A predictive correlation between hard cosmic ray flux (HCRF) near the Earth's surface and sudden increases in the number of cases of cardiovascular disease (CVD) was studied in Vilnius city. Gamma spectrometers were used to measure HCRF. Changes in the total number of impulses registered by these devices were taken as the physical parameter for prediction of an increase in the number of CVD cases. For quantitative assessment of CVD dynamics two empirical criteria for HCRF were proposed: (1) a consistent fall in the HCRF by 200 or more impulses for 4 or more hours per day; (2) the difference (no less than 15 impulses per hour) between the average number of impulses registered in 2 (subsequent and previous) days. The periods analyzed were those when the number of CVD cases exceeded the average monthly level by 10% and 15%. HCRF fluctuations were used as an indirect indicator of variations in the geomagnetic field, and a leap in CVD cases was predicted 1-3 days following a change in the HCRF according to the two criteria mentioned above. The predictive reliability of an increase in CVD cases within 2-3 days exceeded 80%, and within 1-2 days 70%. No essential difference in predictive reliability was observed when the number of CVD cases exceeded the average monthly level by 10% or 15%. Geomagnetic field variations contribute only insignificantly to leaps in the number of CVD cases, which are evoked by the sum effects of other factors. The results of the present study should be regarded as preliminary.

The mechanism of primary cosmic particle transformation into secondary radiation near the ground surface is analysed. It is known that the main part of secondary cosmic radiation consists of muons. They are formed after nuclear reactions between primary protons and the nuclei of atmospheric gases. Maximum muon concentrations are formed at an altitude of 15 km from the ground surface. Because of a short existence time of muons (2 μs), the amount of these particles near the ground surface depends on variations in the altitude of the above‐mentioned atmospheric layer. Therefore, an unstable flux of muons is registered near the ground surface. Their variations are connected with the Sun's radiation instability, geomagnetic field variations, meteorological process changes, etc. Measurements of the hard cosmic radiation component only near the ground surface are carried out. To this purpose protection of the detector of gamma‐spectrometer was improved. Small gaps between lead plates were made to abolish the shower phenomenon caused by cosmic radiation and the effect of weak‐energy particles and as a result to improve the measurement accuracy. It is defined that lead protection of the thickness of 9 cm of the detector fully absorbs muons with 1,6 MeV energy. It is registered that the gamma‐quanta of 1,6 MeV energy of radionuclide 232Th lose 70 % of the initial energy only in the same lead protection. In 2001–2002 a study was made of the course of the hard cosmic ray flux (HCRF) near the ground surface in four energy intervals: 1 ‐ 0,3–1,2 MeV, 2 ‐ 1,2–1,6 MeV, 3 ‐ 1,6—4 MeV, 4–4 MeV and more. Various course of the HCRF in the mentioned intervals is obtained.

Data on a prognostic relationship between the hard cosmic ray flux (HCRF) and the leaps of cardiovascular diseases (CVD) in Vilnius in 2008-2009 are presented. A gamma spectrometer with a scintillation detector were used to register the HCRF near the ground surface. Data on CVD over a period of 24 months (2008-2009) were obtained from the Vilnius Ambulance Service. Information on CVD was selected for all age groups in accordance with the international codes for identification of diseases (ICD). The present study was restricted to time periods when the cosmophysical and medical data could be compared. For the processing of experimental results, empirical criteria in the analysis of HCRF and CVD were used. The criterion in HCRF change is a decrease of HCRF values by 200 impulses and more during a period of 4 hours. The CVD number exceeding the monthly average value by 10, 15, 20% was analysed. A correlation between the above parameters was studied in the range of 1-3-day period. The efficiency of the prognosis of CVD leaps by HCRF decrease in 1-2 days in 2008 was 74-82% and in 2009 65-70%, and for 2-3 days in 2008 54-60% and in 2009 63-65%. The human factor was analysed, too.