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    I Pair production proximity

    Does anyone know how close a photon needs to be to a nucleus (an ion really, no shielding from electrons) for pp to occur? I assume it's a probability as a function of distance, any ideas/equations? Thanks
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    Refractive index of BEC

    Does a BEC still have a very large refractive index for X Ray's and gamma rays?
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    Free electron laser weapon -- operating wavelength for the US navy's 1MW FEL?

    I know fel operate a wide range of wavelengths, but does anyone know the main operating wavelength for the US navy's 1MW fel?
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    Destructive interference at a surface

    Take two lasers of the same intensity and wavelength and aim them at 30 degrees at the same spot on a mirror, so that at the surface the waves cancel perfectly. What happens? How can the wave be reflected if there is no field present?
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    Quantum tunneling instantaneous Does this mean that the tunnelling time was actually zero, and the electron 'skips' over the gap, or does it mean that the electron wave travelled at the speed of light followed by an instantaneous jump later on
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    Light interaction with charged particles

    Does anybody know what happens when say a laser accelerates charged particles? Do photons get absorbed and the intensity of the laser drops, or do they get absorbed and scattered and there's a redshift of the photon etc
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    Wave particle duality

    In the single slit experiment, individual photons may be diffracted. The electric field of the em wave should accelerate charged particles in the screen (if it were a capacitor for example) but only one packet of energy exists. The photon may be absorbed after many wavelengths of light have...
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    Gravity in particle colliders

    What prevents the beam of protons in say the lhc from falling at 9.81 m/s? I've never heard of an electric or magnetic field that prevents it...
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    Accelerating charge emits em waves or pulse

    Does an accelerating charge, such as one turning a corner emit an em wave or just a pulse? Classical logic dictates it should just be a pulse as there is no oscillation. But which is it?
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    Laser through electron cloud

    A high intensity continuous wave laser passes through an electron cloud. Please discuss what would happen and in relative amounts. Thanks
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    Tokamak particle acceleration

    In a tokamak design what accelerates the plasma? Is it the current from the primary coils driving the plasma round?
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    Laser interaction with ions

    Will a laser exposed to ions (doped fibre) spread out in the direction of polarisation as momentum sends the peaks in one direction and the troughs in another. Or, as total momentum is 0 does the wave continue on straight.
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    Diffraction limited laser

    Why can a laser only be focussed to within its wavelength? It says due to it being diffraction limited, what about focussing lenses and mirrors they don't involve diffraction. Please explain
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    Anti hydrogen - hydrogen annihilation

    I would like to know what exactly hydrogen and anti hydrogen decay products are. Thanks
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    Object falling into the sun

    Does an object falling into the sun reach approximately the speed of light?
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    Ionisation rate

    I need to ionise lots of particles quickly. Upwards of 1kg /sec. What's the best way of doing this? I'd consider pre ionised solutions boiling etc. Thanks
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    Momentum or Kinetic Energy to find Acceleration?

    Hi all, I have charged particles (protons) accelerated by an electric field. If I add up all the momentum and find the change in momentum per sec I can find the acceleration of my craft by dp/dt /M = a If I add up all the kinetic energy of the particles and find the KE per sec, I can find the...
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    Solar Sail/ Mirror Redshift & Blueshift

    Hi all, I was hoping you could help me out with this one. Im trying to calculate the redshift or blueshift of a photon that strikes a mirror and reflects. I know E=pc, and that 2p is the momentum transfer. I also know that kinetic energy is 2p/M (of the mirror). However, this says that...
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    Light- Matter Interactions

    Could someone please clear this up for me. We have, Reflection (metal, mirror) Reflection (colour) Absorption (heat) Emission (heat) Transmission (glass) Sry but I use photoelectric effect to reference electrons absorbing photons of specific energies to be excited to higher energy levels, I...
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    Time Dilated Acceleration

    At v = c, time (hence physics) stands still. You can never reach c, but lets say near enough. Therefore if you accelerate at an extremely high rate, from 0 - c in perhaps a fraction of a second, wouldn't the slowing rate of physics prevent you from being crushed? ie, is there a way of...
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    Quanta of Light

    Trying to understand small increments of light. From a particle perspective, a photon is the smallest increment, dependent on frequency as E=hf. From Maxwell's wave perspective, light propagates as a result of the energy passing between the E field and the B field. The rate at which this...