# Meaning of Negative Numbers For Generalised Particles

Dear FLUKA experts,

I hope you are all well. I am running a simple simulation with He ions in water in order to see what type of particles deposit energy before the Bragg peak. For that matter, I used a comscw.f subroutine (because I intend to modify the output later depending on the particle) to score in an external file “data.txt” the particles that are scoring energy except for the primary He particles and protons (please find attached the simulation files).

Everything works fine and I obtain the following types of particles:
[-38., -8., -7., -5., -4., -3., -2.])

• -3 to -5 can be found in The official FLUKA site: FLUKA Online Manual.
• -2 is a heavy ion, but is there any way to find what type it is? Maybe scoring its charge or other properties?
• -7 and -8 are fission fragments but I do not know of what kind.
• -38, I do not know what it represents, so it would be great if anyone could shed some light on it.

It would also be great if someone could explain what each negative JTRACK below -8 means.

Best wishes,
Daniel

let.inp (2.3 KB)
comscw.f (1.3 KB)

Hi Daniel,
`JTRACK = -2 ` refers indeed to a transported ion heavier than an alpha particle. Its actual identity is given runtime by IBARCH(JTRACK) and ICHRGE(JTRACK), namely its number of nucleons and protons, respectively.
`JTRACK = -7, -8, ..., -12` are again ions heavier than alphas, being transported below threshold, whose identity - as in the previous case - is not associated to the JTRACK value, rather to IBHEAV(-JTRACK) and ICHEAV(-JTRACK), which are the equivalent of the above variables. In your case, they are not produced by fission, rather fragmentation (Fermi break-up).
`JTRACK = -38` is a (more exotic) label to identify once more an ion heavier than alphas that was involved in an electromagnetic dissociation event, as emitting a virtual photon absorbed by the reaction partner. In your case, it can be for instance a 16O nucleus interacting with a secondary deuteron (that is going to break as a result of the virtual photon absorption) and thereby recoiling at low energy. The ion properties are in IBHEAV(-JTRACK) and ICHEAV(-JTRACK) as well.
Last, for the sake of consistency, please refer to the manual distributed with the code (doc/fluka.manual), accessible via Flair pressing F1, or its online version freshly renovated for your convenience (and welcome feedback).

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Dear @ceruttif,

• Are there more exotic particles like JTRACK = -38? If so, could you tell me where to find a list with them in case I need them in newer simulations? I could not find such a list in the manual myself.

• Just to confirm, for each particle in the simulation, only one JTRACK is recorded, right? For example, you would not find that the same particle records JTRACK = -2 and -38 during the simulation because it is a heavy ion and takes part in an electromagnetic dissociation event.

Best wishes,
Daniel

• While the JTRACK value directly corresponds to the particle identity if >= -6, as documented (with the notable exception of -2, which does not give you the exact identity of the particle, retrievable instead in real time from IBARCH(-2) and ICHRGE(-2)), lower values have no deep meaning and are just a link to IBHEAV(-JTRACK) and ICHEAV(-JTRACK). So you should just refer to the latter variables in order to figure out which particle is. In other words, JTRACK = 1 is always a proton, JTRACK = -6 is always an alpha particle, but JTRACK = -7 changes its actual identity in the course of the simulation. In this sense, the list you invoke is ill-defined.

yes

No, you wouldn’t.

Dear @ceruttif,

Thank you very much for your response. That makes sense but what I meant was that if there was a list outlining what each negative JTRACK meant below -8, just like JTRACK = -38 means ion involved in an electromagnetic dissociation, maybe let’s say JTRACK = -24 means ion involved in some other process.

Best wishes,
Daniel

Normally you may find numbers in the -7 to -12 interval, where any value shares the same meaning, echoing the corresponding (positive) range indicated in fheavy.inc. The -38 case was the indicated exception.

Dear @ceruttif,

I see, thank you very much for all your help!

Best wishes,
Daniel