Volume 1, Issue 1 (April 2016)

Original research papers



Nevenka M. Antović, Sergey K. Andrukhovich, Alexandr V. Berestov

Pages: 31-35

DOI: 10.21175/RadJ.2016.01.06

Received: 14 FEB 2015, Received revised: 11 MAR 2015, Accepted: 15 MAR 2015, Published Online: 28 APR 2016

Parapositronium – a singlet positronium ground state, has the total angular momentum of electron and positron forming the atom Js = 0, magnetic quantum moment m = 0, and its annihilation spectrum is dominantly created by the 511 keV discrete photons. A process of cooperative emission of annihilation photons (cooperative annihilation) by a system of positronium atoms, i.e., annihilation superradiance, had been considered by other researchers, and the theory of annihilation superradiance in a system of parapositronium atoms for two-photon annihilation was constructed (two interacting parapositronium atoms; emission of the 1022 keV photons flying apart at an angle of 180°). The 32-crystal spectrometer ARGUS, with 16 detector pairs at an angle of 180° capable of registering double gamma coincidences, with lead collimators (80 mm in diameter) mounted on each detector – was used to test the phenomenon. Parapositronium annihilation spectra were acquired using 22Na (A = 4×105 Bq) as a positron source, and SiO2 (as „positronium forming“ medium; probability: 32 %), as well as Al (as „positronium not forming“ target) used as a blank – for estimation of the background events. In the case when after emission of two starting positrons from 22Na (i.e., the 1275 keV nuclear photons) coincident registration (respecting the spectrometer time resolution) of four annihilation photons should be considered as a six-fold coincidence event, experimentally obtained counting rates were – 0.25 s-1 (SiO2) and 0.23 s-1 (Al), while theoretically predicted – 0.34 s-1. The main background process competitive to a registration of the parapositronium cooperative annihilation is four-fold coincidence event (the two 180° detectors register 1275 keV photons, and two – summing of the 511 keV annihilation photons), with experimental counting rates – 0.026 s-1 (SiO2) and 0.023 s-1 (Al), as theoretically predicted – 0.023 s-1. On the other hand, cooperative annihilation should be a four-fold coincidence event (the two 180° detectors register 1275 keV photons, and two – 1022 keV photons), which has not been registered by the ARGUS spectrometer (theoretically predicted counting rate – 1.7×10-5 s-1). The analyses showed that probability of detecting the parapositronium cooperative annihilation will increase significantly with increasing positron source activity, but also with decreasing diameter of lead collimators.

  1. В.И. Гольданский, Физическая химия позитрона и позитрония, Москва, Россия: Нука, 1968. (V.I. Goldanskii, Physical Chemistry of Positron and Positronium, Moscow, Russia: Nauka, 1968.)
  2. M. Chiba, R. Hamatsu, T. Hirose, T. Matsumoto and J. Yang, “Measurement of Electron-Positron Annihilation at Rest into Four and Five Photons,” Nukleonika, vol. 42, no.1, pp. 61-68, Jan. 1997.
  3. S.K. Andrukhovich et al., “Investigation of Orthoposi-tronium 3g-Decay Using a Multidetector Spectrometer,” Nucl. Instrum. Meth. Phys. Res. Sec. B: Beam Int. Mat. Atoms, vol. 207, no. 2, pp. 219-226, June 2003.
    DOI: 10.1016/S0168-583X(03)00458-0
  4. B.K. Arbic, S. Hatamian, M. Skalsey, J. van House, W. Zheng, “Angular-Correlation Test of CPT in Polarized Positronium,” Phys. Rev., vol. 37, no. 9, pp. 3189-3194, 1988.
  5. S.K. Andrukhovich, N. Antovich, A.V. Berestov and O.N. Metelitsa, “Test CPT in the Decay of Polarized Positroni-um Using Multidetector spectrometer,” Mater. Sci. For., vol. 363-365, pp. 591-593, Apr. 2001.
    DOI: 10.4028/www.scientific.net/MSF.363-365.591
  6. P.A. Vetter and S.J. Freedman, “Search for CPT-Odd Decays of Positronium,” Phys. Rev. Lett., vol. 91, no. 26-31, p. 263401, Dec. 2003.
    DOI: 10.1103/PhysRevLett.91.263401
  7. Р.А. Власов, О.Н. Гадомский, В.В. Самарцев,
    “Аннигиляционное сверхизлучение в системе атомов позитрония и позитронная поляризация среды,” Теоретическая и математическая физ., т. 79, №. 3, с. 423-436, 1989. (R.A. Vlasov, O.N. Gadomskii and V.V. Samartsev, “Annihilation Superradiance in a System of Positronium Atoms and Positron Polarization of the Medium,” Theor. Math. Phys., vol. 79, no. 3, pp. 423–436, 1989.)
  8. O.N. Gadomskii, “The Positronium Atom in the Field of an Optical Laser: Radiation-Induced Energy Shifts and Annihilation Decay Kinetics,” J. Exp. Theor. Phys., vol. 83, no. 4, pp. 676-684, Sep. 1996.
  9. O.N. Gadomskii and T.T. Idiattulov, “Long-Lived Positro-nium Atom in the Field of an Optical Laser,” Quant. Electron., vol. 28, no. 6, pp. 469-473, 1998.
    DOI: 10.1070/QE1998v028n06ABEH001251
  10. L. B. Madsen and P. Lambropoulos, “Scaling of Hydroge-nic Atoms and Ions Interacting with Laser Fields: Posi-tronium in a Laser Field,” Phys. Rev. A, vol. 59, no. 6, pp. 4574-4579, June 1999.
    DOI: 10.1103/PhysRevA.59.4574
  11. L.B. Madsen, “Positronium in Laser Fields,” Nucl. Instr. Meth. B: Beam Inter. Mat. Atoms, vol. 221, no.1, pp. 174-181, July 2004.
    DOI: 10.1016/j.nimb.2004.03.051
  12. N. Antovic, “Investigation of Rare Positronium Decays on Multidetector Gamma-Coincidence Spectrometers,” PhD thesis, Faculty of Physics, University of Belgrade, Serbia, 2000. (in Serbian).
  13. С.К. Андрухович, А.В. Берестов, Ф.Е. Зязюля, Б.А. Марцынкевич, Е.А. Рудак, А.М. Хильманович, “Авто-матизированна регистрирующа гамма-установка совпадений (АРГУС), препринты в ИФ АН БССР, №. 408-409, 1986. ИФ АН БСС (S.K. Andrukhovich, A. V. Berestov, F.E. Zyazyulya, B.A. Marcinkevich, E.A. Rudak and A.M. Hil’manovich, [Automated Device for Registration of Gamma-Coincidences (ARGUS)],” Preprint in IF AN BSS, no. 408-409, 1986.)
  14. N.M. Antovic, S.K. Andrukhovich and A.V. Berestov, “A Contribution of the Compton Scattered Radiation from Mn-54 to Double Gamma Coincidences Spectra at the 32-Detector System,” in Proc. RAD 2014, Nis, Serbia, pp. 127-130.
  15. S.K. Andrukhovich, N.M. Antovich and A.V. Berestov, “Effect of Cascade Gamma-Radiation Summation Processes on the Precision of Calculating the Probability of Three-Photon Annihilation of Positronium,” Phys. Sol. State, vol. 42, но. 9, pp. 1648-1651, Sep. 2000.
    DOI: 10.1134/1.1309445