Re: Secondary Alpha and Recoil Nuclei

Fawaz, it is for you to see what is what you want and what'a not. Lots
have been said about not seeing; a simple demo takes only a few minutes.
One single history is sufficient. Here is what I see from a single 40 eV
(low enough?) neutron bombarding PMMA:

- C-13 and O-17 (RESNUCLEi and mgdraw consistently confirming each
other);

- DETECT and USRBIN in mutual agreement (also in exact agreement with
mgdraw).

Transport would be an issue for fluence scoring. DETECT, USRBIN and
RESNUCLEi, however, do not require transport in order to score.
Transported or not, the energy is always deposited.

If you are looking at the pulse height spectra in a TEPC, please check the
validity of the kerma approximation for your application, whether there is
enough material to avoid the single-collision scenario, either rule in or
rule out the known artefact explained in:

http://www.fluka.org/web_archive/earchive/new-fluka-discuss/4472.html

:) mary signing off from this thread

On Fri, 18 May 2012, Alberto Fasso' wrote:

> On Fri, 18 May 2012, Fawaz Ali wrote:
>
>> Thanks Alberto. Just to clarify, I am irradiating my target with 14.8 MeV
>> neutrons. Will the DETECT card be able to score the kinetic energy
>> deposited by the recoil Carbon, Oxygen, and Nitrogen recoil nuclei produced
>> by these incident 14.8 MeV neutrons?
>
> No. The only explicit recoils from neutrons with energies < 20 MeV are
> protons.
>
> Alberto
>
>>
>>
>> On 5/18/12 9:05 AM, Alberto Fasso' wrote:
>>> Dear Fawaz,
>>>
>>> I copy here Section 10.3.3 of the manual:
>>>
>>> 10.3.3} Generation of charged particles
>>> Recoil protons and protons from N(n,p) reaction are produced and
>>> transported explicitly, taking into account the detailed kinematics
>>> of elastic scattering, continuous energy loss with energy straggling,
>>> delta ray production, multiple and single scattering.
>>>
>>> The same applies to light fragments (alpha,3-H) from neutron
>>> capture in 6-Li and 10-B, if pointwise transport has been
>>> requested by the user. All other charged secondaries, including
>>> fission fragments, are not transported but their energy is deposited
>>> at the point of interaction (kerma approximation).
>>>
>>> As you can see from the last sentence, Carbon, Oxygen, and Nitrogen
>>> recoils
>>> produced by neutrons with energies < 20 MeV are not transported. Their
>>> energy,
>>> deposited in the kerma approximation, cannot be attributed to a particular
>>> individual nucleus. Those recoils also cannot be "seen" by the mgdraw
>>> routine.
>>> On the other hand, Carbon, Oxygen, and Nitrogen ions produced by particles
>>> with energy > 20 MeV, will be transported, scored by DETECT, and can be
>>> "seen" by mgdraw, provided you asked for ion transport with the IONTRANS
>>> card.
>>>
>>> Alberto
>>>
>>>
>>> On Thu, 17 May 2012, Fawaz Ali wrote:
>>>
>>>> Hi Mary,
>>>>
>>>> Thanks for your response. I am doing microdosimetry simulations in FLUKA
>>>> (simulating the response of a Tissue Equivalent Proportional Counter to
>>>> low
>>>> energy neutron irradiation) and generally, the following is observed in
>>>> the
>>>> pulse height spectrum:
>>>>
>>>> - Protons produced by neutron elastic scatter with H-1 and by 14N(n,p)
>>>> deposit
>>>> roughly between 13 - 133 keV of kinetic energy
>>>>
>>>> - Alphas produced by fast neutron capture with C-12, O-16, and N-14
>>>> deposit
>>>> between 133 - 667 keV of kinetic energy
>>>>
>>>> - Carbon, Oxygen, and Nitrogen recoil nuclei deposit 667 - 1333 keV of
>>>> kinetic
>>>> energy
>>>>
>>>> In the pulse height spectrum I obtained from the DETECT card, I only see
>>>> the
>>>> proton region populated (i.e. counts are present between the 13 - 133 keV
>>>> span). However, no counts have been registered in the energy spans
>>>> pertaining
>>>> to alpha and heavy recoil nuclei energy deposition. I will certainly
>>>> have a
>>>> look at USRBIN and RESNUCLEi to see if I can score the kinetic energy
>>>> deposited by these particles in the sensitive volume of the counter.
>>>>
>>>> Thanks,
>>>> Fawaz
>>>>
>>>>
>>>> On 5/17/12 3:03 PM, Mary Chin wrote:
>>>>> Hello Fawaz,
>>>>>
>>>>>> Is this because FLUKA does not transport these particles?
>>>>>
>>>>> *I assume you mean heavy ions. FLUKA does transport them if the user:
>>>>> - requests so via the IONTRANS card; or
>>>>> - asks for an ion beam.
>>>>>
>>>>>> Is this because ...
>>>>>
>>>>> *No. Even without ion transport activated, ions are ranged out and the
>>>>> energy IS always deposited.
>>>>>
>>>>>> I am applying the DETECT card
>>>>>> I am seeing the protons but I am not seeing the alpha and C, O, N
>>>>>
>>>>> *How do you "see protons but not alphas, C, O, N" in the DETECT output?
>>>>>
>>>>> Residual nuclei are typically scored using the RESNUCLEi card.
>>>>>
>>>>> Energy deposition can be scored not only using DETECT but also USRBIN.
>>>>> DETECT is for (anti-)coincidence, trigger and/or pulse-height spectrum
>>>>> (i.e. multiple energy depositions resulting from the same primary are
>>>>> summed as one count). USRBIN is generally more versatile.
>>>>>
>>>>> If you really need to see each recoil in action, then mgdraw would be
>>>>> the
>>>>> user routine to go for.
>>>>>
>>>>> :) mary
>>>>>
>>>>> On Thu, 17 May 2012, Fawaz Ali wrote:
>>>>>
>>>>>> Hello Everyone,
>>>>>>
>>>>>> I am performing a simulation whereby low energy neutrons (with kinetic
>>>>>> energy on the order of keV) are irradiating a target. I am applying
>>>>>> the
>>>>>> DETECT card to the sensitive volume of the target and I am expecting to
>>>>>> see the following secondary particles which will contribute to the
>>>>>> counts vs. energy deposited spectrum: protons, alpha, and recoil
>>>>>> Carbon,
>>>>>> Oxygen, and Nitrogen nuclei (note that I have set their respective
>>>>>> transport thresholds down to 1 keV). I am seeing the protons but I am
>>>>>> not seeing the alpha and C, O, N recoil nuclei. Is this because FLUKA
>>>>>> does not transport these particles? Would I have to go into the
>>>>>> USERDUMP tape to find the kinetic energy they deposit in the sensitive
>>>>>> volume?
>>>>>>
>>>>>> I appreciate any help that can be provided.
>>>>>>
>>>>>> Thanks,
>>>>>> Fawaz
>>>>>>
>>>>>>
>>>>
>>>>
>>>
>>> --
>>> Alberto Fasso`
>>> SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
>>> Phone: (1 650) 926 4762 Fax: (1 650) 926 3569
>>> fasso_at_slac.stanford.edu
>>>
>>
>>
>
> --
> Alberto Fasso`
> SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
> Phone: (1 650) 926 4762 Fax: (1 650) 926 3569
> fasso_at_slac.stanford.edu
>
Received on Fri May 18 2012 - 22:03:40 CEST