Fermi Style Estimation Question

[Spitfire-Adam]

Have been set a rather tricky question in physics, and wondered if you had any ideas on how I would go about answering it...
It is based on Fermi style estimation to try and encourage one to estimate and guess, the question is... 'How many particles of ionising radiation pass through your head every second?', I really have no idea how I would go about even guessing inaccurately the answer of this, never mind accurately so any help would be appreciated, thanks.

 

[Meir Achuz]

Just estimate the area of the top of your head and multiply by the radiation flux
(in particles/m^2) which you will have to get from some handbook.

 

[CarlB]

The answer probably depends on how close you are to the nuclear detonation.

Carl

 

[Spitfire-Adam]

as it is an estimation I've decided its probably of the average atmospheric content of radiation, does anyone know what this is? and is there anyway of finding the number as particles per cm cube or litre, and how many particles would travel through in a given time

 

[CarlB]

As an upper limit, take a look at the limits on how well air conducts electricity. I would guess that a major contribution to conduction is due to ionizing radiation.

The number of cosmic rays in the atmosphere is given by a figure in units of number per cubic centimeter per solid angle. A practical book on particle theory will give the number, but if you know it, it's easy enough to compute the number going through your head. By the way, it's a rather large number.

Carl

 

[Spitfire-Adam]

had a think, could the answer possibly be 0?
gamma is not paticles, its waves.
beta is blocked by 1.5 cm of skull, so would be blocked, therefor not goin through
alpha wouldn't pass through skin
just a thought

 

[CarlB]

had a think, could the answer possibly be 0?

Charged muons will penetrate a skull nicely and are ionizing. The rate is around one per square cm per minute, or maybe a couple per second through a brain sized object.

Carl

 

[Spitfire-Adam]

i think muons decay too fast to travel through our entire head

 

[CarlB]

The lifetime of a stationary muon is about 2.2 usec. Travelling at near c, that's long enough time to go about a half mile. Of course anything traveling at close to c ends up having its lifetime extended by relativity.

There is another aspect to the problem, and that is explaining why muons don't get absorbed in your skull. For that, you might consider how thick the atmosphere is, measured in grams per square centimeter, and compare this to your skull.

Carl