Background Measurements Background Measurements and Activities @ Boulby for and Activities @ Boulby for

JRA1JRA1

Tim LawsonTim Lawson

University of SheffieldUniversity of Sheffield

IAP, Paris, 14th February 2006

Overview of Boulby JIF Overview of Boulby JIF FacilityFacility

Low-b/g* salt-rock (*How low? Low-b/g* salt-rock (*How low? – see later).– see later).

>1500 m>1500 m22 floor area divided floor area divided into main experimental into main experimental hallway + 2 stubs; ancilliary hallway + 2 stubs; ancilliary rooms (workshop, store, rooms (workshop, store, mess,…).mess,…).

Cleanroom protocol for entry / Cleanroom protocol for entry / exit; HEPA-filtered air.exit; HEPA-filtered air.

One stub has secondary air One stub has secondary air filtration – for use as ‘ultra-filtration – for use as ‘ultra-clean’ room (in-house low-b/g clean’ room (in-house low-b/g tests, detector tests, detector commissioning, etc.)commissioning, etc.)

Crane facilities in Crane facilities in experimental areas (x-y in experimental areas (x-y in Main hall).Main hall).

Air conditioning, telephone, Air conditioning, telephone, 100Mbit/s optical link to 100Mbit/s optical link to surface.surface.

……Overview of JIF FacilityOverview of JIF Facility

Dark Matter JIF Area.

Stub BStub A

Low BGLab

>2.0m >2.0m

12ZEPLIN-II

DRIFT-II Detectors /Vacuum Chambers gas systems, fume hood

& extraction hose DRIFT-I

Lab

Mess

Gas/fire sensorControl roomEntranc

ecorridor

WorkshopStore room

2x LN2 generators

ZEPLIN-IIIzone

5.5m

~75m

~18m

……Overview of JIF Facility: Low BG Overview of JIF Facility: Low BG LabLab

5.6

7.68m

0.8m

4.28m

11.96m

6.0m

Small Proj Bay

Sto

rag

e

Desk

Sto

rag

e

Sto

rag

e EntranceClean-Off 6.0m

DRAFT Plan for JIF Low BackgroundLab (Stub A)SMP - Nov 05

0.5T swing crane(in place)

AC unit

Project Assembly Area

HEPA

Bench

Ben

ch

Ge

• Class 1000 clean room.

• Floor area ~70m2.

• 0.5 tonne swing crane.

• HPGe detector operational (Pb/Cu castle under construction).

• NaI – based detector in place and operational.

• RAD-7 radon detector operational.

Previous Measurements @ Previous Measurements @ BoulbyBoulby

[1] PF Smith et al, Astroparticle Physics 22 (2005), 409

ConclusionConclusion: plasterboard wall reduces : plasterboard wall reduces neutron flux by ~8%; main neutron neutron flux by ~8%; main neutron background dominated by average background dominated by average U/Th concentration in rock.U/Th concentration in rock.

Results:Results:• Calculated n-production from rock Calculated n-production from rock (NaCl): ~3E-8 g(NaCl): ~3E-8 g-1-1 s s-1-1..• Neutron flux from rock: 3.0E-6 cmNeutron flux from rock: 3.0E-6 cm-2-2 ss-1-1

• Neutron flux shielded by Neutron flux shielded by plasterboard wall: 2.7E-6 plasterboard wall: 2.7E-6 cmcm-2-2 s s-1-1

• Neutron flux added by plasterboard: Neutron flux added by plasterboard: 6E-8 cm6E-8 cm-2-2 s s-1-1

• Net neutron flux: 2.76E-6 cmNet neutron flux: 2.76E-6 cm-2-2 s s-1-1

• Feb 2003Feb 2003: Unshielded 2kg Ge : Unshielded 2kg Ge detector exposed to open cavern in detector exposed to open cavern in JIF stub-2, obtaining average JIF stub-2, obtaining average γγ spectrum from all walls of the spectrum from all walls of the caverncavern (See ref [1].) (See ref [1].)• 4 4 γγ lines from U and 4 from Th lines from U and 4 from Th compared to Monte Carlo.compared to Monte Carlo.

……Recent Background StudiesRecent Background Studies Recent measurementsRecent measurements11 with with

portable HPGe-detector and portable HPGe-detector and radon monitor at several radon monitor at several test-points within / around JIF test-points within / around JIF lab (see talk by Jan Keisel).lab (see talk by Jan Keisel).

4040K (1460 keV) dominates K (1460 keV) dominates γγ--spectrum.spectrum.

137137Cs (661 keV) line also Cs (661 keV) line also present.present.

Typical integrated Typical integrated γγ counting counting rate: 20 – 24 counts kgrate: 20 – 24 counts kg-1-1 s s-1-1..

Typical Typical 222222Rn concentration Rn concentration in all tested locations: 2.5 in all tested locations: 2.5 ± ± 1.6 Bq/m1.6 Bq/m33. Similar results . Similar results obtained with our own Rn obtained with our own Rn detector (Burridge Rad-7).detector (Burridge Rad-7).

[1] J.Keisel & J.Dorda (Inst. Phys., U. Silesia, Katowice, Poland), Aug 2005.

Ongoing / Planned Background Ongoing / Planned Background StudiesStudies

NUTSNUTS: 6.5L Gd-loaded scintillator detector. : 6.5L Gd-loaded scintillator detector. Two-pulse signature (proton recoils followed by Two-pulse signature (proton recoils followed by gammas from neutron capture) is used to gammas from neutron capture) is used to distinguish n events. (see talk by E.Tziaferi).distinguish n events. (see talk by E.Tziaferi).

DRIFT-IIaDRIFT-IIa: 1m: 1m33 (167g) low pressure CS (167g) low pressure CS22, , Negative Ion Drift TPC detector. Neutron-Negative Ion Drift TPC detector. Neutron-induced recoils produce distinctive high dE/dx induced recoils produce distinctive high dE/dx tracks.tracks.

ZEPLIN-II vetoZEPLIN-II veto: Gd-lined liquid scintillator. Plans : Gd-lined liquid scintillator. Plans for a muon-induced neutron investigation are for a muon-induced neutron investigation are currently under consideration.currently under consideration.

Investigation of radon levels, radon-progeny Investigation of radon levels, radon-progeny plate-out / deposition and additional n-flux due plate-out / deposition and additional n-flux due to associated (to associated (αα, n, n) reactions…) reactions…

Is Radon a Problem?Is Radon a Problem? U-238 U-238

contamination contamination on surfaces on surfaces within and within and around lab.around lab.

Resulting Rn can Resulting Rn can diffuse – diffuse – resulting plate-resulting plate-out / deposition out / deposition is not expected is not expected to match to match distribution of distribution of original original contamination.contamination.

Highest-energy Highest-energy αα’s in U-238 ’s in U-238 decay chain decay chain produced by Rn produced by Rn – progeny.– progeny.

((αα, n) cross-, n) cross-sections tend to sections tend to increase with increase with energy (typically energy (typically 0.1-1 barn)0.1-1 barn)

Low-B/G Facility: HPGe-Low-B/G Facility: HPGe-detectordetector

Castle for HPGe Castle for HPGe detector currently under detector currently under construction (8cm OFHC construction (8cm OFHC Cu, surrounded by 15 Cu, surrounded by 15 cm Pb).cm Pb).

Ge-detector castle Ge-detector castle contained within contained within Rn-’shroud’ – box over-Rn-’shroud’ – box over-pressured with dry Npressured with dry N22 to to displace Rn gas and displace Rn gas and reduce activity from Rn reduce activity from Rn progeny.progeny.

Estimated sensitivity: Estimated sensitivity: ~1e-9 g/g~1e-9 g/g

Material Radiopurity Material Radiopurity TestingTesting

[2] http://hepwww.rl.ac.uk/ukdmc/Radioactivity/Index.html

Extensive library of tested detector Extensive library of tested detector materials and components exists on materials and components exists on UKDM websiteUKDM website22 with links to other with links to other radiopurity databases.radiopurity databases.

Radio-purity analysis using mass Radio-purity analysis using mass spectrometry (principally ICPMS and spectrometry (principally ICPMS and GDMS).GDMS).

Recent measurements include Perspex Recent measurements include Perspex and steel for the DRIFT-II detector, and steel for the DRIFT-II detector, polypropylene, plywood & floor timber for polypropylene, plywood & floor timber for DRIFT-II neutron shielding. DRIFT-II neutron shielding.

Latest measurements include samples of Latest measurements include samples of salt rock from JIF cavern and overlying salt rock from JIF cavern and overlying potash (KCl, Kpotash (KCl, K22COCO33, KOH,…) seam., KOH,…) seam.

……Material Radiopurity TestingMaterial Radiopurity Testing

Raw rock samples crushed using geology

dept. facilities at Sheffield

Samples sent for GDMS testing

SummarySummary

Background studies:Background studies: Repeats of earlier Ge-detector & Rn detector tests Repeats of earlier Ge-detector & Rn detector tests

underway,underway, N-b/g measurements with DRIFT-II,N-b/g measurements with DRIFT-II, N-b/g measurements with NUTS,N-b/g measurements with NUTS,Low B/G Lab:Low B/G Lab: Shielding for Ge-detector under construction,Shielding for Ge-detector under construction, Other infrastructure (crane, HEPA-filter,…) in place.Other infrastructure (crane, HEPA-filter,…) in place.Radiopurity testing:Radiopurity testing: Samples of cavern rock being tested.Samples of cavern rock being tested. Large publicly-accessible database of results Large publicly-accessible database of results

continually growing…continually growing…