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].