Figure 2. Spectrograms of the natural gamma radiation
responsible for the enhancement of the count rate at low energies. The
spectrograms are observed by an ORTEC precise spectrometer with high
resolution (FWHH ∼7.7%).
In the second column of Table I, we show the enhancement of radiation
relative to background radiation measured at fair weather before and
after the event. In the following columns we show the enhancement for
each identified spectral line and its percent relative to overall
enhancement.. In the last two columns, we summarize the characteristics
of the NGR enhancement: the share of the continuous spectrum (CR
+Compton scattered) and the sum of the peaks correspondent to
radio-nuclides spectral lines. Energies of most of the NGR emitters
measured by the NaI spectrometer are below 1.2 MeV (85%). And most of
the gamma radiation below 1.2 MeV comes from Radon and Thoron chain
isotopes (75%).