Various digital methods were examined for determining the relative arrival times of pulses from?20 mm × 5 mm LaBr3 scintillators. In this study, pulses from the photomultiplier tubes (PMTs) were digitized by DRS4 evaluation board, a switched capacitor array (SCA) produced by the Paul Scher-rer Institute (PSI). The high bandwidth, low power consumption and short readout time make DRS4 attractive for many experiments, replacing traditional ADCs and TDCs. The sampling signals were post processed with multiple techniques. These techniques include: (1) constant-fraction discrimination (CFD), (2) pulse-shape fitting, (3) mean PMT pulse model and (4) median filtered zero crossing method. The implemented CFD in the digital regimes did not improve the resolution of using analog equipment with average time resolution. The pulse-shape fitting yielded as good resolution as digital CFD, however, is much more time consuming. The median filtered method were easy to implement, and had a resolution on the order of sampling time. Average timing resolutions of 195.4 ps were obtained with mean PMT pulse model, which is better than the analog constant-fraction-zero-crossing with average resolution of 254.7 ps.

In order to satisfy high precision requirement for the modern nuclear physics experiment detectors and radiologic imaging technology equipments, we do some researches in improving the resolution of the detector with LaBr3:Ce scintillator.

During carbon ion therapy,lots of positron emitters such as11C,15O,10C are generated in irradiated tissues by nuclear reactions,and can be used to track the carbon beam in the tissue by a positron emission tomography（PET）scanner.In this study,an dual-plate in-room PET scanner has been designed and evaluated based on the GATE simulation platform to monitor patient dose in carbon ion therapy.The dual-plate PET is designed to avoid interference with the carbon beamline and with patient positioning.Its performance was compared with that of four-head and full-ring PET scanners.The dual-plate,four-head and full-ring PET scanners consisted of 30,60,60detector modules,respectively,with a 36 cm distance between directly opposite detector modules for dose deposition measurements.Each detector module consisted of a 24×24 array of 2 mm×2 mm×18 mm LYSO pixels coupled to a Hamamatsu H8500 PMT.To estimate the production yield of positron emitters,a 10 cm×15 cm×15 cm cuboid PMMA phantom was irradiated with 172,200,250 MeV/u12C beams.3D images of the activity distribution measured by the three types of scanner are produced by an iterative reconstruction algorithm.By comparing the longitudinal profile of positron emitters along the carbon beam path,it is indicated that use of the dual-plate PET scanner is feasible for monitoring the dose distribution in carbon ion therapy.

Monte Carlo simulation plays an important role in the study of time of flight (TOF) positron emission tomography (PET) prototype. As it can incorporate accurate physical modeling of scintillation detection process, from scintillation light generation, the transport of scintillation photos through the crystal(s), to the conversion of these photons into electronic signals. The Geant4 based simulation software GATE can provide a user-friendly simulation platform containing the properties needed. In this work, we developed a dedicated module in GATE simulation tool. Using this module, we simulated the light yield, energy resolution, time resolution of LYSO pixels with the same cross-section ($4\times4 mm^{2}$) of different lengths: 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, coupled to a PMT. The experiments were performed to validate the GATE simulation results. The results indicate that the best time resolution (484.0$\pm$67.5 ps) and energy resolution (13.3$\pm$0.4 %) could be produced by using pixel with length of 5 mm. The module can also be applied to other cases for precisely simulating optical photons propagating in scintillators.

The projectile fragmentation reactions of Ar-40 at 57 MeV/nucleon on Be-9 and Ta-181 targets have been studied by the Radioactive Ion Beam Line in Lanzhou (RIBLL) at the Heavy-Ion Research Facility in Lanzhou (HIRFL). The momentum distributions of fragments have been measured and the competition between different mechanisms are observed. The production cross sections have been obtained and compared with the empirical parametrization of fragmentation cross section (EPAX), abrasion-ablation (AA), and heavy-ion phase space exploration (HIPSE) models, and the target dependence of fragment cross sections has also been discussed.

A time rectification system for a In-Beam TOF-PET was described.It consists of a pair of BaF2(φ40 mm×45 mm) crystals coupled to Philips photomultipliers XP2020Q and a time coincidence electronic system using standard NIM modules.The best coincidence timing resolution of the system for pairs of 511 keV gamma rays is 576 ps.Some factors affecting the time resolution were primarily discussed,such as the types of photomultiplier tubes(PMT),the model of signal readout,the effects of different discriminators and timing amplifiers.The experiment results show that the signal read from the PMT dynode can get the optimum resolution;the PMT types,especially the rise time and electronic transmit time greatly affect the system performance.The shorter the rise time and electronic transmit time for the PMTs is,the better the timing performance is.The system timing performance is also related to the electronic combination.

A prototype of time-of-flight positron emission computed tomography（TOF-PET） has been developed for acquiring the coincident detection of 511 keV γ-rays produced from positron annihilation.It consists of two 80.5 mm×80.5 mm LYSO scintillator arrays（composed of 35 ×35 pixel finger crystals） with the position sensitive photomultiplier tubes R2487 as the readout.Each array is composed of 2 mm ×2 mm×15 mm finger crystals and the average pixel pitch is 2.30 mm.The measured results indicate that the TOF information has the potential to significantly enhance the image quality by improving the noise variance in the image reconstruction.The best spatial resolution（FWHM） of the prototype for the pairs of 511 keV γ-rays is 1.98 mm and 2.16 mm in the x and y directions,respectively,which are smaller than the average pixel pitch of 2.30 mm.

The proton resonant properties in 18 Ne, which determine the reaction rate of the key stellar 14 O(α,p) 17 F reaction, have been studied by using a technique of proton resonant elastic scattering of 17 F+p. A 4.22 MeV/nucleon 17 F radioactive ion (RI) beam was produced via a projectile-fragmentation reaction, and separated by a Radioactive Ion Beam Line in Lanzhou (RIBLL). By bombarding a thick (C H 2) n target, the energy spectra of the recoiled protons were measured by two Δ E - E silicon telescopes at the center-of-mass scattering angles of θ c.m. ≈175°±5°, θ c.m. ≈152°±8°, respectively. Several proton resonances in 18 Ne were observed clearly. A further R-matrix analysis of the experimental data is under way to determine the resonant parameters. The present work reports the preliminary results briefly.

A knockout reaction induced by 6He at 61.2 MeV/u was carried out at the HIRFL-RIBLL radioactive beam line. The α core fragments at forward angles were detected in coincidence with the recoiled protons at large angles. From this coincident measurement the valence nucleon knockout mechanism and the core knockout mechanism can be separated according to the polar angle correlation between the core fragments and the recoiled protons. It is demonstrated that, when reconstructing the resonant state of a weakly bound nucleus, the contamination resulting from the core knockout mechanism should be eliminated in order to obtain the correct structure information.

Knockout reaction experiment was carried out by using the 6 He beams at 61.2 MeV/u impinging on a CH 2 target. The α core fragments at forward angles were detected in coincidence with the recoiled protons at larger angles. From this exclusive measurement the valence nucleon knockout mechanism and the core knockout mechanism can be distinguished by the relation between the polar angles of the core fragments and the recoiled protons, respectively. It is demonstrated that the core knockout mechanism may result in some strong contamination to the real invariant mass spectrum.

为实现重离子肿瘤治疗临床实验中对照射束流状态的实时监测,研制了束流强度及剂量监测系统,包括积分电离室、后续电流频率转换电路及LabVIEW数据获取处理三部分.利用闪烁体探测器和标准剂量计测试了系统的线性响应和得到剂量的准确性,结果表明:系统在束流临床照射流强范围内的线性响应好于90%,其实时反馈的临床照射剂量偏差小于5%.同时束流强度及剂量监测系统与安全控制系统相结合,保证束流照射状态满足临床照射的安全要求.

Resonant properties in 18Ne relevant to the stellar reaction of 14O(α,p)17F have been investigated through a resonant elastic scattering of 17F+p.The 17F RI beam was produced via a projectile-fragmentation reaction,and subsequently separated and purified by Radioactive Ion beam Line in Lanzhou(RIBLL).After a series of energy degradation,a 4.22 AMeV 17F beam bombarded a thick(CH2)n target at T2 terminal.Energy and angle of the recoiled protons were measured by two sets of ΔE-E silicon telescope at θlab≈2.3°,14° respectively.Several resonances in 18Ne were observed,and their resonant parameters including energy,spin-parity and decay width have been determined by an R-Matrix analysis of the experimental excitation function.

We measured the total reaction cross sections of 12N in Si at 36.2 MeV/u using B.adioactive Ion Beam Line in Lanzhou (RIBLL) with a new method. The reaction target was installed at the intermediate focusing point T1 at RIBLL. This scheme allows us to identify particles before and after the reaction target unambiguously. The total reaction cross section (1760 ± 78 mb) of 12N in Si is obtained. Assuming that 12N consists of a core 11C plus one halo proton, the excitation function of N on the Si and C targets is calculated with the Glauber model and the Fermi–Fermi density distributions. It can fit the experimental data very well. A large diffusion of the protons density distribution supports the halo structure for 12N.

The principle and structure of a 8×8 CsI(Tl) array detector were described in this paper.For each unit,there are a CsI(Tl) crystal,an optical conductor and a photoelectric multiplier tube.The length of CsI(Tl) crystal is about 50 mm with a 21 mm×21 mm front surface and a 23.1 mm×23.1 mm back surface.The energy resolution is 2.7% for 30 MeV proton and 1.5% for 170 MeV 7Be,which was tested on the RIBLL(Radioactive Ion Beam Line in Lanzhou).It can be used to identify the charged particles in the nuclear experiments induced by the radioactive beam.

The mirror nuclei N-12 and B-12 are separated by the Radioactive Ion Beam Line in Lanzhou (RIBLL) at HIRFL from the breakup of 78.6 MeV/u N-14 on a Be target. The total reaction cross-sections of N-12 at 34.9 MeV/u and B-12 at 54.4 MeV/u on a Si target have been measured by using the transmission method. Assuming N-12 consists of a C-11 core plus one halo proton, the excitation function of N-12 and B-12 on a Si target and a C target were calculated with the Glauber model. It can fit the experimental data very well. The characteristic halo structure for N-12 was found with a large diffusion of the protons density distribution.

The Isochronous Mass Spectrometry is a high accurate mass spectrometer. A secondary electrons time detector has been developed and used for mass measurements. Secondary electrons from a thin carbon foil are accelerated by an electric field and deflected 180° by a magnetic field onto a micro-channel plate. The time detector has been tested with alpha particles and a time resolution of 197 ps (FWHM) was obtained in the laboratory. A mass resolution around 8×10−6 for Δm/m was achieved by using this time detector in a pilot mass measurement experiment.

A high performance Time-of-Flight detector has been designed and constructed for isochronous mass spectrometry at the experimental Cooler Storage Ring (CSRe). The detector has been successfully used in an experiment to measure the masses of the N≈Z≈33 nuclides near the proton drip-line. Of particular interest is the mass of 65As. A maximum detection efficiency of 70% and a time resolution of 118±8ps (FWHM) have been achieved in the experiment. The dependence of detection efficiency and signal average pulse height (APH) on atomic number Z has been studied. The potential of APH for Z identification has been discussed.

Timing and amplitude properties of a prototype scintillator TOF counter at an external target facility are studied with a cosmic rays test. The dependence of signal pulse height and time resolution on the coordinate along the scintillator TOF counter is investigated with two different discriminators. A time resolution of 165 ps can be achieved at the center of the counter with a constant fraction discriminator. Time resolution better than 150 ps is obtained at the center with a leading edge discriminator after time walk correction is applied for off-line analysis.

To achieve a better time resolution of a scintillator-bar detector for a neutron wall at the external target facility of HIRFL-CSR, we have carried out a detailed study of the photomultiplier, the wrapping material and the coupling media. The timing properties of a scintillator-bar detector have been studied in detail with cosmic rays using a high and low level signal coincidence. A time resolution of 80 ps has been achieved in the center of the scintillator-bar detector.