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From: Santana, Mario <msantana_at_SLAC.Stanford.EDU>

Date: Wed, 3 Jul 2013 08:57:32 -0700

Hi,

To what Sunil wrote I will add that, looking at your plots, one would tend to say 0.0003 is the best setting as the results have far less variance, but of course this is achieved at the expense of way more CPU time.

So in order to do a fair comparison of results, instead of plotting the variance as the error bar, you could plot a related number that accounts for the CPU time (e.g. Variance*CPU).

Also bear in mind that if you use a too low value, simulations could crash, and also if you are planning on transporting those neutrons and having them interact with other elements, you could greatly increase the weight dispersion, which can ultimately harm your variance (e.g when computing the total dose).

Mario

From: Sunil C <csunil11_at_gmail.com<mailto:csunil11_at_gmail.com>>

Date: Wednesday, July 3, 2013 2:55 AM

To: fluka-discuss <fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>>

Subject: Re: About LAM-BIAS

Hi

A good approximation for the LAM-BIAS value is the ratio of the photo nuclear (g,n) cross section to the total photon interaction cross section.

For the (g,n) reaction, consider the GDR cross section as it is the dominant mode of photo-neutron production . You can find those numbers in Dietrich, S. S. and B. L. Berman, 'Atlas of photoneutron cross sections obtained with monoenergetic photons.' Atomic Data and Nuclear Data Tables, 38(2), 199-338, (1988). The NIST website allows you to calculate the photon interaction cross section.

Typically the GDR cross section varies from tens to hundreds of mb while the total photon interaction cross section is about a few tens of barns. The ratio will be then 1e-2 to 1e-3, which is similar to what the manual suggests.

Sunil

On Wed, Jul 3, 2013 at 10:35 AM, <pkrai_at_barc.gov.in<mailto:pkrai_at_barc.gov.in>> wrote:

Hi ,

I have run three fresh cases for Photonuclear reaction with hadronic

inelastic interaction length given in LAM-BIAS card ,

1) With No LAM Bias

2) With hadronic inelastic interaction length in LAM Bias=0.03

3) With hadronic inelastic interaction length in LAM BIAS=0.0003

For each case number history taken is 1000000 for 10 number of cycle for

better stastics.

I am attaching usrbdx result of one way scoring of current for three cases.

for case 1) integrated neutron/pr=1.7109856e-5

for case 2) integrated neutron/pr=2.0231091e-5

for case 3) integrated neutron/pr=1.9353341e-5

Result is of the same order, with maximum variation of 15% between result

of NO LAM-BIAS and Result of LAM-BIAS=0.03

I am sending the corresponding FLUKA input file and plots.

Please suggest me how to optimize the value of hadronic inelastic

interaction length to get the result in the energy value given in the

input card?

From,

Pravin Rai

*> Hi
*

*>
*

*> The best to really compare the impact of the value used for the LAMBIAS
*

*> card would be to plot the three curves on the same graph with the error
*

*> bars computed when you are summing the different output files.
*

*> Also it would be good if you could send your input file(s) to see what
*

*> other transport settings you may have use that could have an influence on
*

*> the spectra shape.
*

*> Best regards
*

*> Joachim
*

*>
*

*>
*

*> -----Original Message-----
*

*> From: owner-fluka-discuss_at_mi.infn.it<mailto:owner-fluka-discuss_at_mi.infn.it>
*

*> [mailto:owner-fluka-discuss_at_mi.infn.it<mailto:owner-fluka-discuss_at_mi.infn.it>] On Behalf Of pkrai_at_barc.gov.in<mailto:pkrai_at_barc.gov.in>
*

*> Sent: 21 June 2013 07:13
*

*> To: fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>
*

*> Subject: [Fwd: Re: About LAM-BIAS]
*

*>
*

*>
*

*>
*

*> I have a doubt regarding USRBDX result,
*

*>
*

*> I have run three cases for Photonuclear reaction,
*

*> 1) With No LAM Bias card
*

*> 2) With hadronic inelastic interaction length in LAM Bias card =0.03
*

*> 3) With hadronic inelastic interaction length in LAM Bias card =0.0003
*

*>
*

*> I am attaching usrbdx result of one way scoring of current for three
*

*> cases.
*

*> for case 1) integrated neutron/pr=1.9914856e-5 for case 2) integrated
*

*> neutron/pr=1.9187546e-5 for case 3) integrated neutron/pr=1.9493287e-5
*

*> Approximately similar.
*

*>
*

*> But neutron distribution are totally different for these three cases.
*

*>
*

*> why is the difference? I am sending you three distribution files.
*

*>
*

*>
*

*>
*

*>
*

*>
*

*>
*

*>> The distribution will always be the same. Biasing, if it is done
*

*>> correctly, doesn't change the result but converges faster to it.
*

*>> Your problem is, if you overdo it, you will flood the stack with too
*

*>> many particles and in the end you will not gain in efficiency as you
*

*>> should.
*

*>>
*

*>> But try it, and see what happens!
*

*>>
*

*>> Alberto
*

*>>
*

*>>
*

*>> On Wed, 5 Jun 2013, pkrai_at_barc.gov.in<mailto:pkrai_at_barc.gov.in> wrote:
*

*>>
*

*>>> But in my case photonuclear target is Beryllium.
*

*>>> In this case there is a reaction 9Be(r,n)8Be.The threshold energy for
*

*>>> this photonuclear reaction is 1.666 MeV.And cross-section for this
*

*>>> reaction is
*

*>>> ~2 milibarn in the energy range below 10MeV.
*

*>>>
*

*>>> so If I keep the reduction factor of the hadronic inelastic
*

*>>> interaction length around 0.0003 or 0.03 or 0.0, will the result will
*

*>>> be same or different?(that means I will get same neutron ditribution
*

*>>> or not?)
*

*>>>
*

*>>> Pravin Rai
*

*>>>
*

*>>>
*

*>>>> If the energy of primary electron and photon is about 10 MeV, there
*

*>>>> will be practically no photonuclear interaction! Or very little.
*

*>>>> The threshold is generally close to 8 MeV and even above threshold
*

*>>>> the cross sections are very small. Secondary photons have certainly
*

*>>>> not enough energy to interact.
*

*>>>> Therefore, I don't think that 0.0003 will over predict.
*

*>>>>
*

*>>>> Alberto
*

*>>>>
*

*>>>> On Wed, 5 Jun 2013, pkrai_at_barc.gov.in<mailto:pkrai_at_barc.gov.in> wrote:
*

*>>>>
*

*>>>>>
*

*>>>>>
*

*>>>>> I have a question regarding LAM-BIAS,
*

*>>>>>
*

*>>>>>
*

*>>>>> It is written in the manual that,Biasing of the hadronic inelastic
*

*>>>>> interaction length can be applied also to photons (provided option
*

*>>>>> PHOTONUC is also requested) and For photons, a typical reduction
*

*>>>>> factor of the hadronic inelastic interaction length is the order of
*

*>>>>> 0.01-0.05 for a shower initiated by 1 GeV photons or electrons, and
*

*>>>>> of 0.1-0.5 for one at 10 TeV.
*

*>>>>>
*

*>>>>> But what about if the energy of primary electron and photon is
*

*>>>>> about
*

*>>>>> 10
*

*>>>>> MeV? By what amount I have to keep the reduction factor of the
*

*>>>>> hadronic inelastic interaction length?
*

*>>>>>
*

*>>>>> In my case I have kept it around 0.0003, is it ok? or it will over
*

*>>>>> predict?
*

*>>>>>
*

*>>>>>
*

*>>>>> From,
*

*>>>>> PRAVIN RAI
*

*>>>>
*

*>>>>
*

*>>>
*

*>>>
*

*>>>
*

*>>
*

*>> --
*

*>> Alberto Fass
*

*>>
*

*>
*

Received on Wed Jul 03 2013 - 18:45:44 CEST

Date: Wed, 3 Jul 2013 08:57:32 -0700

Hi,

To what Sunil wrote I will add that, looking at your plots, one would tend to say 0.0003 is the best setting as the results have far less variance, but of course this is achieved at the expense of way more CPU time.

So in order to do a fair comparison of results, instead of plotting the variance as the error bar, you could plot a related number that accounts for the CPU time (e.g. Variance*CPU).

Also bear in mind that if you use a too low value, simulations could crash, and also if you are planning on transporting those neutrons and having them interact with other elements, you could greatly increase the weight dispersion, which can ultimately harm your variance (e.g when computing the total dose).

Mario

From: Sunil C <csunil11_at_gmail.com<mailto:csunil11_at_gmail.com>>

Date: Wednesday, July 3, 2013 2:55 AM

To: fluka-discuss <fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>>

Subject: Re: About LAM-BIAS

Hi

A good approximation for the LAM-BIAS value is the ratio of the photo nuclear (g,n) cross section to the total photon interaction cross section.

For the (g,n) reaction, consider the GDR cross section as it is the dominant mode of photo-neutron production . You can find those numbers in Dietrich, S. S. and B. L. Berman, 'Atlas of photoneutron cross sections obtained with monoenergetic photons.' Atomic Data and Nuclear Data Tables, 38(2), 199-338, (1988). The NIST website allows you to calculate the photon interaction cross section.

Typically the GDR cross section varies from tens to hundreds of mb while the total photon interaction cross section is about a few tens of barns. The ratio will be then 1e-2 to 1e-3, which is similar to what the manual suggests.

Sunil

On Wed, Jul 3, 2013 at 10:35 AM, <pkrai_at_barc.gov.in<mailto:pkrai_at_barc.gov.in>> wrote:

Hi ,

I have run three fresh cases for Photonuclear reaction with hadronic

inelastic interaction length given in LAM-BIAS card ,

1) With No LAM Bias

2) With hadronic inelastic interaction length in LAM Bias=0.03

3) With hadronic inelastic interaction length in LAM BIAS=0.0003

For each case number history taken is 1000000 for 10 number of cycle for

better stastics.

I am attaching usrbdx result of one way scoring of current for three cases.

for case 1) integrated neutron/pr=1.7109856e-5

for case 2) integrated neutron/pr=2.0231091e-5

for case 3) integrated neutron/pr=1.9353341e-5

Result is of the same order, with maximum variation of 15% between result

of NO LAM-BIAS and Result of LAM-BIAS=0.03

I am sending the corresponding FLUKA input file and plots.

Please suggest me how to optimize the value of hadronic inelastic

interaction length to get the result in the energy value given in the

input card?

From,

Pravin Rai

Received on Wed Jul 03 2013 - 18:45:44 CEST

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