Coincidence Time Spectra Research Articles

Field-programable-gate-array-based distributed coincidence processor for high count-rate online positron emission tomography coincidence data acquisition

For positron emission tomography (PET) online data acquisition, a centralized coincidence processor (CCP) with single-thread data processing has been used to select coincidence events for many PET scanners. A CCP has the advantages of highly integrated circuit, compact connection between detector front-end and system electronics and centralized control of data process and decision making. However, it also has the drawbacks of data process delay, difficulty in handling very high count-rates of single and coincidence events and complicated algorithms to implement. These problems are exacerbated when implementing a CCP on a field-programable-gate-array (FPGA) due to increased routing congestion and reduced data throughput. Industry companies have applied non-centralized or distributed data processing to solve these problems, but those solutions remain either proprietary or lack full disclosure of technical details that make the techniques unclear and difficult to adapt for most research communities. In this study, we investigated the use of a set of distributed coincidence processors (DCP) that can address the CCP problems and be implemented relatively easily. Each coincidence processor exclusively connects one detector pair and selects coincidence events from this detector pair only, which breaks a centralized coincidence process to a collection of independent and parallel processes. DCP can significantly minimize the data process delay, maximize count-rates of coincidence events and simplify implementation by implementing a single coincidence processor with one detector pair and replicating it to the rest. A prototype DCP with 42 coincidence processors was implemented on an off-the-shelf FPGA development board for a small PET with 12 detectors configured with 42 detector pairs. DCP performances were tested with both pulsed signals and gamma ray interactions. There was no coincidence data loss up to the detector’s maximum singles count-rate (250 k s−1). Approximately 1.2 k registers were utilized for each coincidence processor and the FPGA resource utilization was proportional to the number of coincidence processors. Coincidence timing spectra showed the results from accurately acquired coincidence events. In conclusion: complementary to CCP, DCP can provide high count-rate capability, with a simplified algorithm for implementation and potentially a practical solution for online acquisition of a PET with a larger number of detector pairs or for ultrahigh-throughput imaging.

Energy correlated timing spectra in target neutron techniques

Abstract An associated particle imaging (API) experimental setup with nanosecond precision electronics was constructed and tested. This API setup has the ability to measure alpha-gamma coincidence (timing) spectra, time correlated energy gamma spectra, and energy correlated timing spectra. The speed of 14.1 MeV neutron was defined from measurement of carbon energy correlated timing spectra. The measured value (5.2 cm/ns) agreed with reference data that confirmed a proper working setup and authenticated experimental results. Test experiments with graphite samples demonstrated that the minimal detectible level (MDL) of carbon with the appropriate timing window in API mode is 2.5 times lower than in continuous mode. Results indicate that this API method is quite promising for soil carbon analysis due to significantly improved MDL.

A fully automated and scalable timing probe-based method for time alignment of the LabPET II scanners

A fully automated time alignment method based on a positron timing probe was developed to correct the channel-to-channel coincidence time dispersion of the LabPET II avalanche photodiode-based positron emission tomography (PET) scanners. The timing probe was designed to directly detect positrons and generate an absolute time reference. The probe-to-channel coincidences are recorded and processed using firmware embedded in the scanner hardware to compute the time differences between detector channels. The time corrections are then applied in real-time to each event in every channel during PET data acquisition to align all coincidence time spectra, thus enhancing the scanner time resolution. When applied to the mouse version of the LabPET II scanner, the calibration of 6 144 channels was performed in less than 15 min and showed a 47% improvement on the overall time resolution of the scanner, decreasing from 7 ns to 3.7 ns full width at half maximum (FWHM).

The observation of the pair of Lyman-α and Lyman-β photons produced in the photodissociation of H2

SynopsisWe have measured the coincidence time spectra for the pair of the Lyman-α and Lyman-β photons produced in the photodissociation of H2 in the range of the incident photon energy 32.5 - 42 eV. The result shows that the pair of H(2p) and H(3p) fragments is produced in the photodossociation of H2 molecules.

Luminescence and scintillation timing characteristics of (LuxGd2−x)SiO5:Ce single crystals

The luminescence and scintillation characteristics of cerium-doped lutetium-gadolinium orthosilicate (LuxGd2−xSiO5:Ce; x=0, 0.8, 1.8) single crystals were investigated. At 662keV γ-rays, the light yield of 29,800±3000phMeV−1 obtained for Lu1.8Gd0.2SiO5:Ce is higher than that of 20,200±2000 and 11,800±1200phMeV−1 obtained for Lu0.8Gd1.2SiO5:Ce and Gd2SiO5:Ce, respectively. The fast component decay time of 32, 18 and 17ns was measured in the scintillation decay of Gd2SiO5:Ce, Lu0.8Gd1.2SiO5:Ce and Lu1.8Gd0.2SiO5:Ce, respectively. The coincidence time spectra for 511keV annihilation quanta were measured in reference to a fast BaF2 detector and time resolution was discussed in terms of a number of photoelectrons and decay time of the fast component. The mass attenuation coefficient for studied crystals at 60 and 662keV γ-rays was also evaluated and discussed.

Timing Performance of TlBr Detectors

The timing performance of TlBr detectors was evaluated at room temperature (22 °C). 0.5-mm-thick planar TlBr detectors with Tl circular electrodes with a diameter of 3 mm were fabricated from TlBr crystals grown by the traveling molten zone method using a zone-purified material. The pulse rise time of the TlBr detector was measured using a digital oscilloscope as the cathode surface of the device was irradiated with a 22Na gamma-ray source. Coincidence timing spectra were obtained between the TlBr detector and a BaF2 scintillation detector when both detectors were irradiated with 511 keV positron annihilation gamma-rays. The timing resolution of the TlBr detector was found to be inversely proportional to the applied bias voltage. The TlBr detector, in coincidence with the BaF2 detector, exhibited timing resolutions characterized by a 6.5 ns full width at half maximum (FWHM) and an 8.5 ns FWHM with and without an energy window of 350 keV-560 keV, respectively.

Influence of lutetium content on the scintillation properties in (Lu x Y1−x )AlO3 :Ce single crystals

The absorption, luminescence, and scintillation characteristics of cerium-doped lutetium-yttrium perovskite (LuxY1−x AlO3:Ce; x = 0, 0.3, 0.7) single crystals were investigated. The values of light yield, scintillation decay time, and coincidence time resolution were evaluated. At 662 keV γ-rays (137Cs source), the light yield of 30 700 ph MeV−1 obtained for YAlO3:Ce is much higher than that of 16 200 and 10 600 ph MeV−1 obtained for Lu0.3Y0.7AlO3:Ce and Lu0.7Y0.3AlO3:Ce, respectively. Scintillation decays are dominated by a fast component with decay time value of 16–20 ns, which nearly coincides with the photoluminescence decay time value of 17.5 ns. In scintillation decays the intensity of the fast component becomes reduced and the content of slower components considerably increased with increasing lutetium content in the crystals. The coincidence time spectra for 511 keV annihilation quanta were measured in coincidence experiment using a BaF2-based detector and time resolution was also discussed in terms of a number of photoelectrons and decay time of the scintillation pulse. The photofraction for all the crystals under 662 keV γ-ray excitation was also evaluated and discussed.

Dynamics of entangled H(2p) pair generated in the photodissociation of H2

We have measured the coincidence time spectra of two Lyman-α photons emitted by a pair of H(2p) atoms in the photodissociation of H2 at the incident photon energy of 33.66 eV and at the hydrogen gas pressures of 0.40 Pa and 0.02 Pa, from which the angular distributions of two Lyman-α photons have been obtained. The experimental angular distributions indicate the generation of the entangled pair of H(2p) atoms as predicted by the theory of our group (Miyagi et al 2007 J. Phys. B 40 617) and the role of a new kind of reaction, i.e. the reaction of the entangled pair of H(2p) atoms with an H2 molecule that efficiently changes the entanglement. It has turned out that more entangled pairs of H(2p) atoms survive at 0.02 Pa than at 0.40 Pa. The decay time constant in the coincidence time spectrum at 0.02 Pa is approximately half the lifetime of a single H(2p) atom, 1.60 ns, while the decay time constant at 0.40 Pa is in agreement with the lifetime of a single H(2p) atom. It follows that the decay faster than the lifetime of a single H(2p) atom originates from the entanglement in the pair of H(2p) atoms.

Recent Development of TlBr Gamma-Ray Detectors

Planar detectors, strip detectors, and double-sided strip detectors were fabricated from TlBr crystals grown by the traveling molten zone method using zone-purified material. The detector performance including the leakage current, energy resolutions, and timing performance were evaluated in order to assess the capability of the detectors for PET and SPECT applications. The TlBr detectors exhibited excellent spectroscopic performance at room temperature. An energy resolution of 3.4% FWHM at 511 keV was obtained from a TlBr planar detector 1 mm thick. A TlBr strip detector 1 mm thick with four anode strip electrodes exhibited almost uniform detector performance over the strips with the average energy resolution of 4.4% FWHM at 511 keV. A TlBr double-sided strip detector exhibited an energy resolution of 6.3% FWHM for 122 keV gamma-rays. Coincidence timing spectra between a TlBr planar detector and a BaF2 scintillation detector were recorded at room temperature. Timing resolutions of 14 ns and 24 ns were obtained from TlBr detectors 0.5 mm and 1 mm thick, respectively. By cooling the detector to 0° C, an improved timing resolution of 12 ns was obtained from a TlBr detector 1 mm thick.

Comment on “Effect of entanglement on the decay dynamics of a pair of H(2p) atoms due to spontaneous emission”

Tanabe et al (Phys. Rev. A {\bf 82} 040101(R) 2010) have experimentally demonstrated that the emission properties of unstable atoms in entangled and product states are different. The authors define an apparent decay time as a fitting parameter which falls below the lifetime of the single atom for entangled pairs. We argue that their results about coincidence time spectra are correct, but those concerning lifetimes cannot be considered conclusive because they assume the emission of photons by the two atoms to be independent processes, a doubtful hypothesis for entangled states. We suggest an improved evaluation of the lifetimes based on a rigorous approach, which demands some modifications of the experimental procedure.

Effect of entanglement on the decay dynamics of a pair of H(2p) atoms due to spontaneous emission

We have measured the coincidence time spectra of two Lyman-{alpha} photons emitted by a pair of H(2p) atoms in the photodissociation of H{sub 2} at the incident photon energy of 33.66 eV and at the hydrogen gas pressures of 0.40 and 0.02 Pa. The decay time constant at 0.02 Pa is approximately half the lifetime of a single H(2p) atom, 1.60 ns, while the decay time constant at 0.40 Pa is in agreement with the lifetime of a single H(2p) atom. It turns out that the decay faster than the lifetime of a single H(2p) atom originates from the entanglement in the pair of H(2p) atoms. We have demonstrated an effect of entanglement on atomic decay.

Recent progress in thallium bromide detectors for X- and γ-ray spectroscopy

Recent progress in the development of room-temperature TlBr detectors is presented. Higher-performance TlBr detectors have been fabricated from high-purity TlBr crystals grown by the traveling molten zone method. The TlBr crystals have exhibited large mobility–lifetime products of 2.6×10 −4 and 3.7×10 −5 cm 2/V for electrons and holes, respectively. An energy resolution of 29.8 keV (5.8%) FWHM has been recorded for 511 keV γ-rays with a TlBr detector at room temperature. Timing properties of the TlBr detectors have been studied by recording the coincidence timing spectra between a TlBr detector and a BaF 2 scintillator coupled to a photomultiplier tube. Timing resolution of 21.3 ns FWHM has been measured for 511 keV positron annihilation γ-rays from a 22Na source. By using a single TlBr detector in current mode, an X-ray CT scanner system of a first-generation type has been developed. The performance of the system has been evaluated by observing tomographic images. Images with good spatial resolution have been obtained by the scanner with the TlBr detector.

Evaluation of p-terphenyl and 2,2″ dimethyl-p-terphenyl as wavelength shifters for barium fluoride

p-Terphenyl (PTP) and 2,2″ dimethyl-p-terphenyl (DMT) have been investigated for use as wavelength shifters (WLSs) for barium fluoride (BaF 2) scintillation emission. These two organic fluors are attractive due to their high quantum efficiency, fast fluorescence decay time, and emissions above the wavelength cut-off of borosilicate glass. Measurements of these WLSs dissolved in cyclohexane are presented. Coincidence time spectra and fluorescence decay spectra measured with BaF 2 as the pump source, are shown. The fluorescence decay time and the ratio of fast to slow intensities were determined from the fluorescence decay spectrum. The increase in signal resulting from using a WLS between the borosilicate end-window photomultiplier tube and the BaF 2 crystal is measured. The motivation behind this work is the development of a gamma-ray spectrometer suitable for high count rate applications. We are also investigating the possibility of separating the fast and slow emissions of BaF 2 using optical techniques. PTP and DMT both can spectrally separate BaFe 2 emissions to a marginal extent.

Cherenkov radiation in photomultiplier windows and the resulting time shift in delayed coincidence time spectra

Pulses from bare photomultipliers, irridiated by γ-rays, are attributed to Cherenkov radiation, induced by Compton electrons. Due to this effect certain time spectra of delayed coincidences, measured with scintillators mounted on photomultipliers, consist of two components. Additional to the normal spectrum a weak spectrum, shifted with respect to the first one, is observed. This spectrum consists of delayed coincidences between the pulse due to a γ-rays detected in a scintillator and the pulse due to the other γ-ray, which was detected by the Cherenkov effect in the window of the photomultiplier. A possible systematic error in lifetime measurements, caused by this effect, is indicated, and a method to discriminate against this component in the time spectrum is described. The time resolution obtainable, using this Cherenkov radiation, is discussed.

A time-staggered system for multi-counter particle-gamma angular correlation measurements

An angular correlation system consisting of two particle counters and two gamma counters is described in which a time-to-amplitude convertor spectrum is produced containing all the correlation data, namely, four separate particle-gamma coincidence time spectra. This allows multiple counter and therefore simultaneous multiple angle coincidence measurements to be made with a small extension to a basic two detector (one angle) coincidence system.

Zur Auswertung von Lebensdauermessungen nach der Methode der verz�gerten Koinzidenzen

The various methods of evaluating delayedγ—γ coincidence time spectra are discussed and used to determine the half-life of the 81 keV-level in133Cs. A value ofT1/2=(6,25 ± 0,05) ns was obtained.

G-factor of 482 keV state of 181Ta measured with the differential method

Coincidence time spectra for the 133 to 482 kev gamma - gamma cascade were taken using two scintillation counters and having the source located in an external magnetic field perpendicular to the plane of successive gamma rays. Measurements were performed at theta /sub 1/ = (5 pi /8) and theta /sub 2/ = (7 pi /8) between counter axes and for the two opposite directions of the magnetic field. Four coincidence time spectra were obtained. It is indicated that perturbation of the angular correlation could be present. (L.N.N.)