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

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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

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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

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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

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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).