Light Pulse Shape Research Articles

Light yield non-proportionality of undoped YAP scintillator

Scintillation properties of undoped YAP crystal were studied. The emission spectra show a very intense light component at 360 nm. Analysis of the light pulse shape resulted in five components, four of them, with time constants of 38±2 ns, 92±3 ns, 7.5±0.5 μs and 24±3 μs, representing high light intensity. The light yield was found to be temperature dependent, Nph= 3090±130 ph/MeV at liquid nitrogen temperature and Nph= 1440±60 ph/MeV at room temperature. Also the light yield non-proportionality shows temperature dependence and is more pronounced at room temperature.

Measuring the shape of Cherenkov radiation pulses from extensive air showers in the TUNKA experiment

An optical detector and an electronic system have been developed for studying the shape of Cherenkov light pulses from extensive air showers in the TUNKA experiment. Results of measurements on the described experimental setup are presented.

Light Pulse Shape Dependence on $\gamma$-Ray Energy in CsI(Tl)

A detailed study of the scintillation light pulse shape in CsI(Tl) at room temperature as a function of incoming photon energy in 6-662 keV energy range is presented. Three samples of CsI(Tl) of different amount of Tl dopant (0.01, 0.06 and 0.25 mol%) were used in measurements. A delayed coincidence single photon counting method was applied to measure the decay times in the microsecond range. Three-exponential function was fitted to the time spectra to describe the light pulse shape, which resulted in three components of tau1 = 730 plusmn 30 ns (fast), tau2 = 3.2 plusmn 0.3 mus (slow) and tau3 = 16 plusmn 2 mus (tail). The intensity of the second component was found to be sensibly independent of photon energy, whereas the intensities of the first and third ones varied with the energy of absorbed photon in low energy region. For a given crystal the most intense fast component was measured for 6-keV X-rays from 55Fe at the cost of decreasing intensity of the slowest one. Furthermore, the intensity of the fast component depends on Tl concentration and reaches its maximum value for the 0.06 mol% doping, close to the well-know optimal concentration of 0.1 mol%.

Scintillation Properties of Undoped CsI and CsI Doped With CsBr

The light output, energy resolution, and nonproportionality characteristics were measured for undoped CsI and several samples of CsI with different doping by CsBr. A correlation between nonproportionality of the light yield and the intrinsic energy resolution was confirmed. Contrary to previously published results the light yield of the tested samples was found to be degraded with increasing bromine concentration. The inspection of light pulse shapes was done by the single photon coincidence method. Decay times of the scintillation pulse were measured for undoped and bromine doped crystals, showing the main scintillation in tens of nanoseconds range.

Origination of gamma-ray burst pulses associated with the Doppler effect of spherical fireballs or uniform jet

Ryde and Petrosian have pointed out that the rise phases of gamma-ray burst (GRB) pulses originate from the widths of the intrinsic pulses and their decay phases are determined by the curvature effect of the expanding fireball surface based on their simplified formula. In this paper we investigate in detail the issue based on the formula in Ref. [20], which is derived based on a model of highly symmetric expanding fireballs, where the Doppler effect is the key factor to be concerned about, and no terms are omitted in their derivation. Our analyses show that the decay phases of the observed pulses originate from the contributions from both the curvature effect of the expanding fireball and the two timescales of the local pulses, and the rise phases of the observed pulses only come from the two timescales of the local pulses. Associated with a local pulse with both rise and decay portions, the light curve of GRBs in the rise portion is expected to undergo a concave phase and then a convex one, whereas that in the decay portion is expected to evolve by an opposite process. And the ratio of the concave timescale to the convex one in the rise phase of the observed pulse linearly increases with the ratio of the rising timescale to the decay one of the local pulse (rrd), whereas the ratio of the convex timescale to the concave timescale in its decay phase linearly decreases with rrd. The two correlations are independent of the local pulse forms and the rest-frame radiation forms. But the different forms of local pulses and the different values of rrd gives rise to the diversity of the light curve pulse shapes. We test a sample of 86 GRB pulses detected by the BATSE instrument on board the Compton Gamma Ray Observatory and find that the characteristics do exist in the light curve of GRBs.

Cerium-doped mixed-alkali rare-earth double-phosphate scintillators for thermal neutron detection

Previous measurements of the scintillation properties of members of the single-alkali, rare-earth double-phosphate family have demonstrated high light output and fast decay times when exposed to ionizing radiation. Because of the ease with which the alkali constituents (Li, Na, K, Rb, Cs) of the crystal matrix may be interchanged (e.g. K 2CsLu(PO 4) 2 and CsLi 2Lu(PO 4) 2), the rare-earth double-phosphate family of scintillators provides an ideal system for the study of matrix effects on scintillation efficiency and kinetics. New members of the rare-earth double-phosphate family have been synthesized by high-temperature flux growth. These new samples, represented by the general formula (A,B) 3Lu(PO 4) 2:Ce where A and B are alkali elements, incorporate lithium as one of the components and varying levels of Ce doping. Characteristics important to gamma-ray and thermal neutron excitation are calculated for three model systems which incorporate total lithium-ion substitution. Light output, scintillation decay times, and photoluminescence measurements for the most promising of the samples to date are reported. Future work includes (1) synthesis of mixed-alkali scandium and yttrium double-phosphates in which Li ions are substitutional in the structure with varying lithium-ion content up to and including total lithium–ion substitution on the alkali ion site and (2) measurements of light output and pulse shape using thermal neutron excitation.

Cooling of atoms below the recoil energy under multizone Raman excitation

Cooling of atoms below the temperature determined by the recoil energy is proposed on the basis of the Raman excitation of three-level atoms by the field of standing waves with a relative spatial shift. The advantage of this cooling mechanism is a weak sensitivity to the shape and duration of light pulses used for the transfer of population under Raman excitation. It is shown that the effectiveness of such cooling increases sharply when multizone excitation is used and already several interaction zones are enough for deep transverse cooling of an atomic beam to a temperature significantly lower than the recoil energy.

Characterization of CaWO 4 scintillator at room and liquid nitrogen temperatures

The properties of CaWO 4 (CaWO) crystals in γ-spectrometry were studied at room and liquid nitrogen(LN 2) temperatures. Two small samples of 10×10×4 mm 3 and 10×10×8 mm 3 size were tested, coupled to a Photonis XP3212 photomultiplier at room temperature and a large area avalanche photodiode at LN 2 temperature. Light pulse shape and light output at room and LN 2 temperatures were measured. Energy resolution and non-proportionality of the CaWO response versus γ-ray energy were studied and compared with those of small BGO and CdWO 4 crystals to discuss further the origin of the intrinsic resolution of undoped scintillating crystals. A high light output of 4800±200 phe/MeV and a good energy resolution of 6.6±0.2% for 662 keV γ-rays from a 137Cs source were measured for the small samples coupled to the XP3212 photomultiplier.

Shaping Quantum Pulses of Light Via Coherent Atomic Memory

We describe proof-of-principle experiments demonstrating a novel approach for generating pulses of light with controllable photon numbers, propagation direction, timing, and pulse shapes. The approach is based on preparation of an atomic ensemble in a state with a desired number of atomic spin excitations, which is later converted into a photon pulse. Spatiotemporal control over the pulses is obtained by exploiting long-lived coherent memory for photon states and Electromagnetically Induced Transparency in an optically dense atomic medium. Using photon counting experiments, we observe Electromagnetically Induced Transparency based generation and shaping of few-photon sub-Poissonian light pulses.

Scintillation properties of mixed LuYAP crystals in view of their use in a small animal PET scanner in phoswich configuration

Phoswich detectors are currently being considered by a number of investigators for depth-of-interaction (DOI) measurements in PET. In this work, the scintillation properties of several batches of Lu/sub 0.7/Y/sub 0.3/AlO/sub 3/ crystals doped with cerium were studied. The scintillators exhibited an excellent energy resolution and a light output comparable to BGO. The light pulse shape showed two components with 25 ns and around 250 ns. The light yield nonproportionality on photon energy was studied as well as the intrinsic energy resolution. Absorption, excitation and emission spectra were measured in a range extending from visible to ultraviolet. First results in the combination of these LuYAP crystals with LSO:Ce crystals in phoswich geometry for the final PET scanner are presented. The experimental results show that the new DOI detector is applicable for high-resolution PET systems.

Scintillation properties and mechanism in Lu 0.8Y 0.2AlO 3:Ce

In this paper we present results of light yield, light pulse shape and low-temperature thermoluminescence (ltTL) measurements of Lu 0.8Y 0.2AlO 3:Ce (0.4 and 0.55%) crystals. The light output was measured as between 1510±50 and 2190±70 phe/MeV and energy resolution at 662 keV ranged over 10–21% FWHM. Light pulse shapes consisted of two decay components, 20.0±1 ns (65%) and about 160 ns (35%). Performed ltTL measurements revealed three major peaks at 109, 160 and 195 K. A correlation between 109 and 160 K peaks and low light yield was observed.

Organic luminescent polycrystalsas novel materials for detectingionizing radiations

Organic molecular polycrystals obtained by the pressing technique of our design and their scintillation characteristics are discussed. The analysis of the dependence between structural features and radioluminescent characteristics of polycrystalline systems is based on the results of investigation of their light yield and pulse shape.

Efficient All-Optical Interband Light Modulation by Ultrafast Manipulation of Intersubband Transitions in an Asymmetric Quantum Well*

An efficient modulation scheme at relatively lower control light intensities is proposed using ultrashort interband and intersubband-resonant coupling light pulses in a novel asymmetric InxGa1-xAs/AlAs semiconductor quantum well structure. The shape of the intersubband-control light pulses can manipulate the interband-signal light pulse absorption. The carrier relaxation rate of the quantum well system can be estimated from the interband nonlinear optical parameters induced by the intersubband control light field. The modulation efficiency in the proposed structure is twice than in a conventional symmetric quantum well structure. This reduces the threshold optical energy below 1 pJ in a 100-µm2 waveguide structure on using 500 fs control light pulses owing to the enhanced optical nonlinearities in the proposed structure.

Resolving the Sonoluminescence Pulse Shape with a Streak Camera

The shape of the short light pulses emitted from a single air bubble trapped in a resonant sound field in degassed water has been measured directly for the first time with a streak camera. At low driving pressures the pulse shape is nearly Gaussian with a slightly slower decay. With increasing driving pressure the fall time and thereby the width of the pulse increases, while the rise time remains almost constant.

Pulse width and shape in single bubble sonoluminescence

To test the different theoretical models describing the light emitting process in SBSL measurements of the width and shape of the emitted light pulses are essential. The light pulses have been characterized by two independent methods: with time-correlated single photon counting and with a streak camera. Both methods lead to the same results. The pulse width strongly depends on the parameter’s driving pressure, gas and gas concentration and temperature and varies between 60 ps and more than 300 ps, and there is no difference between the red and uv part of the spectrum. The streak camera results additionally show that the pulse shape is slightly asymmetric with a steeper ascent and a slower descent. This asymmetry increases with decreasing temperature.

Properties of the YAP : Ce scintillator

Light yield, light pulse shape due to γ-rays and α-particles, energy and time resolutions for a 10 × 10 × 5 mm 3 YAB crystal coupled to the XP2020Q photomultiplier were studied. The measured light output of 17000 ± 850 photons/MeV includes a correction for the calibrated quantum efficiency of the XP2020Q. The fast component of the light pulse with the decay time constant of 26.7 ± 0.12 ns also shows a finite rise time described approximately by the time constant of 380 ± 45 ps. The YAP crystal which was studied exhibited an energy resolution of 5.7% for 662 keV γ-rays fron a 137Cs source. This very good energy resolution is due to a low intrinsic energy resolution of 3.4%. These characteristics, together with a good time resolution for 60Co γ-rays of 160 ps measured at the threshold of 1 MeV, suggest a broad range of applications for the YAP scintillator.

Investigation of some scintillation properties of YAG:Ce crystals

A light output expressed in the photoelectron (phe) number, a relative light yield for α-particles and light pulse shapes for γ-rays and α-particles excitation of the YAG:Ce crystals with different Ce doping between 0.012 and 1.08 mol% were studied. The highest light output of 1420 ± 70 phe/MeV was measured for the sample doped with 0.21 ± 0.03 mol% Ce, while the fastest pulse was observed for the sample doped with 1.08 ± 0.08 mol% Ce showing, however, lower light yield by 10%. The relative light yield for α-particles of 0.21 ± 0.03 as compared to γ-rays was approximately the same for all the samples studied. In conclusion, the YAG:Ce crystal doped with about 1 mol% of Ce is the most appropriate for different applications. For this crystal the α-γ discrimination by digital charge comparison method was studied. A clear separation was observed with the YAG crystal coupled to the XP2020Q photomultiplier for 5.49 MeV α-particles from 241Am source and 6.04 MeV as well as 8.77 MeV from ThC source. However, this separation was inferior compared to that known for CsI(Tl).

Properties of the new LuAP:Ce scintillator

The scintillation properties of LuAP (lutetium aluminum perovskite, LuAlO 3) have been investigated at three different levels of Ce doping: ≥ 0, 0.035 and 0.105 mol%. The light yield, in photoelectrons per MeV, was measured as 122±20, 1300±100 and 2850±200, respectively. The light pulse shapes were largely exponential, with a decay constant of 16.5±1 ns for all the samples studied. In all cases, however, an additional slow component, amounting to about 10±3% of the total light, was also found, characterized by a time constant of 74±7 ns. The sample doped with 0.105 mol% Ce showed an energy resolution of 9.3% for the 662 keV full energy peak from a 137Cs source. The high detection efficiency of the material for γ-rays (because of its high density of 8.4 g/cm 3) is confirmed by a photofraction of about 13% for a specimen with a volume of only 0.05 cm 3. The time resolution for 60Co γ-rays at a 1 MeV threshold was measured as 160 ps, somewhat poorer than expected. Nevertheless, the high light yield, fast light pulse, high detection efficiency for γ-rays and excellent time resolution make this material a very attractive scintillator, particularly in positron emission tomography.

Time evolution of CO vibrational populations during photodesorption by light pulses

We describe the direct photodesorption of CO from the Ni(001) metal surface during the absorption of a short pulse of UV light by the adsorbate and account for the dynamics of the desorbing species coupled to electronic excitations of the substrate, which lead to energy dissipation. The interaction potentials and couplings for the ground and excited states are obtained from electronic structure calculations and from experimental information. The time evolution of CO vibrational populations is studied for propagating wavepackets for the adsorbate–substrate complex with a split-operator algorithm, followed by a perturbative treatment of dissipation and response to the light pulse. Direct photodesorption is found to occur predominantly in the excited electronic state and is compatible with dissipation. Results are presented for CO photodesorption by Gaussian pulses with several durations to show the effect of light pulse shapes on the time evolution of populations. Shorter pulses in the femtosecond range are shown to give relatively larger populations of excited vibrational states during the desorption of CO. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 71–83, 1997

Timing properties of GSO, LSO and other Ce doped scintillators

Abstract Light pulse shape, number of photoelectrons per energy unit and time resolution for a 1 × 1 × 1 cm 3 GSO crystal coupled to a XP2020Q photomultiplier were studied and compared with similar measurements performed earlier on a LSO crystal. The observed time resolution of the time spectra, FWHM = 700 and 965 ps for the energy threshold set at 1 and 100 keV on the 60 Co γ-spectrum, are inferior compared to those for LSO because of the slow rise of the light pulse of GSO and a lower light yield. The time resolution obtainable with the GSO and LSO crystals is discussed based on the Hyman theory of timing. It allows discussion of the advantages and limitations of new Ce doped scintillators in fast timing.