Fast method for measuring the Sr-90 activity with Cherenkov radiation in silica aerogel

 

Povzetek

Cerenkovo sevanje, ki ga v prozorni snovi povzrocijo hitri nabiti delci, je temelj razlicnih metod za detekcijo in identifikacijo delcev. Kot izvore Cerenkovega sevanja so do sedaj uporabljali plinske in trdne (oziroma tekoce) sevalce. Prag za sevanje fotonov je za pione v plinskih sevalcih nad 2,5 GeV/c, v trdnih (teko?ih) pa pod 0,2 GeV/c, medtem ko vmesno podrocje ostane nepokrito. Gre za kinematicno obmo?je, ki je bistveno pri proucevanju redkih razpadov mezonov B. Ti procesi so predmet raziskav vecih eksperimentov, od teh nekateri ze potekajo, drugi pa so v pripravi. Resitev prinasa silicijev aerogel, porozna snov z lomnim kolicnikom med 1,005 in 1,06. Rezultati, dobljeni pri eksperimentih HERMES in BELLE kazejo, da bi bilo smiselno tak sevalec uporabiti tudi v detektorju Cerenkovih obrocev s tankim sevalcem brez fokusiranja s sistemom zrcal (t.i. proximity focusing RICH). Prednost takega tipa detektorjev je v kompaktnosti, ki je posebej pomembna pri spektrometrih ob visokoenergijskih trkalnikih. Z uporabo boljsih aerogelov ter v zadnjem casu razvitih vecanodnih fotopomno?evalk nameravamo razviti uporabno metodo za detekcijo Cerenkovih fotonov. Pri tem bomo za odpravo ucinka neaktivne povrsine fotopomnozevalk uporabili sistem zbiralnih lec. Razvoj stevca Cerenkovih fotonov ponuja potencialno uporabo pri detekciji izvorov beta. Posebej zanimiva je detekcija visoko radiotoksicnega izotopa Sr-90 v okolju. Z izbiro aerogela s primernim lomnim kolicnikom lahko dosezemo, da le beta elektroni z dovolj visoko energijo sevajo cerenkove fotone, tako je na primer prag v aerogelu z lomnim kolicnikom n=1,06 pri 1 MeV. Na ta nacin lahko locimo prispevke razlicnih radioaktivnih izotopov. V okviru predlaganega projekta bomo z modeliranjem fizikalnih procesov, ki jih povzrocijo beta elektroni, ter ozadja zarkov gama in kozmicnih delcev, optimizirali parametre detektorja.  

Summary

Cherenkov radiation caused by fast charged particles in a transparent medium is the basis for different methods of particle identifiaction. Up to the present, gaseous and solid (or liquid) radiators have been used as sources of Cherenkov radiation. The threshold for photon emission of pions is above 2.5 GeV/c in gases and below 0.2 GeV/c in solids (or liquids). The intermediate uncovered gap is essential for the investigation of rare B meson decays, which are the research subject of many experiments, some in progress, others in preparation. A solution to the problem is offered by silica aerogels, a porous material with refractive index between 1.005 and 1.06. The results obtained in two particle physics experiments, HERMES and BELLE indicate that it would be meaningful to use such a radiator also in Cherenkov detectors with thin radiators without focusing systems of mirrors (so called proximity focusing RICH).The advantage of such detectors is their compactness, which is especially important for experiments at the high energy colliders. By making use of improved aerogels, recently developed multianode photomultiplier tubes and additional lens systems for elimination of the inefficiency due to the PMT inactive surface, we propose to develop a method for detection of Cherenkov photons. A possible application of the Cherenkov photon detector could be for detection of beta particles. Of special interest is the detection of the highly radiotoxic isotope Sr-90 in the environment. A choice of aerogel with suitable refractive index allows one to select the threshold energy of beta electrons, which would radiate Cherenkov photons. Thus one may separate the contributions of different radioactive isotopes, in particular the rather energetic ones from Sr-90 daughter isotope Y-90. By modeling the physical processes produced by beta electrons and the gamma and cosmic ray backgrounds, we intend to optimize the detector parameters to allow for quick measurements of low activities of the isotope Sr-90 in environmental samples.  

  • Less is more with aerogels
  • Description of the technique - poster
  • Application for the project at MSZS , II , I

    Current setup:

     

    Strontium 90

  • Toxicity Summary for STRONTIUM-90

    Silica aerogels references

  • Recent results on aerogel development for use in Cherenkov counters , NIM A494 p.491
  • Measurement of the dispersion law for hydrophobic silica aerogel SP-25 , NIM A480 (2002) p.456
  • Silica Aerogel
  • Silica Aerogel
  • Properties of silica aerogels
  • E. Aschenauer eta al., Optical characterisation of n=1.03 silica aerogel used as a radiator in the RICH of HERMES, Nucl. Instr. and Meth. A440 (2000) p.338
  • R. De Leo et al., Chromatic aberration and forward scattering of light in silica aerogel, NIM A457 (2001) p.52
  • A.R.Buzykaev et al., Measurements of optical parameters of aerogel, Nucl. Instr. and Meth. A433 p.396-400
  • T. Sumiyoshi et al., Silica aerogel Cherenkov counter for the KEK B-factory experiment, Nucl. Instr. and Meth. A433 (1999) 385-391

    Reconstruction

  • J.Pinto.Cunha et al., On the reconstruction of Cherenkov rings from aerogel radiators NIM A452 (2000) p.401-421
     

    Sr references

  • K.Walter et al.,Simultaneous Determination of Strontium-90 and Strontium-89 by Cerenkov-Radiation and Liquid-Scintillation Counting: a Re-Evaluation for Low-Level Counting Radiochimica Acta 62 (1993) p.207-212

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    Photon detector references

  • P. Krizan, Tests of a multianode PMT for the HERA-B RICH, Nuclear Instruments and Methods in Physics Research A394 (1997) 27-34
  • I.Arinyo et al.: The HERA-B RICH, October 2000, Nucl. Instr. and Meth. in Phys. Res. A453 (2000) 289-295
  • S. Korpar, Multianode Photomultipliers as Position Sensitive Detectors of Single Photons, Nucl. Instr. and Meth. A442 (2000) 316-321
  • S. Korpar et al., The HERA-B RICH , Nucl. Instr. and Meth. in Phys. Res. A433 (1999) 128-135
     
     

    Related:

  • Toru Iijima, Aerogel Cherenkov Counter in Imaging Mode JPS meeting, September 23, 1997, Tokyo Metropolitan Univ.