Re: Secondary Alpha and Recoil Nuclei

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