Radiation detectors dedicated to time-of-flight positron emission tomography (PET) have been developed, and coincidence time resolution (CTR) of sub-100 ps full width at half maximum (FWHM) has been ...achieved by carefully optimizing scintillators and photodetectors. Achieving a CTR of 30 ps FWHM by using a pair of annihilation γ-rays would allow us to directly localize the annihilation point within an accuracy of 4.5 mm. Such direct localization can potentially eliminate the requirement of image reconstruction processes in clinical PET systems, which would have a huge impact on clinical protocols and molecular imaging. To obtain such a high CTR, researchers have investigated the use of prompt emissions such as Cherenkov radiation and hot-intra band luminescence. Although it is still challenging to achieve a CTR of 30 ps FWHM even with a Cherenkov-based detector, the experimentally measured CTR is approaching the goal. In this work, we developed a Cherenkov-radiator-integrated micro-channel plate photomultiplier tube (CRI-MCP-PMT), where there are no optical boundaries between the radiator and photocathode, and its timing performance was investigated. By removing the optical boundaries, reflections are eliminated and transmission to the photocathode is improved, resulting in high timing capability. As a result, a CTR of 30.1 ± 2.4 ps FWHM, which is equivalent to a position resolution of 4.5 ± 0.3 mm along a line of response (LOR), was obtained by using a pair of CRI-MCP-PMTs.
The proposed Mitchell Institute Neutrino Experiment at Reactor (MINER) experiment at the Nuclear Science Center at Texas A&M University will search for coherent elastic neutrino-nucleus scattering ...within close proximity (about 2m) of a 1MW TRIGA nuclear reactor core using low threshold, cryogenic germanium and silicon detectors. Given the Standard Model cross section of the scattering process and the proposed experimental proximity to the reactor, as many as 5–20events/kg/day are expected. We discuss the status of preliminary measurements to characterize the main backgrounds for the proposed experiment. Both in situ measurements at the experimental site and simulations using the MCNP and GEANT4 codes are described. A strategy for monitoring backgrounds during data taking is briefly discussed.
Timing-performance evaluation of Cherenkov-based radiation detectors Ota, R.; Nakajima, K.; Hasegawa, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2019, Letnik:
923
Journal Article
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With the upgradation of detector components, such as scintillators and photodetectors, the PET-image signal-to-noise ratio of time-of-flight positron emission tomography (TOF-PET) systems has been ...improved, compared to those of ordinary nonTOF-PET systems. A TOF-PET with an ultrahigh time resolution, for example a coincidence time resolution (CTR) better than few tens of picoseconds, can not only improve the image quality, but also remove the image reconstruction process, significantly impacting medical imaging. Therefore, it is crucial to develop a high-time resolution PET detector. We focus on the prompt emission of Cherenkov radiation, owing to the instantaneousness of which, a high time resolution can be expected. One of the candidates for the Cherenkov radiator is lead fluoride (PbF2) due it has excellent properties, including transparency toward the ultraviolet region, high refractive index (n = 1.82), and high density (7.77 g/cm3). Moreover, it does not contain radioisotopes, unlike lutetium-based scintillators, which are commonly used in the currently available TOF-PET detectors. In this work, we experimentally investigate the timing performance of PbF2-based Cherenkov detectors, breaking down the timing performance into physical components. 3×3×5 mm3 and 9.6×9.6×5 mm3 PbF2 crystals are used as Cherenkov radiators; both are attached to a microchannel plate photomultiplier tube (MCP-PMT) because the single channel MCP-PMT is one of the best photodetectors in terms of the SPTR, which is 25 ps full width at half maximum (FWHM). All the surfaces, except the end surface where the MCP-PMT is connected, are wrapped in black tape to suppress the reflections of the Cherenkov photons in the crystal. The CTR is measured by placing a detector pair face-to-face, using an 22Na point source, and an oscilloscope at 20 GS/s with a set bandwidth of 4.2 GHz. A CTR of 46.9 ps FWHM, corresponding to a position resolution of 7.0 mm, is obtained, consistent with our simulation results.
In order to achieve the ultimate goal of reducing coincidence time resolution (CTR) to 10 ps, thus enabling reconstruction-less positron emission tomography, a Cherenkov-radiator-integrated ...microchannel plate photomultiplier tube (CRI) reaching CTR of sub-50 ps full width at half maximum (FWHM) has been developed. However, a histogram of time differences between a pair of the CRIs shows undesirable side peaks, which are caused by gamma rays directly interacting with the micro channel plates (MCPs). Such direct interaction events are detrimental to the timing performance of the CRI. In this paper, we demonstrate an analytical method of deconvolving MCP direct interaction events from the timing histogram. Considering the information of the main and the two side peaks, the timing uncertainty caused by the MCP direct interaction events is deconvolved and the CTR of the CRI is analytically investigated. Consequently, the CTR is improved from 41.7 to 40.5 ps FWHM by the deconvolution. It means that a mixture of the Cherenkov radiator events and the MCP direct interaction events contribute to the CTR by a factor of 10 ps. The timing performance of the MCP direct interaction events are also evaluated. The CTR between the two MCPs is found to be 66.2 ps FWHM. This indicates that a photocathode-free radiation detector with high timing performance is possible. Elimination of the photocathode from the detector would make detector construction easier and more robust.
To linearly estimate the decay time and pulse height of a scintillation detector with low power consumption, a dual time-over-threshold (dual-ToT) method is proposed in this paper. The results of ...comparative experiments conducted using a 3×3×3 mm3 LYSO crystal and 3×3 mm2 MPPC with 50 μm cells indicated that the resolution of the estimated decay time using the dual-ToT method was 3.8 ns standard deviation (SD), whereas 3.5 ns SD was obtained using fully digitized waveforms. Additionally, a linear relationship between the dual-ToT-based and the analog-to-digital converter (ADC)-based pulse height was successfully observed. The estimated pulse height resolution using the dual-ToT method and post analysis technique was 12–13% FWHM at 511 keV, which is comparable to that of the ADC-based measurement. These capabilities potentially indicate that the dual-ToT method could be an alternative to the ADC method, with the advantage of lower power consumption and being applicable to the phoswich detector and particle identification applications.
The energy calibration system for CANDLES using (n,γ) reaction Iida, T.; Mizukoshi, K.; Ohata, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2021, Letnik:
986
Journal Article
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Calcium fluoride for the study of Neutrinos and Dark matters by Low-energy Spectrometer (CANDLES) searches for neutrino-less double-beta decay of 48Ca using a CaF2 scintillator array. A high Q-value ...of 48Ca at 4268 keV enabled us to achieve low background, however, at the same time it causes difficulties in calibrating the detector’s Q-value region because of the absence of a standard high-energy γ-ray source. Therefore, we have developed a novel calibration system based on γ-ray emission by neutron capture on 28Si, 56Fe, and 58Ni nuclei. In this paper, we report the development of the new calibration system as well as the results of energy calibration in CANDLES up to 9 MeV.
We have studied the neutrino-less double beta decay(0νββ) of 48Ca with the CANDLES III system, which consists of CaF2(pure) scintillators. Rejection analyses for background events from radioactive ...contaminations in the CaF2(pure) scintillators were effective to reduce backgrounds in Qββ-value region. As the results, no events were observed in the region for the data of 131 days × 86 kg. It gave a lower limit 6.2 × 1022 year (90 % C.L.) for the half-life of 0νββ of 48Ca. For higher sensitive measurement of 48Ca 0νββ, we have developed new techniques for 48Ca enrichment and CaF2 scintillating bolometer. In this paper, we will also show current status of these techniques.
In a neutrinoless double-beta decay (<inline-formula> <tex-math notation="LaTeX">0\nu \beta \beta </tex-math></inline-formula>) experiment, energy resolution is important to distinguish between ...<inline-formula> <tex-math notation="LaTeX">0\nu \beta \beta </tex-math></inline-formula> and background events. CAlcium fluoride for studies of Neutrino and Dark matters by Low Energy Spectrometer (CANDLES) discerns the <inline-formula> <tex-math notation="LaTeX">0\nu \beta \beta </tex-math></inline-formula> of 48 Ca using a CaF 2 scintillator as the detector and source. Photomultiplier tubes (PMTs) collect scintillation photons. At the <inline-formula> <tex-math notation="LaTeX">Q </tex-math></inline-formula> value of 48 Ca, the current energy resolution (2.6%) exceeds the ideal statistical fluctuation of the number of photoelectrons (1.6%). Because of CaF 2 's long decay constant of 1000 ns, a signal integration within 4000 ns is used to calculate the energy. The baseline fluctuation (<inline-formula> <tex-math notation="LaTeX">\sigma _{\mathrm{ baseline}} </tex-math></inline-formula>) is accumulated in the signal integration, thus degrading the energy resolution. This article studies <inline-formula> <tex-math notation="LaTeX">\sigma _{\mathrm{ baseline}} </tex-math></inline-formula> in the CANDLES detector, which severely degrades the resolution by 1% at the <inline-formula> <tex-math notation="LaTeX">Q </tex-math></inline-formula> value of 48 Ca. To avoid <inline-formula> <tex-math notation="LaTeX">\sigma _{\mathrm{ baseline}} </tex-math></inline-formula>, photon counting can be used to obtain the number of photoelectrons in each PMT; however, a significant photoelectron signal overlapping probability in each PMT causes missing photoelectrons in counting and reduces the energy resolution. "Partial photon counting" reduces <inline-formula> <tex-math notation="LaTeX">\sigma _{\mathrm{ baseline}} </tex-math></inline-formula> and minimizes photoelectron loss. We obtain improved energy resolutions of 4.5%-4.0% at 1460.8 keV (<inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-ray of 40 K) and 3.3%-2.9% at 2614.5 keV (<inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-ray of 208 Tl). The energy resolution at the <inline-formula> <tex-math notation="LaTeX">Q </tex-math></inline-formula> value is estimated to be improved from 2.6% to 2.2%, and the detector sensitivity for the <inline-formula> <tex-math notation="LaTeX">0\nu \beta \beta </tex-math></inline-formula> half-life of 48 Ca can be improved by 1.09 times.
Scintillation characteristics of CsPbCl3 single crystals Kobayashi, M.; Omata, K.; Sugimoto, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2008, Letnik:
592, Številka:
3
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