1. 1 T. Otto, TIS-RP Contamination of the ISOLDE Vacuum System André Muller (CERN, TIS-RP) Presented by Th. Otto

2. Contamination of the ISOLDE Vacuum System 2 A. 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 separation  Contamination of the vacuum system

3. Contamination of the ISOLDE Vacuum System 3 A. Muller TIS-RP front-end Separator-magnet GPS Mass separator

4. Contamination of the ISOLDE Vacuum System 4 A. Muller TIS-RP Target materials TargetRadiologically important contamination Characteristic half-life U, Th  -emitters 227 Ac, 226,228 Ra, 210 Pb/Po … fission products 20 a, 1600 a, 5 a 22 a various Pb 194 Hg/Au520 a Ta Lanthanides (  ): 148 Gd, 150 Gd75a, 1.8E6 a Other in Ta-container mainly as for Ta

5. Contamination of the ISOLDE Vacuum System 5 A. 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

6. Contamination of the ISOLDE Vacuum System 6 A. Muller TIS-RP Contamination of an extraction electrode (2 years of cooling) Isotope Half-life T 1/2 / y Authorisation limit (CH)/kBq Contamination found/kBq 125 Sb2.7620009000 148 Gd74.60.2  100 208 Po2.92  100 210 Po0.382  250 227 Ac21.770.09  5 228 Ra/Th5.751  10

7. Contamination of the ISOLDE Vacuum System 7 A. 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

8. Contamination of the ISOLDE Vacuum System 8 A. Muller TIS-RP Gamma-doserate from a roughing oil pump (mainly 206 Po/Bi, 205 Bi)

9. Contamination of the ISOLDE Vacuum System 9 A. Muller TIS-RP Volatiles Isotopes found in roughing pump oil Volatile Isotope L A /MBq Contamination of one pump (3 l) /MBq 68 Ge0.6 0.8 75 Se3.017.0 124 Sb 1.0 8.3 125 Sb 2.012.1 121m Te, 123m Te, 127m Te 0.8 - 1.012 – 13 125 I0.7600.0 194 Hg0.31.1

10. Contamination of the ISOLDE Vacuum System 10 A. Muller TIS-RP Non volatiles Isotopes found in roughing pump oil Volatile parent Isotope L A /MBq Contamination of one pump (3 l) /MBq 137 Xe 137 Cs0.78.0 195,195m Hg 195 Au4.065.0 207,211 Rn, 207,211 At 207 Bi2.05.6 208,212 Rn, 208 At 208 Po0.00240.0 209 Rn, 209 At 209 Po0.002 1.0 210 Rn, 210 At 210 Po0.002 36.6

11. Contamination of the ISOLDE Vacuum System 11 A. Muller TIS-RP Retention Balloons Capacity of 24 m 3 Emptied every few months with a flow rate of 0.5 m 3 /h (Ventilation: 6400 m 3 /h) Measurement techniques: Micropore filter and Activated charcoal: 125 I, 68 Ge, 75 Se Differential ionisation chamber: 3 H equivalent Gas sample of 0.25 l: noble gases by gamma spectrometry

12. Contamination of the ISOLDE Vacuum System 12 A. Muller TIS-RP Annual Release from Balloons IsotopeT 1/2 (a)Release 1999/ MBq 3H3H12.36000 42 Ar331.3 85 Kr10.7685 127 Xe0.1165

13. 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).