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International Journal of Modern Physics A
Vol. 32 (2017) 1743001 (14 pages)
c World Scientific Publishing Company
DOI: 10.1142/S0217751X17430011
Review of technical features in underground laboratories
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by GRIFFITH UNIVERSITY on 10/25/17. For personal use only.
Aldo Ianni
Laboratorio Subterráneo de Canfranc, Paseo de los Ayerbe S/N,
22880 Canfranc-Estación, Huesca, Spain
aldo.ianni@lngs.infn.it
Received 19 September 2017
Accepted 22 September 2017
Published 23 October 2017
Deep underground laboratories are multidisciplinary research infrastructures. The main
feature of these laboratories is the reduced cosmic ray muons flux. This characteristic
allows searching for rare events such as proton decay, dark matter particles or neutrino
interactions. However, biology in extreme environments and geophysics are also studied
underground. A number of ancillary facilities are critical to properly operate low background experiments in these laboratories. In this work we review the main characteristics
of deep underground laboratories and discuss a few of the low background facilities.
Keywords: Underground laboratory; radioactivity; background radiations; cosmic rays.
PACS numbers: 29.40.Ka, 29.40.Mc, 39.30.+w, 98.70.Vc
1. Introduction
Deep Underground Laboratories (DULs) are research infrastructures with a rock
overburden larger than 1000 meters of water equivalent (m.w.e.). At present, there
are 13 DULs in operation and three underway in a timescale from 2018 to 2027.1
In Fig. 1 the geographic distributions of DULs worldwide are shown. DULs in
operation are all excavated in the northern hemisphere. Among the new DULs, two
out of three will be excavated in the southern hemisphere.
DULs are multidisciplinary research infrastructures. The main research activity
in DULs is about neutrino physics, dark matter and rare events such as proton
decay and neutrinoless double beta decay. However, biology in extreme environments2 and geophysics are also studied in DULs. In addition, the next generation
of gravitational wave detectors will be built underground. As a matter of fact,
the Kamioka Gravitational Wave Detector (KAGRA)3 is under construction at the
Kamioka underground laboratory in Japan. In Fig. 2 we show the total underground
volumes of present and future DULs. At present, the total excavated volume for
1743001-1
BACK
hydroelectric power company in Sichuan province,
· Three other mid-size underground laboratories have
been active in Europe since the 1980s: Boulby Laboratory on the north-east coast of England, UK; Modane
Laboratory in the French Alps; and Canfranc Laboratory
under the Spanish Pyrenees.
China. At 2400 m beneath JinPing mountain, it is the
world record holder for depth beneath the Earth’s
DeepUndergroundLaboratories
World-wide
surface.
· Kamioka Laboratory in Kamioka-cho, Gifu, Japan, has
· Sandford Underground Research Facility was built in a
A. Ianni
the world’s largest underground neutrino detector.
former gold mine in South Dakota, USA. This pioneer
Groundbreaking neutrino experiments have been car-
underground laboratory was where the first studies of
ried out at this lab over the past two decades.
Boulby Underground
Laboratory, UK
CallioLab, Finland
Laboratoire Souterrain
de Modane, France
Baksan, Russia
Laboratori Nazionali
del Gran Sasso, Italy
SNOLAB,
Canada
New Y2L, South Korea
Laboratorio Subterráneo
de Canfranc, Spain
Sandford Underground
Research Facility, USA
Kamioka Observatory,
Japan
Soudan Underground
Laboratory, USA
Yangyang Underground
Laboratory, Korea
INO, India
ANDES
SUPL
Image courtesy of Susana Cebrián
Fig. 1. (Color online) Deep Underground Laboratories worldwide. In red bullets are the infrastructures under construction or proposed. A.Ianni
14
As 99% of the energy liberated in a
supernova is thought to be radiated
away in the form of neutrinos, their
300information
000
detection provided much
about what actually happens when
a star collapses. Neutrinos
250produced
000
by radioactive beta decays within
Earth have also been detected: these
Volume [m3 ]
geoneutrinos could become a priceless
tool for geophysics (Bellini et al., 2011),
as they provide information about the
size and location of radioactive sources
within Earth’s interior, where access is
completely impossible.
Neutrinos from the Sun puzzled
scientists for several decades. The
200 000
number of neutrinos detected overall
was much lower than scientists
expected the Sun to produce, based
on detailed calculations of nuclear
fusion processes. The problem was
solved in 2001 when it was found that
neutrinos, which exist in three types
called ‘flavours’, can flip from one type
18 I Issue 39 : Spring 2017 I Science in School I www.scienceinschool.org
150 000
100 000
50 000
SUP
L
ARF
AND
ES
CJPL
Kam
ioka
Y2L
LSM
Calli
oLab
Baks
an
SUR
F
Lab
LNG
S
LSC
Boul
by
0
SNO
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China JinPing Underground
Laboratory, China
Fig. 2. (Color online) Underground volumes for present (blue) and future (red) DULs. The
extension in SURF is for DUNE, the long-baseline neutrino experiment.
DULs is about 7.1 · 105 m3 . In case all new proposals will be completed by 2027,
the total excavated volume will be about 106 m3 .
In DULs the flux of muons from primary cosmic rays is much reduced with
respect to the Earth’s surface. In DULs the flux of muons and their angular distribution depend on the specific outside surface morphology. A number of DULs are
built under a mountain, namely LNGS, LSC, LSM, Baksan, CJPL, Kamioka, Y2L,
ARF and ANDES. ANDES will be built on a side of a road tunnel from Argentina
1743001-2
Muon flux [cm-2 s-1]
Review of technical features in underground laboratories
10−6
10−7
10−8
WIPP
Y2L LSC
Soudan Kamioka
ARF
BUL INO
SUPL LNGS
CLAB
DULs in EU
other DULs
new DULs
ANDES LSM
Baksan
SURF
10−9
SNOlab
Jinping
−10
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10
1
2
3
4
5
6
7
Equivalent depth under flat surface [km w.e.]
Fig. 3. Cosmic ray muons flux underground in different DULs. CLAB stands for CallioLab and
Jinping for China JinPing Laboratory (CJPL).
to Chile. Astroparticle Research Facility (ARF) will be built in an operating iron
mine in South Korea. The others, namely SNOLab, Boulby and SURF, are built
under a flat surface. SUPL will be excavated under a flat surface in a gold mine
environment.
The slope of the mountain will affect significantly the total muons flux and
muons angular distribution in underground. For DULs which are built under a
flat outside surface a more homogeneous cosmic muons distribution underground is
expected. In Fig. 3 we show the muons flux against an equivalent flat outside surface
for the present and future DULs. The reduced muons flux is the first fundamental
characteristic of DULs and allows to search for rare events. In addition, in underground the neutron flux from (α, n) interactions and spontaneous fission is also
reduced by a factor of 10–100 with respect to the Earth’s surface. The overall low
background environment (from muons and other ionizing particles) is the starting
point to perform research activities in DULs. In Fig. 3 we show the muons fluxes in
WIPP, Soudan and INO. More details on these infrastructures are not reported in
other plots so we give them in the following. WIPP is a repository for transuranic
waste in New Mexico, USA, excavated in a salt bed environment. The site has
been used to run a number of experimental activities in astroparticle and neutrino
physics. The Soudan underground laboratory is excavated in an old iron mine in
Minnesota, USA. This site is put in operation in 1980 to search for proton decay.
More recently, the site has been used to host long-baseline neutrino experiments
(MINOS and NOνA), and for dark matter search with CDMS-II. Indian-based
Neutrino Observatory (INO) is an underground infrastructure in India to study
atmospheric neutrinos.
DULs being closed environments, the air underground can be contaminated
with radon. Radon (mainly 222 Rn from the 238 U radioactive chain) is a radioactive
1743001-3
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40
15 Bq/m3
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Air change / day
30
<3 Bq/m3
20
100 Bq/m3
40 Bq/m3
10
130 Bq/m3
70 Bq/m3
80 Bq/m3
80 Bq/m3
300 Bq/m3
0
SNOLab
LNGS
LSC
Boulby
LSM
CallioLab SURF
Kamioka
Y2L
Fig. 4. Daily air change in DULs for the whole laboratory volume. For each DUL the average
radon level is reported.
noble gas naturally produced from radium (226 Ra). Radon can diffuse and in an
underground environment the activity can easily reach 1000 Bq/m3 or much more.
Therefore, it is important to reduce this activity mainly for health risk associated
to radon exposure. The maximum activity of radon in workplaces below ground can
change in different countries, however a level above 400 Bq/m3 asks for restrictions
to limit the exposure (IRR99). Reducing radon also implies limiting the overall
ionizing background in the underground area. At present, in operating DULs a
forced fresh air ventilation reduces the radon level to below 300 Bq/m3 in the worst
case. In addition, the average radons value in DULs shows a seasonal variation of 15–
25% which is correlated with the relative humidity in the underground environment.
The maximum activity is detected in summer. As far as radon in DULs is concerned
there is an important exception. In the Boulby Underground Laboratory (BUL) in
the UK the radon level is naturally below a few Bq/m3 . The reason is the low
environmental background. Boulby is built in a potash and salt mine where the
contaminations of 238 U and 232 Th are very low with respect to standard rocks.
On the contrary, the 40 K is higher than in other DULs. In Fig. 4 we show the
air change per day in DULs and the corresponding average radon level. The air
change reported corresponds to how many times the air in the laboratory volume
(see Fig. 2) changes per day. Small laboratories such as LSM (see Fig. 2) with a
high daily air exchange can have a low radon level in spite of the rock radioactivity
level.
1743001-4
Review of technical features in underground laboratories
Table 1.
Summary of some DULs’ characteristics (H = horizontal and V = vertical).
SNOLab
Canada
Since
Volume (m3 )
Depth (m)
Access
LNGS
Italy
LSC
Spain
BUL
UK
LSM
France
CallioLab
Finland
Baksan
Russia
SURF
USA
CJPL
China
Kamioka
Japan
Y2L
South
Korea
2003
1987
2010
1989
1982
1995
1967
2007
2009
1983
2003
30,000
180,000
10,000
7200
3500
1000
23,000
7160
300,000
150,000
5000
2070
1400
850
1100
1700
1440
1700
1500
2400
1000
700
V
H
H
V
H
V+drive in
H
V
H
H
drive in
130
80
100
<3
15
70
40
300
40
80
40
Average
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Rn (Bq/m3)
Another important feature of DULs is the access. In some DULs the access is
horizontal and it is possible to drive to the underground area. In other cases the
access is vertical by means of an elevator in a shaft. This is the case for DULs
excavated in a mine environment (SNOLab, SURF and CallioLab). There are also
DULs with a vertical and inclined driving access (CallioLab and ARF). In Table 1
we report some information on DULs in operation around the world.1 We notice
that Baksan is 50 years old and played an important role in paving the way in
the exploration of rare processes in underground infrastructures. In addition, we
underline that the research activities in the SURF and SNOLab locations started in
1967 and 1999, respectively, with the Homestake and SNO experiments.4 Therefore,
the tradition to work in underground environments in the framework of astroparticle
physics is some 50 years old. Fundamental breakthroughs, such as the discovery of
neutrino oscillations, have been achieved in DULs.
DULs need a number of ancillary facilities to support the experimental activity
underground. Besides the basic facilities needed to operate the infrastructure such as
water distribution plant, electrical power, ventilation and fire extinguishing system,
DULs are equipped with a number of low background setups. In particular, we mention the following: radioactivity screening facility, Cu electroforming setup, radon
abatement system,6 low sensitivity (mBq/m3 ) radon detectors, radon emanation
detectors, neutron detectors, gamma-ray detectors, water purification plant, cleaning facility, clean rooms, liquid scintillator purification plant, radon-free nitrogen
system and active shielding to tag mainly muons. All these facilities are common
in DULs and are fundamental to properly operate experiments to search for rare
events, dark matter or neutrino interactions. In the following we briefly review these
setups in the framework of DULs. More details will be given in the reviews enclosed
in the present issue.
2. Low Background Facilities in DULs
In this section we review some important and common ancillary facilities in operation in DULs. This section is complementary to more detailed reviews reported
in this issue. In Fig. 5 we show the layout of the new underground laboratory
under construction in South Korea, ARF, which we have mentioned above. We use
this layout as an example to discuss equipment which support research activities
1743001-5
A. Ianni
lounge
(2F,70m2)
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HPGe
(1F,70m2)
Electroformcopper
(2F,100m2)
Watershielding
Tank(φ 10m)
Testrooms
(1F,50+50m2)
Fig. 5.
Machineshop
Cleanroom
(1F,200m2)
controlroom
(2F,50+50m2)
Electricalroom
Networkroom
Crystalgrowingroom
(1F,70m2)
storage(1F,100m2)
Electricalroom(1F)
Lounge(2F)
Gasstation(2F)
Rnfreeairsys.(1F)
Layout of the ARF to be built in South Korea in an iron mine environment.
in DULs. The underground infrastructure foresees a number of general use facilities, namely: a high purity germanium (HPGe) detector facility for radioactivity
screening;5 one or more clean rooms for cleaning and assembling of detectors’ components; a workshop to have the possibility to work on small detectors’ components
without going on surface; a radon abatement system to provide radon-free air to
a clean room, to the HPGe facility or to any other area where one has to reduce
radon contamination and mainly radon daughters plate out; a gas station to store
nitrogen, argon or other gases to be used in the underground; and a waste repository to dispose chemicals used mainly for cleaning. In addition, other facilities are
becoming of interest in DULs, in particular we mention about a crystal growing
infrastructure and a Cu electroforming laboratory. It is of great interest to grow
NaI, Ge or other crystals in underground to avoid cosmogenic activation. Some
cosmogenic activated radioactive isotopes take years to decay. Therefore, having
the opportunity to produce crystals in underground is an important advantage.
It has been shown7,8 that electroformed Cu is much less radioactive than commercial high quality Cu. So, for some sensitive components of a specific detector a
higher radiopurity is critical. To avoid cosmogenic activation, mainly of 54 Mn and
60
Co, it is important to install the electroforming facility underground.
New generation experiments to search for low energy (MeV range) neutrino
interactions, neutrinoless double beta decay and dark matter are built inside the
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Review of technical features in underground laboratories
instrumented water tanks. The sensitive apparatus is installed at the center of
the water tank. The water tank is equipped with photomultipliers and works as a
Cherenkov muons veto. In addition, a 1–2 m of water shielding reduces the neutron
background from the underground environment. The water tank is made from low
radioactivity stainless steel which stops high energy gamma rays from natural radioactivity. A standard water tank can contain as much as 1000 m3 of deionized and
radon-free water. Therefore, a water purification plant is needed in underground.11
Water purification plants are in use underground at LNGS for Borexino, DarkSide50, and Xenon1t, at SNOLab for SNO+ and at Kamioka for SuperKamiokande,
KamLAND and XMASS.
Special cleaning of detectors’ components must be carried out before assembling.
Therefore, precision cleaning facilities are often installed in clean rooms in underground. Large volumes (100–1000 tons) of liquid scintillator can be used to detect
neutrinos (Borexino, KamLAND and SNO+). In addition, smaller masses (10 tons
scale) can be deployed to operate as an active veto against radiogenic and cosmogenic neutrons (DarkSide5010 ). These detectors need fluid handling systems and
purification systems to operate the large volume of scintillator. It is a good practice
to perform a precision cleaning on as-built large fluid handling systems before commissioning and operations. This is the case, as an example, in Borexino12 at the
LNGS. For this specific task Borexino is equipped with a dedicated cleaning facility.
Besides ancillary facilities in underground, DULs are supported with a number of
complementary infrastructures on surface. We mention, in particular, clean rooms,
large workshops, chemistry laboratory, assembling and storage spaces. As far as
low background facilities are concerned an important component is the ICP-MS for
further screening of radioactivity.13
In the following more details on some of the facilities of common use in DULs are
reported. In particular, we discuss HPGe facilities in the framework of DULs,a the
electroforming of copper, the Borexino Cleaning Module and the BiPo facility at
the LSC. These facilities have been selected to report complementary information
with respect to the reviews collected in this issue.
2.1. Radioactivity screening facility
A critical facility in DULs consists in a collection of HPGe detectors for screening
of radioactivity by gamma spectroscopy.5 It is fundamental to make a radioactivity
screening prior of selecting the materials for detectors to be installed in DULs.
This work is done in order to reduce the overall detector background. In addition,
considering the large excavated volumes underground the concrete for lining is
also screened before use to select low radioactivity materials. Similarly, painting
for buildings and infrastructures in underground is screened as well as all other
materials to be used in large quantity. This helps making the overall DUL less
a More
specific details are given in this issue.5
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A. Ianni
Fig. 6. An HPGe detector inside its Cu and Pb shieldings during assembling. The inner Cu
shielding which has a higher level of radiopurity can be seen. The outer shielding can also be
made of ancient Pb, which has a lower 210 Pb contamination.
Table 2.
Number of HPGe detectors at work or expected in DULs screening facilities.
Number of
HPGe detectors
SNOLab
LNGS
LSC
BUL
LSM
Baksan
SURF
CJPL
Kamioka
5
15
7
4(+3)
18(+6)
2(+2)
4(+1)
10
6
radioactive. The same procedure is used for selecting the stainless steel to make
water tanks, cryostats or large storage vessels for specific detectors and ancillary
systems. Due to the huge number of measurements required to build detectors in
DULs, a large number of HPGe detectors are deployed in different facilities. In
Table 2 we report the number of HPGe detectors in operation and expected in a
number of DULs.
HPGe detectors are installed with an inner high radiopurity copper shielding
surrounded by a lead shielding. When possible ancient lead is preferred due to the
less 210 Pb contamination. As an example, in Fig. 6 we show an HPGe detector
inside its shielding during assembling at the LSC. In Fig. 7 we show the HPGe
detector facility at the LSC.
1743001-8
Fig. 7. The HPGe detector facility at the LSC as an example of a radioactivity screening infrastructure in DULs.
Counts/day
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Review of technical features in underground laboratories
105
104
10
3
102
10
1
10−1
10−2
10−3
500
1000
1500
2000
2500
3000
Energy [keV]
Fig. 8. (Color online) Energy spectra of an HPGe detector recorded at the LSC with (green) and
without (red) the Pb and Cu shieldings.
In Fig. 8 we show the energy spectra of one HPGe detector at the LSC with
and without the shielding.
Commercial HPGe detectors have a sensitivity of the order of 0.5–1 mBq/kg for
uranium and thorium. This sensitivity corresponds to 0.04–0.08 ppb for 238 U and
0.1–0.25 ppb for 232 Th. Custom detectors5 can reach a level of 10–50 µBq/kg.
1743001-9
A. Ianni
Table 3. Bulk radiopurity of electroformed copper
made at the LSC in comparison with those of the
initial OFHC copper.
Sample
OFHC Cu
e-formed Cu
238 U
(ppt)
0.20 ± 0.01
< 0.05
232 Th
(ppt)
1.00 ± 0.06
0.040 ± 0.002
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In some special case, a coordination between DULs is necessary to face a huge
number of measurements which are carried out over several years. As an example,
for screening the gadolinium salt needed to run the SuperKamiokande detector with
gadolinium after 2018, Kamioka, LSC, Boulby and LNGS are all participating to
support a huge campaign of measurements.
2.2. Cu electroforming facility
Copper electroforming is a well-known process to obtain high radiopurity copper.8
In this process the copper is produced through electrodeposition of a metal, copper
in this specific case, onto a mold. The LSC has two setups on the surface to make
electroformed copper. The copper to be used and the one produced are both stored
in underground to avoid cosmogenic activation. The SURF has had a copper electroforming facility to make copper for the Majorana experiment.7 Majorana is a large
array of ultra-low background germanium detectors, enriched in 76 Ge, designed
and built to search for neutrinoless double beta decay. The detector makes use of
electroformed copper for detector components and shielding.
At the LSC, in particular, the technique in use is direct fixed-current-density
electroplating.8 The materials employed are OFHC copper bars, which are stored
in underground. The setup allows making a few mm thick hollow cylinder of about
600 g in five working days. In Table 3 we report the bulk radiopurity of the final
products measured by ICP-MS.9
At the LSC the facility has been used to make photomultiplier and divider
housings for the ANAIS experiment. ANAIS is a 112 kg array of high radiopurity
NaI(Tl) scintillators to search for dark matter. In ANAIS there are nine crystals
and each crystal is viewed by two photomultipliers.
In general a copper electroforming facility is of great interest in DULs due to
the high level of radiopurity which can be achieved. In DULs in preparation (CJPL
and ARF) such a facility is among the ones to be installed underground.
2.3. The Borexino cleaning module
Borexino is a massive liquid scintillator detector12 running at the LNGS. The main
goal of Borexino is searching for MeV range neutrinos from the Sun, the Earth and
supernovae. Borexino operates 300 tons of ultra-pure liquid scintillator and about
1 kton of pseudocumene (C9 H12 ) for shielding. In order to operate the scintillator
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Fig. 9.
The Cleaning Module of the Borexino detector.
purification plants,14 Borexino needs a huge fluid handling system and a number of
stainless steel storage vessels. It is critical to make a precision cleaning of the fluid
handling system as-built so that no radioactive impurities are introduced in the
purified scintillator. This work is performed with a dedicated ancillary equipment,
the Cleaning Module. In Fig. 9 we show a photo of the system. The Cleaning Module
consists of a buffer vessel to store chemicals for cleaning to perform pickling and
passivation, a pump to move the liquid to the system to be treated, filters to remove
particulates and a heating unit to heat the cleaning solution. The system is installed
inside a compact movable metal structure.
This system can be coupled to vessels or units of the Borexino fluid handling
system for cleaning operations. In addition, the system can receive deionized water
from the water purification plant11 for rinsing and nitrogen for drying at the end of
the operation. During rinsing samples of water can be taken to count the residual
particles and assign the cleanliness level achieved according to the MILSTD-1246C.
Special Millipore paper filters are used to count the particulates and determine the
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Number of particles per liter
A. Ianni
105
Class25
104
Class50
Class100
1000
100
10
5
10
50
100
Particle size [μm]
Fig. 10. Particulate number density against particulate size for different cleanliness classes according to the MILSTD-1246C.
size. Based on the size and number of particles, a cleanliness class is determined
and compared with the reference deionized water cleanliness. In Fig. 10 we show the
number of particles per liter as a function of size for different cleanliness classes. A
satisfactory cleaning should result in a class better than 50. In this case the residual
contaminations of uranium and thorium are at the level of less than 0.06 µBq/kg.
The Cleaning Module has been a fundamental ancillary equipment for properly
operating the Borexino detector where an extreme level of radiopurity is required.
2.4. The BiPo facility at the LSC
We report briefly about a unique low background facility named BiPo. The BiPo
facility is installed at the LSC for the SuperNEMO experiment.15 SuperNEMO is
designed to search for neutrinoless double beta decay in 82 Se. The detector makes
use of thin selenium foils, enriched in 82 Se. In order to determine the surface contamination in uranium and thorium at µBq/kg level the BiPo facility has been
built. The basic idea is to use the Bi–Po decay β − α sequence in the 238 U and
232
Th radioactive chains to measure the contamination at this ultra-low level. In
Fig. 11 we show the concept of the BiPo detector. A sample foil is deployed between
an array of plastic scintillators over a 3.6 m2 surface. The scintillator is viewed by
photomultipliers on both side, as shown in Fig. 11. The setup is able to detect
the decay sequences of β and α from 214 Bi–214 Po from 238 U and 212 Bi–212 Po from
232
Th. The A = 212 sequence is faster. A prompt β-like signal is followed by a space
and time correlated α-like signal. In this way the setup can reach a sensitivity of
the order of 10 µBq/kg.
The BiPo facility is being used by other Collaborations in the next future to
measure surface contamination on planar samples.
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Fig. 11. Concept of the BiPo facility at the LSC to determine uranium and thorium contaminations on a planar geometry sample.
3. Cleanliness in DULs
Cleanliness is a fundamental parameter in DULs. Therefore, a few words on this
matter are in order. Dust from soil or concrete powder, which can be found in
underground, contains particulates with 1–10 ppm level of uranium and thorium.
As a consequence detector components must be kept away from this source of
contamination. The basic recipe to avoid this background is working for detector
assembling in a clean room environment. Small detector components can be handled
in ISO5 (class 100) or ISO6 (class 1000) clean rooms.
Assuming 2.7 g/cm3 density for soil, a class 100 cleanliness level (MILSTD1246C) contains some 67 µg of particulates per liter of air. Considering the
ppm levels of uranium and thorium contaminations, this small mass turns to be
0.67 mBq/kg and 0.22 mBq/kg for 238 U and 232 Th, respectively. A class 1000 will
be a factor of 104 more radioactive.
Large assembling, as an example photomultipliers installation inside a water
tank or large vessels (10 m scale), can be carried out in ISO7 or ISO8 environments.
In special cases one can also reach a better cleanliness level between ISO6 and ISO7.
In order to turn a large vessel into a clean room of this class, filtered air can be
forced inside and standard clean room access protocol can be put into operation.
We report two specific examples. For the installation of photomultipliers and nylon
vessels inside the stainless steel sphere of Borexino (13.7 m in diameter) filtered
synthetic air is used. Operators are working in clean room suits and each equipment
taken inside is cleaned according to clean room cleaning protocols. The DarkSide50
neutron veto16 is connected to a radon-free class 100 clean room. This allowed to
install the cryostat and the TPC in a controlled clean environment.
Medium- or small-size DULs (SNOLab, LSM, LSC, SURF at Davis Campus
and Boulby) can be organized to reach an overall high cleanliness level. SNOLab
is organized as a class 2000 clean room with a demanding access protocol. This is
1743001-13
A. Ianni
a crucial protocol for SNOLab, considering the outside mining environment in the
underground area. SURF at the Davis Campus is organized with a less demanding protocol and classified as class 3000. For large DULs (LNGS and CJPL) this
approach is not practical. However, special care is taken to protect sensitive detectors’ components from dust, using clean room procedures.
Int. J. Mod. Phys. A Downloaded from www.worldscientific.com
by GRIFFITH UNIVERSITY on 10/25/17. For personal use only.
4. Conclusion
Underground laboratories are important multidisciplinary research infrastructures.
At present, there are 13 laboratories in operation and three underway. Some of
these laboratories have been already in operation for 50 years. In this work we
have discussed a number of main features in underground laboratories. We have
given some general characteristics for these research infrastructures. We have also
discussed a number of facilities to support the construction, commissioning and
running of experiments in DULs. We have not considered a number of important
facilities because they are discussed in the specific reviews enclosed in this issue.
References
1. A. Ianni, Considerations on Underground Laboratories (TAUP, Sudbury, Canada,
2017).
2. Deep Underground Laboratory Integrated Activity in Biology (DULIA-bio), Canfranc
Laboratory, Spain, October 3–4, 2015, https://indico.cern.ch/event/436589/.
3. KAGRA Collab. (K. Somiya), Class. Quantum Grav. 29, 124007 (2012).
4. A. Ianni, Prog. Part. Nucl. Phys. 94, 275 (2017).
5. M. Laubenstein, Int. J. Mod. Phys. A 32, 1743002 (2017).
6. M. Wojcik and G. Zuzel, Int. J. Mod. Phys. A 32, 1743004 (2017).
7. Majorana Collab. (N. Abgrall et al.), arXiv:1601.03779.
8. S. Borjabad et al., Proceedings of Low Radioactivity Techniques, 2017.
9. Pacific Northwest National Laboratory (I. J. Arnquist and E. W. Hoppe), private
communication.
10. DarkSide Collab. (P. Agnes et al.), J. Instrum. 11, P03016 (2016).
11. M. Giammarchi, Int. J. Mod. Phys. A 32, 1743011 (2017).
12. Borexino Collab. (G. Alimonti et al.), Nucl. Instrum. Methods A 600, 568 (2009).
13. S. Nisi et al., Int. J. Mod. Phys. A 32, 1743003 (2017).
14. L. Miramonti, Int. J. Mod. Phys. A 32, 1743010 (2017).
15. SuperNemo Collab. (I. Nasteva), arXiv:0909.3167.
16. DarkSide50 Collab. (P. Agnes et al.), Phys. Lett. B 743, 456 (2015).
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