Problem 956

Summary:	meta stable states are missing
Product:	Geant4	Reporter:	Jing Liu <jingliu>
Component:	processes/hadronic/models/neutron_hp	Assignee:	dennis.herbert.wright
Status:	RESOLVED WONTFIX
Severity:	normal	CC:	tkoi
Priority:	P5
Version:	8.3
Hardware:	All
OS:	All
Attachments:	showing the peaks missing in the simulation Brief description and "dirty" patch to overcome the problem

Description Jing Liu 2007-07-08 20:13:04 CEST

HI, 

I am using Geant4.8.3 with G4NDL3.10 to simulate the neutron (E<20 MeV) interactions with the germanium detector. In the energy spectrum measured by the detector, there are two gamma peaks coming from the following processes:

1. n + Ge74 -> Ge75(meta-stable state), Ge75(meta-stable state) -> Ge75(ground state) + gamma (E_gamma = 139 keV)

2. n + Ge70 -> Ge71(meta-stable state), Ge71(meta-stable state) -> Ge71(ground state) + gamma (E_gamma = 198 keV)

There is no these two peaks in the simulation, which can be seen in the attached plot. Seems that the meta-stable states due to the neutron capture cannot be created in the simulation.

Comment 1 Jing Liu 2007-07-08 20:14:45 CEST

Created attachment 4 [details]
showing the peaks missing in the simulation

Comment 2 tkoi 2007-07-10 01:13:15 CEST

Hi, 
Thank you for reporting problem.

However there is no Capture FS data for G4NDL(3.11).
So that G4PhotonEvaporation creates final states.
I reassign this to the coordinator of hadronic processes.

Tatsumi

Comment 3 dennis.herbert.wright 2008-01-31 20:56:34 CET

We have looked into this problem and found that Geant4 does not support
meta-stable states.  The photon evaporation code is used instead for a very
rough approximation, but it will not generate the lines you want.

To add this capability would be a large job which we cannot undertake at this
time.

Comment 4 Luciano Pandola 2008-04-01 08:59:51 CEST

Created attachment 24 [details]
Brief description and "dirty" patch to overcome the problem

As discussed by Dennis Wright, the implementation of the capability to produce isomeric nuclear states following neutron captures is very heavy and it is not possible at the moment. 

For some applications (e.g. neutrinoless double beta decay) for which the production of specific isomeric states from neutron capture is relevant (e.g. Ge-76 --> Ge-77m), one can "hack" the Geant4 code with the "dirty" ad-hoc solution described in the document. Although it does not consider the variation of production cross section vs. energy, and is valid only for hard-coded nuclei, it is a workable solution for specific use-cases.