From: Joachim Vollaire <joachim.vollaire_at_cern.ch>

Date: Mon, 6 Dec 2010 14:19:25 +0000

Date: Mon, 6 Dec 2010 14:19:25 +0000

Dear Beatrice,

Here are a few comments on your questions which I hope will help you in

your study.

Cordially

Joachim

Question 1 :

- "To see if neutrons are actually

produced I used a USBRDX card to get the neutron

spectrum out of the target; I saw from the

output file that the number of stars per proton

is nearly 6E-2 and the 95% is reached in terms

of percentage. Can this confirm that the numbers of primaries is enough?"

To verify if the number of primary transported is sufficient check the

quantity of interest you are scoring. If the statistical error is less

than 10 % the result can be considered as reliable (less than 5 % is

better). For a spectrum you will have bins we higher errors but you can

look at the integrated value to have an idea of the quality of the

result. I also suggest to use rather 5 independent runs (minimum)

instead of 3.

Question 2

- "What is a reasonable standard deviations

for the results (readable from the usrbin and

usrbdx files produced after prcessing)?"

Same as above (Question 1), quoting the MCNP manual, results are

doubtful above 20 % error and meaningless above 50 %. 10 % results start

to be reliable 5 % is better of course…. For USRBIN/USRBDX this of

course concerns your region/bins of interest…

Question 3

- "For USRBIN fluence graph I normalized

by 1,87*10**15 p/s (being the proton beam

300microA) to get results in terms of n/(cm2

s); For USRBIN energy deposition graph should I

use the same factor 1,87*10**15 p/s to get

results in terms of GeV/(cm3 s)? If I need

deposition on an unit area (per cm2) should I multiply for which length?

For the same graph if I want to convert GeV/(cm3s) into °C/s

I need to divide by 6,27*10**9 (from MeV to W) to divide by concrete density

(2,33g/cm3) and concrete conductivity (0,949 J/(g °C)) and to multiply

by 1,87*10**15 p/s.

This way I obtain 1,35 °C/s. If I consider the target will work

5000hours per year I get 2E7°C.

Is it possible to have such a thermal incre from ambient temperature due

to radiation?"

I think there is a mistake in your conversion, 300 microA should be

1.87e12 and not 1.87e15 ? It should make other results more reasonable…

Question 4

"As for the USRBDX graph how do I read the y axis of the plot, the x

axis being [GeV], if I choose as USRBDX Type: phi1,LogE,LinOmega that is:

fluence scoring, one way scoring, logarithmic in energy, linear in

angle? For my specific case

how should I normalize it?"

You should normalize using the factor corresponding to 300 microA

(1.87e12 proton per sec) to obtain the results in cm-2/s-1…. Note that

this is only true if you input the surface between the two areas in your

one way scoring (otherwise there is a factor equal to the surface)….

"Is it correct to say the spectrum is a typical fission spectrum?"

Hard to tell from the plot, if the maximum is in the 1 MeV range and the

average in the 2 MeV range I would say yes it has the characteristics of

a fast neutron induced fission spectrum…..

"I plotted a 1D graph of neutrons flux density through the thickness

(n/(cm2 s) vs cm): are

error bars acceptable? Can I catch the thermal and the fast neutron

behavior separately within the same graph.

And can I superpose similar 1-D graphs from different shielding material

(i.e. different input files)?"

You can do this with flair when selecting the file from which you take

the 1-D plot… Just browse to the folder where you have the files you are

interested in….

- "In order to see fluences in all the shielding I have further applied

biasing;

order not to complicate geometry I have biased

with the usrbin.f subroutine I provide in attachment; however as you can

see from graphics

I did not better so much my analysis (just to clear, I applied two

different resolutions fo

the scoring: 5cm for biasing and 10cm for not biasing).

Is the biasing correct?"

As a beginner I would suggest splitting your geometry even if it adds

some complication and using region based biasing to really see the gain….

From: beatrice pomaro

Date: Wed, 17 Nov 2010 08:48:08 +0100

Dear Fluka users,

thank you for the previous reply on USRBIN

processing, I cope with the problem; I forgot

to mention I am using the 2010 pre-release 0.8-4.

I would be grateful to have a check of my

analysis with you, since I am a Fluka

beginner. My problem/input file is in

attachment (inside the folder: 1E7 biasing). I

have some questions on my results (I give in

attachment also the USRBIN and USBRDX scores

for 1E7 ran particles with and without biasing applied).

My geometry is quite simple: a target made of

UC2 directly impinged by a proton beam

(300microA, 70MeV), within a concrete target bunker.

I am interested in the neutron fluence in the shielding.

I ran 1E7 particles and 3 cycles. I have some

specific questions I have tried to list here below:

- To see if neutrons are actually

produced I used a USBRDX card to get the neutron

spectrum out of the target; I saw from the

output file that the number of stars per proton

is nearly 6E-2 and the 95% is reached in terms

of percentage. Can this confirm that the numbers of primaries is enough?

- What is a reasonable standard deviations

for the results (readable from the usrbin and

usrbdx files produced after prcessing)?

- For USRBIN fluence graph I normalized

by 1,87*10**15 p/s (being the proton beam

300microA) to get results in terms of n/(cm2

s); For USRBIN energy deposition graph should I

use the same factor 1,87*10**15 p/s to get

results in terms of GeV/(cm3 s)? If I need

deposition on an unit area (per cm2) should I multiply for which length?

For the same graph if I want to convert GeV/(cm3

s) into °C/s I need to divide by 6,27*10**9

(from MeV to W) to divide by concrete density

(2,33g/cm3) and concrete conductivity (0,949

J/(g °C)) and to multiply by 1,87*10**15 p/s.

This way I obtain 1,35 °C/s. If I consider the

target will work 5000hours per year I get 2E7°C.

Is it possible to have such a thermal incre

from ambient temperature due to radiation?

As for the USRBDX graph how do I read the y axis

of the plot, the x axis being [GeV], if I choose

as USRBDX Type: phi1,LogE,LinOmega that is:

fluence scoring, one way scoring, logarithmic in

energy, linear in angle? For my specific case

how should I normalize it? Is it correct to say

the spectrum is a typical fission spectrum? I

plotted a 1D graph of neutrons flux density

through the thickness (n/(cm2 s) vs cm): are

error bars acceptable? Can I catch the thermal

and the fast neutron behavior separately within the same graph.

And can I superpose similar 1-D graphs from

different shielding material (i.e. different input files)?

- In order to see fluences in all the

shielding I have further applied biasing;

order not to complicate geometry I have biased

with the usrbin.f subroutine I provide in

attachment; however as you can see from graphics

I did not better so much my analysis (just to

clear, I applied two different resolutions fo

the scoring: 5cm for biasing and 10cm for not biasing).

Is the biasing correct?

I am sorry if my questions are many or can

result trivial: I tried to put all in one mail.

I thank you in advance for a kind reply by your side,

Yours sincerely,

Beatrice Pomaro

Received on Mon Dec 06 2010 - 16:24:49 CET

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