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RE: " we're evolved for radiation " - geophysicist on pole reversals



Jim,

Fascinating stuff.  But what do I disbelieve?  Please check what I ask, not

what you think I am asking.  (A hint:  does the magnetic field of the earth

protect us from cosmic radiation, or is it the atmosphere.)  By the way, you

do prove some of my point because if the magnetic rigidity exceeds the

geomagnetic cutoff value, the charged particle will enter the upper

atmosphere.  It is the atmosphere that protects the earth from the high-LET

particles that the astronauts are exposed to.  NCRP report 98 is a good

reference on exposure in space.



Hove a good week.



-- John 

John Jacobus, MS

Certified Health Physicist 

3050 Traymore Lane

Bowie, MD  20715-2024



E-mail:  jenday1@email.msn.com (H)      



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

From: Muckerheide [mailto:muckerheide@attbi.com]

Sent: Tuesday, November 05, 2002 1:36 AM

To: Jacobus, John (NIH/OD/ORS); Jaroslav Franta;

radsafe@list.vanderbilt.edu

Subject: Re: " we're evolved for radiation " - geophysicist on pole re

vers als





on 11/4/02 11:11 PM, Jacobus, John (NIH/OD/ORS) at jacobusj@ors.od.nih.gov

wrote:



> Jim,

> The magnetic fields shield the earth for the electron and protrons that

are

> ejected from the sun.  However, they do not protect us from the high

energy

> cosmic radiation that penetrates into the atmosphere.  (It is one of those

> physics things.)  What plain physics fact were you talking about?



John, 

A little 'physics thing' help re space radiation, e.g.:



"1.3.1 Geomagnetic Shielding



"For cosmic rays to reach a spacecraft in Earth orbit, they must penetrate

the Earthıs magnetic field. Since they are moving, charged particles, they

will tend to be deflected by the magnetic field. However, this tendency is

opposed by the energy of the particles as they move at high velocity towards

the Earth. A particleıs penetrating ability is determined by its momentum

divided by its charge, and this quotient is referred to as its OEmagnetic

rigidityı. A cosmic ray will require a minimum magnetic rigidity to reach

each point within the Earthıs magnetic field. Particles below the minimum

will be deflected and this minimum is called the geomagnetic cutoff value.

As mentioned earlier, geomagnetic disturbances may affect the cutoff,

usually lowering it.



"The cutoff value falls to zero at the edges of the magnetosphere and at the

Earthıs magnetic poles. Since the cosmic ray flux is highest at low

energies, a satellite in Earth orbit will be protected to some extent from

cosmic rays by the magnetic field..."



Not to mention the earth's surface!



http://www.estec.esa.nl/gpqwww/paso/padocs/refer/uecsre/handbook.htm



Maybe you can "undisbelieve" now?

. . .

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