Short lived nuclei's deexcitation is not included in "G4DecayTable"?

Physics Processes, Models and Cross Sections
#1

I am trying to use the G4DecayTable instances of radioactive nuclei to find out what decay products are created in a nuclear decay.

For most unstable nuclei it works perfectly. Although when I ask for the daughters of excited nuclei, like Rh101[181.780], the G4DecayTable belonging to Rh101[181.780] returns only Rh101 as a decay product.

The problem is that when I let Geant4 to do all the decays from Rh101[181.780], Rh101[157.320] is also created. This Rh101[157.320] is an isomer with a very long half-life.

What am I missing? Is there a different class similar to “G4DecayTable” belonging to the decay products of short lived isomers?

#2

G4RadioactiveDecay process uses RadioactiveDecay and PhotonEvaporation data set. I hope Dennis Wright or Laurent Desorgher can explain you how this process works.
In file RadioactiveDecay5.4/z45.a101 you will see that metastable Rh101[157.32] is quoted with all its decay channels.
Below a macro for example rdecay01 to illustrate decay of Rh101[181.78]
Rh101.mac.txt (167 Bytes)

#3

You are right, I can see the Rh101[157.32] state in the RadioactiveDecay5.4/z45.a101 file. To be more specific what I would like to do is to get all decay channels of Rh101[181.780] including the branching ratios of the decay channels.

But when I call G4RadioactiveDecay->GetDecayTable( Definition Of Rh101[181.780] )->GetDecayChannel(i) it only returns the ground state of Rh101 as a daughter with a branching ratio of 100%. Although the decay channel with Rh101[157.32] as a daughter should be among the decay channels.

My guess is that there is some other way I can get decay channels belonging to very short lived excitation states like for Rh101[181.780] which is not included in the default G4DecayTable.

#4

The full details of nuclear structure and energy levels are not treated in Geant4, mostly because they aren’t well settled in the literature (you’d have to pick a model, plus its parameters, and know which isotopes it may or may not apply, etc.).

Below a minimum lifetime (it looks like 1442.7 ns, accord to the RDM and PreCompound info dumps), isomers aren’t treated as “states” as such. Rather the excited nucleus is “relaxed” with continuous gamma emission, or even evaporation of nucleons if the excitation is high enough.

If there is a long lived isomeric state, the relaxation will stop at that state, and it’ll get handed off to RadioactiveDecay for handling. That sounds like what you’re seeing here.

#5

So Rh101[181.780] is not treated as a “nuclear decay state”. I understand that the decay scheme of such very very short lived excited states is not well understood, that is why I guess these excitation are not included in the G4DecayTables.

Somehow though Geant4 calculates the “branching ratio” of the discrete de-excitation of Rh101[181.780] to the state Rh101[157.320].

I checked and from 22 cases Rh101[181.780] actually decayed / de-excited to Rh101[157.320] with a 50% chance. I would need to obtain this branching ratio or decay propability for any state of Rh101 that can be created during activation. (E.g. Rh101[478.060], Rh101[747.800], Rh101[905.690], Rh101[1789.490], Rh101[1696.330] etc.)

Which class could give me the decay propability / branching ratio for any very short lived state by providing it the G4ParticleDefinition?

I tried to use G4PhotonEvaporation::BreakItUp() function assuming it is the function that can do what I want. Though I got it working for “Rh101[747.800]” as a test it returned the definition of two gammas and an electron so propably it can not be called like this.

#6

Hello,

raddiactive decay of Geant4 does not exist as a separate instance but may be used as a component in HEP simulation together with nuclear interaction and de-excitation including photon evaporation. Because these components interact to each other, there is no one single table for the decay chain. The best what can be offered is to use $G4INSTALL/examples/extended/radioactive_decay/rdecay01

VI

#7

Hello,

Right. I am developing a HEP simulation for CubeSat teams to simulate long term activation. What I want to do was already done by other satellite teams in a very similar fashion, like for Hitomi so it is possible to do hopefully solely with Geant4.

What I need to do is to create linearized decay chains and solve the Bateman eq. for each so the simulation can be speed up by 100x compared to only having MC.

For this I used the decay tables avaliable in Geant4. It worked the only problem I am having is how to deal with excited states. Since Geant4 worked for this purpose I would like to use Geant4 as well. (It is by far the best choice as the detector response to the activated isotopes would be also simulated in G4.)

Is there any simple way, like a function I can call to get the decay propabilites of a very short lived excited state into other states? For example the decay propability of Rh101[181.780] -> Rh101[157.320] and Rh101[181.780] -> Rh101[0] states.

Thank you,
Gábor