How successful is pair production?

[Michio Cuckoo]

when a photon interacts with a nucleus, a positron and an electron are created, provided the photo has enough energy.

But what is the probabilty of this occurring? If i fire 100 photons at a nucleus, how many electron-positron pairs will i create?

Also, has anyone ever succeeded in creating a proton-antiproton pair from gamma rays?
Is it possible?

 

[mathman]

First question: It depends on the photon energy (minimum is 1.022 Mev) and the nucleus - heavier the better.

Second question: http://hal.in2p3.fr/docs/00/01/73/55/PDF/democrite-00013743.pdf

 

[mfb]

But what is the probabilty of this occurring? If i fire 100 photons at a nucleus, how many electron-positron pairs will i create?

The question is not well-defined, even if you define photon energy and the nucleus. You have to use something like "photons per area" or "nuclei per area", otherwise it depends on the beam characteristics.
Usually, this probability is expressed as cross-section with the unit of an area. You can view it like "if a photon (randomly) hits this small area, it will do pair-production".
For heavy nuclei, the cross-section is comparable to the size of the nuclei, which is some femtometer^2. However, I do not know precise values.