Question about which material to use ambient dose equivalent in

Dear FLUKA experts,

Excuse me, I have a question to ask for your help. The description is as follows:

I’m running a simulation where electrons(energy>=8MeV) hit a tungsten target and X-ray produces photoneutrons. In addition, there are several other structures input as the structure of a medical LINAC head.

I want to know the dose of neutrons at the isocenter, so I calculated it in two different ways:

  1. Place a water phantom at the isocenter and calculate DOSE-EQ at the depth of 1cm (using AUXSCORE, WHAT(2)=NEUTRON and SDUM=AMB74 to calculate ambient dose equivalent). The isocenter is on the surface of the water phantom.

  2. No water phantom at the isocenter(i.e. vacuum), but still DOSE-EQ as above.

Which one is more reasonable? I know how ambient dose equivalent was defined in ICRP 60 and FLUKA code, hence I think the second one is more reasonable. I found both in related literature, however, which confuses me so much.
(1)Investigation of LINAC Structural Effects on Photoneutron Specified Parameters Using FLUKA code

Attached to the email are inp files written by me, and it will be very nice of you if you can help me check whether I made other mistakes.
the first method.inp (5.2 KB)
the second method.inp (5.7 KB)

Thank you very much!

Dear Yinuo Zhu,

welcome to the FLUKA Forum and thank you for your question.

The question is: What are you actually interested in and what is the scenario/case you want to model? This should answer your question. The water phantom will obviously have an influence on your neutron fluence at your point of interest.

The quantity AMB74, or H*(10), is a point-like quantity, calculated here by folding the particle fluence with a set of dose conversion coefficients. You don’t need to score the quantity in a certain depth of the phantom to get the actual dose equivalent. So both ways are correct, but of course only you know what is reasonable here for the case/question you would like to answer.

We cannot validate your input files, but it is generally recommended to use the default settings, unless you have a particular reason to limit or adjust certain parameters.

Kind regards,


Dear Markus Widorski,

Thank you very much for your answer! What I’m interested in is the dose of neutrons that a human body receives around the isocenter, and the water phantom is used to simulate human tissue. As I understand it, H*(10) is a operational radiation quantity that can be used as an estimate of the human effective dose at the location of a real dosimeter.

So for my purpose, I don’t need a water phantom. Is that correct? Or should I consider the effect of human tissue on the neutron spectrum, in which case a water phantom is necessary? I don’t know which one is more reasonable, but I think in the definition of H*(10) ICRU sphere has already been used to simulate human tissue, so it seems that there is no need to consider the effects of water on neutron energy spectrum for my purpose. If so, when do I need to consider the effects of water on neutron flux, for example, in a simulation of a person in a swimming pool?

Please forgive me if I misunderstand what you mean.

Best regards,
Yinuo Zhu

yes in that case I would recommend to score the dose equivalent at a point (in air). The effects of a human body on the neutrons in the point of interest are already included in the dose conversion coefficients. All the surrounding environment should be included in your geometry. The photoneutrons in your case however are only created in the target (which might however be a valid simplification).



Thank you very much for your answer, which solved my question very well.