- #1
Anisur Rahman
- 9
- 1
How Can I Simulate a Narrow Spectrum X-Ray Beam Using MCNP?
- #2
Alex A
Gold Member
- 246
- 156
I ran that at 1/100th the nps in MCNP5 and it produces a spectrum for me. The electron voltage might be set at the RMS of the supply voltage of the tube. That would limit the spectrum a bit, it's not fully correct.
Also of note "e0 0.001 100i 0.328" is a linear interpolation and an electron at 47.9keV can't produce an X ray photon above 47.9keV so most of the spectrum must be blank under these conditions.
If you still think you are getting nothing add your output file to a post.
Also of note "e0 0.001 100i 0.328" is a linear interpolation and an electron at 47.9keV can't produce an X ray photon above 47.9keV so most of the spectrum must be blank under these conditions.
If you still think you are getting nothing add your output file to a post.
- #3
Anisur Rahman
- 9
- 1
Here is my output.
- #4
PSRB191921
- 183
- 89
in your file "sdef par=2" emits photons not electrons. You must write par=3
- #5
Alex A
Gold Member
- 246
- 156
Oh wow, good catch @PSRB191921!
@Anisur Rahman, the output file looks otherwise fine but incomplete. Like the program has been told not to run the problem, or it's crashing or it's being killed. 3e6 on one core of my old laptop took 15mins, 3e8 would have taken a full day, what do you see and do when you run it?
@Anisur Rahman, the output file looks otherwise fine but incomplete. Like the program has been told not to run the problem, or it's crashing or it's being killed. 3e6 on one core of my old laptop took 15mins, 3e8 would have taken a full day, what do you see and do when you run it?
- #6
PSRB191921
- 183
- 89
I make some modifications (see my input and output).
first I modified sdef :
"sdef POS= 5 0 0 PAR=3 ext=0 ERG= 0.06 AXS= -1 0 0 vec -1 0 0 DIR= 1 RAD=d1"
I put "par=3" to emit electrons and not photons
I create an electrons beam on the W target (POS= 5 0 0 ext=0 AXS= -1 0 0 vec -1 0 0 DIR= 1 RAD=d1)
It gives :
I transport electrons only in cell 100 and 107 (imp:e 1 0 0 0 0 0 1 0 0), because there is no point in transporting electrons outside of these areas except to increase the calculation time!
I put a F5 tally at 3 cm (in front of the aluminum filter) and F15 at 10 cm (behind the aluminum filter) note that F4 and F1 did not converge with few particles
it gives this results :
hope it's help
first I modified sdef :
"sdef POS= 5 0 0 PAR=3 ext=0 ERG= 0.06 AXS= -1 0 0 vec -1 0 0 DIR= 1 RAD=d1"
I put "par=3" to emit electrons and not photons
I create an electrons beam on the W target (POS= 5 0 0 ext=0 AXS= -1 0 0 vec -1 0 0 DIR= 1 RAD=d1)
It gives :
I transport electrons only in cell 100 and 107 (imp:e 1 0 0 0 0 0 1 0 0), because there is no point in transporting electrons outside of these areas except to increase the calculation time!
I put a F5 tally at 3 cm (in front of the aluminum filter) and F15 at 10 cm (behind the aluminum filter) note that F4 and F1 did not converge with few particles
it gives this results :
hope it's help
- #7
Anisur Rahman
- 9
- 1
Hi @Alex A and @PSRB191921. I am sorry, i uploaded the incomplete output file. In the mean time, i have changed the geometry. I have changed the par and tally too. But when the electron is emitted, it doesn't collide with the tungsten target. I am not sure why this is happening. Can you help me please? I am uploading the input and the output file here.
- #8
Alex A
Gold Member
- 246
- 156
You have a fatal error,
" fatal error. 9 entries not equal to number of cells = 10."
This seems to apply to,
This is the same as,
So you've assigned 9 importances when you need 10.
" fatal error. 9 entries not equal to number of cells = 10."
This seems to apply to,
Code:
imp:e 1 0 1r 1 0 4r $ 100, 109
Code:
imp:e 1 0 0 1 0 0 0 0 0 $ 100, 109- #9
Anisur Rahman
- 9
- 1
I have corrected this fatal error, but still no photon is being recorded. i am attaching the input and output file.
- #10
Alex A
Gold Member
- 246
- 156
Your void cell is 107, this cell needs to have 0 importance for all (both in this case) particles.
1. What is MCNP and how is it used for simulating X-ray beams?
MCNP (Monte Carlo N-Particle) is a general-purpose Monte Carlo radiation transport code designed to track all types of particles over all energy ranges. It is widely used in physics and engineering fields for simulating nuclear processes, including the interaction of X-ray beams with matter. For simulating a narrow spectrum X-ray beam, MCNP allows users to define specific beam characteristics such as energy, intensity, and spatial distribution, enabling detailed analysis of the beam's behavior and interaction with different materials.
2. How do I define a narrow spectrum X-ray beam in MCNP?
To define a narrow spectrum X-ray beam in MCNP, you need to specify the energy distribution and spatial characteristics of the beam. This is typically done using the 'SOURCE' card where you can set a Gaussian or another narrow distribution centered around your desired peak energy. You must also define the geometry of the source to focus or collimate the beam, ensuring that it remains narrow as it propagates through the system.
3. What materials and geometries are best for collimating a narrow spectrum X-ray beam in MCNP simulations?
For collimating a narrow spectrum X-ray beam in MCNP, materials with high atomic numbers and densities, such as tungsten or lead, are typically used due to their effective photon attenuation properties. The geometry of the collimator is also crucial; commonly used shapes include conical, cylindrical, or slit collimators. The choice depends on the specific application and required beam shape and size. The design should minimize scattering and absorption while maintaining the beam's integrity over the desired distance.
4. How can I verify the accuracy of my simulated X-ray beam in MCNP?
Verifying the accuracy of a simulated X-ray beam in MCNP involves comparing simulation results with experimental data or theoretical predictions. This can include checking the beam's energy spectrum, spatial distribution, and intensity at various points. It is also important to perform sensitivity analyses by varying input parameters and assessing their impact on the beam characteristics. Utilizing MCNP’s built-in tally systems helps in measuring and analyzing the energy and flux distributions effectively.
5. What are some common challenges in simulating narrow spectrum X-ray beams in MCNP and how can they be addressed?
Common challenges include achieving the desired beam collimation and managing computational resources effectively. Beam collimation issues can often be addressed by refining the geometry and materials of the collimator. Computational challenges, such as long simulation times and large data outputs, can be managed by optimizing the simulation setup, such as using variance reduction techniques and parallel computing. Ensuring that the physical model is as close to the real scenario as possible and validating the model against experimental data are crucial steps in overcoming these challenges.
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