Papers by Keyword: Energy Resolution

Abstract: The scintillation response of Lu_0.7Y_0.3AP:Ce and Bi₄Ge₃O₁₂ scintillation crystals have been compared using photomultiplier tube readout for photon energies ranging from 22.1 to 1274.5 keV. Lu_0.7Y_0.3AP:Ce showed a light yield non-proportionality of about 20% upon lowering energy from 1,274.5 to 22.1 keV, which is better than that of about 39% obtained for Bi₄Ge₃O₁₂. Lu_0.7Y_0.3AP:Ce showed the light yield of 13,400 ph/MeV and energy resolution of about 8 % for 662 keV gamma rays from a ¹³⁷Cs source. The photofraction of Bi₄Ge₃O₁₂ is better than that of Lu_0.7Y_0.3AP:Ce. The intrinsic resolution of the crystals versus energy of gamma rays has been determined after correcting the measured energy resolution for photomultiplier tube statistics.

Abstract: The luminescence and gamma-ray detection properties of the new cerium-doped rare-earth scintillator lutetium-yttrium oxyorthosilicate ( Lu_1.95Y_0.05SiO₅:Ce, LYSO:Ce) were investigated and compared to those of cerium-doped yttrium oxyorthosilicate ( Y2SiO5:Ce, YSO:Ce) crystal. The light yield and energy resolution were measured using photomultiplier tube (PMT) readout. The non-proportionality of the light yield and energy resolution versus γ-ray energy were measured and the intrinsic resolution of the crystals was calculated. In spite of significant progress in light yield and luminescence properties, the energy resolution of LYSO:Ce appears to still suffer from an excess variance in the number of scintillation photons. The mass attenuation coefficient of LYSO:Ce and YSO:Ce for 662 keV gamma rays was also measured by transmission method and compared with the theoretical values calculated by WinXCom program.

Abstract: The luminescence and gamma-ray detection properties of cerium-doped scintillators, namely, Lu_0.3Y_0.7AlO₃:Ce (Lu_0.3Y_0.7AP:Ce), Lu_0.7Y_0.3AlO₃:Ce (Lu_0.7Y_0.3AP:Ce ), and YAlO₃:Ce (YAP:Ce) were investigated. UV excitation and emission spectra of studied crystals were compared. The light yield and energy resolution were measured using photomultiplier tube (PMT) readout. The light yield non-proportionality and energy resolution versus gamma-ray energy were measured and the intrinsic resolution of the crystals was determined after correcting the measured energy resolution for PMT statistics. For 662 keV gamma rays (¹³⁷Cs source), YAP: Ce showed the highest light yield of 28,500 ph/MeV and the best energy resolution of 4.4 % , while its photofraction is worst.

Abstract: A report on the crystal growth, luminescence and scintillation characteristics of two developed scintillators, CsCe2Cl7 and Cs2NaCeCl6 are presented. CsCe2Cl7 is a new scintillation material. These crystals were grown by the Czochralski pulling technique. The X-ray diffraction technique was used to verify the structure of crystals. Under the X-ray excitation emission, the CsCe2Cl7 showed a broad emission band in the wavelength range from 370 to 470 nm while the Cs2NaCeCl6 crystal showed a spectrum in the wavelength range from 370 to 440 nm. The energy resolutions (FWHM of peak position) for the 662 keV full energy peak of 5.5% and 8.3% were observed at room temperature for the CsCe2Cl7 and Cs2NaCeCl6 crystals, respectively. The scintillation decay time measurement curves showed that, CsCe2Cl7 crystal has a single exponential decay function with a decay time of 50 ns. The Cs2NaCeCl6 crystal exhibited three main decay time components, a short component with a decay time constant of 91 ns and 36% intensity, an intermediate component with a decay time constant of 601 ns and intensity 33%, followed by a long component with a 3.2 µs decay time constant and an intensity of 31% of the total light yield. On the basis of the scintillation results of these materials grown, it is believe that these scintillation crystals can find a place in medical imaging and radiation detection system.

Abstract: The spectrometric characteristics of detectors based on 4H-SiC films with ion-doped p+–n junctions in a temperature range from 25 to 375 °C have been studied. The experiments with 5.8-MeV α-particles in a high-temperature chamber were performed. The interference factors of the detectors operation in a mode of spectrometry are established. The energy resolution of 1.35% is received. An increase of the efficiency of the diffusion–drift charge transport with increasing temperature has been observed. The last is explained by an increase in the diffusion length of minority carriers.

Abstract: The charge collection efficiency (ССЕ) of SiC-detectors preliminarily irradiated with 8 MeV protons at a fluence of 1014 cm-2 has been studied. Nuclear spectrometric techniques with 5.4 MeV α-particles were employed to test the detectors. The concentration of primarily created defects was estimated to be 4×1016 cm-3. A strong compensation of SiC was observed, which allowed connection of the structure in the forward mode. The experimental data obtained were processed using a simple two-parameter model of signal formation. The model makes it possible to separate the contributions of electrons and holes to the ССЕ. An additional irradiation at a fluence of 2×1014 cm-2 reduced the ССЕ value by a factor of 2 and gave rise to polarization. The latter indicates that radiation-induced centers are not only actively involved in carrier localization (with a decrease in the lifetime), but also in transformation of the electric field within the detector.

Abstract: The detector structures based on Al ion-implanted p+-n junctions in 4H-SiC have been manufactured and tested at temperatures up to 170oC by α-particles with energies of 3.9 and 5.5 MeV. Structural peculiarities of thin Al high dose ion implanted layers before and after short high temperature activation annealing were studied by combination of Rutherford back scattering/channeling spectrometry and cross-sectional transmission electron microscopy. The detector structures fabricated on this thin ion implanted p+-n junctions operated in the temperature range of 16-170 oC with reproducible stable spectrometric characteristics. The charge collection efficiency and the energy resolution of detectors improved with rising temperature up to 170 oC, that was obtained in SiC detectors for the first time.

Abstract: A full modeling of deceleration of α-particles in SiC is carried out using a Monte-Carlo method. The distribution of energy losses in nuclear elastic collisions is calculated. The spectrum has a characteristic asymmetric form and the line width at half peak maximum is 4.62 keV. The final form of a spectral line is obtained by convolution with a Gaussian peak, and including the contribution of ionization fluctuations and noise. The resulting value of the line width was 8.75 keV (at a noise dispersion of detector and equipment of 1.7 keV). The resolution of detectors reached in practice is twice the lowest calculated value. It is shown that charge losses during transport of nonequilibrium carriers through the volume of the detector are insignificant, while a resolution divergence may result from a non-optimized “entrance window”.

Abstract: The effect of irradiation with protons, electrons, neutrons, x-ray radiation and gamma-ray photons as well as with different ions on properties of starting SiC material and devices based on it was studied. The rectifying properties of the diode structures, which degraded as a result of irradiation with high energy particles, were recovered at higher operation temperatures. The transistor structure SiC-based detectors were realized with the signal amplification by a factor of tens under irradiation. The energy resolution of 0.34 %, commensurable with Si-detectors, has been achieved for SiC detectors and is correct for all classes of short range ions. The maximum signal amplitude corresponds, in SiC, to a mean electron-hole pair creation energy of 7.7 eV.

Abstract: The spectrometric characteristics of the detectors based on 4H-SiC using 4.8-7.7 MeV a-particles were determined. The Cr Schottky barriers with areas of 1×10-2 cm2 were performed^by vacuum thermal evaporation on 4H-SiC epitaxial layers grown by chemical vapor deposition (CVD) with thickness 26 and 50 µm. The concentrations of the uncompensated donors into CVD epitaxial layers were (6-10) ×1014 cm-3, that allowed to develop a detector depletion region up to 30 µm using reverse bias of 400 V. The energy resolution less than 20 keV (0.34%) for lines of 5.0- 5.5 MeV was achieved that is twice as large of the resolution of high-precision Si-based detectors prepared on specialized technology. The maximum signal amplitude of 4H-SiC - detectors corresponding to the average electron-hole pair generation energy was found to be 7.70 eV.