Pair production with 1 MeV positron beam?

Physics, Transport and Magnetic Fields
2

Ahoi,

Two remarks:

  1. Pair production is possible: the available energy is not only the positron kinetic energy E (the primary kinetic energy minus whatever was lost to electronic stopping), but E+2m_ec^2, where m_e is the electron mass (keep in mind the positron annihilates with a poor electron, hence twice m_ec^2).

  2. Positron annihilation in flight leads to the emission of two photons, whose energies E1 and E2 can be asymmetric (but still verifying E1+E2=E+2m_ec^2). It can happen e.g. that E1 is slightly larger than 2m_ec^2: this photon may then go on to generate an electron/positron pair in a material. In mgdraw.f you’ll find the ICODE for positron annihilation at rest vs in flight to refine your analysis.

Cheers,

Cesc