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Radiation absorption and temperature changes in matter

by Alexander83
Tags: heating, radiation, solid, temperature, x-ray
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Alexander83
#1
Sep10-13, 09:43 PM
P: 19
Hi there,
I've been studying mechanisms by which high-energy radioactive decay products (beta particles, x-rays, gamma rays) are attenuated as they pass through matter. From my readings in introductory and intermediate level textbooks, the general mechanisms by which these particles and rays are described as interacting with matter generally involves interactions with electrons in the target material either causing ionization or electronic excitation.

My gut feeling is that the net effect of all of these interactions will (eventually) be an increase in the temperature of the target material. The mechanisms that are commonly described in books for attenuation of radiation such as photoionization or Compton scatter in the case of photons, or Bremsstrahlung production or collisional ionization in the case of energetic electrons. These mechanisms would seem to result in the production of simply more particles (free electrons) or photons in the target material.

My (very) naive understanding of what a change temperature means in a solid structure would be something along the lines of excitation of vibrational or rotational modes in an atomic lattice with the resulting increase in the kinetic energy of the atoms of the substance resulting in what we perceive as an increase in temperature... is this correct?

My question then is this: how do the interactions I mentioned earlier ultimately result in a temperature change in the target? My gut feeling is that secondary radiation produced in a target continuously decreases in energy level until it is at the correct energy level to excite vibrational or rotational modes in the target, causing what we think of at a macroscopic level as "heating" but I can't find anywhere where this is spelled out. Introductory texts seldom go into much detail much beyond discussing the mechanism of the initial attenuation of high energy radiation and not subsequent steps.

Thanks for you time!

Chris.
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mfb
#2
Sep11-13, 04:55 AM
Mentor
P: 11,601
All charged particles are ionizing (and the slow electrons then collide with atoms and other electrons and heat the material) and/or directly transfer momentum to atoms (-> heat). Neutral particles can hit nuclei, or produce secondary radiation with charged particles.
If heating due to radiation is significant, the radiation levels are really high.
Alexander83
#3
Sep11-13, 03:02 PM
P: 19
mfb, thanks for the post. I think I'm trying to ask about the process that you described as

"the slow electrons then collide with atoms and other electrons and heat the material"

I think I'm struggling to think about what it means to say that the material is heated... is this an excitation of vibration of the atoms in a lattice in solids which is what we conceive of as a temperature increase? If that's the case, why is it that slower moving particles cause this excitation and heating and not higher energy particles?

Chris

mfb
#4
Sep11-13, 04:02 PM
Mentor
P: 11,601
Radiation absorption and temperature changes in matter

Excitation of vibrations of atoms and excitations of electrons.

If that's the case, why is it that slower moving particles cause this excitation and heating and not higher energy particles?
Both do it, but the high-energy particles tend to transfer high energies to particles they "hit", so it takes some steps to get to thermal energies (~1/40 eV at room temperature).


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