[ RadSafe ] [EXTERNAL] Bq/kg soil

Mon Dec 5 20:30:21 CST 2011

Hello Karen:

My experience with modeling exposure has been with GENII, which I rewrote in
2003 to accommodate stochastic modeling.

Let me first say that I agree with Mike.  However, in practical terms, the
nature of soil radioactivity (R/A) must be assessed.  I can easily imagine a
natural soil far exceeding 5,000 Bq/Kg.  For instance, if a soil developed
from a marine black clay (e.g. Chattanooga Shale, Kolm Shale, or Pierre
Shale), the concentration of uranium could easily be 25 mg/kg in equilibrium
with progeny and as much as 125 mg/kg.  The activity of the uranium alone
would be about 630 Bg/Kg, as would each of the progeny. nλ = n1λ1 = n2λ2 =
etc. (Definition of radiometric equilibrium) in which the activity of the
parent and all progeny reach a state of equilibrium.  For uranium, this
requires 1-2 million years.

U-238 has quite a few progeny until it reaches stable Pb-206.
U-238  - 630
Th-234 - 630
Pa-234 - 630
U-234  - 630
Th-230 - 630
Ra-226 - 630
Rn-222 - 315 (assuming 1/2 of the radon escapes)
Po-218 - 315
Pb-214 - 315
Bi-214 - 315
Po-214 - 315
Pb-210 - 315
Bi-210 - 315
Po-210 - 315
Pb-206 ---------
Total - 6,300 Bq/Kg (Just in the uranium series) and as much as 31,500 Bq/Kg
at 125 mg/kg U.

If the shale contained 5% Potassium, the activity of the naturally occurring
K40 would be about 155 Bq/Kg.

Ignoring thorium, this natural soil would have almost 6,500 Bq/Kg total
activity.

Dan ii

--
Dan W McCarn, Geologist
108 Sherwood Blvd
Los Alamos, NM 87544-3425
+1-505-672-2014 (Home - New Mexico)
+1-505-670-8123 (Mobile - New Mexico)
HotGreenChile at gmail.com (Private email) HotGreenChile at gmail dot com

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Brennan, Mike
(DOH)
Sent: Monday, December 05, 2011 17:12
To: The International Radiation Protection (Health Physics) MailingList
Subject: Re: [ RadSafe ] [EXTERNAL] Bq/kg soil

Hi, Karen.

The first point to keep in mind is that all becquerel are not created
equal, especially when trying to start with soil concentrations and end
up with dose from ingestion.  You really can't say anything until you
know what isotope you are dealing with.  You need to know this for two
reasons:

First, knowing the isotope lets you know the element, which will usually
give you an idea about how well the plants in question will remove the
isotope from the soil and make it part of the plant (you obviously need
to know what plant you are talking about, too).  Different elements
differ wildly on how, or even if, they are taken up by different plants.

Second, knowing the isotope lets you know the half-life, which gives you
important information about how long the radioactive material is going
to be around.  This lets you know if it is potentially going to be a
problem.  If, for example, the isotope of concern is iodine-131 (I131),
with an 8 day half life, you know it will be an issue if it is on a
field of lettuce scheduled to be harvested this week.  If it is on
pumpkins to be harvested in three months, then canned for consumption
next year, it is much less of an issue.

In an event like Fukushima, it can be a challenge figuring out which
isotope is the one to be most concerned about in a given area, for a
given crop, at a given time (as time goes by the isotope that will
produce the greatest dose will change, as the ones with the shortest
half lives decay away).  

If this is a useful level of detail, let me know, and I will continue.

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Karen Street
Sent: Monday, December 05, 2011 3:33 PM
To: The International Radiation Protection (Health Physics) Mailing List
Subject: Re: [ RadSafe ] [EXTERNAL] Bq/kg soil

Pretend I'm a lay person who blogs on climate change and energy issues
and wants to put the 5,000 Bq/kg limit in Japan in context. Be kind.

I used to teach high school physics so I understand the really easy
stuff.

> RESRAD is OK, but you NEED to understand your scenario, and make sure
> the assumptions that go into it are reasonable.  RESRAD will happily
> allow scenarios that have little connection with reality.  
> 
> If you are plugging in a bunch of isotopes quantified through gamma
> spec, make sure you leave out K40.  In many soils (and water, for that
> matter) K40 may be the isotope with the highest activity, but it
> actually does not contribute any actual dose through ingestion
pathways
> (because the body regulates potassium so well) and if there is enough
> K40 in the soil for significant external dose, you aren't farming it.
> 
> -----Original Message-----
> From: radsafe-bounces at health.phys.iit.edu
> [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Wasiolek,
> Maryla
> Sent: Monday, December 05, 2011 1:47 PM
> To: The International Radiation Protection (Health Physics) Mailing
List
> Subject: Re: [ RadSafe ] [EXTERNAL] Bq/kg soil
> 
> Activity concentration in the soil gets converted to doses by using
the
> environmental transport and exposure models.  ResRad
> (http://web.ead.anl.gov/resrad/home2/) is a good example of software
> that uses such model.
> 
> -----Original Message-----
> From: radsafe-bounces at health.phys.iit.edu
> [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Karen Street
> Sent: Monday, December 05, 2011 2:31 PM
> To: The International Radiation Protection (Health Physics) Mailing
List
> Subject: [EXTERNAL] [ RadSafe ] Bq/kg soil
> 
> I see Japan has a standard of 5,000 Bq/kg soil, and that a sizable
> amount of acreage is affected.
> 
> What are the standards of other countries, and how the heck does this
> get converted into mmSv, assuming this is agricultural land?
> 
> I assume there is variation by crop.
> 
> What do I not know? 
> 

--
Best wishes, 
Karen Street
Friends Energy Project
blog http://pathsoflight.us/musing/index.php

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