1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Effects of radiation on Electric Field

  1. Jul 28, 2011 #1
    How does radiation (e.g. x-ray) affect the flow of electrons in an electric field? More specifically how does this affect for instance the resistance of a resistor.

    Thanks in advance. :smile:
  2. jcsd
  3. Jul 28, 2011 #2
    x-ray radiation is high frequency and typical electronic circuits (such as would include a resistor) are low frequency, so there is little direct effect between the electric field in the x-ray beam and the the circuit's current. However, there may be indirect effects. For example, the x-ray could heat up a resistor so that it's resistance increases. Or the x-rays could remove electrons such as in the photoelectric effect. But I think such effects are small enough that you will not see them unless you are looking for them.

    If the radiation is at comparable frequencies (kHz-GHz) to those used in AC circuits, then the radiation will induce additional currents in your circuit, known as signal interference. For instance, when you turn on a blender, it's motor generates radio waves that make an analog antenna TV (remember those) show a fuzzy picture. Unwanted interference can be minimized by electromagnetic shielding. If the induced current is desired, then you get into the complex world of antenna design.
  4. Jul 28, 2011 #3
    It will depend on your beam characteristics. If your circuit is running DC and beam intensity is very high, if polarization of field radiation from resistor matches the polarization of your beam than some interference at the electrical level is possible. Also if intensity is high, that might cause increase in heat of the resistor thus it might operate outside of the linear region. From my experiences I know that a heat increase of ~10C results in a deviation of around %2~3 in resistance for off-the-shelf common resistors. SMD components have less tolerance than standard ones. Heating up too much will make it go outside it's tolerance region and it might end up as an unstable component. There are military grade version of almost each component that is designed to operate in extreme conditions.

    On the other hand if you are running AC in your circuit first case I mentioned will not be observed. Because of the higher frequency of the beam, it will interact with the field oscillations from resistor in a way that you will probably not be able to observe the effects of this in electrical level. It depends on your measurement precision, you need to have very high sampling rates to see ripples in electrical scale because they will be very high in frequency. Heating up too much option is always valid no matter what the circuit is or even resistor is connected to a circuit or not.

    Radiation can effect the flow of electrons but in a limited region. To make electrons propagate where you want them to be (in limits of the wire) can be achieved by precisely generated waves. If you were asking about controlling the position of a molecule or a bigger concept in size than an electron then optical tweezers could do what you want very precisely.

    From relativistic model of electron radius is appoximated as ~2.8 x 10-15 which corresponds to 1.071x1021Hz. If you have an em source radiates at this frequency you can move an electron precisely in space-time, neglecting the wave-electron interactions at quantum scale.
    Last edited: Jul 28, 2011
  5. Jul 28, 2011 #4
    Thank you for your reply. Regarding additional heating of the component. Is it possible to compute it given that we know how much radiation is being emitted from the source? If so, how can this be done?
  6. Jul 29, 2011 #5
    Yes it is possible. Assuming the system is isolated (only the resistor and beam) you can very precisely derive the characteristic curve of heat transfer between source and target.Heat increase is dependent on the beam intensity which is a function of amplitude of the electric field.

    1 - What are the specs of the circuit ? (that resistor is connected to)
    2 - What are the specs of the beam source ? (that radiates over the resistor)
    3 - What is the distance between source and the resistor ?
  7. Jul 29, 2011 #6
    It should be pretty straightforward to estimate the heating of irradiated materials.

    The mechanisms of heating would mostly be secondary interactions of the energized electrons that the primary photons interacted with. Those electrons gain kinetic energy and deposit it into the material lattice, which you would see as heating on the macro scale of the device.

    If you know roughly the material composition of the components and the energy of the photons in question then you can determine interaction mechanisms for your primary radiation, estimate how much of the transferred energy is deposited back into your components and then the corresponding temperature rise. Much of that information is likely tabulated in published tables.

    If your primary photons have energy much greater than nuclear binding energies for your components then you would start seeing photodisintegration effects where protons and neutrons are ejected from nuclei. Neutron radiation has been shown to be damaging to many materials, and proton radiation has very localized energy deposition characteristics that can also damage electronics.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook