The conversion of carbon to boron by decreasing the number of protons from 6 to 5 and increasing neutrons is an example of beta minus decay.

In beta minus decay, a neutron is converted to a proton, emitting a beta particle (an electron) and an antineutrino.

The reaction for this process is:

$$n \rightarrow p + e^- + \bar{\nu}_e$$

In this case, the carbon nucleus would capture an electron from its surroundings, converting a proton into a neutron and emitting a neutrino. This would result in a boron nucleus with 5 protons and 6 neutrons.