  New results on the study of radiation effects in solid nitrogen and
N$_2$-doped Ne matrix are presented with a focus on the so-called $\gamma$-line
origin. The irradiation was carried out in dc regime with an electron beam of
subthreshold energy. Relaxation dynamics was monitored by emission spectroscopy
- cathodoluminescence (CL) and nonstationary luminescence (NsL), along with
current activation spectroscopy. Thermally stimulated luminescence (TSL) and
exoelectron emission (TSEE) of pure nitrogen and N$_2$ in the Ne matrix were
measured in a correlated manner. Three emission bands were recorded in the NIR
CL spectra of solid N$_2$: 794, 802, and 810 nm. The band at 810 nm was
detected for the first time. These three bands are characterized by similar
behavior and form molecular series with spacing between adjacent vibrational
energy levels of the ground state of 125 cm$^{-1}$ and 123 cm$^{-1}$. These
data cast doubt on the recently made assumption that the $\gamma$-line is
attributed to the emission of the nitrogen anion N$^-$ [19]. The processes of
an electron attachment and neutralization of positively charged species are
discussed. It has been established that the $\gamma$-line in the TSL spectra of
pure nitrogen and N$_2$-doped Ne matrix correlates with TSEE currents and
recombination emission of O$^+$, N$_2^+$, and N$_4^+$ ions, which indicates its
connection with the neutralization reaction. The measurement of NsL supported
this conclusion. A new possible assignment of the $\gamma$-line and its
satellites to the emission of tetranitrogen N$_4$ is discussed.
