Hello, I have a question regarding dose rate calculation.
My radiation source is an isotropic cylindrical gamma source, and the medium is nitric acid solution. I defined it using BEAMSPOT and specified the cylindrical source and center position using BEAMPOS.
Question 1: For the isotropic cylindrical source, should I specify the direction as POSITIVE in BEAMPOS?

Question 2: I want to calculate the dose rate (Sv/h) in the region. I defined the REGION USRBIN and X-Y-Z in USRBIN, which are geometrically same. However, the dose results are inconsistent. Could there be an issue with my definition? I understand that calculating the results using the region requires considering the volume of the region (cm^3).

looking forward to reply,
best regards,
hurrican 1.flair (4.5 KB)

1.) To define the angular distribution you have to add a BEAM card, where in the 3rd parameter you can define the divergence. If you set this value to > 2000 * pi then you will get an isotropic distribution. With this additional option set the cosx, cosy & Type definition of the BEAMPOS card will become meaningless.

2.) A region based scoring will give you the quantity for the full (!) region by default. You would have to normalize it by the region’s volume if you want to have an average value per cm3. In the XYZ mesh scoring you defined a mesh and the scoring will give you the quantity for each mesh cell. If for example you defined the size of one mesh cell as 1 cm3 then you would the value per cm3 for each mesh cell. However, even in this case the value might diverge from the average value per cm3 of the full region scoring, which averages over a larger volume!
Provided that the mesh coincides exactly with your region then an integration over the mesh values will give you exactly the same value that you would find for the region scoring.

Is this an isotropic volume source or an isotropic point source? (My intention was to define an isotropic cylindrical source).

Question 2: I want to calculate the dose in REGION Imp (unit: Sv) defined in Scoring - USRBIN-23BIN. Is my definition correct? My calculation result shows that the volume is 8 cm^3, so the normalized dose in REGION Imp is calculated as 1.21657E-3/8 = 1.52E-4 Sv. Is this calculation correct?

Q1: yes it’s a volumetric source definition. But the easiest way to verify such a setup yourself is to plot the fluence in the XY and in the YZ plane for example.

Q2: your assumption is almost correct. Indeed you need to divide the result by the region volume to have it per cm3 but FLUKA’s canonical unit for dose equivalent is pSv and not Sv!

Hello, thank you for your reply. I followed your advice and tried to project the fluence, defined as USRBIN -22BIN. The projection on the X-axis is shown in the figure below.

The radiation source is in the direction of the detector, and the result is symmetric about the X-axis. However, the results that appear are inexplicable according to physical laws. I am not sure where the problem is in my code.

I am not sure what you expected in your 1D plot to see and how exactly you created your projection.
The best and easiest way to my mind is to create a 2D planar plot at the center of your volumetric source, where you look only at 1 bin in depth (e.g. Z axis) while plotting the X and Y axis. Then you create another plot with 1 bin along the Y axis and plot X and Z.

So practically you cut out the two center planes of a cylinder that are orthogonal to each other.

Thanks a lot. Thank you for your response, it was very helpful to me.

I have followed as you adviced. I found that the cylindrical volume source created using BEAMPOS-type CYLI-VOL turned into a point source after adding SPOTBEAM. How can I solve this problem? My intention was to create a cylindrical volume source.

actually your problem is two-fold. You want a volumetric source and you want different energies. Your search already pointed you to a possible solution. There are basically 2 options:

1.) You can program a source routine where you sample the energy and the position. For a cylindrical spatial distribution you could sample within a box surrounding your cylinder and accept only coordinates that fall within. The test for such points is relatively simple. Assuming that the height is in Z direction, you could check if the sampled X and Y coordinates fulfill the condition X^2 + Y^2 <= R^2 and if Z is within the Zmin and Zmax of your cylinder. Another option is to analytically sample this distribution. To do this you need two uniform samples (s1, s2, s3) in the interval [0,1). Then you can calculate:
phi = 2pi * s1
r = Rmax * sqrt(s2)
x = r * cos(phi)
y = r * sin(phi)
z = s3

2.) Take a look at the following post below. The routines there allow you to define the shape and position of your beam via the input cards and the energy spectrum. If you need quasi-monoergetic lines with uniform probability you just need to define for each line a very small energy bin, the energy and an arbitrary fluence that must be the same for each entry. For example:

Emin, Emax, fluence_per_bin

0.00042787 0.000427871 1

For the other photon energies you would add similar lines, changing only the energy bin data. However, please note that you must not have holes in the spectrum. This means that for example if you have a line at 1 GeV and another one at 3 GeV you should define the spectrum like this:

Thank you for your reply.
It sounds like these two methods cannot be implemented through the input card SOURCE, and can only be achieved by writing code, such as source.f file?