MCNP: Can I input the X-Ray tube voltage in MCNP source specification?

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Discussion Overview

The discussion revolves around the input of X-ray tube voltage in the source specification of MCNP (Monte Carlo N-Particle Transport Code). Participants explore how to represent the energy of electrons in simulations and the relationship between tube voltage, current, and particle energy.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that the X-ray tube voltage is not directly input into MCNP, but rather the energy or energy spectrum of the photon source is specified.
  • It is proposed that an X-ray tube powered at 100kV can be simulated using a beam of electrons with energy of 0.1 MeV, as the energy gained by an electron falling through a potential difference is equivalent to the voltage in electron volts.
  • Participants discuss the role of current (mA) in determining the number of particles per second, while the accelerating potential defines the energy per particle.
  • One participant notes that MCNP outputs results per source particle, and that simulations for different current values at the same voltage can yield similar results, with post-simulation calculations differing based on real-world source activity.
  • A question is raised regarding where to input the electron source intensity in MCNP and how to determine the number of particles for a specific X-ray tube intensity.
  • A participant challenges another's understanding of basic concepts such as coulombs and unit charge.

Areas of Agreement / Disagreement

Participants express differing views on the direct input of X-ray tube voltage in MCNP, with some asserting it is not an input while others provide methods to simulate it. The discussion remains unresolved regarding the best approach to inputting source intensity and the implications of current on simulations.

Contextual Notes

There are unresolved aspects regarding the assumptions made about the relationship between voltage, current, and particle energy, as well as the specifics of inputting source intensity in MCNP.

Anisur Rahman
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TL;DR
Source Specification
Can I input the X-Ray tube voltage in MCNP source specification?
 
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Anisur Rahman said:
TL;DR Summary: Source Specification

Can I input the X-Ray tube voltage in MCNP source specification?
One would put in energy or energy spectrum for a photon source. I am not aware that voltage for an X-ray tube is an input.
 
An electron falling through a potential difference of 1V gains 1eV of kinetic energy.

So an X-ray tube powered at 100kV would be simulated with a beam of electrons of energy 0.1 MeV (SDEF ERG= are in MeV) directed at a target.
 
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Alex A said:
An electron falling through a potential difference of 1V gains 1eV of kinetic energy.

So an X-ray tube powered at 100kV would be simulated with a beam of electrons of energy 0.1 MeV (SDEF ERG= are in MeV) directed at a target.
Even if the current value (mA) differs?
 
mariem said:
Even if the current value (mA) differs?
The current determines the number of particles (mA/e) per sec, were e is the unit charge.

The accelerating potential determines the energy per particle.

The total energy/sec or power would be the number of particles/sec * energy/particle, and the total energy or dose deposited would be related to the integral over time of the (particles/sec * energy/particle).
 
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Yes, as @Astronuc says the intensity is the other part of the problem. Almost all answers output by MCNP are per source particle. So no one would attempt to simulate one mA-second (a milli coulomb) of electrons. Enough particles are simulated to get a statistically useful answer and then the results which are per source particle are multiplied by the real world source activity to get flux or dose rate answers, or the total number of real world particles to get dose.

It also means that if you are simulating a 1mA tube and a 10mA tube (the same tube at the same voltage) that only one simulation needs to be done because these situations are the same. Only the maths done afterwards differs.
 
Where can I input the electron source intensity in MCNP? How many particles will I have for an X-ray tube set at an intensity of 10 mA?
 
Do you understand coulombs, do you understand unit charge (the charge on an electron)?
 

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