Re: VARIATIONS IN BACKGROUND

[Muckerheide <muckerheide@attbi.com>]

Note that NCRP 94, 1987, updates that report. A lot of measurements between

them :-)



Regards, Jim



on 9/11/02 4:36 PM, JGinniver@AOL.COM at JGinniver@AOL.COM wrote:



> While looking into the original question a bit further I "discovered" a copy

> of NCRP report No. 45 Natural Background Radiation in the United States

> gathering dust on one of my bookshelves.  Section 8.2 covers the variability

> across the US.  To summarise it states:

> 

> 8.2.1  Cosmic radiation - the variations of cosmic radiation with latitude,

> solar cycles and the amount of structural shielding within the US are of the

> order of 10%.  Altitude is a significant factor, with a doubling of sea-level

> dose equivalent rate at about 2000 meters.

> 

> 8.2.2 Cosmogenic Radionuclides - the average dose equivalent rate is <1

> mrem/y, so that variations are not significant.

> 

> 8.2.3  External Terrestrial Radiation - The variability in external

> terrestrial radiation is larger than that for other natural sources of human

> exposure.  The dose is largely determined by the concentrations of K-40 and

> the members of the uranium and thorium series in the soil.  The report

> describes 3 general areas in section 5.4 (Atlantic and Gulf Coastal Plains,

> for the majority of the US and for an indeterminate area along the Rocky

> Mountains).  The external terrestrial dose equivalent rates to the whole body

> of 15, 30 and 55 mrem/y.

> 

> 8.2.4  Inhaled Radionuclides - Variability is dependant on local

> concentrations of Rn-222.  There is some increase in areas with elevated soil

> radium levels and a decrease in coastal regions during periods of onshore

> winds.

> 

> 8.2.5  Radionuclides in the Body - This mode of exposure is dominated by the

> 20 mrem/y whole body dose equivalent rate from K-40 which is under

> homeostatic control in the body.  Variation in age and sex are given in

> section 7 of the report.  Variations in inhalation and ingestion do not

> produce large changes in dose equivalent for the air and diet levels existing

> in the US for all radionuclides.  The greatest variation would occur in the

> Ra-226 contribution from drinking water and in the lunbg dose from the long

> lived daughter products of Rn-222.

> 

> 8.2.6 Overall variability - In looking at the possible exposure variability,

> it must be kept in mind that many differences become blurred in an urbanized

> society.  Most city dwellers have little exposure to bedrock or soil,

> building materials are rarely of local origin and diets are frequently based

> on foods with nationwide distribution.  Thus the exposure of the total US

> population is probably more uniform than would be indicated by comparison of

> terrestrial gamma radiation levels on a geographic basis.

> 

> Please note the above is just a summary of section 8.2 of the NCRP report.

> there is considerably more detail in each section of the report which deals

> with each exposure pathway in turn.

> 

> Warmest regards

>                  Julian Ginniver

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