The design of the TASD (totally active scintillator detector) prototype

Totally active and magnetic segmented scintillation neutrino detectors are developed for the nextgeneration accelerator neutrino experiments. Such detectors will incorporate scintillation modules with scintillation counters that form X and Y planes. A single counter is a 7 × 10 × 90 mm³ scintillation bar with gluedin wavelength-shifting fibers and micropixel avalanche photodiodes. The results of measurements of the parameters of these detectors are presented.

     

PET探测器技术的新进展

PET设备中探测器的研发, 一直是很活跃且具有高创新性的领域。 提高现有基于闪烁晶体探测器的性能, 研究适用于多模式成像设备（PET/CT和PET/MRI）的新型探测器, 满足TOF和DOI技术的需求并促进其发展应用, 构成PET探测器的几个主要研究方向。 介绍了PET探测器在闪烁晶体、 光电探测器和半导体探测器等方面的最新进展, 指出未来最有潜力的探测器设计方案。 The research on PET detector is a very active and highly innovative field. The main research interests of PET detector include improving performances of scintillation crystal detectors, investigating new detectors being suitable for multimodality imaging (e.g., PET/CT and PET/MRI), meeting needs of TOF and DOI technologies in order to promote their development and application. In this paper, new developments in PET detector technology about scintillation crystal, photodetector and semiconductor detector are introduced and the most potential detector design scheme in the future is brought forward.     

Capabilities of the Gamma-400 Gamma-ray Telescope for Observation of Electrons and Positrons in the TeV Energy Range

The space-based GAMMA-400 gamma-ray telescope will measure the fluxes of gamma rays in the energy range from ∼20 MeV to several TeV and cosmic-ray electrons and positrons in the energy range from several GeV to several TeV to investigate the origin of gamma-ray sources, sources and propagation of the Galactic cosmic rays and signatures of dark matter. The instrument consists of an anticoincidence system, a converter-tracker (thickness one radiation length, 1 X₀), a time-of-flight system, an imaging calorimeter (2 X₀) with tracker, a top shower scintillator detector, an electromagnetic calorimeter from CsI(Tl) crystals (16 X₀) with four lateral scintillation detectors and a bottom shower scintillator detector. In this paper, the capability of the GAMMA-400 gamma-ray telescope for electron and positron measurements is analyzed. The bulk of cosmic rays are protons, whereas the contribution of the leptonic component to the total flux is ∼10⁻³ at high energy. The special methods for Monte Carlo simulations are proposed to distinguish electrons and positrons from proton background in the GAMMA-400 gamma-ray telescope. The contribution to the proton rejection from each detector system of the instrument is studied separately. The use of the combined information from all detectors allows us to reach a proton rejection of up to ∼1 × 10⁴.

     

RF cavity simulations for superconducting cyclotron C400

Compact superconducting isochronous cyclotron C400 [1] has been designed at IBA (Belgium) in collaboration with the JINR (Dubna). This cyclotron will be the first cyclotron in the world capable of delivering protons, carbon and helium ions for therapeutic use. ¹²C⁶⁺ and ⁴He²⁺ ions will be accelerated to 400 MeV/u energy and extracted by electrostatic deflector, H₂⁺ ions will be accelerated to the energy of 265 MeV/u and extracted by stripping. It is planned to use two normal conducting RF cavities for ion beam acceleration in the cyclotron C400. Computer model of the double gap delta RF cavity with 4 stems was developed in the general-purpose simulation software CST STUDIO SUITE. Necessary resonant frequency and increase of the voltage along the gaps were achieved. Optimization of the RF cavity parameters leads us to the cavity with quality factor about 14000, RF power dissipation is equal to about 50 kW per cavity.     

Micropixel avalanche photodiodes and the possibility for their application in positron-emission tomography

Micropixel avalanche photodiodes (MAPDs) are new instruments for detecting low-intensity light. They consist of many microcounters (pixels integrated on a common silicon wafer). A unique design by the Joint Institute for Nuclear Research (JINR) (Z. Sadygov)??deep-microwell MAPD??provides an order of larger pixel densities without losses in photon-detection efficiency. These instruments are beginning to find use in precision electromagnetic calorimetry. MAPDs can be most widely applied as photodetectors in scanners for positron-emission tomographs (PETs), particularly the time-of-flight PETs becoming popular now. The possibility of using MAPDs in PETs is shown, and the time resolution of a pair of quanta detected by Lutetium Fine Silicate scintillation crystals with MAPD readout is obtained at the level of 400 ps.     

Response of timepix detector with GaAs:Cr and Si sensor to heavy ions

The response of the Timepix detector to neon ions with kinetic energy 77 and 158.4 MeV has been studied at the cyclotron U-400M of the JINR Flerov Laboratory of Nuclear Reaction. Sensors produced from gallium arsenide compensated by chromium and from silicon are used for these measurements. While in Timepix detector with Si sensor the well-known so-called “volcano effect” observed, in Timepix detector with GaAs:Cr sensor such effect was completely absent. In the work the behavior of the Timepix detector with GaAs:Cr sensor under irradiation with heavy ions is described in comparison with the detector based on Si sensor. Also the possible reason for absence of “volcano” effect in GaAs:Cr detector is proposed.     

Internal cancellation of spikes using two avalanche photodiodes in series for single photon detection

<正>We propose a method of improving the performance of InGaAs/InP avalanche photodiodes by using two avalanche photodiodes in series as single photon detectors for 1550-nm wavelength.In this method,the raw single photon avalanche signals are not attenuated,thus a high signal-to-noise ratio can be obtained compared with the existing results.The performance of the scheme is investigated and the ratio of the dark count rate to the detection efficiency is obtained to be 1.3×10~(-4) at 213 K.     

Silicon photodiodes as Thomson scattering detectors in experiments on the Tuman-3M tokamak and in bench experiments

Experiments on Thomson scattering in the Tuman-3M tokamak plasma with silicon photodiodes applied as radiation detectors are performed. Bench tests and numerical simulation are used to compare the efficiency of detector modules based on conventional and avalanche photodiodes in recording weak pulses of various durations against uniform background light. When the pulse duration increases to several hundreds of nanoseconds, the increase in sensitivity due to avalanche gain disappears. This is of importance for diagnosing the tokamak plasma, where the background radiation is relatively intense.     

Response of Makrofol polycarbonate plastic track detector to 1.1 MeV/N 54 132 Xe-ion

Makrofol polycarbonate plastic track detectors have been exposed to ₅₄ ¹³² Xe -ions of energy 1.1 MeV/N from the cyclotron beam. The bulk etch rate and track etch rate are measured for different temperatures and the activation energies are calculated. The maximum etched track length is compared with the theoretically computed range. The critical energy loss is (dE/dx) _c =5 MeV cm² mg⁻¹ for this detector material.     

高分辨率及高灵敏度小动物PET研究进展

作为一种高灵敏度且具有定量测量能力的功能分子影像技术,小动物PET越来越广泛地用于各种生物医学研究,例如疾病动物模型研究、新药物研发和新治疗方法评估等。首先回顾小动物PET成像系统的发展历史、效率和空间分辨率等性能的改进和产业化;其次,讨论了影响PET空间分辨率和效率的各种因素,包括晶体大小、探测器几何、正电子射程、光子非共线效应、图像重建算法和阻碍PET系统同时达到高空间分辨率和高效率的相互作用深度不确定效应;最后,介绍了小动物PET成像系统在以下几个方面的取得的最新进展:（1）高密度、小的光衰减常数和高光产额的闪烁晶体;（2）体积小、增益大、时间性能好、工作电压低和磁兼容的新型硅光电倍增管光探测器;（3）各种深度测量PET探测器,详细介绍了一个可达到分辨0.43 mm×0.43 mm×20 mm晶格和达到2.4 mm深度分辨率的双端读出探测器;（4）使用深度测量探测器的小动物PET成像系统,详细介绍了一个使用高分辨率双端读出探测器,全视野达到0.55 mm平均位置分辨率的小动物PET原型系统;（5）磁兼容插件式小动物PET成像系统和PET/MRI同时成像的优点;（6）小动物PET图像重建和数据校正的特点、传统的滤波反投影算法和新的迭代算法的优缺点和PET图像重建算法未来的发展方向。As the most sensitive and quantitative molecular imaging technique,small animal positron emission tomography (PET) has become a widely used tool in biomedical research such as in animal model of human disease,development of new drugs and the evaluation of new therapeutics.In this paper,first the history,the efforts to improve the spatial resolution and sensitivity as well as the commercialization process of small animal PET scanner are reviewed.Then the factors that affect the spatial resolution and sensitivity of PET scanner such as crystal size,detector geometry,positron range,photon noncollinearity and imaging reconstruction are discussed in detail.The depth of interaction effect which hinders the simultaneous achievement of PET spatial resolution and sensitivity are also discussed.Finally the recent progress made in the following areas of small animal PET instrumentation are introduced:(1) high density,short light decay constant and bright scintillator,(2) compact,high gain,good timing resolution,low bias voltage and MRI compatible silicon photomultiplier,(3) depth encoding detectors by using different methods,a detector using dual-ended readout,identifying 0.43 mm×0.43 mm×20 mm crystals and achieving a 2.4 mm depth of interaction resolution was introduced in detail,(4) small animal PET scanners using depth encoding detectors,a prototype scanner using high resolution dualended readout detectors and achieving an average of 0.55 mm spatial resolution in the whole field of view was introduced in detail.(5) MRI compatible small animal PET inserts and the advantage of simultaneous PET/MRI imaging,(6) image reconstruction and data correction of small animal PET,the filter back projection and iterative reconstruction algorithms are compared and a few key directions of PET image reconstruction will be presented.     

双束质子辐照砷化镓光电导探测器的I-V特性

 对用能量为7.5MeV和20MeV,注量为10¹¹～10¹³cm^-2的质子辐照后的砷化镓材料制作的光电导探测器的光电流和暗电流进行了测试，并由此推得电导率的变化。结果表明，经过能量为7.5MeV的质子改性后的砷化镓探测器相对于未改性的附加光电导率Δσ减少，而且随着辐照注量的增加而越小，而对于先用能量为20MeV质子辐照后再用能量为7.5MeV的质子辐照的砷化镓材料制作的探测器，其附加光电导率Δσ的减少则更为明显。对上述现象进行了分析，并根据其相应关系预测了该种探测器的响应时间、灵敏度、拖尾现象及受X射线激发的输出脉冲的后延的变化情况。     

Feasibility studies towards future self-sufficient supply of the 99Mo-99mTc isotopes with Japanese accelerators

In order to establish a self-sufficient supply of ^99mTc, we studied feasibilities to produce its parent nucleus, ⁹⁹Mo, using Japanese accelerators. The daughter nucleus, ^99mTc, is indispensable for medical diagnosis. ⁹⁹Mo has so far been imported from abroad, which is separated from fission products generated in nuclear reactors using enriched ²³⁵U fuel. We investigated ^99mTc production possibilities based on the following three scenarios: (1) ⁹⁹Mo production by the (n, 2n) reaction by spallation neutrons at the J-PARC injector, LINAC; (2) ⁹⁹Mo production by the (p, pn) reaction at E_p = 50–80 MeV proton at the RCNP cyclotron; (3) ^99mTc direct production with a 20 MeV proton beam from the PET cyclotron. Among these three scenarios, scenario (1) is for a scheme on a global scale, scenario (2) works in a local area, and both cases take a long time for negotiations. Scenario (3) is attractive because we can use nearly 50 PET cyclotrons in Japan for ^99mTc production. We here consider both the advantages and disadvantages among the three scenarios by taking account of the Japanese accelerator situation.     

Positron emission isotope production cyclotron in DLNP JINR (Status Report)

A C10-cyclotron for radioisotope production is under construction at the Dzhelepov Laboratory of Nuclear Problem, Joint Institute for Nuclear Research (DLNP JINR). It is a compact isochronous cyclotron for accelerating H⁻ ions to the energy of about 10 MeV. The magnetic system, vacuum chamber and accelerating system is being built now. Results of the calculation and forming of the cyclotron magnetic field and the study of the beam dynamics from an ion source to an extraction system in calculated magnetic field are presented. The text was submitted by the authors in English.     

Evolution of nuclear spectroscopy at Saha Institute of Nuclear Physics

Experimental studies of nuclear excitations have been an important subject from the earliest days when the institute was established. The construction of 4 MeV proton cyclotron was mainly aimed to achieve this goal. Early experiments in nuclear spectroscopy were done with radioactive nuclei with the help of beta and gamma ray spectrometers. Small NaI(Tl) detectors were used for gamma-gamma coincidence, angular correlation and life time measurements. The excited states nuclear magnetic moments were measured in perturbed gamma-gamma angular correlation experiments. A high transmission magnetic beta ray spectrometer was used to measure internal conversion coefficients and beta-gamma coincidence studies. A large number of significant contributions were made during 1950–59 using these facilities. Proton beam in the cyclotron was made available in the late 1950’s and together with 14 MeV neutrons obtained from a C-W generator a large number of short-lived nuclei were investigated during 1960’s and 1970’s. The introduction of high resolution Ge gamma detectors and the improved electronics helped to extend the spectroscopic work which include on-line (p ₇ p′γ) and (p ₇ nγ) reaction studies. Nuclear spectroscopic studies entered a new phase in the 1980’s with the availability of 40–80 MeV alpha beam from the variable energy cyclotron at VECC, Calcutta. A number of experimental groups were formed in the institute to study nuclear level schemes with (α ₇ xnγ) reactions. Initially only two unsuppressed Ge detectors were used for coincidence studies. Later in 1989 five Ge detectors with a large six segmented NaI(Tl) multiplicitysum detector system were successfully used to select various channels in (α ₇ xnγ) reactions. From 1990 to date a variety of medium energy heavy ions were made available from the BARC-TIFR Pelletron and the Nuclear Science Centre Pelletron. The state of the art gamma detector arrays in these centres enabled the Saha Institute groups to undertake more sophisticated experiments. Front line nuclear spectroscopy works are now being done and new informations are obtained for a large number of nuclei over a wide mass range. Currently Saha Institute is building a multi-element gamma heavy ion neutron array detector (MEGHNAD), which will have six high efficiency clover Ge detector together with charged particle ball and other accessories. The system is expected to be usable in 2002 and will be used in experiments using high energy heavy ions from VECC.     

Measurement of the fusion rate in μd3He

Many atomic and molecular processes may occur after a muon has been stopped in a mixture of hydrogen and helium isotopes. In particular, the muonic molecule μd³He can be formed. This molecule either decays or undergoes muon catalyzed fusion. Theory predicts a fusion rate much lower than the decay rate; moreover, the various theoretical predictions differ from each other by several orders of magnitude. With the experiment presented here we intend to measure the effective fusion rate via the detection of the 14.7 MeV fusion proton. A new target and gas mixing system, designed at JINR, were used in a ten-day test run at PSI. The fusion protons and products from other transfer and background reactions were measured with several different detectors (plastic scintillators, BGO, Germanium, neutron, and Silicon detectors). The formation rate of the μd ³He molecule and an upper limit for the effective fusion rate have been measured and are presented here. This revised version was published online in August 2006 with corrections to the Cover Date.     

HgCdTe avalanche photodiodes: A review

This paper presents a comprehensive review of fundamental issues, device architectures, technology development and applications of HgCdTe based avalanche photodiodes (APD). High gain, above 5×10³, a low excess noise factor close to unity, THz gain-bandwidth product, and fast response in the range of pico-seconds has been achieved by electron-initiated avalanche multiplication for SWIR, MWIR, and LWIR detector applications involving low optical signals. Detector arrays with good element-to-element uniformity have been fabricated paving the way for fabrication of HgCdTe-APD FPAs.     

Technology of manufacturing micropixel avalanche photodiodes and a compact matrix on their basis

A technology for manufacturing a new micropixel avalanche photodiode (MAPD) with deeply buried pixels (including two epitaxial layers between which an array of n ⁺) regions is formed by ionic doping) is described. A new method for manufacturing the compact MAPD matrices with minimum dead zone is proposed.     

单光子探测技术

近年来,以量子密钥分配为代表的各种量子信息技术应用获得了飞速发展,这些应用对单光子探测器的性能提出了非常苛刻的要求,以光电倍增管和雪崩光电二极管为代表的传统单光子探测器件已经无法满足需求。在此背景下,出现了以超导单光子探测器为代表的新型低温单光子探测器件,其性能比现有商用单光子探测器有了本质性的提升。本文综述了迄今为止各种类型的单光子探测器,并指出各自在量子信息技术应用中的优势和不足之处以及发展方向。     

Testing of a cryogenic source of slow monochromatic positrons

The results of testing a cryogenic source of slow monochromatic positrons based on the ²²Na isotope, designed and constructed at JINR, are presented. A solid neon moderator was used to generate a monochromatic beam from the continuous β⁺ spectrum of 0–0.5 MeV, with solid neon being frozen to the base layer, which is cooled to the temperature of 5–7 K. Test source of the ²²Na isotope allows the forming of a slow positron beam of intensity 5.8 × 10³ part./s and the average energy 1.2 eV at a spectrum width of 1 eV. The efficiency of moderation is 1% of the total positron flux.     

Experimental study for the production cross sections of positron emitters induced from 12C and 16O nuclei by low-energy proton beams

In proton therapy, positron emitters are induced from ¹²C and ¹⁶O nuclei by protons on the beam path in the patient. Many studies for monitoring positron emitters with beam-induced PET technique have been performed by various groups to verify the proton beam range and the dose in the patient for quality assurance (QA). The QA methods proposed by some groups require accurate production cross sections of the positron emitters produced by protons, especially in the low-energy region. The aim of this study was to develop a method for measuring the production cross sections of positron emitters using standard equipment for proton therapy, and to measure the cross sections of positron emitters produced by low-energy protons and verify them in comparison with data of previous experiments. An 80-MeV proton beam was produced by a synchrotron, and the energy was degraded by polyethylene blocks to obtain various beam energies. The number of protons was estimated from the charge induced in a parallel-plate ionization chamber by protons. Low-energy protons of 14–70 MeV were used to bombard ¹²C-rich and ¹⁶O-rich target materials: namely, polyethylene and gelatinous water. The time-activity curve was then measured by a high-sensitivity PET scanner to extract the number of positron emitters produced in the target. The production cross sections for four reaction channels: ¹⁶O(p, pn)¹⁵O, ¹⁶O(p, 3p3n)¹¹C, ¹⁶O(p, 2p2n)¹³N, and ¹²C(p, pn)¹¹C were then measured. The cross sections for the ¹⁶O(p, pn)¹⁵O reaction channel were consistent with data of previous experiments within the uncertainties, while those of ¹²C(p, pn)¹¹C were generally lower than data of previous experiments. These results suggested that further measurements of the production cross sections will be necessary.