05, July, 2012, Moscow Session: SH ID: rd European Cosmic Ray Symposium Registration of Forbush decrease 2012/03/08 with a global net of the thermal neutron scintillation en-detectors Viktor Alekseenko Russia: D. Gromushkin, O. Shchegolev, Yu. Stenkin, V. Stepanov Italia: F. Arneodo, G. Bruno, W. Fulgione

1. The results I will show you are by-side, but interesting, product of activity on study of hadrons component of Extensive Air Showers with a novel thermal neutron methods. Yuri Stenkin “Thermal neutrons in EAS: a new dimension in EAS study” Nucl. Phys. B (Proc. Suppl), , (2008), Rem: en-detector :: e – electron n - neutron Premises & first Reference

2. As usually, appearance of the novel type method or detector raises both healthy skepticism and necessity of some procedure for calibration of a novelty. We are lucky in the sense that there is such a phenomenon in Nature as Forbush decrease - the effect which doesn’t depends both on prejudices of experts and is well studied during decades with neutron monitors. Hence, comparison of behavior of the of en- detector’s counting rate with those of neutron monitors during Forbush decrease may leads to some conclusions on recording ability of the en- detector. Continuation of Premises

3.Aim of the presentation is to show the evidence for ability of the detector to detect both neutron flux and its variations, so to convince the community in adequacy of the detector to cosmic ray study and geophysical researches. End of Premises

And now about our by-side product, starting from schematic lay- out of the en-etector of thermal neutrons essense compound : 6 LiF+ZnS(Ag) Nuclear reaction in use: 6 Li + n  3 H + α Mev. Efficiency = 20 % Resulting particles produce in ZnS(Ag) scintillations which are registered by PMT 5-min Counting Rate points, day after day, during months.... at different geo sites 1 - PMT 2 – working compound 3 - box for compound 4 – cap for PMT

Detectors are located at four different geographic points: Moscow (37E, 56N) Obninsk (36E, 55N) Gran Sasso, Italy (13E, 42N) Baksan (43E, 43N) Global net of the thermal neutron scintillation en-detectors

Baksan Baksan Neutrino Observatory, INR RAS North Caucasus, Elbrus region, 43 о E 43 о N, ~ 1700 m a.s.l.

Forbush decrease happened to be on 08, March, !! Deep in counting rate on 13 th march !! Amplitude ~ 8 %, !! ~ 3% deep in counting rate on 13 th March !!

Records from net of world spread neutron monitors Excellent quality agreement in behavior of curves makes it easy to compare results obtained from neutron monitors and en-detectors located at different geographical points. Decrease is equal to ~ percents. Deep in counting rate on 13 th March !!

Some characteristics of detectors DetectorLocationSquare, m 2 Count.Rate/5minStat error of day point, % BaksanUnderground 5m.w.e LNGS ~1000m a. s. l. Surface MoscowSurface ObninskSurface

Baksan underground en-detector, shield = 5 m.w.e. Comparison of counting rate before and after 8th March let us to draw a conclusion about ~ 1 % decreasing of counting rate or 8 times as lower as Baksan neutron monitor shows. This implies an impact of atmospheric neutrons being approximately 10 %. Barometric coefficient = 0.07+/-0.03 % / mm Hg  indirect evidence of approximately 10% impact of atmospheric neutrons.

LNGS surface en-detector sigma = 0.33% decrease ~ 8 %

Left: Moscow March Right : Obninsk sigma = 0.31 % decrease ~ 8 % sigma = 0.46 % Amplitudes of the effect at different en-detectors are in agreement with those at neutron monitors. Also, it is remarkable that deep in neutron monitors counting rate on 13 th March is either visible in the data of en-detectors.

Conclusion & second Reference Forbush decrease was recorded for the first time with a global net of the neutron scintillation detectors developed in INR RAS. Fact of Forbush decrease registration shows and proofs not only the detector’s ability to detect variations of neutron flux but also unbiasly support the nuclear physics method developed by us as a novel technique and approach in cosmic ray study and geophysical researches. Alekseenko V et al, ”Correlation of variations in the thermal neutron flux from the Earth’s crust with the Moon phases and seismic activity” Izvestia, Physics of the Solid Earth,2009, 45 №8,

Who knows, but I hope it’s not the End, …my feeling - we are just at the youth stage …