Table of contents

1. Overview
2. Physics scenarios
3. Global production cuts-in-range
4. References

Overview

Advanced users can select a physics scenario and define global cuts-in-range. These settings are used as an input by Multi-Layered Shielding Simulation (Mulassis), Geant4-based Microdosimetry Analysis Tool (GEMAT) and Geant4 Radiation Analysis for Space (Gras).

Note that this page is not accessible when geantino is selected as the source particles.

Physics scenarios

Geant4 has a rich selection of physics models. In most cases there are more than two models from which the user can choose for a given physics process. For the electromagnetic (EM) physics for example, there are the standard EM processes, which are valid from 1 keV and above, and low-energy EM processes, which are valid down to 250 eV for electrons and gammas. The table below explains what Geant4 physics processes are used for treating the various particle types in Mulassis, GEMAT and GRAS.

Particle	Energy range of source	Physics processes
Proton	< 10 GeV	Standard EM or Low-Energy EM G4Binary
	> 10 GeV	Above + G4QGSM
Ion	< 10 GeV/n	Standard EM or Low-Energy EM G4BinaryforLightIons
Neutron	thermal - 20 MeV	G4Neutron_hp or G4Binary
	> 20 MeV	G4Binary + G4QGSM
Electron/Gamma	< 1 keV	Low-energy EM
	> 1 keV	Standard EM or low-energy EM
Other		G4LEHEP

The first decision the user has to make is whether the low-energy EM physics should be used instead of the standard one, depending on whether very low energy EM interactions are important to the simulation or not.

Then the user has to decide whether hadron physics (i.e. nuclear interactions) should be treated. If so there are two further options:

1. Is detailed treatment of the low energy neutrons needed? Some times the detailed treatments of low energy neutrons are unnecessary, for example if one is only interested in the attenuation of the incident protons by the shielding layers.
2. Is the transport of the secondary leptons and gammas needed? When for instance dealing with high energy proton interactions, it is often unnecessary to treat the detailed electron-positron-gamma transport, and simply assume all energy from these particles is deposited locally.

For further information about the physics models used in the Geant4 tools implemented in SPENVIS, the reader is referred to the Geant4 Physics Reference Manual^[2].

The default is standard EM and no nuclear interaction treatment.

Global production cuts-in-range

The general principles in Geant4 regarding secondary particle production cuts are the following:

1. Each process has its intrinsic limit(s) to produce secondary particles.
2. All particles produced (and accepted) will be tracked up to zero range.
3. Production cuts-in-range are assigned to regions.

A region is a collection of geometry volumes. There is always a default region covering the whole geometry, for which there is a suggested global cut-in-range for gamma, electron and positron productions. The user has the option of changing the global production cuts. It can be a single cut for gamma, electron and positron productions, or different cuts for each type of the three particles.

The default values for the global cuts-in-range length is 1 µm.

References

1. Geant4 website
2. Geant4 Physics Reference Manual