T' Otto,

1
Contamination of the ISOLDE Vacuum System

• André Muller (CERN, TIS-RP)
• Presented by
• Th. Otto

2
ISOLDE Operation

• Bombardment of heavy targets with protons, E1.4
  GeV
• Production of radioisotopes by spallation,
  evaporation or fission
• Ionisation of isotopes
• Mass separation
• Contamination of the vacuum system

3
GPS Mass separator
Separator-magnet
front-end
4
Target materials
5
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 an extraction electrode (2 years
of cooling)
7
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
Gamma-doserate from a roughing oil pump (mainly
206Po/Bi, 205Bi)
9
Volatiles Isotopes found in roughing pump oil
10
Non volatiles Isotopes found in roughing pump oil
11
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

12
Annual Release from Balloons
13
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).