222Rn
measurements
H. Richter, H. Simgen, G. Zuzel
Max-Planck-Institut für Kernphysik, Heidelberg
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Outlook



Short introduction
Emanation from the cryostat – Hardy’s talk
Samples measured in Heidelberg:
- Kalrez gaskets
- Coaxial cables
- Padova HV-feedthrough
- Solders
- Welds
- Cryogenic valves
- Others

Future tests:
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Introduction
Ar
Counter
flange
P10
Getter pump
Pressure
gauge
To the
bubbler
To the
pump
NaOH
trap
Chromosorb trap
Main line
Molecular Si-Ge
sieve trap trap
Charcoal trap
for He purification
with flowmeter
He
Radon
transport
trap
Pusher
Hg diff.
pump
Töpler pump
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Absolute detection limit
30 – 100 µBq (15 – 50 atoms)
Introduction
Saturation
value
ARa – emanation rate (226Ra activity seen via 222Rn emanation)
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Cryostat 222Rn emanation
Atot ~ 30 mBq
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Different cryo-containers
Tank from
Quality of
stored gas
Vol.
[m3]
activity in
saturation [mBq]
specific 222Rn
act. [mBq/m3]
Westfalen AG
technical
3
177  6
59  2
Westfalen AG
6.0
0.67
42  2
63  3
SOL
6.0
16
65  6
4.1  0.4
LINDE
7.0
3
2.7  0.3
0.9  0.1
Air Liquide
technical
0.67
1.8  0.4
2.7  0.6
LINDE
technical
6.3
3.5  0.2
0.56  0.03
114
~60
~ 0.5
65
~ 30
~ 0.5
BOREXINO
GERDA
HP
222Rn
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Kalrez gaskets (lock)
A = (0.05  0.03) mBq
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Coaxial cables
Sample description
Emanation rate
Others
Habia teflon cable,
514 g, 346 m
(0.34  0.09) mBq/kg
(0.50  0.13) Bq/m
Ra: < 1.8 mBq/kg
U: < 59 mBq/kg
Th: < 4.7 mBq/kg
Teledyne Reynolds
HV cable (teflon
coated)
292 g, 197 m
(1.9  0.5) mBq/kg
(1.8  0.5) Bq/m
Ra: < 1.3 mBq/kg
U: < 9 mBq/kg
Th: 6 mBq/kg
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Padova HV-feedthrough
A < 0.05 mBq
(vessel-side only)
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Solders
8 Cu strips 220 cm
with solders
(some tens of grams)
A < 0.04 mBq
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Welds
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Welds
Sample
Description
7 plates
Total surface (both
sides): 1.5 m2
Weld length: 2.53 m
Emanation
rate [mBq/m]
Comments
0.36  0.04
Standard workshop cleaning procedure
(alkaline bath), optically clean.
A lot of gas in the Rn samples
2 plates
Total surface (both
sides): ~0.4 m2
Weld length: ~0.8 m
< 0.1
After 2-hour etching (20 %*) HNO3 + 1.7
% HF + water) and 30-min passivation
(15 % HNO3 + water).
Not much gas in the Rn samples
4 plates
Weld length: ~1.2 m
0.10  0.04
4 plates
Weld length: ~1.2 m
< 0.04
Electropolished (3 zones)
Electropolished and etched
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Welds
Etched and passivated plate
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Welds
Sample
Emanation
rate [mBq/m]
Description
7 plates
Total surface (both
sides): 1.5 m2
Weld length: 2.53 m
2 plates
Total surface (both
sides): ~0.4 m2
Weld length: ~0.8 m
< 0.1
4 plates
Weld length: ~1.2 m
0.10  0.04
4 plates
Weld length: ~1.2
m
< 0.04
0.36  0.04
Comments
Standard workshop cleaning procedure
(alkaline bath), optically clean.
A lot of gas in the Rn samples
After 2-hour etching (20 % HNO3 + 1.7 %
HF + water) and 30-min passivation (15
% HNO3 + water).
Not much gas in the Rn samples
Electropolished (3 zones)
Electropolished and etched
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Welds
Electropolished / etched plate
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Welds
electropolished stainless steel
etched stainless steel
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Welds
electropolished stainless steel
electropolished weld
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Welds
Sample
Description
7 plates
Total surface (both
sides): 1.5 m2
Weld length: 2.53 m
Emanation
rate [mBq/m]
Comments
0.36  0.04
Standard workshop cleaning procedure
(alkaline bath), optically clean.
A lot of gas in the Rn samples
2 plates
Total surface (both
sides): ~0.4 m2
Weld length: ~0.8 m
< 0.1
After 2-hour etching (20 %*) HNO3 + 1.7
% HF + water) and 30-min passivation
(15 % HNO3 + water).
Not much gas in the Rn samples
4 plates
Weld length: ~1.2 m
0.10  0.04
4 plates
Weld length: ~1.2 m
< 0.04
Electropolished (3 zones)
Electropolished and etched
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Welds
Sample
Description
7 plates
Total surface (both
sides): 1.5 m2
Weld length: 2.53 m
Emanation
rate [mBq/m]
Comments
0.36  0.04
Standard workshop cleaning procedure
(alkaline bath), optically clean.
A lot of gas in the Rn samples
2 plates
Total surface (both
sides): ~0.4 m2
Weld length: ~0.8 m
< 0.1
After 2-hour etching (20 %*) HNO3 + 1.7
% HF + water) and 30-min passivation
(15 % HNO3 + water).
Not much gas in the Rn samples
4 plates
Weld length: ~1.2 m
0.10  0.04
4 plates
Weld length: ~1.2 m
< 0.04
Electropolished (3 zones)
Electropolished and etched
Etching works !
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Consequences for cryostat
~80 m2
Emanation of stainless steel: ~ 5 Bq/m2
----------->
Not treated welds: 0.36 mBq/m
----------->
Etched welds: < 0.04 mBq/m
----------->
100 m
100 m
~ 0.4 mBq
~ 20 mBq
< 2 mBq
The aim, but probably difficult to
achieve by cryostat cleaning
Rather conservative
The same range as measured activity,
other sources should still be considered
(flange and its components, residual dust)
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Cryogenic valves - WEKA
222Rn
A = 150 mBq
C ~ 1 kBq/m3
O-ring
gasket
222Rn
Stamp gasket
source:
source
Emanation rate [Bq]
Diffusion rate [Bq]
Teflon
75  15
< 13
PCTFE
-
37  13
TRCH 1000
GERDA General meeting, 18-22.02.2008
Krakow, Poland 43  16
-
Comments
Original gasket
Cryogenic valves - KAMMER
NPT / VCR connections
Connection
Emanation rate [Bq]
Diffusion rate [Bq]
NPT
111  23
-
VCR ½”
53  15
28  14
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Comments
Teflon sealed
Full metal sealed
Cryogenic valves - WTA
Teflon:
Valve status
Open
“Kammprofil”
gasket
Closed
Teflon / In
gaskets
Emanation rate [mBq]
2.0  0.2
0.64  0.15
In:
Valve status
Open
Closed
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Emanation rate [mBq]
2.2  0.2
0.79  0.11
Cryogenic valves - WTA
Body status
Not treated
Etched (BAMA)
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Emanation rate [mBq]
1.8  0.2
0.11  0.04
Reduction by a
factor of ~ 20 !
Other samples
Sample
Glass wool
(142 g)
Perbunan O-ring
SIMIC (5 mm, 3.2 m)
Induction sensors
(10 pieces)
“Micro-camera”
(1 piece)
GERDA General meeting, 18-22.02.2008
Krakow, Poland
Emanation rate
(20.6  0.2) mBq/kg
(1.8  0.4) mBq
(16  3) Bq/piece
< 70 Bq/piece
Future tests




Next cryostat emanation tests: in present state
and after copper mounting (GS)
Emanation of the lock (Munich)
Routine material checks on requests
Systematic investigation of different welding
procedures and welds cleaning
GERDA General meeting, 18-22.02.2008
Krakow, Poland