Re: [fluka-discuss]: Using info. from USRBIN

From: Santana, Mario <msantana_at_slac.stanford.edu>
Date: Tue, 13 May 2014 21:17:45 -0700

Mina,

Regarding the saw-tooth behavior that you mention, it is typical of too
high energy cut-off thresholds. Adjust that and look again.

As for the second part, if you are using slices of 0.001 cm, it seems
weird that you set the maximum step size to 0.010 cm (ten times bigger).
Moreover, yes, you should use cylindrical coordinates, otherwise you are
averaging over a volume 22% larger than that of the cylinder, and if the
surrounding media is much more dense and your beam is broad enough, this
could explain part of the discrepancy between the two scorings.

Also, as I pointed out in our previous communication, you may want to look
into MULSOPT card.

Mario
 


On 5/13/14 5:20 PM, "Mina Nozar" <nozarm_at_triumf.ca> wrote:

>Hello everyone,
>
>I have an inconsistency which I have not been able to resolve.
>I score deposited energy distribution using USRBIN and plot the 2-D or
>the 1-D projections and extract the corresponding data files.
>
>If I plot the 2-D projection, deposited energy is averaged in the third
>dimension (over the chosen slice, if any), so to get the total deposited
>energy in some region, I would need to multiply the value in a given bin
>by the slice width and the widths of the bin for that value, correct?
>
>And if I plot the 1-D projection, deposited energy is averaged in the
>other two dimensions (over the slices I have chosen), so to get the
>total deposited energy in some region, I would need to multiply the
>value in a given bin by the width of the bin and widths of the slices in
>the other two dimensions.
>
>I am looking at the power deposition in the entrance and exit windows
>(0.013 cm or 130 microns, so very thin) of a Rb target. The windows are
>discs with a radius of 1.35 cm. The beam is 110.5 MeV protons.
>
>
>I look at the 1D projection of the deposited energy as a function of
>depth or Z (i.e. longitudinal direction or direction of the beam). I
>choose a 1 cm slice in X and Y. I am attaching the figure
>(STF-PD_TopView_Z_lin.jpg). Results are based on 200 M primaries. The
>red lines are drawn at the entrance and exit windows and the Rb target
>sits in B/N. Bin width is 1 mm. I can see the Bragg peak in the water
>but do not understand the 'saw-thooth or step-like behaviour' of the
>energy deposition inside the target region. I see the same behavior if
>I look at the proton fluence as a function of proton energy inside the
>target (can send out that figure if anyone is interested).
>
>Suppose I wanted to find the total deposited energy in the upstream
>window. So I take the value at the first red line (entrance window),
>i.e. 1034.5 Watts/cm^3 and multiply it by (1cm x 1cm x 0.1 cm) = 103.45
>Watts.
>
>But when I look at the output files for total deposited energy in
>different volumes, I see: 58.34 Watts in the upstream window. The
>reason I am off here by almost a factor of two has to do with the coarse
>USBRIN binning, i.e. 1mm in the Z direction (while the window thickness
>is 0.13 mm) so I am looking at a larger volume than the volume of the
>window.
>
>I defined another usrbin card with finer binning along Z (0.001 cm bin
>size) in the upstream window region. X and Y slices are still 1 cm wide
>each. I set the max. step size to 0.01 cm. I plot the 1D projection as
>a function of Z. I have attached the figure (STF-PD_usW_Z.jpg).
>
>So in principle, I should be able to add up all the values in the data
>file from the 1-D projection, multiply the total by (0.013) and get the
>total energy deposition in the upstream window (or close to it -
>cylindrical binning would have been a better choice). The slice widths
>in X and Y are both 1 cm. I get 203 Watts! So I am not converging to
>the total energy deposition I see via the simple SCORE card (58.34 Watts).
>
>Am I doing something wrong?
>
>I am also attaching a side-view of the geometry showing target region.
> From left to right, you'll see the beam pipe, the beam pipe exit
>window, air gap, water jacket entrance window, water, target entrance
>window (too thin to see), target, target exit window (too thin to see),
>Target container box, Graphite.
>
>
>Thanks and best wishes,
>Mina
>
>
Received on Wed May 14 2014 - 07:31:14 CEST