Development of a novel high-sensitivity LAr purity monitor based on an α-source
- Working Paper
A novel liquid argon (LAr) purity monitor was developed with a sensitivity to electronegative impurities of the order of ppb (O 2 equivalent). Such a high purity is e.g. needed in a LAr drift chamber. The principle is to measure the lifetime of quasifree electrons in LAr, since this is the important parameter for the operation of a drift chamber. Free electrons are produced by ionizing the LAr with α -particles emitted by the 210 Po chain daughter of an isotope 210 Pb source. From a measurement of the charge of the electron cloud at the beginning and at the end of a drift path, together with the drift time, the lifetime of the electrons is obtained. The α -particles have a very short range of about 50 \muminLArandtheionizationdensityisveryhigh,typicallybetween 750\div 1500\rm MeV/cm,leadingtoahighrecombinationrate.Tosuppresstherecombinationoftheargonionswiththeelectrons,the \alpha−sourcewasputinastrongelectricfieldof 40\div 150$ kV/cm. This was achieved by depositing the source on the surface of a spherical high voltage cathode with a diameter of about 0.5 mm. The anode was also made as a sphere of about the same diameter as the cathode, thus, close to the axis between the two electrodes the electric drift field was approximately a dipole field Show more
SubjectPurity monitor; Liquid Argon purity
Organisational unit03503 - Rubbia, André
NotesSubmitted on 26 December 2004.
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