Expert: Jayendra Upadhye - 10/16/2005

Question
Dear
While I was reading about cosmic rays on the web I came across the fact that cosmic rays rarely travel in a straight line, because they are heavily influenced and deflected by magnetic fields which are present everywhere in space. I have also read and heard about ultra high energy cosmic rays (more than 10^20 eV). Keeping in mind that such really energetic particles exist, can we define a threshold at which a cosmic ray is no longer susceptible to deflection by a magnetic field? Moreover I believe this should be dependant upon the strength of the magnetic field. Is this true?
Best regards,
Leila


Answer
Hi Leila,
you may read this link as a reference:-
http://education.yahoo.com/reference/encyclopedia/entry/cosmicra

Actually, there is good co-relation in behaviour of matter under one of the 3 primary forces (weak)
1 - electricity
2 - magnetism
3 -gravitation

In all 3 cases, speed is of no consequence at all to acceleration under force (due to any of these 3 forces).

Imagine an electron spiralling in the magnetic field in a gas chamber. (the classic bubble experiment).

The right hand palm rule tells us how a charged particle will behave when it is moving under the influence of a magnetic field.

1 - As the magnetic field grows stronger, for a given velocity, the spiral tightens.

2 - As the velocity increases, for a given magnetic field, the spiral tightens.

you see, no matter what the velocity, the difference if any with acceleration is just the "degree" of tightness of the spiral.

Meaning, that irrespective of the velocity, the magnetic field will deviate the particle (ofcourse depending on incident angle).

The determining factors are strength of the fields, the charge (alpha particles will have more charge, protons less) of the particle, and velocity.

But at NO velocity value does the particle CEASE to be affected.
speed does not make a particle immune from the influence of magnetic fields, just as it does not make one immune from gravitational influences of matter in space. (having sufficient escape velocity from one planet is NO GAURANTEE one will not be captured / affected by the gravitation of another planet in ones path!

This principle of equivalence of behaviour in these 3 natural forces (weak) helps us to study by analogy, many physical processes that are dificult to understand.


Leila, has it occured to you (this is something unrelated to what you are asking, but is very important and interesting)..I am talking of TIME DILATION!
As most cosmic ray particles travel at very close to speed of light, they undergo time dilation.

Meaning time slows down for the particle. Scientists have proven this by measuring their survival lifetimes in the earth's atmosphere. They find that the "predicted" physical time is not long enough for the particle to even reach the earth's surface. But these particles routinely do that. This discrepancy is explained by TIME DILATION.

I am NOT an expert on THAT subject, but i am sure you can surf on the web and dig out this matter on your own.

Jayen