RU2094823C1 - Inorganic scintillator - Google Patents

Abstract

FIELD: selective detection and displaying of heavy-density pulse electron beams in background α-, β-, γ radiation of nuclides, in particular, for electron beams generated by heavy-current amplifiers of electrons. SUBSTANCE: method involves usage of semiconductor crystals of HgI₂ (red tetragonal modification) as inorganic scintillator. EFFECT: increased efficiency for detection of heavy-density electron beams, practical insensitivity to α-, β-, γ- radiation of nuclides. 1 dwg , 1 tbl

Description

 The invention relates to the field of scintillation detectors of ionizing radiation, mainly to the field of scintillation detectors for visualizing and recording pulsed electron beams of high density.

Inorganic scintillators are known for detecting pulsed electron beams based on NaI-Tl, CsI-Tl, Bi ₄ Ge ₃ O ₁₂ and others [1, 2] They have sufficiently high effective atomic numbers, respectively, Z _eff = 49.8; 54, 71.7, i.e. suitable for recording high-energy radiation. However, the known scintillators are sensitive to all types of radiation, i.e., they do not have the necessary selectivity: with their help, high-density pulsed electron beams generated by high-current accelerators cannot be detected against the background of nuclear α, β, and γ radiation.

Known detectors g and x-ray radiation based on crystals of mercury iodide using the semiconductor properties of this material [1, 3-9] ie semiconductor detectors based on HgI ₂ red, tetragonal modification are known.

Detectors based on tetragonal HgI ₂ have parameters [1, 3-9]
density, g / cm ³ 6.38
melting point, ^o C 250
phase transition temperature, ^o C to yellow modification 127
band gap at 300 K, eV 2.13 (582 nm)
dielectric constant 9.2
average carrier lifetime:
Electrons, μs 1.0 [1]
holes, µs 3.5 [1]
recorded energy range, keV 1 1000
bias voltage, V 200 2000
leakage current, pA 50 100
energy resolution:
uncooled detectors, eV 750 30000 [1]
cooled detectors, eV 200 653 [8]
In all known publications, mercury iodide crystals are used as a direct-gap semiconductor radiation detector [1, 3–9]. Thus, US patent [9] describes a combined detector containing a scintillator and a body of mercury. Ionizing radiation is detected by a scintillator. A light flash arising in the scintillator then hits the body from HgI ₂ . The body of HgI _{2 is} used as a semiconductor detector, in it, in HgI ₂ , current arises under the action of a light flash coming from the scintillator.

Systematic studies of mercury iodide crystals of HgI ₂ (tetragonal, red modification) made it possible to detect light flashes (scintillations) arising in these crystals at room temperature 295-300 K directly upon exposure to pulsed high-density pulsed electron beams of 300 ± 100 A / cm ² at energy 160 200 keV. In all known publications on mercury diiodide, other authors did not find such an effect. A feature of HgI ₂ crystals is their selectivity, namely, that scintillations in them are observed only in the case of excitation by high-density pulsed electron beams, while excitation by a-particles (Pu 239, E 5.12 MeV) or b-particles (γ -90; Sr-90, E $\genfrac{}{}{0ex}{}{\text{max}}{\text{β}}$ = 2.18 MeV) or g-quanta (Cs 137; 662 keV) did not cause scintillations in them that exceeded the background. Those. HgI ₂ crystals are not sensitive as a scintillator to these types of nuclear radiation. The scintillation properties of HgI ₂ crystals corresponding to the effects of high-density pulsed electron beams are given in the table.

 The spectral region of the pulsed emission of mercury iodide is 515 615 nm. The maximum of the emission spectrum is located at 575 580 nm with an absorption edge of 589 590 nm.

 The drawing shows a spectrum of scintillation flash.

The intrinsic luminescence of HgI ₂ with a maximum at 575 580 nm is supra marginal. It is due to radiative recombination of unrelaxed electrons and holes near the lattice defects of mercury iodide. Recombination is of an electronic-vibrational nature, the linearity of the luminescence spectrum with a single excitation indicates the participation of phonons in this process (drawing, curve 1). Under pulsed-periodic exposure, the phonon repetition spectrum is blurred (drawing, curve 2), however, the nature of the electron-vibrational luminescence remains over-edge with a maximum at 575-580 nm. Under the action of pulsed electron beams, yellowish-orange flashes are observed in HgI ₂ crystals. The scintillation efficiency of mercury iodide is C _rel = 10.1% relative to that for the CsI-Tl standard. This is an unexpected result. If we consider that the bulk of the intrinsic radiation HgI ₂ with the wavelength l _rad 575-580 nm absorbed by the crystal (the latter is transparent only to 582 590 nm), the C value = 10.1% _RH should be considered abnormally high. Since the scintillation efficiency is close to zero during normal excitation of mercury iodide crystals (when excited by α-, β-, γ-radiation of radionuclides), the anomalously high scintillation efficiency of HgI ₂ C crystals is _rel = 10.1% when high-current pulsed electron beams are exposed to them the nano- and picosecond high-density ranges can be caused only by threshold density effects of a percolation nature. This is facilitated by the low energy of formation of a pair of charge carriers (electron and hole), equal to W 4.2 eV. [one]
In the decay of HgI ₂ scintillations, only one component of an exponential nature is observed with a duration of 2.1 ± 0.07 μs, which is comparable with the hole lifetime of 2.5 μs [1] in HgI ₂ . Apparently, the recombination process responsible for scintillation in HgI ₂ is determined by the hole component.

As can be seen from the table, the proposed scintillator based on HgI ₂ has a higher effective atomic number Z _eff = 67.3 than the widely used industrial CsI-Tl scintillator, i.e. it is more than a standard suitable for recording high-energy radiation of high density.

The main advantage of the proposed scintillator based on HgI ₂ in comparison with the CsI-Tl standard and other known scintillators is its selectivity to high-current electron beams of nano- and picosecond duration, it confidently registers them (with an efficiency of 10.1% against CsI-Tl) against the background nuclear a-, β-, γ-radiation, remaining practically insensitive to the latter as a scintillator.

Used literature:
1. Horn L.S., Khazanov B.I. Modern instruments for measuring ionizing radiation. Energoatomizdat. M. 1989, 232 p.

 2. Shulgin B.V. Polupanova T.I. Kruzhalov A.V. Skorikov V.M. Bismuth orthogermanate. Vneshtorgizdat, Yekaterinburg, 1992.

 3. Avchiev I.A. Platova A.I. Semiconductor detectors in the technique of nuclear physical measurements. Overview of VNIIGPE. The most important inventions of the year. Series Technical Physics, M. 1987, p. 22 26.

 4. Van den Berg L. Wited R.C. //IEEE Trans. Nucl. Sci. 1978, v. 25, N 1, p. 395 397.

 5. Zaletin V.M. Nozhkina I.N. Fomin V.I. et al. Atomic Energy, 1980, v. 48, no. 3, p. 169 172, 1982, v. 52, no. 3, p. 193 195.

 6. Dabrowsky A.I. et al. Nucl. Instrum and Methods. 1983, v. 213, N 1, p. 89 94.

 7. Geisler V. A. Zaletin V. M. et al. Mercury diiodide. Science, Novosibirsk, 1984, 104 pp.

 8. Revenko A.G. Factory Laboratory, 1992, N 6, p. 12 19.

 9. US patent N 4613756, 1986, G 01 T 1/24.

Claims (1)

 The use of crystalline mercury diiodide of tetragonal modification as an inorganic scintillator for detecting high-current pulsed electron beams of nano- and picosecond duration.

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