Problem 807

Dear GEANT4 developer,

In a method, G4BraggModel::SampleSecondaries,
a negative value can be passed to sqrt()
at the line number of 213 in G4BraggModel.cc.

213   G4double sint = sqrt(1.0 - cost*cost);

It makes a new momentum direction of a particle after the step NAN.

For my case,
the tracked particle is Ar40[0,0] in the standard air,
and its momentum vector is (116,258,-25.3),
and 1.0-cost*cost = -6.85e-13.

Is it due to the precision of the calculation?

Anyway, I think it can be fixed by
adding some check against the negative value before sqrt().

Could you fix this problem?

Best Regards,
Hajime
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High Energy Physics Group, Department of Physics,
Kyoto University
Hajime Nanjo
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