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RE: Re: " we're evolved for radiation " - geophysicist on pole re vers als
Greetings
Near the top of the atmosphere the earth's magnetic field modifies the
incoming cosmic ray distribution significantly (by the way there are very
few primary electrons from either the sun or the galaxy! Most of the
elctrons at satellite altitudes are electrons from interactions in the
atmosphere and then trapped in the dipole field in a way simiar to that in
fusion reactors). As was said, closer to the magnetic poles of the earth
the primaries can stream in along the filed lines. Closer to the equator
the field reflects them back away from the earth. The upper energy for
this sort of effect is 1-2 GeV for protons. So there is an effect
everywhere of the earth's magnetic field on galactic cosmic radiation.
The effect is much more marked for solar flares which mainly give protons
of less than several 100 MeV.
At ground level you have to remember you are sitting behind a good shield
called our atmosphere which is equivalent to about 4 metres of concrete,
and this is a fairly efficient field for lower energy protons. So this
reduces variations due to the earth's magnetic field.
This is meant to be very simple-minded introduction. Better people have
written better explanations, but I felt unable to keep out of this one.
Graham
+----------------------------------------------------------------+
| Graham R. Stevenson, | Email: Graham.Stevenson@cern.ch |
| Radiation Protection Group, | Tel: +41 22 767 4623 |
| CERN, 1211 Geneva 23, | Fax: +41 22 767 5700 |
| Switzerland. | |
+----------------------------------------------------------------+
On Mon, 4 Nov 2002, Jacobus, John (NIH/OD/ORS) 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?
>
> When I get a chance, I will crack open my old file of cosmic radiation
> studies that I started to collect 10 years ago.
>
> -- John
> John Jacobus, MS
> Certified Health Physicist
> 3050 Traymore Lane
> Bowie, MD 20715-2024
>
> -----Original Message-----
> From: Muckerheide
> Sent: 11/4/2002 8:46:41 PM
> To: Jacobus, John (NIH/OD/ORS); Jaroslav Franta; radsafe@list.vanderbilt.edu
> Subject: Re: " we're evolved for radiation " - geophysicist on pole revers
> als
>
> on 11/4/02 1:56 PM, Jacobus, John (NIH/OD/ORS) at jacobusj@ors.od.nih.gov
> wrote:
>
> > Jaro,
> > My comments are based on my disbelief that the magnetic field of the earth
> > has any influence of the radiation we receive from space,
>
> How do you "disbelieve" a plain physics fact!? (It's not even biology!)
>
> Regards, Jim
>
> >whether it is
> > ionizing or UV. I was wonder why the comment was made "we're evolved for
> > radiation" in the context of the article.
> > By the way, I believe that Mars lacks a magnetic field. Of course, we do
> > not know if life exist there, so maybe a magnetic field is necessary.
> . . .
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