Cerenkov Photon Creation.

During the propagation of electrons, positrons or gammas, the EGS code, via the routine EGSCER, will leave a set of Cerenkov bundle vertices (CBVs). These vertices are later processed using the routines UNPCER and VXCERN. The Cerenkov photon is emitted at an angle $\theta_{c} = \cos^{-1}1/\beta n$ with respect to the electron's^13.1 direction of travel^13.2, and at a random azimuthal angle. The necessary information (the electron's energy and directional cosines) is stored in the dummy track linking the EGS vertex to the Cerenkov creation vertex. In the electron's frame of reference (defining the origin to be the electron's current location), and in spherical polar coordinates, the direction of the Cerenkov photon will be given by

$$\underline{\hat{a}}= \cos\theta_{c}\hat{\underline{r}}-\sin\... ...line{\theta}} +\sin\theta_{c}\sin\alpha \hat{\underline{\phi}}$$ (13.1)

where $\alpha$ is the (random) azimuthal angle. When transformed into detector coordinates, the direction, $\underline{\hat{a}}$ of the Cerenkov photon becomes

$$\underline{\hat{a}}= \begin{array}{c} \hat{\underline{i}}(\c... ...{c}\cos\theta - \sin\theta_{c}\cos\alpha\sin\theta) \end{array}$$ (13.2)

where $\theta$ and $\phi$ have their usual spherical polar coordinates definitions.

The frequency distribution of the Cerenkov photons is flat^13.3, and is randomly set in the range between the two cutoffs set in the MCMA titles bank. The polarisation of the Cerenkov photon is in the plane defined by the directional cosines of the emitting particle and the direction of the photon, and perpendicular to the direction of propagation of the photon.