JRA1 – Low Background Techniques for Deep Underground Science Status report on WP1 Measurement of...

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 1 Year 2 Year 3 Year 4Collecting 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


WP1 The working group

LNGSN. Ferrari, C. Tomei, M. Laubenstein, A. Ianni, C. Broggini, C. Cattadori, L. MiramontiW. Plastino, C. Vignoli, G.L. Raselli, A. Cesana

LSM

G. Gerbier, D. Lalanne

Boulby V. Kudryavtsev, J. McMillan, J. Lewin, B. Camanzi, E. Tziaferi

LSCM.L. Sarsa, G. Luzon, S. Cebrian, M. Martinez, B.Beltran, J. Ruz, A. Rodriguez, H. Gomez


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


Environmental gamma ray background

LNGSLNGS:A lot of data have been acquired at LNGS with different detectors placed in different locationsNaI detector 3’x3’Portable Ge detectorBGO detector 5’x5’


BoulbyBoulby: 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).

LSMLSM: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.

LSCLSC: 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


Energy (keV)

Rat

e (c

ps/k

eV)

208Tl

40K

Internal

Exit Hall AExit Hall COPERA BOX10 cm Pb shielding

In the following we show some examples of the data acquired at LNGS

Energy (keV)

Rat

e (c

ps/k

eV)

Hall CHall B

OPERA BOX10 cm Pb shielding

(2) Ge portable detector

… Other measurements performed in Hall B and Hall A by J. Kisiel


(3) BGO detector 5x5

E interval (MeV) counting rate---------------------------------------------------0.3-0.5 MeV 32 cps0.5-1.0 MeV 38 cps1.0-2.0 MeV 23 cps2.0-3.0 MeV 3.9 cps3.0-3.5 MeV 0.24 cps3.5-4.0 MeV 58 cpd4.0-4.5 MeV 3.7 cpd4.5-5.0 MeV 1.1 cpd5.0-6.0 MeV 1.1 cpd6.0-7.0 MeV 0.8 cpd7.0-8.0 MeV 0.58 cpd8.0-9.0 MeV 0.19 cpd9.0-10.0 MeV 0.076 cpd10.0-11.0 MeV 0.017 cpd> 11.0 MeV 0.062 cpd

Gamma from nat. radioactivity

n captures (?)


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


Measure background directly– Ge detector survey

of JIF area rockResult: U: 70 ppb Th: 125 ppb K: 1130 ppm

Gamma Backgrounds at Boulby


Measurement of radiopurity of rock and concrete in the lab

LNGSLNGS: 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)


LSCLSC: 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

6.8

0.42

0.66

1.0

2.2

0.06

0.06

0.6

160

160

160

?

LSM rock

concrete

0.84

1.9

2.4

1.4

213

77

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


LNGSLNGS:

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.A112:819-831,1999 P. Belli, et al., Il Nuovo Cim. 101A (1989) 959.E. Bellotti et al., INFN/TC-85/19, October 1985.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 0.3 10-6 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.

LSMLSM:

A measurement of the neutron flux and spectrum was performed using a liquid scintillator doped with 6LiChazal et al., Astr. Part. Phys. 3 9(1998)163

4.0 10-6 n cm-2 s-1 (2-6 MeV)

Boulby:

No direct measurements were available up to now.

Calculations give: 2.8 10-6 n cm-2 s-1 (>100 keV)

1.3 10-6 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: 3.8 10-6 n cm-2 s-1


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


Transparency from N. Spooner

Neutron Flux Apparatus now at Boulby


Transparency from N. Spooner

Rn monitoring in the air and water

222Rn-Impulses / 30min

0

500

1000

1500

2000

2500

3000

11.0

3.03

18:

36

16.0

3.03

16:

36

21.0

3.03

14:

36

26.0

3.03

12:

36

31.0

3.03

10:

36

05.0

4.03

08:

36

10.0

4.03

06:

36

15.0

4.03

04:

36

20.0

4.03

02:

36

25.0

4.03

00:

36

29.0

4.03

22:

36

04.0

5.03

20:

36

09.0

5.03

18:

36

14.0

5.03

16:

36:0

0

19.0

5.03

14:

36:0

0

24.0

5.03

12:

36:0

0

29.0

5.03

10:

36:0

0

03.0

6.03

08:

36:0

0

08.0

6.03

06:

36:0

0

13.0

6.03

04:

45:0

0

18.0

6.03

02:

45:0

0

23.0

6.03

00:

45:0

0

27.0

6.03

22:

45:0

0

02.0

7.03

20:

45:0

0

07.0

7.03

18:

45:0

0

12.0

7.03

16:

45:0

0

17.0

7.03

14:

45:0

0

22.0

7.03

12:

45:0

0

27.0

7.03

10:

45:0

0

01.0

8.03

08:

45:0

0

06.0

8.03

06:

45:0

0

11.0

8.03

04:

45:0

0

16.0

8.03

02:

45:0

0

21.0

8.03

00:

45:0

0

25.0

8.03

22:

45:0

0

30.0

8.03

20:

45:0

0

04.0

9.03

18:

45:0

0

Rn

[cp

m]

M 2.6 M 3.7

M 2.9 M 2.8 M 2.8M 2.9M 2.9

M 3.3M 2.4

expected trend

LNGSLNGS: 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 800-1000 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)


J. Wiegand, W. Plastino

LSCLSC : 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.


BoulbyBoulby: 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 2005. Typical levels are of the order of 5 Bq/m3

Muon flux


LNGSLNGS : 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) 301Astropart. Phys. 7 (1997) 109Phys. Rev. D 52 (1995) 3793Phys. Rev. D 56 (1997) 1407Phys. Rev. D 56 (1997) 1421Phys. Rev. D 59 (1998) 012003

BoulbyBoulby: The average flux is 1.5 µ m-2 h-1 recently measured by Zeplin

LSMLSM: The average flux is 0.17 µ m-2 h-1

Relevant references:………………

LSCLSC : 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 scintillatorsRelevant references for present lab:………………

• Measured using ZEPLIN-I Compton Veto– 0.93 tonnes liquid scintillator (30 cm thick

surrounding layer)– 10x 8’’ PMT tubes MuonMuon

Muon flux measured as 4.09+/-0.15 x 10-8 cm-2s-1

Corresponding to 2805 45 m w.e. (Comparable to Kamioka & Gran Sasso)

Mean muon energy: 260 GeVRobinson et al. NIMA 511 (2003) 347

Muon Background at Boulby


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


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