# How to score air kerma via usrbin

Dear FLUKA experts and users!

I have a question regarding USRBIN scoring. I have a cone beam of X-rays with some energy spectrum, I want to obtain at some distance from the cone apex the value of air kerma and the distribution for this value on some area of cone section, I want to use usrbin for that. How to properly score air kerma via usrbin? What is the proper settings for this? Could you advise the correct workflow. Do I need to define some external user routine for that (to convert fluence value to kerma while execution maybe)?

I do understand, that I can define USRTRACK detector in some place to get fluence spectrum and later apply the formula:

K=\int_0^{E_\text{max}}\frac{d\Phi(E)}{dE}\cdot\left(\frac{\mu(E)}{\rho}\right)\cdot E dE

to get the kerma, but how to do it with USRBIN?

P.S. I thought that MathJax is working on this forum
P.P.S @horvathd thanks for the edit!

Regards,
Ivan

Hello Ivan

kerma is “kinetic energy released in matter”. To score it at a point, or in a USRBIN cell, you must make sure that no kinetic energy in form of electrons and positrons can escape this cell. Therefore, you must set the transport cutoff for e+/e- to a high value. For example, the highest primary photon energy is a safe choice.
Then, following the manual, you can also set the production cutoff to the same, high, value. If in the rest of the air volume of your problem you would like to transport secondary e+/e-, you must create two air-materials, with different cutoff values.

Dear Thomas!

Thank you for this suggestion! I am aware of this option, but I wonder if any other ways exist…

Best wishes,
Ivan

Hi @Ivan ,

You can score fluence using USRTRACK inside the detector volume and then use that fluence to convert it into air kerma using fluence to kerma conversion factor (from ICRP 74). You can use an external program (fortran, matlab, python or any other) for this conversion following interpolations technique.

Regards,

Riya

Hello @riya !

Yes, this is a known procedure that I also mentioned in my original post. But how to do this for mesh in usrbin scoring?

Regards,
Ivan

Dear Ivan,

you can implement the fluence to air kerma conversion factors in the fluscw.f user routine, to apply it to URSBIN (and other types of) scorings during runtime.

Cheers,
David

Dear Dávid!

Thanks! Seems this is the most appropriate way for my case. Do you have some examples of fluscw user routines as reference to start with? Will try to implement this feature!

Regards,
Ivan

Dear Ivan,

The only difference is that you need to add the usrbin.inc and use the TITUSB variable for the name of the USRBIN scoring.

Cheers,
David

Dear Dávid,

Great! Thanks once again, have a good day!

Cheers,
Ivan