Production threshold expressed in range

In Geant4 the threshold for producing secondaries are expressed in range, universal for all medium. This range is converted in energy for each kind of particle and each material. (writeup)
We illustrate here the advantages of this procedure.

Description

The setup is a sandwich of non-dense and dense materials:

Liquid Argon(4 mm)--Lead(4 mm)--Liquid Argon(4 mm)--Lead(4 mm)

The incident particle is a ionising particle: proton of 500 MeV.
The threshold to produce delta-rays is 1.5 mm. For an electron, it means:

Threshold in range	e- Energy in Liquid Argon	e- Energy in Lead
1.5 mm	455 keV	2 MeV

On the picture, one can see the delta-rays produced and travelling in Liquid Argon, while nothing in produced in Lead.
(on purpose the multiple scattering is off, and 1000 events are surimposed)

Geant3

On Geant3 one must set the cut for delta-rays (DCUTE) either to the Liquid Argon value, and producing many small unnecessary d-rays in Lead, or to the Lead value, and killing the d-rays production everywhere.

case 1 : dcute = 455 keV
case 2 : dcute = 2. MeV

G3: DCUTE	Edep in lArg	Edep in Pb	Track length in lArg	Track length in Pb
455 keV	2.30 MeV+- 329 keV	13.45 MeV+- 991 keV	8.32 mm+- 1 mm	8.47 mm+- 500 mum
2 MeV	2.21 MeV+- 339 keV	13.48 MeV+- 1.03 MeV	8 mm+- 0. mm	8 mm+- 0. mm

Stability of results

It should be noticed that the relevant physics quantities are quite stable versus the production threshold, both in Geant4 and in Geant3 (see above).

G4: threshold in range	Edep in lArg	Edep in Pb	Track length in lArg	Track length in Pb
1.5 mm	2.17 MeV+- 322 keV	13.06 MeV+- 949 keV	8.37 mm+- 1.04 mm	8.02 mm+- 80 mum
0.15 mm	2.17 MeV+- 341 keV	13.15 MeV+- 940 keV	8.83 mm+- 1.28 mm	8.67 mm+- 557 mum

Changing the threshold by a factor 10 lets the energy deposit unchanged (as it must be: the energy loss is independant of DCUTE)
and the charged track length variation within 1 percent. (Remember that on the pictures 1000 events are surimposed)

The code of this example is in geant4/examples/extended/electromagnetic/TestEm3 run07.mac

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