dorsal/arxiv
View SchemaDevelopment of a novel high-sensivitiy LAr purity monitor based on an $\alpha$-source
| Authors | A. Badertscher, M. Laffranchi, A. Rubbia |
|---|---|
| Categories | |
| ArXiv ID | physics/0412166 |
| URL | https://arxiv.org/abs/physics/0412166 |
Abstract
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 $\alpha$-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 $\alpha$-particles have a very short range of about 50 \mu$m in LAr and the ionization density is very high, typically between $750\div 1500\rm MeV/cm$, leading to a high recombination rate. To suppress the recombination of the argon ions with the electrons, the $\alpha$-source was put in a strong electric field of $40\div 150$ 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.
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"abstract": "A novel liquid argon (LAr) purity monitor was developed with a sensitivity to\nelectronegative impurities of the order of ppb (O$_2$ equivalent). Such a high\npurity is e.g. needed in a LAr drift chamber. The principle is to measure the\nlifetime of quasifree electrons in LAr, since this is the important parameter\nfor the operation of a drift chamber. Free electrons are produced by ionizing\nthe LAr with $\\alpha$-particles emitted by the $^{210}Po$ chain daughter of an\nisotope $^{210}Pb$ source. From a measurement of the charge of the electron\ncloud at the beginning and at the end of a drift path, together with the drift\ntime, the lifetime of the electrons is obtained. The $\\alpha$-particles have a\nvery short range of about 50 \\mu$m in LAr and the ionization density is very\nhigh, typically between $750\\div 1500\\rm MeV/cm$, leading to a high\nrecombination rate. To suppress the recombination of the argon ions with the\nelectrons, the $\\alpha$-source was put in a strong electric field of $40\\div\n150$ kV/cm. This was achieved by depositing the source on the surface of a\nspherical high voltage cathode with a diameter of about 0.5 mm. The anode was\nalso made as a sphere of about the same diameter as the cathode, thus, close to\nthe axis between the two electrodes the electric drift field was approximately\na dipole field.",
"arxiv_id": "physics/0412166",
"authors": [
"A. Badertscher",
"M. Laffranchi",
"A. Rubbia"
],
"categories": [
"physics.ins-det"
],
"title": "Development of a novel high-sensivitiy LAr purity monitor based on an $\\alpha$-source",
"url": "https://arxiv.org/abs/physics/0412166"
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