# RE: [fluka-discuss]: FW: FLUKA

From: Joachim Vollaire <joachim.vollaire_at_cern.ch>
Date: Mon, 15 Aug 2016 08:14:57 +0000

Hi James

To the questions in your slide, “Shouldn’t Source be 0 to 30 cm?”

What you are defining is the height of two cylinders. One with 30 cm (external boundary) and one with 0 cm (internal boundary). Thus your source is a cylinder centred on zero and extending on a height of 30 cm (from -15 cm to 15 cm). You can add a second BEAMPOS card to specify the centre of the cylinder (shift it by 15 cm) to have the source extending from 0 – 30 cm.

See slide 8 fpr the cylindrical shell source description.

1 - What are the units on the cb axis for “photon”?

As you are scoring photon fluence, it is photon/cm2 for one Cs-137 isotope decay. (note that it is a 2 D projection averaged over all the z bins). You could multiply by the source activity to have photons/cm2/s.

2 - What are the units on the cb axis for “dose”?

For dose (energy deposited per unit of mass) the unit in FLUKA is expressed in GeV/g (and again this is the average deposited energy for a single decay). You can convert it to Gray (J/kg) and multiply again per the activity to compare with your setup.

3 - How do I calculate the total dose absorbed by the target?

From the existing runs you can have a look at the .out files which have been generated. Look for the summary table for deposited energy (make a query for “All cases handled by Feeder” in the files the table is just after). Then you have for each region the deposited energy. In this case this is GeV/cm3 (but as you are not specifying the volume of the region it is in reality GeV). You need to devide by the weight of material in the region and change the unit to get Gray.

Similar result can be obtained by calculating DOSE with a USRBIN per region (instead of Cartesian based). In this case you can use the different post processing utility to average the results and have the estimate of the statistical uncertainty (transform the averaged file to ascii to read the values).

Cheers
Joachim

From: James Wetzel [mailto:jwwetzel_at_icloud.com]
Sent: 15 August 2016 05:08
To: Joachim Vollaire <joachim.vollaire_at_cern.ch>
Cc: fluka-discuss_at_fluka.org
Subject: Re: [fluka-discuss]: FW: FLUKA

Hi Joachim,

This has been extremely helpful, and I feel like I am almost there.

I tried to figure the following questions out on my own, but couldn’t quite get there.

I’ve attached 4 slides as a PDF showing my results, and my main question deals with interpreting them.

Namely:

1 - What are the units on the cb axis for “photon”?
2 - What are the units on the cb axis for “dose”?
3 - How do I calculate the total dose absorbed by the target?

Thank you very much for all your help so far!!

James

On Aug 12, 2016, at 2:19 AM, Joachim Vollaire <joachim.vollaire_at_cern.ch<mailto:joachim.vollaire_at_cern.ch>> wrote:

Hi
You are missing the following cards for the activation of the decay of the “source” isotope (semi-analogue mode)

And to associate the detectors (two USRBIN) to score from decay particles

DCYSCORE -1.0 0. 0. doses doses USRBIN

DCYSCORE -1.0 0. 0. photon photon USRBIN

It should work adding those cards and you should be able to check that it is consistent with the “mono-energetic” photon source
Cheers
Joachim

From: James Wetzel [mailto:jwwetzel_at_icloud.com]
Sent: 11 August 2016 21:33
To: Joachim Vollaire <joachim.vollaire_at_cern.ch<mailto:joachim.vollaire_at_cern.ch>>
Cc: fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>
Subject: Re: [fluka-discuss]: FW: FLUKA

Alright many thanks for your help this far -

The geometry makes sense and looks good in the viewer without any errors.

I was able to get dose values on a map with the extended source of mono energetic photons, however, when trying to set up the isotope, my plots are empty! And I think there are errors, but I’m not seeing any on the output.

I’ve attached my updated inp file - I assume I am probably initializing the isotope incorrectly.

On Aug 11, 2016, at 1:10 PM, James Wetzel <jwwetzel_at_icloud.com<mailto:jwwetzel_at_icloud.com>> wrote:

Thank you very much!

In this case, the entire radiator is exposed to the scintillator, there is no collimation, which should create a 1/r effect, compared to a 1/r^2 effect, naively, so I think I need to simulate the entire cylinder as being an activated source.

Will this still accomplish that?

On Aug 11, 2016, at 11:56 AM, Joachim Vollaire <joachim.vollaire_at_cern.ch<mailto:joachim.vollaire_at_cern.ch>> wrote:

Hi James

Looking at your input a few things.

The geometry errors:

You define your blakchole external and internal surface with the same sphere radius (use a big number for the blakchole)

SPH blkbody 0.0 0.0 0.0 50.0
* Air sphere
SPH air 0.0 0.0 0.0 50.0

To define the blackbody replace :

BLKBODY 5 +blkbody -(air+Plastic)
By (“Plastic” is already contained inside air…)
BLKBODY 5 +blkbody -air

The error problem should be solved with the above.

For scoring, you can use a region based USRBIN Scoring for DOSE (GeV/g) in the region describing your scintillator.

For accuracy of the results, did you consider simulating the collimation system of the irradiator and a point source and isotropic source inside ? I have no experience with irradiator but I am not sure how you can derive from the source activity the photon fluence out of the collimator. I guess that using only solid angle does not work due to scattering effect ?

For the source description, note that instead of using mono-energetic 667 keV photon you can use an isotope as the source and benefit from the decay data in FLUKA (of interest for more complicated cases and to get accurate branching ratio which for example is not 100 % for decay of Cs-137 in Ba-137m emitting the 661.6 keV gamma…).
To do so look at the course material related to definition of sources slide 21 in the following presentation (don’t forget to activate the decay of the particle by calling the RADDECAY card:

https://indico.cern.ch/event/442634/contributions/1096523/attachments/1186817/1721027/18_Activation_2015.pdf

For normalization, the results (deposited energy) will be by isotope decay so you just need to multiply the results by the source activity ( in Bq)

Cheers
Joachim

From: James Wetzel [mailto:jwwetzel_at_icloud.com]
Sent: 11 August 2016 17:26
To: Joachim Vollaire <joachim.vollaire_at_cern.ch<mailto:joachim.vollaire_at_cern.ch>>
Cc: Giuseppe Battistoni <giuseppe.battistoni_at_mi.infn.it<mailto:giuseppe.battistoni_at_mi.infn.it>>; Paola Sala <Paola.Sala_at_cern.ch<mailto:Paola.Sala_at_cern.ch>>
Subject: Re: FLUKA

Thank you very much!

Attached is my .inp file I am working with.

I have a cylindrical gamma radiator of cesium 137, with dimensions Diameter: 2.54 cm and Length: 30.48 cm, and 6 Ci activity.

I have a sample of plastic scintillator with dimensions 10cm x 10cm x 0.1cm, which is placed a distance 5 cm from the radiator as in the picture below, where the 10x10cm scintillator plane is parallel with the cylinder, and the center of the plastic is aligned with the center of the cylinder, as below:

5cm

Plastic Scint: ———

What I need at the end of the day is the total dose absorbed by the plastic scintillator, in Gy or Mrad.

I am getting Geometry errors (I think), and I’m not sure how to get the dose out properly with scoring.

Thank you very much for your help!

<CS173.inp>

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Received on Mon Aug 15 2016 - 14:17:31 CEST

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