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detect and identify
Measurement of
Tritium in Helium
Dr. Alfred Klett
Berthold Technologies, Bad Wildbad, Germany
22nd Annual Air Monitoring Users Group (AMUG) Meeting Palace Station Hotel, Las Vegas, Nevada, USA, 5th May 2010
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Alfred Klett May 5, 2010 2
Overview
Introduction
New Physics at CERN
Large Hadron Collider LHC
Cryogenic System
Tritium in Helium Measurement
Concept
Monitor Berthold LB110
Calibration
Minimum Detectalble Activity Concentrations
Regulations
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Alfred Klett May 5, 2010 3
Berthold Technologies in Bad Wildbad
German Manufacturer of instruments for
Industrial Process Control
Bioanalytics
Radiation Protection
Nicely located in the Black Forest (close to Karlsruhe)
Since more than 60 years reliable products MADE IN GERMANY
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Dr. Alfred Klett 17.10.2008 4
Large Hadron Collider at CERN Geneva
LHC was designed to collide two counter rotating beams of protons or heavy ions
p-p collisions at 7 TeV/per beam
1232 supraconducting dipoles on 27 km circumference
1st operation started in September 2008
Reference: http://www.cern.ch
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Dr. Alfred Klett 17.10.2008 5
Detectors at the Large Hadron Collider
ALICE (Heavy Ion Physics)
ATLAS (Higgs-Particle)
CMS (Calorimeter for high E)
LHCb (CP-Violation)
Reference: http://www.cern.ch
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Dr. Alfred Klett 17.10.2008 6
ATLAS Detector at the LHC
General purpose detector 46 x 25 x 25 m³ (L x W x H) 7000 tons weight
Detector components Inner tracker (semiconductor pixel, silicon microstrip, straws)
Calorimeter (sensors liquid argon & plastic scint in metal plates)
Muon Spectrometer (large straws)
Magnet System
Trigger System
Data Acquisition System
Computing System
1700 scientists from 159 institutes in 37 countries
Reference: http://www.cern.ch
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Dr. Alfred Klett 17.10.2008 7
Magnets at LHC
1232 Superconducting dipole magnets
cooled down to 1.9°K (liquid helium)
11.700 Ampere
8.4 Tesla
Length: 14.3 m
Weight: 35 tons
Cost: 0.5 Mio. CHF
Reference: http://www.cern.ch
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Helium Cooling System
Total mass of helium in operating conditions
15 tons per sector
120 tons total in the eight LHC sectors
Helium storage capacity
27 tons liquid in helium dewars
50 tons gaseous at ambient temperature
Liquid helium from the CERN liquid storage is taken by external suppliers and returned to CERN on request
The helium shall not be contaminated with radionuclides exceeding exemption / clearance levels
Alfred Klett May 5, 2010 8
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Production & Decay of Tritium in Helium
Alfred Klett May 5, 2010 9
e-
Tritium
3He 4He
Radiation
= 12.3 a
Estimated total annual Tritium activation: 3.7 GBq
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Dr. A. Klett Nov 17, 2008 10
Tritium Monitor LB 110 (P10) Proportional counter (1.3 liter)
1 : 4 mixing ratio air/counting gas P10
0.260 liter sensitive volume
1.25 liter/min flow
Tritium counting efficiency 55%
Calibration factor 7 kBq/m³ per cps
Background rate in tritium channel 1 to 3 cps
Risetime discrimination against external gamma radiation
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Dr. A. Klett Nov 17, 2008 11
Tritium Monitor LB 110 (P10)
Minimum detectable activities
5400 Bq/m³ within 30 s
3800 Bq/m³ within 60 s
1200 Bq/m³ within 10 min
500 Bq/m³ within 1 h
100 Bq/m³ within 24 h
Spillover
5% – 7% for 137Cs
3% – 5% for 85Kr
23% – 25% for 14C
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Dr. A. Klett Nov 17, 2008 12
Design of Tritium Monitor LB 110
Proportional counter tube
Detector housing (cathode)
Principal layout of electrodes
Outer anode plane (20 wires)
Inner cathode plane (40 rods)
central anode wire
HV on anodes, virtual ground on cathodes, anode readout
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Dr. A. Klett Nov 17, 2008 13
Primary Ionization Tritium Event Track of a low energy beta particle from a tritium decay
Primary ionization along the track
Primary electrons are drifting towards anode wires
Drift ranges are approximately equal
All charges are arriving at nearly the same time
Fast rise time of signal
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Dr. A. Klett Nov 17, 2008 14
Primary Ionisation Cs-137 Event Track of a fast electron in the detector volume
Primary ionization along the track
Primary electrons are drifting towards anode wires
Drift distances are very different
There are very short and very long drift times
Slow rise time of the signal
Photon
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Dr. A. Klett Nov 17, 2008
Fortbildung Strahlenschutz
15
Tritium
fast electrons
time
PH
Tritium Rise Time Discrimination
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Dr. A. Klett Nov 17, 2008
Fortbildung Strahlenschutz
16
Rise times of anode signals
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National Physical Laboratory - NPL
National Metrological Institute of the UK
one of the UK's leading science & research facilities
a world-leading centre of excellence in developing and applying the most accurate standards, science and technology available
Ionising radiation science areas
Dosimetry
Neutron Metrology
Radioactivity
Alfred Klett May 5, 2010 17
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Tritium in Helium Calibration Procedure LB 110 attached to NPL tritium calibration rig
Monitor and rig were pre-filled and gases mixed
Helium at a nominal pressure 33.3 kPa
P10 gas (90% Argon, 10% Methane) was then admitted to
the system until pressure reached a nominal 100.7 kPa
A vessel previously filled with standardised tritium in hydrogen was opened to the rig
The tritium gas had been previously standardised in a manner traceable to national standards of radioactivity
the gases were then mixed using the rig circulation pump until homogenity was achieved
Alfred Klett May 5, 2010 18
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Tritium in Helium Calibration Procedure The addition of tritiated hydrogen made no significant difference to the overall pressure within the system
The monitor’s gas mixing equipment was not used during the calibration procedure
The monitor’s response to tritium in this atmosphere was recorded
The tritium activity concentrations are expressed as the total activity of tritium divided by the total volume of hydrogen and helium in the rig
The reported uncertainties are based on standard uncertainties multiplied by a coverage factor k=2, which provides a level of confidence of approximately 95%
Alfred Klett May 5, 2010 19
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Tritium in Helium Calibration
Tritium calibration performed by Hilary Philipps / NPL & Alfred Klett Nov. 18-19 and Nov. 24-25, 2009
NPL calibration rig (on the right)
Berthold Tritium Monitor LB 110 (on the left)
Alfred Klett May 5, 2010 20
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The Monitor under Calibration
Alfred Klett May 5, 2010 21
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NPL Calibration Rig
Alfred Klett May 5, 2010 22
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Tritium in Helium Calibration Results
Alfred Klett May 5, 2010 23
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MDA & Decision Threshold
Alfred Klett May 5, 2010 24
calculated according
to ISO 11929-1:2000
600 s measuring time
background
5% error probability
for errors of the 1st
and 2nd type
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MDA & Decision Threshold
Alfred Klett May 5, 2010 25
calculated according
to ISO 11929-1:2000
600 s measuring time
background
5% error probability
for errors of the 1st
and 2nd type
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Tritium in Helium Calibration Summary
Alfred Klett May 5, 2010 26
Quantity Value Unit
Monitor’s Response to Tritium 0,458 cps / (kBq/m³)
Calibration Factor 2,18 kBq/m³ per cps
Background Counting Rate 0.78 cps
Minimum Detectable Activities with Tbgrd = Tsample = 600s
MDA Volumetric Activity Concentration 137 Bq/m³
MDA Mass Activity Concentration O,7 Bq/g
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Tritium Regulations
IAEA Safety Guide No. RS-G-1.7 100 Bq/g
CERN‘s clearance & exemption limits
activity concentration 200 Bq/g
total activity release 200 kBq
Germany’s tritium limits
exemption 1000 kBq/g
clearance 1000 Bq/g
Alfred Klett May 5, 2010 27
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Dr. A. Klett Nov 17, 2008
Fortbildung Strahlenschutz
28
1) Operating Manual Tritium Monitor LB 110
Berthold Technologies Ident. No.: 80872 BA2, Rev. 02, May 20, 2009
2) National Physical Laboratory NPL, Calibration Certificate, Berthold Type LB 110
S/N 6010, Reference: 2009100203 , February 10, 2010, Teddington, UK
3) IAEA, Application of the Concepts of Exclusion, Exemption and Clearance
IAEA Safety Guide No. RS-G-1.7, Vienna, Austria, August 2004
References