseline is the US population-weighted average of 3 mSv/yr.

The man-made addition to background comes from nuclear weapon fallout (principally strontium), reactor incidents (iodine and caesium) and medical waste (mostly iodine). The man-enhanced addition is from natural radionuclides released into the air by industrial processes such as smelting and burning of fossil fuels. The sum is generally less than 0.1% of the baseline and varies very little from year to year, though there is some concern about the increase in medical waste.

The radionuclide content of steel is measured routinely but it is very variable (pre-1945 naval gun barrels are worth a fortune to the scientific instrument industry) and doesn't contribute to any sensible notion of background unless you live in a ship. Other building materials generally contribute more to your personal dose, but the ventilation of the building (to remove radon) is usually far more important.


Quote
As I understand it, the power of the average medical X-Ray has been decreasing a lot over time,

Depends on your definition of "average"!  The required dose for a given plane radiograph decreased very rapidly in the first 20 years of radiography thanks to Edison's invention of the "intensifying screen", then again by a factor of 2 -4 in the 1980s with the introduction of rare-earth screens, but the delivered dose has actually crept upwards since 2000 as modern digital imaging systems produce a "cleaner" image if you increase the dose (unlike film, which saturates if overexposed).

Meanwhile the introduction of CT has pretty much doubled the population dose from diagnostic x-radiation in the last 30 years. For every advance we make in detector sensitivity, there is an increase in demand for image quality and quantity.
« Last Edit: 31/12/2014 07:53:36 by alancalverd »
 

Offline yor_on

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Re: does a picture say more than a thousand words?
« Reply #283 on: 02/01/2015 19:47:37 »
Alan, you're a good man. It's a pleasure reading you, as far as I'm concerned, then again :) It won't guarantee me agreeing. but it won't stop me from enjoying your thoughts, and learn something new.
 

Offline yor_on

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Re: does a picture say more than a thousand words?
« Reply #284 on: 02/01/2015 19:55:59 »
The real stuff, if there now is any real stuff. Is not about individuals, but about species. We seem to have some statistical balance relative our life expectancy as a whole. And no, I don't know by which mathematical formula I could 'prove' that thesis. But I seem to see it, never the less. It exist, with or without me.

We live by it, but I don't think we count in millenniums.
 
 

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Re: does a picture say more than a thousand words?
« Reply #284 on: 02/01/2015 19:55:59 »

 

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