1 T. Otto,TIS-RP
Contamination of the ISOLDE Vacuum System
André Muller (CERN, TIS-RP)
Presented byTh. Otto
Contamination of the ISOLDE Vacuum System 2A. Muller TIS-RP
ISOLDE Operation
•Bombardment of heavy targets with protons, E=1.4 GeV
•Production of radioisotopes by spallation, evaporation or fission
•Ionisation of isotopes•Mass separationContamination of the vacuum system
Contamination of the ISOLDE Vacuum System 3A. Muller TIS-RP
front-end
Separator-magnet
GPS Mass separator
Contamination of the ISOLDE Vacuum System 4A. Muller TIS-RP
Target materialsTarget Radiologicall
y important contamination
Characteristic half-life
U, Th -emitters227Ac, 226,228Ra, 210Pb/Po …fission products
20 a, 1600 a, 5 a22 avarious
Pb 194Hg/Au 520 a
Ta Lanthanides ():148Gd, 150Gd 75a, 1.8E6 a
Other in Ta-container
mainly as for Ta
Contamination of the ISOLDE Vacuum System 5A. Muller TIS-RP
Contamination of Front-end & Magnet
•Interior of targets: refractory elements
•On the extraction electrode•Focal plane of separator: not-selected isotopes (protected by removable covers).
•Around the slit of the switchyard•Noble gases: virtually everywhere, by diffusion
Contamination of the ISOLDE Vacuum System 6A. Muller TIS-RP
Contamination of an extraction electrode (2 years of cooling)
Isotope Half-life T1/2 / y
Authorisation limit (CH)/kBq
Contamination found/kBq
125Sb 2.76 2000 9000
148Gd 74.6 0.2 100
208Po 2.9 2 100
210Po 0.38 2 250
227Ac 21.77 0.09 5
228Ra/Th 5.75 1 10
Contamination of the ISOLDE Vacuum System 7A. Muller TIS-RP
Contamination of Vacuum system
•Volatile elements can be pumped and contaminate the vacuum system
•There they may decay into non-volatile elements and attach to walls Contamination found in• Turbomolecular pumps• Roughing pump oil• Retention balloons
Contamination of the ISOLDE Vacuum System 8A. Muller TIS-RP
Gamma-doserate from a roughing oil pump (mainly
206Po/Bi, 205Bi)
Contamination of the ISOLDE Vacuum System 9A. Muller TIS-RP
Volatiles Isotopes found in roughing pump oil
Volatile Isotope
LA /MBq Contamination of one pump
(3 l) /MBq
68Ge 0.6 0.875Se 3.0 17.0124Sb 1.0 8.3125Sb 2.0 12.1
121mTe,123mTe,127m
Te0.8 - 1.0 12 – 13
125I 0.7 600.0194Hg 0.3 1.1
Contamination of the ISOLDE Vacuum System 10
A. Muller TIS-RP
Non volatiles Isotopes found in roughing pump oil
Volatile parent
Isotope LA /MBq
Contamination of one pump (3 l) /MBq
137Xe 137Cs 0.7 8.0195,195mHg 195Au 4.0 65.0207,211Rn, 207,211At
207Bi 2.0 5.6
208,212Rn,208At
208Po 0.002 40.0
209Rn, 209At 209Po 0.002 1.0210Rn, 210At 210Po 0.002 36.6
Contamination of the ISOLDE Vacuum System 11
A. Muller TIS-RP
Retention Balloons
•Capacity of 24 m3
•Emptied every few months with a flow rate of 0.5 m3/h (Ventilation: 6400 m3/h)
•Measurement techniques: • Micropore filter and Activated charcoal:
125I, 68Ge, 75Se• Differential ionisation chamber: 3H
equivalent• Gas sample of 0.25 l: noble gases by
gamma spectrometry
Contamination of the ISOLDE Vacuum System 12
A. Muller TIS-RP
Annual Release from Balloons
Isotope T1/2(a) Release 1999/MBq
3H 12.3 6000
42Ar 33 1.3
85Kr 10.76 85
127Xe 0.1 165
Contamination of the ISOLDE Vacuum System 13
A. Muller TIS-RP
Conclusions
•Volatile elements migrate in the whole vacuum system
•They or their decay products present an important contamination risk
•Most parts of vacuum system – even far from the source – have to be considered as radioactive waste
•Multitude of isotopes makes analysis difficult (pures emitters).
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