Conclusions
We analyzed a winter flux enhancement and its relation to RREA and radon
progeny radiation. We demonstrate that flux enhancement observed on 9
January 2019 is due to 222Rn progeny radiation only and no RREA process
occurred in the atmosphere. Precise measurement of radiation lines and
continuum spectrum in the energy domain 0.3-3 MeV demonstrate that the
enhanced isotope line radiation (63.9%), related do it continuum
radiation of Compton scattered gamma photons in the body of NaI
spectrometer (24.5%), and positron annihilation 511 KeV line (11.6%)
are responsible for the flux enhancement. The large peaks and large
energies of TGE particles originating from the particle avalanches
cannot be observed if the electric field inside the cloud does not
exceed the runaway threshold. In winter the shape of the flux
enhancement is a Gaussian-like with a long, exponentially decaying tail.
The near-surface electric field of a few kV/m is another indicator that
the intracloud electric field is below the avalanche initiation
threshold (≈1.8 kV/cm at 5-6 km height). The count rate of NaI
spectrometer with energy threshold 4 MeV and STAND3 detector with energy
threshold ≈2MeV show no enhancement at the time when NaI spectrometer
with energy threshold 300 KeV demonstrate large peaks. Thus, as we
present in Fig. 4, no RREA can occur on Aragats in winter, all observed
flux enhancements are due to the isotope enhanced radiation only.
ACKNOWLEDGMENTS
We thank the staff of the Aragats Space Environmental Center for the
operation of the NaI network on Mount Aragats. The authors thank S.
Chilingaryan for his continuous efforts at maintaining and improving
Web-based data analysis facilities for a large stream of data coming
online from the Mount Aragats research station. The data for this
article are available by accessing the multivariate visualization
software ADEI in numerical and graphical type on the website of the
Cosmic Ray Division of the Yerevan Physics Institute [11].