Re: temporal? variations in background

[Kai Kaletsch <info@eic.nu>]

From: "Franz Schoenhofer" <franz.schoenhofer@chello.at>

To: "Kai Kaletsch" <info@eic.nu>; "Ted de Castro" <tdc@XRAYTED.COM>



> This is wrong. When rain pours onto the open soil, there is no possibility

> for radon and its progeny to emanate to the air, since rain closes all

> pores.



So, if it rains on a place with no houses and there is an impervious clay

layer at 2m depth, do you predict that the water stays on the surface

forever (or until it evaporates), because there is no mechanism for it to

displace the air in the voids? I don't think so! Water will go into the soil

in some places and the air will come out in other places. (There may be a

lag between the start of the rain and the emanation, when the air is being

compressed before it finds a way out.) The bottom line is that for every

liter of water that enters the soil, a liter of air will escape somewhere

sometime. (The water can also go down through the soil like a piston,

pulling clean air behind it. One liter of water will then in effect displace

more than one liter of radon laden pore space air, which has to come out

somewhere.)



> Environmental emanation is therefore decreased, but emenation into

> dry places like a house is clearly enhanced.



I observed increased radon both in my basement (the mechanism is obvious)

and near an open window on the main floor, where most of the air is from the

outside. There are always areas that are drier than others and these are

conduits for massive pressure driven radon transport into the air. The 50 cm

next to your house that are protected by the roof overhang are one such

example.



Since we are talking about dose to people, and most people are inside during

a rain, the spike in indoor radon with rain is the only thing that is

relevant. Nevertheless, the physics is interesting, so here goes:



The word "Emanation" is often used for 2 different processes:



1    escape of radon from the radium bearing matrix.

2    exhalation of radon into the air



At least for ore, the first process is actually enhanced by water. When

radium decays the Rn atom recoils and can escape the ore matrix. In ore, the

space between the crystals is small enough, so that if it is filled with

air, the recoiling Rn atom blasts right through and it gets permanently

embedded in the adjacent crystal. If there is some water in the space, the

recoiling Rn atom gets stopped in the water and is available for later

release.



Adding a little bit of water has no significant effect on the second

process. The water has to actually cut off the path between pore spaces,

before it effects the macroscopic movement of radon. The measured emanation

rates for moist ore are higher than for dry ore.



Once the ore is saturated with water, the diffusion length is decreased by

orders of magnitude and the diffusive emanation in the second process

essentially stops.



To have any effect on long term radon release, however, the soil has to be

saturated for several days to allow the radon to decay. Otherwise, all the

stored radon simply puffs out when the water evaporates or gets used by

plants etc. In my area, it is not usual to have soil completely saturated

for a long time. It is unusual for the sandy soil to get saturated at all.



> Again wrong. There is clearly an enhancement of terrestrial gamma dose

rate

> in the course of a rain fall. The reason is simple: Radon progeny is

washed

> out by rain and is deposited onto the ground, causing an enhanced

> gamma-radiation doserate.



I was commenting on an observation made by Ted where he claims the wash out

is not a major effect. Ted lives in the San Francisco bay area, downwind of

the Pacific, so I think his observation might be correct. The Pacific Ocean

does not emanate that much radon whose progeny can be washed out later.



> Your exposure cannot be 3.0 mSv, it has to have an error, which means,

that

> it might be 3.0 +- 1.0 mSv.



My exposure is X without any error. The measurement of my exposure is Y with

some error. X is the relevant quantity if you are looking for heath effects.

The difference between X and Y is a complicating factor for epidemiologists,

but Y and the error in Y is of no relevance to the person exposed. My

exposure would still be X (without any error), even if no one tried to

quantify it.



> > > How do these temporal variations in natural BG compare with events

such

> as

> > > atmospheric weapons testing, Chernobyl etc...?



> So, if you want to have some information about the topics you asked for,

> please "refine your search", because otherwise you would not receive much

> responses, at least no relevant ones.



I was interested in the Chernobyl effects on Scotland and Wales. Somewhere,

I saw a value of 0.1 mSv from Chernobyl. So to make my question more

specific: 1    Can someone confirm the 0.1 mSv value?

2    How does 0.1 mSv compare to the variations in year over year average

dose for the populations of Scotland and Wales?



I'll also take any other tidbits of information such as doses from weapons

testing fallout on the US during the testing years.



Best Regards,

Kai

http://www.eic.nu



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