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Forum: Fields: Magnetic and Otherwise
Re: Question discripancy between firing a particle with a given energy and using electric field to accelerate it to the same energy (Robert Nnaemeka)
Re: Feedback Re: discripancy between firing a particle with a given energy and using electric field to accelerate it to the same ener (Gumplinger Peter)
Re: Feedback Re: discripancy between firing a particle with a given energy and using electric field to accelerate it to the same ener (Robert Nnaemeka)
Date: 30 Apr, 2015
From: Michael H. Kelsey <Michael H. Kelsey>

On Wed, 29 Apr 2015 22:57:04 GMT, Robert Nnaemeka wrote:
> I have a box filed with nitrogen gas at very low pressure. I Then
> created a uniform magnetic field and associated it with the box logical
> volume. The electric field strength is such that when a proton is
> released from one end it will accelerate to a kinetic energy of 120 keV
> when it reaches the opposite end. The purpose is to study electron
> production via ionization at low pressure. However, there is no
> ionization. But if I deactivate the field and fire a proton with 120 keV
> kinetic energy I get some electrons as should be expected.

I have a few observations. When you "release" the proton in your job, do you give it exactly zero energy, or do you give it a small but finite energy (e.g. 0.1 eV)? Geant4 does not have a mechanism to "restart" a particle which is Stopped; a stopped proton will simply be killed. If you give it a small energy, then G4Transportation will be able to apply the E field during the step and accelerate it.

Second, from your description, the two tests are different. When you launch a very slow proton at one end, it is probably too low energy to ionize until it gets partway through the box. The 120 keV at the far end is the _maximum_ energy, not the average.

Finally, as you know, ionization energy loss is a steeply rising function as you go down to zero energy. I'm not sure that protons will behave the way you think they will: the slowest protons should lose their energy all in one step, with no opportunity to be accelerated very much. Your tests above will tell you for sure, but you may need to be launching your protons with energy above the "single step" limit, so that they can both lose energy and be accelerated by the field, without being stopped.

  -- Michael Kelsey

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1 Feedback: Re: discripancy between firing a particle with a given energy and using electric field to accelerate it to the same ener   (Robert Nnaemeka - 30 Apr, 2015)
(_ None: Re: discripancy between firing a particle with a given energy and using electric field to accelerate it to the same ener   (Mike Kelsey - 30 Apr, 2015)
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