Re: Understanding EMF-CUT and residual dose rate

Dear Stefan,

Thank you for this information which has helped me investigate this puzzle
but I am still having difficulty understanding what is exactly going on
with the EMFCUT for gammas and e+/e- and I would appreciate if someone
could help clarify this.

I have run three sets of runs for a given setup (only varying EMFCUT). I
had run two before your message and I ran one after your message and
reading the EMFCUT and DEFAULTS part of the manual few times, trying to
understand.

Please note in all of these tries I used NEW-DEFAults.

The relevant EMF default cuts here are:
- Particle transport threshold set at 10 MeV
- Delta ray production on with threshold 1 MeV

1st try:
========
EMFCUT card:
EMFCUT 2.0000E-05 2.0000E-05 0.000 0.000 0.000 0.000

Here I am only setting the transport energy cut-off for gammas and e+/e-
(total energy) here but since I did not defined any region, no cut should
have been applied. I had assumed the default behaviour for no region
selected would be (from 1st to last region but I was wrong). But even the
default behaviour in flair for starting and ending regions does not work.

Looking at the output and searching for the Ecut and Pcut for the 11
regions defined, I see:

Ecut = 1.5110E+00 MeV, Pcut = 3.3333E-01 MeV, BIAS = T, Ray. = F,
S(q,Z) = T, Pz(q,Z) = F

===> For all regions, with the exception of BLKHOLE and VACUUM, Ecut is
set to 1.511 MeV (Total E) and 0.33333 MeV for gammas.

Where is the 1 MeV cut for e+/e- and 333.33 keV for gammas coming from???

2nd try:
========
EMFCUT card:
EMFCUT 2.0000E-05 2.0000E-05 0.000 3.000 11.00 0.000

Here I am again only setting the transport energy cut-off for gammas and
e+/e- (total energy) for the regions of interest. So the EMFCUT of 20 keV
should have been applied to e+/e- and gammas. But did it?

Ecut = 1.5110E+00 MeV, Pcut = 2.0000E-02 MeV, BIAS = T, Ray. = F,
S(q,Z) = T, Pz(q,Z) = F

===> Aside from the VACUUM regions, I see that a 20 keV cut is applied to
gammas but no cut is applied to e+/e-.

After re-reading the manual under the EMFCUT, under NOTE 2, I see:

"When instead the transport cutoffs are lower than the production ones,
they are increased to be equal to them."

So I thought, the default production threshold for e+/e- must be set to
higher (1 MeV) and that is why I am seeing this behaviour. Is this from
the DETLA-RAY production threshold from NEW-DEFAults? Then why is the
gamma production threshold not set to 10 MeV?

3rd try:
========
EMFCUT cards:

EMFCUT 2.0000E-05 2.0000E-05 0.000 3.000 710.0 0.000 PROD-CUT
EMFCUT 2.0000E-05 2.0000E-05 0.000 3.000 11.00 0.000

Here I am setting both the transport and production thresholds for gammas
and e+/e- (total energy). So in principle the EMFCUT of 20 keV should now
be definitely be applied to e+/e- and gammas. Did it?

Ecut = 5.1200E-01 MeV, Pcut = 2.0000E-02 MeV, BIAS = T, Ray. = F,
S(q,Z) = T, Pz(q,Z) = F

Now, I see a total energy cut of 0.512 MeV for e+/e- and 20 keV for
photons which sounds about right.

In summary: Ecut (MeV) Pcut (MeV)

1st try 1.5110E+00 3.3333E-01 No
EMFCUT (effectively)

2nd try
EMFCUT (20 keV transport for e+/e- & g) 1.5110E+00 2.0000E-02

3rd try
EMFCUT (20 keV tran. & prod. for e+/e- & g) 5.1200E-01 2.0000E-02

It is clear that setting the production cut for both e+/e- is essential if
the transport cuts are lower than the production cuts. But this is not
the case for gammas.

It is not clear to me where the default production cut for gammas
(3.3333e-1 MeV) comes. In NEW-DEFAults, the default transport cut is set
to 10 MeV. As I understand it, this cut applies to all particles, unless
changed via EMFCUT card for e+/e-, and gammas and via LOW-NEUT card for
neutrons.

At the end of the day, the difference between the 3rd and 1st try in terms
of dose rates 5 years after EOB is about 9% increase for the 3rd try
(which is not much).

Thank you and best wishes,
Mina

> Dear Mina
>
> 1) Please see the manual under EMFCUT Notes 1) and 2) which give some hint
> on the default settings. As Note 2) explains the actual settings can be found in the output file (search for 'Ecut' and 'Pcut').
>
> 2) Yes any modification factors defined with RADDECAY/WHAT(5) apply to the
> EMFCUT settings.
>
> Cheers
> Stefan
>
>
> Re: Understanding EMF-CUT and residual dose rate
> * This message: [ Message body ] [ More options ]
> * Related messages: [ Next message ] [ Previous message ] [ In reply to
]
> From: Mina Nozar <nozarm_at_triumf.ca>
> Date: Tue, 13 Mar 2012 11:58:12 -0700
> I just realized I attached the wrong file with this message. Here is the correct plot showing residual dose rates for
> six targets (separate runs and fluka setups) as a function of time in a cylindrical detector a meter away from the beam
> line. When comparing does rates for a given target at a given cooling time
> (1.2 years after EOB), we are seeing a
> factor of 2 less in dose rates from FLUKA than those measured at the same
> time. I am still trying to figure out why
> this is.
> I have tested few other runs where I don't include an EMFCUT card. The results are the same as the time when I did not
> specify a region for the 20 keV transport card. Confirming this by looking
> at the echoed input in the output files,
> this means the default behaviour as stated in the manual is not correct:
> WHAT(4) = lower bound (or corresponding name) of the region indices with
> electron cutoff equal to |WHAT(1)|
> and/or photon cutoff equal
> to WHAT(2) and/or leading particle biasing
> ("From region WHAT(4)...") Default: = 2.0.
> i.e. not defining any lower and upper bound regions for transport energy cut-offs in the EMFCUT card, does not set the
> lower and upper bound regions to the 2nd region in the drop down menu (on
> the list of Regions) and the EMFCUT is simply
> not applied.
> What I still do not understand are:
> 1) How are the default decay and prompt transport energy cut-offs determined if one does not use an EMFCUT card. My
> results show that the default energy cut-off does not come from PART-THRES
> (10 MeV) in NEW-DEFA.
> and
> 2) Do the decay and prompt cuts in RADDECAY card use the transport cut as
> defined in the EMFCUT card?
> I would appreciate if one of the FLUKA gurus could shed some light on this.
> Thanks again,
> Mina
>
>
Received on Wed Mar 28 2012 - 23:08:41 CEST