Kr-85 activity in KL LS

The Kr-85 activity in KamLAND LS
Alexandre Kozlov
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Last modifications to the system
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Calibrations
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The LS sampling procedure
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Results
KamLAND Collaboration Meeting in Tuscaloosa, USA (2011)
Hardware problems resolved before the last measurements
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In the last report presented at the Amsterdam meeting I mentioned problems
caused by rough vacuum, and liquid pumps.
Problem #1: a low pumping speed, and overheating of the oil sealed rough
vacuum pump (Welch 8905). Overheating was a source of the hydrocarbon
contamination due to the oil backstreaming. In addition, it caused a loss of
pumping speed and a higher ultimate vacuum pressure.
Problem #2: the weakest point in the system was leakage of the LS
circulation line partially made of a soft tube. The tube was used in the
Masterflex peristaltic liquid pump to circulate LS during the Krypton
extraction procedure. A short lifetime of the tube and upredictable changes
in the leakage rate at Swagelok connections (due to the tube shrinking)
were making all positive Krypton results questionable, and therefore
compromised the purpose of the system.
To solve the problems both pumps were replaced
A new dry pump
Varian SH-110: oil free,
3x faster than Welch 8905
The Iwaki MDG-H2T100N liquid pump
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Magnetic drive gear pump
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Made of corrosion resistant materials, automatic shutdown if overheated
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Maximum pumping speed 2.1L/min, 0.4MPa, 20Watt power consumption
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NPT fittings were modified after purchase by welding NPT to VCR adapters
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Not vacuum tight, but a low power consumption, a small size, and
maintanence free operation allowed to construct a cover tank filled with a
pure Helium above std. atm. pressure to isolate it from the air
ISO-F 320mm SS cover tank for the Iwaki liquid pump
Feedthough
for 100V line
VCR connections for a P.G., a vacuum pump, a Helium gas line, IN/OUT LS lines
LS IN/OUT lines
to Iwaki pump
P.G.
Dry pump
100V
Helium
Schematic view of the Krypton measurement system
The Kr-85 activity measurement in Japan
How to get the Kr-85 activity from the Kr-84 meaurement
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We usually assumed that the Kr-85 activity in the air was 1.4Bq/m3 which
was the published value measured in 1995-2001
However, the same paper also claimed existence of an up going trend at a
rate of 0.03Bq m-3 year-1
I think that one may make a concervative assumption that all Kr-85 in the
KamLAND LS originates from air leaks happened during the last distillation
campaign in 2008.
Therefore, if we take into account that changes to the Kr-85 activity we would
obtain 1.6±0.2Bq of Kr-85 in 1m3 of air in 2008
Using this estimate of the Kr-85 activity in the air and amount of Kr-84
extracted from a 5L LS sample we can calculate Kr-85 activity in 1m3 of LS
The Kr-84 calibration is done using 5.3ml air samples added to the same
amount of helium gas as used in the Krypton extraction from LS samples
The Kr-84 calibration using 5.3ml air samples
P  sample  [kPa ]
× 0 [ ppm]× NA ×1000
P  std  [ kPa]
st. atm. pressure P  std =101.325kPa , Kr concentration  0 =1.14ppm , NA=0.57
Kr84 concentration  1  sample [ ppb]=
Equivalent to a 3.5ppt of Kr-84 in helium
during the LS measurement
Pure helium gas samples
Relation between Kr-84 and the Kr-85 activity in 1m3 of LS
For calibration data we know Kr84 concentration  1  sample [ ppb]
3
Kr85 activity in 1m of air  0=1.6 [ Bq] , thus Kr85 activity in air sample
3
 0 [ Bq]×5.3 [ cm ]  1  sample [ ppb]
  sample  [ Bq]=
6
3
 1  std. atm. [ ppb ]
10 [ cm ]
The same Kr84 amount measured using a 5L LS sample corresponds to
  sample ×1000 [ L] 1
× , where
5 [ L]
E
E=0.835±0.020 is the Kr extraction efficiency during the Helium bubbling
3
Kr85 activity in 1m of LS ,   LS [ Bq]=
Relation between Kr-84 and Kr-85 activity in 1m3 of LS
Sensitivity limitation of the system
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The lowest callibration point shown on the calibration plots corresponds to a
3.5ppt of Kr-84 in a ~3.5L of helium gas, or to 6.3 µBq of Kr-85 in 1m3 of LS
(under assumption of 100% Krypton extraction efficiency)
In principle, system sensitivity to Krypton can be improved by removing the
sublimator pump from the path of gases exiting the warming up Kr trap. That
would improve the S/N ratio at the Krypton peak position.
The problem is, however, that all LS samples from KL or distillation s-m I
have to handle are saturated with the N2 gas. If not removed, N2 gas would
make RGA operation impossible.
In case of clean Helium samples the Krypton sensitivity can be improved
after some calibration efforts.
P.G.
N2 gas
The 8L SS sampling tank
pump
LS IN
LS OUT
Optical windows to monitor LS level
Initial condition: 3.5L and 8L tanks
are under vacuum (flushed 4x using
G-1 N2 gas).
1) Next, LS fills the 3.5L tank from
the bottom while gases are being
pump out from the top by running
vacuum pump.
VCR line to KamLAND
Made and deployed by
Ueshima-san
LS flow
2) After filling the 3.5L drain tank
LS flow is switched to the 8L tank
LS level in both tanks is controlled
through optical CF windows.
LS flow
Optical window to
control LS level in
the 3.5L drain tank
3.5L drain tank
G-1 N2 gas line
LS line from KamLAND
to fill the 8L tank
LS line from KamLAND
to fill the 3.5L drain tank
Aug 10, clean room in the Dome area
LS samples transfer
After filling the 8L tank I carried
it to the miniLAND area. Then
the VCR line was used to move
LS from the 8L tank to Bubbler.
The Krypton measurements summary
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8L samples of the KamLAND LS were taken twice on August 3rd and August
10th. Each time it took 16 hours of continious work at the mine plus two days of
preparation (before and after the sampling).
2L of LS were used to wash Bubbler before loading a 5L LS sample used to
measure the Krypton amount.
On Aug 10th I tried to keep all sampling and measurement procedures exactly
the same as on Aug 3rd to check results consistency.
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The end point of the ss line in the KamLAND corresponded to +1.5m in Z-axis.
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Results for Argon isotopes (Ar-39, Ar-40) were consistent within 10%
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The Kr-84 results agreed within 17%
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The Kr-85 activity was equal to 9.9 and 6.6µBq / m3 of LS at the time of last
purification campaign (needs to be corrected to account for the Kr-85 decay).
The difference between these two “identical” samples can be used as an
estimate of the systematic uncertainty of the measurements (a 50% err.)
Background measurement taken on August 13th with the Iwaki liquid pump
connected to the Bubbler did not show any indications of air leakage.
Summary
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Development of the Krypton measurement system was completed.
All previously reported hardware problems were resolved successfully. The
most difficult part was to make a liquid pump operation stable and leak free.
To achieve that the 30L ss cover tank filled with a pure helium gas was used.
Clean LS sampling from KamLAND was performed using specially developed
sampling tools (3.5 and 8L tanks connected to two vacuum pumps).
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LS samples were loaded using the 12m ss VCR line made by Ueshima-san.
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Sensitivity to Kr-85 reached level of few µBq in 1m3 of LS
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Two measurements of the Kr amount in KL LS were completed.
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The Kr-85 activity was 9.9 and 6.6µBq per m3 of LS (50% syst. error)
TO DO: system needs some repairs