RE: cosmic rays

[Jack_Earley@RL.GOV]

This was also posted as a project daily question:



<Terrestrial radiation is ionizing radiation from naturally occurring

radioactive material in the earth's rocks and soil. Most terrestrial

radiation is from potassium-40 (40K), uranium-235 (235U), uranium-238

(238U), and thorium-232 (232Th), and the many radionuclides to which 235U,

238U, and 232Th decay until stable lead is reached. The annual dose from

terrestrial radiation varies by location. In Richland, the annual dose rate

from terrestrial radiation is about 53 mrad, in Denver it averages 90 mrad,

east of the Mississippi River it averages 23 mrad, and in middle U.S. it

averages 46 mrad. (NCRP Report No. 45, Natural Background Radiation in the

United States). Click on the following link to see maps of the United States

that show the gamma-ray radiation exposure, and concentrations of potassium,

238U, and 232Th.

<http://sedwww.cr.usgs.gov:8080/radon/DDS-9.html> 



Jack Earley

Radiological Engineer





-----Original Message-----

From: BERNARD L COHEN [mailto:blc+@PITT.EDU]

Sent: Sunday, September 29, 2002 6:52 PM

To: john grant

Cc: radsafe@list.vanderbilt.edu

Subject: Re: cosmic rays







On Fri, 27 Sep 2002, john grant wrote:



> How does the fact that the cosmic rays go all the way through the body

factor into

> this?

>

> BERNARD L COHEN wrote:

>

> >         All natural radiation strikes an average person's body about

> > 15,000 times per second. Cosmic rays account for less than 1/4 of this,

or

> > about 3500 times per second.



	These numbers aree estimated from the doses. For total radiation,

I use 80 mrem per year = 80 mrad per year. I take the average energy of

gamma rays in natural radiation deposited in the body to be 0.6 MeV, and

the average mass of the body to be 70 Kg. Using the definition 1 mrad = 1

E-5 joules deposited per Kg, it is straightforward to calculate the number

of gamma rays.

	I didn't do any deep thinking about the difference between cosmic

rays and other natural radiation, but just assumed that the number of

gamma rays was proportional to the dose. My apologies if a more accurate

treatment was required.



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