JRA1 – Low Background Techniques for Deep Underground Science Status report on WP1 Measurement of the backgrounds in the Deep Underground sites WP coordinator: N. Ferrari Modane, 12 January 2005 ILIAS JRA1 meeting – Modane

JRA1 – Low Background Techniques WP1 : Measurement of the backgrounds in the Deep Underground sites WP coordinator: N. Ferrari Objective: To measure the environmental background components (in particular neutrons, gammas, muons, and Rn contamination in the air and in the water) in the four underground sites. Special effort will be devoted in order to collect data in the different sites in a coherent, co-ordinated, and compatible way. Year 1Year 2Year 3Year 4 Collecting existing data Planning new measurements Gamma rays: set-up instrumentation Neutrons: set-up instrumentation Gamma and neutrons: survey in underground labs Set-up of upgraded Radon monitoring systems Radon monitoring Data analysis and interpretation Implementation of results in database Opening and optimising database for UG lab users ILIAS JRA1 meeting – Modane

WP1 The working group LNGS N. Ferrari, C. Tomei, M. Laubenstein, A. Ianni, C. Broggini, C. Cattadori, L. Miramonti W. Plastino, C. Vignoli, G.L. Raselli, A. Cesana LSM G. Gerbier, D. Lalanne Boulby V. Kudryavtsev, J. McMillan, J. Lewin, B. Camanzi, E. Tziaferi LSC M.L. Sarsa, G. Luzon, S. Cebrian, M. Martinez, B.Beltran, J. Ruz, A. Rodriguez, H. Gomez ILIAS JRA1 meeting – Modane

The background components in the deep underground sites 1.Environmental gamma rays 2.Radioactivity of rock, concrete, etc. 3.Neutrons 4.Rn monitoring in the air and in the water 5.Muons ILIAS JRA1 meeting – Modane

Environmental gamma ray background LNGS LNGS: A lot of data have been acquired at LNGS with different detectors placed in different locations NaI detector 3’x3’ Portable Ge detector BGO detector 5’x5’ ILIAS JRA1 meeting – Modane Boulby Boulby: Data collected with Ge detector are available. New work is planned also in connection with a TARI project on gamma background at Boulby. A dedicated Ge gamma survey instrument is planned for operation underground following preliminary tests at Gran Sasso (J. Kisiel). LSM LSM: Environmental gamma-background has been measured using a Ge portable spectrometer in different locations inside the laboratory (R. Gurriaran.). Complete analysis of these data and comparison with previous measurements are under way. LSC LSC: The gamma-ray background will be measured at the centre of the volume of the main hall and the low-background laboratory with suitable HPGe and NaI detectors. We will extract qualitative results from any of the measurements and quantitative from those of the centre of the volume where the distances involved are much greater than the detector dimensions. Additional measurements performed near the walls will be compared to simulations to extract more information.

(1) NaI detector 3x3 ILIAS JRA1 meeting – Modane Energy (keV) Rate (cps/keV) 208Tl 40K Internal  Exit Hall A Exit Hall C OPERA BOX 10 cm Pb shielding In the following we show some examples of the data acquired at LNGS

Energy (keV) Rate (cps/keV) Hall C Hall B OPERA BOX 10 cm Pb shielding (2) Ge portable detector … Other measurements performed in Hall B and Hall A by J. Kisiel ILIAS JRA1 meeting – Modane

(3) BGO detector 5x5 E interval (MeV)counting rate MeV32 cps MeV38 cps MeV23 cps MeV 3.9 cps MeV 0.24 cps MeV58 cpd MeV3.7 cpd MeV 1.1 cpd MeV 1.1 cpd MeV 0.8 cpd MeV 0.58 cpd MeV 0.19 cpd MeV cpd MeV cpd > 11.0 MeV cpd Gamma from nat. radioactivity n captures (?) ILIAS JRA1 meeting – Modane Data especially interesting at E>4 MeV (high energy gammas)

In the next months MC simulations of the detectors based on GEANT4 will be performed. This will allow us to: Extract absolute gamma ray fluxes in different locations at LNGS Test the MC codes (different detectors in the same locations should give the same answer Check the compatibility of the radioactivity of rock and concrete with the observed background ILIAS JRA1 meeting – Modane

Measure  background directly –Ge detector survey of JIF area rock Result: U: 70 ppb Th: 125 ppb K: 1130 ppm Gamma Backgrounds at Boulby ILIAS JRA1 meeting – Modane

Measurement of radiopurity of rock and concrete in the lab LNGS LNGS: Old data are available for the rock of surrounding the lab. New measurements are ongoing measuring radioactivity of the new floor being installed in the lab (M. Laubenstein) ILIAS JRA1 meeting – Modane LSC LSC: The concentration of 40K, 238U and 232Th and other radioactive isotopes will be measured in samples of rock and of building materials by high resolution gamma-ray spectroscopy. These measurements will be carried out in the Ultra Low Background Facility of the new laboratory. This facility will have two new ultra-low background HPGe and some NaI detectors for radio-purity measurements, electronics and active and passive shielding. Data from LSM and Boulby are available U (ppm)Th (ppm)K (ppm) LNGS rock Hall A rock Hall B rock Hall C concrete ? LSM rock concrete Boulby rock concrete 0.07 ? 0.12 ? 1130 ? Some summary data

Measurement of radioactivity of the rock in the Gran Sasso massive LNGS: A study of the radioactivity in the rock of the Gran Sasso massive will be started in spring. This study will be interesting for: - Environmental and geophysics (Collaboration with “Consorzio del Gran Sasso”) - Study of geo-neutrinos The work is carried out by Geology Department of Ferrara and Pavia University in collaboration with LNGS. The work will be partly supported by ILIAS. The activity includes: -Measurements on selected samples of soils and rocks by mass spectrometry - Survey of the environmental gamma radioactivity with large portable NaI detectors

Projects for neutron monitoring ILIAS JRA1 meeting – Modane LNGS LNGS: Several measurements were performed in the past; the agreement among different measurements is not completely satisfactory especially on the shape of the fast neutron spectrum. F. Arneodo et al. Nuovo Cim.A112: ,1999 P. Belli, et al., Il Nuovo Cim. 101A (1989) 959. E. Bellotti et al., INFN/TC-85/19, October M. Cribier, et al., Astropart. Phys. 4 (1995) 23. See the recent paper by Wulandari et al. Astroparticle Physics 22 (2004) 313 – 322 As a reference the fast n flux is n cm -2 s -1 (>2.5 MeV) New measurements are important A detector with 2 liquid scintillator cells is going to be installed at LNGS for long term neutron monitoring (see talk by G. Raselli at this meeting) We have an offer from INR to have at LNGS the 3He liq. scintillator detector used in the past at Baksan and Finland. LSM LSM: A measurement of the neutron flux and spectrum was performed using a liquid scintillator doped with 6 Li Chazal et al., Astr. Part. Phys. 3 9(1998) n cm -2 s -1 (2-6 MeV)

Boulby: No direct measurements were available up to now. Calculations give: n cm -2 s -1 (>100 keV) n cm -2 s -1 (>1 MeV) A new measurement with an 8 liter Gd-loaded liquid scintillaton detector was started in November LSC: No direct measurements are available up to now. Calculations give: n cm -2 s -1 ILIAS JRA1 meeting – Modane

A high flashpoint, low toxicity liquid scintillator based on Diisopropylnaphthalene and containing 0.2 wt % Gd has been developed for neutron measurements in Boulby mine. Dissolution of the Gadolinium compound into the scintillator was facilitated by the use of the extractant Triethylphosphate. Preliminary investigation has shown the attenuation length of the loaded scintillator to be greater than 10 m at 420nm and the light collection to be unchanged within errors when comparing the loaded with the unloaded sample. A stainless steel module with an internal volume of 7 litres and featuring quartz glass end plates was positioned within a castle consisting of 15cm of lead and 10cm of copper in Boulby mine. Calibrations were made using Co-57, Co-60 gamma sources and Cf-252 neutron source. A second smaller vessel is also now available. Measurement of the Neutron Flux in Boulby using a 0.2% Gd Loaded Liquid Scintillator ILIAS JRA1 meeting – Modane Transparency from N. Spooner

Neutron Flux Apparatus now at Boulby ILIAS JRA1 meeting – Modane Transparency from N. Spooner

Rn monitoring in the air and water LNGS LNGS: Rn in the air of the lab is continously monitored online and integrated on several months. It varies from 50 Bq/m3 to 150 Bq/m3 in the ventilated areas, but can reach Bq/m3 in non ventilated corners. The monitoring of the Rn is the water of the Gran Sasso massive is ongoing since several years. Time dependence of the signal is extremely interesting for geophysics. (see talk by W. Plastino) ILIAS JRA1 meeting – Modane J. Wiegand, W. Plastino

LSC LSC : radon will be monitored at the center of the experimental hall and also periodically measurements of radon concentration will be performed at different points: four points at the main experimental hall (the two corridor entrances, the centre and the back of the hall near one of the walls), the corridor, the low-background laboratory and the clean room. The suitable radon meter is a real time detector, with different integration times, depending on the points. Additional radon sensors, like electretes, will be placed also at different points to get integrated values. ILIAS JRA1 meeting – Modane Boulby Boulby: Radon measurements are less urgent at Boulby due to the low U, Th content at the site but new measurements are planned to start during Typical levels are of the order of 5 Bq/m3

Muon flux ILIAS JRA1 meeting – Modane LNGS LNGS : A lot of very detailed information on the muon flux at LNGS (energy spectrum and angular distribution) was acquired by the MACRO experiment. The average flux is 1.1 µ m -2 h -1 Relevant references: Ap. J. 412 (1993) 301 Astropart. Phys. 7 (1997) 109 Phys. Rev. D 52 (1995) 3793 Phys. Rev. D 56 (1997) 1407 Phys. Rev. D 56 (1997) 1421 Phys. Rev. D 59 (1998) Boulby Boulby: The average flux is 1.5 µ m -2 h -1 recently measured by Zeplin LSM LSM: The average flux is 0.17 µ m -2 h -1 Relevant references: ……………… LSC LSC : The muon flux is not expected to be very different from the value we have in the current laboratory (7.2 µ m -2 h -1 ) since this value depends mainly on the depth (2450 mwe in the LSC). However, we will measure the flux of muons in the new laboratory using one of our plastic scintillators Relevant references for present lab: ………………

Measured using ZEPLIN-I Compton Veto –0.93 tonnes liquid scintillator (30 cm thick surrounding layer) –10x 8’’ PMT tubes Muon Muon flux measured as 4.09+/-0.15 x cm -2 s -1 Corresponding to 2805  45 m w.e. (Comparable to Kamioka & Gran Sasso) Mean muon energy: 260 GeV Robinson et al. NIMA 511 (2003) 347 Muon Background at Boulby ILIAS JRA1 meeting – Modane

WP1 web page Responsability: LNGS; Location: LNGS cluster, with link from the JRA1 main page in Zaragoza Status: a lot of existing information for preparation of the web page is collected The first test version of the web page is under advanced development we will open for evaluation to the J1 working groups in february Contents: - Description of the characteristics and importance of the backgrounds in the underground sites - Old and new data on background components in the different labs - Reference papers ILIAS JRA1 meeting – Modane