RE: [fluka-discuss]: Increase in Dose Equivalence after Shielding

From: Tshepo Mahafa <Tshepo.Mahafa_at_necsa.co.za>
Date: Fri, 29 Oct 2021 11:18:23 +0000

Dear Alfredo,

I did what you had suggested by extending my USRBIN backwards, but I could still see an increase in Dose after the shielding.
Things worked out when I also increased the roof size and put a floor and the backwall.
Here find attached the input and the USRBIN 2D plot.

One thing I still need to find out though is if FLUKA can simulate cold neutrons from 0 - 0.025 eV's?

Thanks for your help

Regards

Tshepo

-----Original Message-----
From: alfredo.ferrari_at_mi.infn.it [mailto:alfredo.ferrari_at_mi.infn.it]
Sent: 20 October 2021 06:52 PM
To: Tshepo Mahafa
Cc: fluka-discuss_at_fluka.org
Subject: Re: [fluka-discuss]: Increase in Dose Equivalence after Shielding

Dear Tshepo

I would bet that the increase of the dose after the shielding is due to
neutrons travelling in the air aside the shielding. If I understand
correctly, you start your beam at Z=-100 in air, with air extending more
or less ten metres on all sides. The lateral shielding instead starts at
Z=0 and th beam does not impact onto the frontal part of the shielding
until Z~200 cm. Therefore a fraction, even small, of neutrons can easily
diffuse into the air and, travelling laterally, go around the shielding.

If you look at your 2D plots you can see a hint of that looking at the
colors just outside the shielding around Z=0.

You can prove this hypothesis in two different ways:

a) extend your usrbin backwards (for Z<0) and laterally, and look athe
dose patterns, or the neutron fluence
b) move the source at Z=+1 and put blackhole everywhere for Z<0

Let me know if I am right!

Alfredo


> Dear Fluka Experts and Users,
>
>
> I performed some shielding simulations where I observed from the results
> that the dose equivalent after the shielding increases in the room as
> shown in the attached Figures of 2D and 1D USRBIN plots of Dose
> Equivalence.
> In the simulation, I have three materials (Borated Polyethylene (BPE),
> Concrete (Conc), and Lead (Pb)) used to shield 100 keV neutrons at a flux
> of 3.28e8 n/cm2/sec
> In the one instance the shielding is made up of BPE-Conc-Pb and the other
> made up of BPE-Conc-BPE. The increase is seen in both configurations.
> I also ran the same simulations using 10 MeV neutron beam for the two
> configurations above and still observe the same dose increase after the
> shielding.
> What could be the cause of this increase in dose equivalence after the
> shield?
> Could it be the interaction with air particles in the room after the
> shielding that cause this increase?
>
> Can somebody please check if there is something I am missing.
>
> I’ll greatly appreciate your help.
>
>
>
>
> Warmest Regards
>
> Tshepo Mahafa
>
> [cid:image5cf523.JPG_at_68d4d6d6.418466c8]<http://www.necsa.co.za>
> Tshepo Mahafa
>
>
>
> Tel: PO BOX 582
> Mobile: SOUTH AFRICA
> Email: Tshepo.Mahafa_at_necsa.co.za Web:
> www.necsa.co.za<http://www.necsa.co.za>
>
>
> [cid:imagef7dcbc.JPG_at_b6c60c85.49ac1e06]<http://>
> ________________________________
> This message contains confidential information and is intended only for
> the individual named. If you are not the named addressee you should not
> disseminate, distribute or copy this e-mail. Please notify the sender
> immediately by e-mail if you have received this e-mail by mistake and
> delete this e-mail from your system. E-mail transmission cannot be
> guaranteed to be secure or error-free as information could be intercepted,
> corrupted, lost, destroyed, arrive late or incomplete, or contain viruses.
> The sender therefore does not accept liability for any errors or omissions
> in the contents of this message, which arise as a result of e-mail
> transmission. If verification is required please request a hard-copy
> version from NECSA.
>
>
>
>
> #####################################################################################
> Scanned by MailMarshal - Trustwave's comprehensive email content security
> solution.
> Download a free evaluation of MailMarshal at www.trustwave.com
> #####################################################################################
>



#####################################################################################
Scanned by MailMarshal - Trustwave's comprehensive email content security solution.
Download a free evaluation of MailMarshal at www.trustwave.com
#####################################################################################


__________________________________________________________________________
You can manage unsubscription from this mailing list at https://www.fluka.org/fluka.php?id=acc_info

TopView_TotalDoseEq_FastNeutrons_B.png
(image/png attachment: TopView_TotalDoseEq_FastNeutrons_B.png)

1D_DepthView_TotalDoseEq_FastNeutrons_B.png
(image/png attachment: 1D_DepthView_TotalDoseEq_FastNeutrons_B.png)

Received on Fri Oct 29 2021 - 15:45:17 CEST

This archive was generated by hypermail 2.3.0 : Fri Oct 29 2021 - 15:45:26 CEST