Dear Francesco,
You are right, I am not interested in the lower energy part of the
spectrum. From what you and Anna are saying is that the shape of the
distribution below the threshold is artificial and is not to be pondered on.
Thank you and best wishes,
Mina
On 15-02-26 07:14 AM, Francesco Cerutti wrote:
>
> Dear Mina,
>
> by definition of threshold, the spectrum below threshold is
> meaningless. What you see there is a combination of different effects.
> First, the ranging out mentioned by Anna: a proton reaching the 10 MeV
> threshold is granted a last step bringing it to rest. In differential
> fluence scoring, this is in principle attributed to a 5 MeV proton
> (half of the energy at the beginning of the step). However, in case
> this last step crosses region boundaries, you will see in the spectrum
> a corresponding number of contributions at different energies,
> assuming a constant energy loss over the step (hence the crudity of
> ranging out, which nevertheless assures a good estimation of the
> residual range, i.e. of the last step length). Things are then smeared
> by Landau fluctuations, making not all protons to reach the threshold
> and the ranging out treatment exactly at 10 MeV.
> On top of that, you have evaporation protons generated below threshold
> by nuclear reactions and then ranged out. As well as, in case of
> hydrogen presence, recoil protons generated below threshold by low
> energy neutrons.
>
> In conclusion, if you are really interested in that part of the
> spectrum (I guess not) and yours is not just curiosity about its
> puzzling shape, you have to lower the threshold accordingly.
>
> Kind regards
>
> Francesco
>
> **************************************************
> Francesco Cerutti
> CERN-EN/STI
> CH-1211 Geneva 23
> Switzerland
> tel. ++41 22 7678962
> fax ++41 22 7668854
>
> On Tue, 24 Feb 2015, Mina Nozar wrote:
>
>> Dear Anna,
>>
>> Thank you for the explanation. I now understand that the protons are
>> ranged out; however, I don't understand the shape of the spectrum. I
>> would have expected a gradual drop off of the protons with decrease
>> in energy but what I see is a drop at 10 MeV, then a rise, a bit of a
>> plateau, then a sharp drop off at 1 MeV.
>>
>> What is responsible for the observed distribution?
>>
>> Thank you and best wishes,
>> Mina
>>
>> On 15-02-21 10:28 AM, Anna Ferrari wrote:
>>> Dear Mina,
>>>
>>> in FLUKA setting a threshold for heavy charged particles does not mean
>>> that you stop the transport, but that you stop the very refined
>>> transport:
>>> below the threshold the transport is more crude, but whatever the
>>> threshold is heavy charged particles are ranged out to rest.
>>> An exception is if the energy cutoff has been set by the user > 100
>>> MeV.
>>> As you know, the situation is different for electrons/positrons:
>>> ranging
>>> out is not done, mainly because it is difficult to define with
>>> precision a
>>> residual range (you can see
>>> http://www.fluka.org/web_archive/earchive/prova/1305.html )
>>>
>>> Greetings!
>>> Anna
>>>
>>> Am Thu, 19 Feb 2015 12:56:05 -0800 schrieb Mina Nozar
>>> <nozarm_at_triumf.ca>:
>>> > Hello everyone,
>>> > > I just did a quick study, looking at the energy/power
>>> deposition in an > Al flange, enclosing an Indium seal. The flange
>>> sits upstream of a Be > target (at a 45 deg angle and a distance of
>>> 45 cm from the target). The > target is bombarded by 480 MeV proton
>>> beam.
>>> > > I chose NEW_DEFA as the defaults (so a PART-THR of 10 MeV for
>>> protons). > I did not lower this threshold using PART-THR card.
>>> When I look at the > particle fluences in the Al flange (beam
>>> particles, protons, and > neutrons), I see protons down to 1 MeV
>>> energies and I am wondering why. > It is like seeing a second set
>>> of data from 10 to 100 MeV.
>>> > > Please see the image enclosed.
>>> > > Thank you very much for helping me understand what is going on.
>>> > > Best wishes,
>>> > Mina
>>> > > > >
>>> ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
>>> ~ ~ ~ ~ ~ ~ ~ ~
>>> Dr. Anna Ferrari
>>> Institute of Radiation Physics
>>> Helmholtz-Zentrum Dresden-Rossendorf e.V.
>>> Tel. +49 351 260 2872
>>> a.ferrari_at_hzdr.de
>>> http://www.hzdr.de
>>>
>>> Vorstand: Prof. Dr. Dr. h. c. Roland Sauerbrey, Prof. Dr. Dr. h. c.
>>> Peter
>>> Joehnk
>>> Vereinsregister: VR 1693 beim Amtsgericht Dresden
>>>
>>> __________________________________________________________________________
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>>
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Received on Fri Feb 27 2015 - 04:40:41 CET