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Wir schaffen Wissen – heute für morgen
9. Mai 2011PSI, 9. Mai 2011PSI,
Paul Scherrer Institut
Polonium Evaporation Studies from Liquid Metal Spallation Targets
Matthias Rizzi, Jörg Neuhausen
Seite 2
• INTRODUCTION
• POLONIUM RELEASE
• EXPERIMENTAL TECHNIQUE
transportation method ‐ theory & experimental
• RESULTS & DISCUSSION
• SUMMARY & OUTLOOK
Matthias RIZZI
INDEX
Seite 3
• due to the high beam intensity and the large variety of nuclear interactions the target material becomes highly radioactive
• for a target material with a proton number N, every nuclide from 1 to N +1 can be formed
• production of highly radiotoxic polonium 210 due to neutron capture of bismuth
• lack of thermodynamical data for polonium (vapor pressure, gaseous species)
Radiological issues of spallation targets
Matthias RIZZI
INTRODUCTION
Seite 4
210Po is produced by neutron capture of 209Bi and its following ‐ decay
Matthias RIZZI
BiPb
PbnPbh 209,3.3209
2090208
INTRODUCTION
PbPo
PoBinBid
d
206;4.138210
210;3.521010
209
Seite 5
• biological half‐life of 30‐50 days • high radiotoxicity in case of incorporation (LD50 2‐15 MBq)
• is believed to form a volatile hydrogen species in presence of hydrogen and/or moisture
• for liquid spallation targets risk estimations and dispersion calculations in case of leakage are necessary for licensing
Polonium‐210
Matthias RIZZI
INTRODUCTION
Seite 6
• the apparent vapor pressure of polonium is of main interest for thermodynamic calculations
• the volatile species of polonium and conditions for formation
• influence of cross effects like sputtering and aerosol formation
• stability and possible extraction/absorption of volatile species for filter design in nuclear facilities
release experiments
Polonium
Matthias RIZZI
POLONIUM RELEASE
Seite 7Matthias RIZZI
Abakumov [1982]: release experiments from lead, assumed γPbPo=1, radiometric and direct vapor pressure measurement, T:368‐745⁰C
Feuerstein [1992]: release experiments from Li0.17Pb0.83, XPo=1.5*10‐13, α‐counting, T:350‐700⁰C
Buongiorno [2003]: release experiments from LBE, XPo=2.5*10‐8, Liquid Scintillation Counting (LSC), T:400‐550⁰C
Ohno [2006]: release experiments from LBE, XPo=2.2*10‐10, LSC, T:450‐750⁰C
POLONIUM RELEASE
-12.000
-11.000
-10.000
-9.000
-8.000
-7.000
-6.000
-5.000
-4.000
-3.000
-2.0002.00 1.67 1.43 1.25 1.11 1.00 0.91 0.83
log P P
o
1000/T[K]Ohno, 2006 Buongiorno, 2003Abakumov, 1982 Feuerstein, 1992
Selected vapor pressure data for 210Po
Normalized to XPo=1*10‐6
400⁰C 600⁰C
Seite 8
• a solid or liquid sample gets heated in a constant stream of gas
• the gas phase gets saturated with the gaseous sample species
• quantification of the evaporated material• calculation of the apparent vapor pressure
vapor pressure function f(T)• in case of pure substances, direct calculation of the saturation vapor pressure
apparent vapor pressure functions in our case!
A dynamic method for vapor pressure measurements
Matthias RIZZI
POLONIUM RELEASE
Seite 9Matthias RIZZI
sat
PosatPo V
TRnP
Po
satPoHenry
Po XPK
ANrelease
A
releasePo N
Nn
A is measured at following energies: 286, 338, 522, 807 and 1032keV
detector efficiency , specific ‐Intensity and a sample‐geometry correction factor are included in A
POLONIUM RELEASE
Seite 10
•Closed system to prevent moisture and oxygen entering the rection tube
•Argon with 7% hydrogen in order to reduce the lead surface (PbO)
•Applied atmosphere gets directed through a drying cartridge and a getter furnace in order to remove moisture and oxygen
•quartz reaction tube
•sliding arrangement to apply temperature
EXPERIMENTAL SETUP
Matthias RIZZI
experimental setup scheme
EXPERIMENTAL TECHNIQUE
Seite 11
•irradiated with ‐particles
•lead‐samples of ~0.7g mass
•sample on a quartz filter within a quartz boat
• 53 ml/min of 7%H2/Ar atmosphere applied
•temperatures from 600⁰C up to 1100 ⁰C reaction‐time 60min
EXPERIMENTAL SETUP
Matthias RIZZI
experimental setup scheme
EXPERIMENTAL TECHNIQUE
Seite 12
•sample gets weighed and measured by ‐spectroscopy (detection of 206Po!)
•placement in a quartz‐boat (with quartz filter) within the quartz heating gadget
•closing of the gadget, flush with atmosphere, heating of the furnace
•start of the experiment by sliding the furnace into the right postion
•stop after 60min, cooling down, ‐detection
PROCEDURE
Matthias RIZZI
EXPERIMENTAL TECHNIQUE
Seite 13
saturation of the gas phase with the sample species is crucial!–Selection of the right atmosphere flux, sample and gadget geometry has to be considered
variation of apparent vapor pressure with volumetric flow rate (Viswanathan et al., J. Phys. Chem. B, Vol. 113, No. 24, 2009)
Matthias RIZZI
EXPERIMENTAL TECHNIQUE
Seite 14
500 600 700 800 900 1000-0,1
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
rela
tive
rele
ase
[x]
temperature [°C]
relative release of Polonium from Pb
with the given flux and reaction time calculation of the apparent vapor pressure
Matthias RIZZI
RESULTS & DISCUSSION
-20
-15
-10
-5
0
5
0 0.5 1 1.5 2 2.5 3 3.5
logK
Hen
ry
1000/T [K]
Henry‐constant for 206Po evaporation from leadmeasured in the range 600 ‐ 1100°C
TK Henry
PbPo10126.735209.185.8log
Po
satPoHenry
Po XPK
)(Tf
Seite 15
500 600 700 800 900 1000-0,1
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
rela
tive
rele
ase
[x]
temperature [°C]
relative release of Polonium from Pb
systematically higher apparent vapor pressure for 206Po over a LGE than compared to LBE or lead
Matthias RIZZI
RESULTS & DISCUSSION
TK Henry
LGEPo9962.584805.174.8log
)(Tf
Po
satPoHenry
Po XPK
-20
-15
-10
-5
0
5
0 0.5 1 1.5 2 2.5 3 3.5
logK
Hen
ry
1000/T [K]
Henry‐constant for 206Po evaporation from LGEmeasured in the range 675 ‐ 900°C
Seite 16
evaporation of Po from lead is similar to that from LBE and LGE
600 700 800 900 1000
0.0
0.2
0.4
0.6
0.8
1.0
LBE (Neuhausen et al.) Pb (this work) LGE (this work)
rela
tive
fract
iona
l rel
ease
[x]
Temperature [°C]
Evaporation Behavior of Pb, LBE and LGE
Matthias RIZZI
RESULTS & DISCUSSION
Seite 17Matthias RIZZI
RESULTS & DISCUSSION
-6
-4
-2
0
2
4
600 650 700 750 800 850 900 950 1000 1050 1100
log K H
enry[Pa]
T [K]
Henryconstants for Po from LBE/LGE/Pb
Kurata LBE with H2 Buong. LBE with H2 JN Po from LBE Ar/H2
MR from Pb with Ar/H2 MR from PbAu Ar/H2
Seite 18
use of 206Po instead of 210Po
the calculated saturation vapor pressures are “apparent” vapor pressures – the composition of the gas phase is unknown (PbPo, H2Po,…)
large errors due to experimental uncertainities
fraction of polonium in the sample is not constant, continuous loss of signal
saturation of the vapor is crucial!
Matthias RIZZI
SUMMARY & OUTLOOK
Seite 19
error reduction in our experimental techniqueproof of gas phase saturation
f(T,j) for given flux j at different temperaturesinfluence of sample and gadget geometry
performing experiments under an oxygen‐controlled atmosphere (glove box)
investigation of aerosol formation during transportation method experiments
verification of the volatile polonium species (?)thermochromatographic studies of polonium
Matthias RIZZI
SUMMARY & OUTLOOK
Seite 209. Mai 2011PSI, 9. Mai 2011PSI, Seite 20
R. Eichler , D. Schumann, J. NeuhausenS. Heinitz and S. Lüthi
THANKS TO
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