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Relationship between cosmic ray neutron flux and rain flows in dependence on different latitudes and altitudes Eroshenko ¹ E., Velinov ² P., Belov ¹ A ., Mishev ² A., Pletnikov ¹ E., Tassev ² Y., Yanke ¹ V.

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  1. Relationship between cosmic ray neutron flux and rain flows in dependence on different latitudes and altitudesEroshenko¹ E., Velinov² P., Belov¹ A ., Mishev² A., Pletnikov¹ E., Tassev² Y., Yanke¹ V. ¹1 Puskov Institute of Terrestrial Magnetism, Ionosphere andRadio Wave Propagation RAS, Troitsk MR, 142190, Russia ²Central Laboratory of Solar-Terrestrial Relations BAS Main Tasks: 1. To analyze the experimental data from the CR detectors at different heights during the rain periods: 1) Data from lead-free neutron monitors (st. Moussala -2971m; st. Moscow -200 m); 2) Data from Gamma detectors (Moscow station) 3) Data from detectors of the soft CR component (Moscow), 2. To explain the observable effects. For this aim the model calculations of the absorption curves for neutrons and gamma radiation have been performed for different conditions of the experiment.

  2. Introduction The main detectors of CR measurements are constructed by way to minimize the influence of local meteorological conditions. However, the measurements of epithermal neutrons (0.025 MeV<E<0.5 MeV) by free lead monitors strongly undergo to the local meteorological factors: content of water in the surface soil layer or above it , air humidity, existence of thunderstorm clouds above detector. These effects are necessary to be estimated quantitatively both for their excluding from the observable data and for a solution of some applying (Paquet at al., 2007) and fundamental (Митрофанов at al., 2003, 2004) tasks.

  3. Data and Method Using the data from Moscow (latitude 55 degree) neutron monitors (standard super monitor NM64, lead free monitor 6nmF and 23nmF) , gamma and ionization component detectors and lead free neutron monitor at BEO Moussala (latitude 42 degree and altitude 2971 m above see level), we studied the correlations between rain flows and neutron, gamma and ionization component behavior. We also involved data of local meteo-stations.To explain observable correlations the calculations of neutron and gamma absorption and albedo neutron spectra have been performed on the basis of universal software package FLUKA-2006.

  4. The Basic Environmental Observatory (BEO) Moussala is located on the top of the highest mountain at Balkan Peninsula, namely at 2971 m above sea level. The lead free neutron monitor at BEO Moussala represents complex of six BF3 tubes type SNM-15.The moderator is glycerin, filled in cylindrical tankswith 40 cm diameter and 2.5m length. The detector complex area is 5.28 m2. The capacity of glycerin to thermalize fast neutrons is practically the same as polyethylene moderator. Fig. 1. Disposition of lead free neutron monitor at BEO Moussala

  5. Neutron flux during rain flows at BEO Moussala The variation of neutron flux after pressure correction for two months with significant rain flows ate the top. In addition the relative fluctuation of the mean flux also increases. This is due mainly to the additional moderating affects of the rain, which additionally slows the neutrons in the atmosphere. The possible relation between increasing of the flux and cloud cover is a topic of future investigation.

  6. Detectors of Experimental Hall in IZMIRAN 063x063 (NaJ) – gamma detector 23nmF –detector of epithermal neutrons (23 helium counters, polyethylene)

  7. Detectors of the Mobile Cosmic Ray Laboratory (MCRL) in IZMIRAN 6NMF CT 6nm64 6nmF – detector of epithermal neutrons (6 BF3 counters СНМ-15, polyethylene, 0.025<E<0.5 MeV) CT – counter muon telescope (8+8 counters SGM-14) 6nm64 – standard neutron monitor (6 BF3 counters СНМ-15,)

  8. Data through July- October 2007from IZMIRAN detectors

  9. Very high correlation of the bursts in gamma and ionization components. Such flashes are always observed with an approach of tunderstorm cloud, often without rain. It was shown in (Moore, 2001; Eack, 2007; Enoto, 2007; Torii, 2007) that these clouds and lightning discharges may cause the generation of high energy particles which leads to the photon producing. Herewith the detectors of gamma and ionization components record short enhancements of several minute duration which are associated with thunderstorm clouds. Another behavior is observed in neutron component. The effect here is more long than rain duration, the count rate of lead free NMs is long and big enough, and poorly correlates with the air humidity.

  10. Generation of the neutrons and gamma radiation We supposed that observable effect is caused by the humidity amount in the surface soil layer.The measurements of the humidity content in this layer are necessary to confirm this conception experimentally. Generation of neutron and gamma radiation in the near surface layer of soil.

  11. Spectra of the albedo Neutrons Computation of the neutron spectra are carried out on the basis of the universal program package on the particleinteraction with matter FLUKA-2006 Calculations are made for cylindrical 3D geometry under source distance above the soil – 2.5 m. The cylinder radii is 1 m, its lenhgt is by 1m above and below of the soil surface. The soil composition: О – 52,8%, Si – 28%, Al – 10%, Ca – 1,65%, H – 0,675%.

  12. Albedo neutrons in the wet soil for E0=10 MeV Dependence of albedo flux for thermal (T), epithermal (E) and fast (F) neutrons on the hydrogen content in the soil. Calculated spectra of the albedo neutrons for dry soil, soil with 5% of water and with 30% water.

  13. Detectors which data are used for analysis, observe the neutrons within epithermal energy range and data in this Figure plotted explain our experimental results. With an increase of humidity the larger portion of neutrons is slowed and transferred into thermal range and a part of epithermal albedo neutrons reduces. Thus, 10% humidity leads even to the same decrease of epithermal albedo neutrons. Such a content of humidity is possible even under moderate rain with precipitation of 50 mm and thickness of surface layer of tens cm. It is important to know a response of neutron detector to the moisture amount above the surface layer. In the next Figure the results of spectra computation above the soil for different moisture layers are compared: 0, 10, 40 cm, and for two energies of incident neutrons: 10 and 100 MeV. The moisture content of the soil was accepted as 5%. On the basis of obtained spectra the flux of thermal, epithermal and fast neutrons were derived in dependence on the thickness of water-layer above the surface (see picture). The moisture content of the soil was accepted as 5%.

  14. Neutrons above water layer for E0=10 and 100 MeV Neutron spectra above water layer of 0, 10 and 40 cm thickness for moisture content of the soil of 5%. The spectrum are compared for two energies of incident neutrons: 10 and 100 MeV. Fluxes of thermal, epithermal and fast neutrons upon the water thickness above the surface. Water content of the soil is 5%.

  15. Conclusions • Secondary neutron radiation recorded by lead-free NM, and gamma radiation as well, are strongly affected by meteorological factors. The neutron component behavior depends on the moisture amount of the soil surface, and bursts of gamma radiation seems to be caused by a transformation of the soft component spectrum in the strong electric fields of thunderstorm clouds • Computations performed on the basis of universal software package FLUKA-2006, allow deriving of detailed spectraof albedo neutrons within three energy ranges.The humidity content of soil of 5% leads to an increase of the flux of albedo thermal neutrons in three times, whereas the flux of epithermal neutrons decereses on 6% and flux of the fast neutrons – on 22%. • 3) Water layer above the soil lowers both neutron incident to the surface and albedo neutrons. The result depends strongly on the energy of incident particles. Thus, under 100 MEV energy the flux of epithermal and fast (>0.5 MeV) neutrons is additionally absorbed on 70% by the layer of 10 cm. • 4) Albedo flux of gamma radiation reduces on 25% in water layer of 40 cm thickness under energy Eo=10 MeV.MeV. The calculations perhaps yield a conservative results.

  16. References [1] Ferrari A., P.R. Sala, A. Fasso, J. Ranft. “FLUKA: a multi-particle transport code”, CERN 2005-10 (2005), INFN/TC_05/11, SLAC-R-773, (Fluka-2006). [2] FRLUKA http://www.fluka.org/, официальный сайт, 2008. [3] Митрофанов И. Г., http://ps.iki.rssi.ru/projects.htm и http://ps.iki.rssi.ru/lend_en.htm, 2008. [4] Алексеенко В.В., Д.Д.Джаппуев, В.А.Козяривский, А.У.Куджаев, В.В.Кузьминов, О.И.Михайлова, Ю.В.Стенькин, “Анализ вариаций потока тепловых нейтронов на высоте 1700 м над уровнем моря”, Proc. 29 RCRC, Москва, 2006. [5] Paquet E., Laval M., Belov A.V., Eroshenko E.F., Kartyshov V.G, Struminsky A.B., Yanke V.G., “An application of cosmic-ray neutron measurements to the determination of the snow water equivalent”, Proc. 30th ICRC, Mexico, 2007. [6] Митрофанов И. Г., М. Л. Литвак, А. С. Козырев, А. Б. Санин, В. И. Третьяков, В. Ю. Гриньков, У. В. Бойнтон, К. Шинохара, Д. Хамара, Р. С. Саундерс, “Оценка содержания воды в грунте Марса по данным нейтронных измерений прибора ХЕНД на борту космического аппарата “2001 Mars Odyssey””, Астрономический Вестник, том 38, №4, 253-257, 2004. [7] Митрофанов И.Г., М. Л. Литвак, А.С.Козырев, А.Б.Санин, В.И.Третьяков,У. В. Бойнтон, К.Шинохара, Д.Хамара, С. Саундерс, Д.Дрейк. “Поиск воды в грунте марса по данным глобального картографирования потока нейтронов российским прибором хенд на борту американского аппарата “2001 Mars Odyssey””, Астрономический Вестник, том 37, №5, 400-412, 2003. [8] Kodama M., Nakai K., Kawasaki S., Wada M., “An application of cosmic-ray neutron measurements to the determination of the snow water equivalent”, Journal of Hydrology vol. 41,n 1-2, p. 85-92, 1979.

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