About scattered rays

Dear fluka experts,

I just started to learn fluka recently. I want to use fluka to simulate the scattering effect of X-ray with different energy levels in the phantom and the ray distribution after penetrating the phantom.

I built a simple X-ray generation and filtration model and a simple thigh model.Using 110kev electron beams bombarded tungsten targets to generate bremsstrahring radiation to produce X-rays of different energies, which were filtered through the aluminum plate and passed through the phantom.But my model still lacks a component to show the distribution of rays after passing through the phantom.

1、So my first question , is there any way to show the distribution of rays as they pass through the mode?

On the other hand, I used usrbin score for the entire cone beam to simulate the scattering line results inside the thigh model.However, I think the results obtained are not ideal, as shown in the figure below, with large errors and little effective data for reference.I used 1*E5 primaries,Spawn=5,10 Cycles,the total number of particles is 5 *E6.

2、So, the number of particles should not be the cause of this error, I don’t know if my conjecture is correct?And I want to know how to reduce these errors?

3、Finally, I heard that biasing can be applied to my models, is that true?

XraySystem004.flair (5.8 KB)
XraySystem004.inp (2.9 KB)

Here is my flair and fluka file, can you give me some advice
Best Regards.

Dear @201910101505,

Have a look at the second scoring lecture from the last Fluka course and at the USRBDX card.

The number of primaries does not correspond to the number of x-rays reaching the thigh but it is the number of electrons. These have to undergo bremsstrahlung to generate the x-rays and that comes with a given efficiency. In order to reduce the uncertainties, you have to increase the number of primaries.

For biasing, you can have a look at the biasing lecture from the last course. Unfortunately for you, biasing in air is not a good thing in MC simulations (search on this forum about this, since it has already been discussed) therefore, I don’t think it fits your problem.

Hi amario
Thank you very much for your reply.

1、I will continue to study the course on usrbdx cards.

2、I can’t agree with you more, I know that Bremsstrahring happens and only a small fraction of the X-rays are produced. According to you, in my model, five million particles is still not enough?And I have to keep increasing the number of primaries, right?

3、I will search and read the related posts you mentioned

Finally, this is my first post, I am honored to receive your reply, it is very helpful to me,thank you

The number of primaries is enough when it allows you to reduce the statistical uncertainty down to a level that it good for you. It is only for you to judge when you have achieved a results that is statistically good enough.

I have understood what you mean. I will try the method you proposed. Thank you

Best regards