Muons comprise an important contribution of the natural radiation dose in air (approx. 30 nSv/h of a total dose rate of 65-130 nSv/h), as well as in underground sites even when the flux and relative contribution are significantly reduced. The flux of the muons observed in underground can be used as an estimator for the depth in mwe (meter water equivalent) of the underground site. The water equivalent depth is an important information to devise physics experiments feasible for a specific site. A mobile detector for performing measurements of the muon's flux was developed in IFIN-HH, Bucharest. Consisting of 2 scintillator plates (approx. 0.9 m 2 ) which measure in coincidence, the detector is installed on a van which facilitates measurements at different locations at surface or underground. The detector was used to determine muon fluxes at different sites in Romania. In particular, data were taken and the values of meter water equivalents were assessed for several locations from the salt mine from Slanic Prahova, Romania. The measurements have been performed in 2 different galleries of the Slanic mine at different depths. In order to test the stability of the method, also measurements of the muon flux at surface at different elevations were performed. The results were compared with predictions of Monte-Carlo simulations using the CORSIKA and MUSIC codes.
The feasibility of a next generation neutrino observatory in Europe is being considered within the LAGUNA design study. To accommodate giant neutrino detectors and shield them from cosmic rays, a new very large underground infrastructure is required. Seven potential candidate sites in different parts of Europe and at several distances from CERN are being studied: Boulby (UK), Canfranc (Spain), Fréjus (France/Italy), Pyhäsalmi (Finland), Polkowice-Sieroszowice (Poland), Slanic (Romania) and Umbria (Italy). The design study aims at the comprehensive and coordinated technical assessment of each site, at a coherent cost estimation, and at a prioritization of the sites within the summer 2010.
Measurements of 131 I (T 1/2 = 8.04 days) activities have been performed in the IFIN HH (Horia Hulubei National Institute of Physics and Nuclear Engineering) underground laboratory situated in Unirea salt mine, Slȃnic-Prahova, Romania. The rainwater samples were collected starting on 27 March from Braşov and Slȃnic-Prahova. Also sheep and goat milk samples were collected in the Slȃnic, Braşov and Iaşi areas and measurements were subsequently made on them. The measurements on the samples were made at the IFIN HH's underground laboratory in an ultra-low radiation background, using a high resolution gamma-ray spectrometer equipped with a GeHP (hyperpure) detector having a full width at half-maximum of 1.80 keV at 1332.48 keV for the second 60 Co gamma ray and a relative efficiency of 22.8%. The results show a specific activity of 131 I from <0.063 to 0.75 Bq l −1 for rain. In the milk samples the specific activity varied from <0.12 to 5.2 Bq l −1 .
Precise measurements of the muon flux are important for different practical applications, both in environmental studies and for the estimation of the water equivalent depths of underground sites. A mobile detector for cosmic muon flux measurements has been set up at IFIN-HH, Romania. The device is used to measure the muon flux on different locations at the surface and underground. Its first configuration, not used in the present, has been composed of two 1 m2scintillator plates, each viewed by wave length shifters and read out by two Photomultiplier Tubes (PMTs). A more recent configuration, consists of two 1 m2detection layers, each one including four 1 · 0,25 m2large scintillator plates. The light output in each plate is collected by twelve optical fibers and then read out by one PMT. Comparative results were obtained with both configurations.
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