同位旋依赖的碎块判断方法对重离子碰撞观测量的影响(英文)

该工作提出了一个同位旋依赖碎块判断方法用以描述重离子碰撞过程中的碎块形成。利用该方法可以改善输运理论对于核子以及轻带电粒子产额的描写,其在计算中降低了发射核子产额、增加碎块(特别是丰中子碎块) 的产额。对于丰中子轻带电粒子的增强主要出现在中心快度区。研究表明,该方法对于同位旋敏感的观测量,如,n/p,t/3He,Rmidyield 和isoscaling parameters 等,以及系统的平衡度的量度都会产生影响。We introduce isospin dependence in the cluster recognition algorithms used in the Quantum Molecular Dynamics model to describe fragment formation in heavy ion collisions. This change reduces the yields of emitted nucleons and enhances the yields of fragments, especially for heavier fragments. The enhancement of neutron-rich lighter fragments mainly occurs at mid-rapidity. Consequently, isospin dependent observables, such as isotope distributions, yield ratios of n/p,t/3He, Rmid yield and isoscaling parameters are affected. We also investigate how equilibration in heavy ion collisions is affected by this change.     

HIRFL浅层肿瘤治疗终端治癌碳离子束物理特性的测量

对HIRFL浅层肿瘤治疗终端提供的碳离子束的物理特性进行了首次测量. 结果显示, 能量为80.55MeV/u的¹²C离子束, 其束流强度在0.001—0.1nA范围时, 直径50mm照射野的均匀性为73.48%, 束流强度在一段时间内的稳定性为80.87%. 测得了束流在治疗装置等中心处的深度剂量分布, 其高剂量的Bragg峰位处在13.866mm的水等效深度, 反推出碳离子束在等中心处对应的能量为71.71MeV/u, 与计算值基本吻合. 对自由空气电离室的读数进行了吸收剂量的标定. 测量结果显示, HIRFL浅层肿瘤治疗装置性能与临床治疗的要求相比稍有差距, 为了达到治疗终端进行临床试验的要求, 须对治癌装置性能做进一步的优化.     

HIRFL浅层肿瘤重离子治疗终端束流配送系统性能的实验验证

详细介绍了兰州重离子研究装置(HIRFL)浅层肿瘤重离子治疗终端的被动式束流配送系统, 对该束流配送系统重要组成部件及其整体的性能进行了实验验证. Bragg峰展宽装置脊形过滤器及能量调节装置射程移位器测试结果显示该设备的性能指标达到设计要求. 为验证该被动式束流配送系统的整体性能, 进行了束流成形实验, 模拟对肿瘤靶区的三维适形照射. 结果表明: 利用该束流配送系统可实施对肿瘤的三维适形放射治疗. HIRFL浅层肿瘤治疗装置束流配送系统性能的验证为下一步开展肿瘤重离子束治疗临床试验奠定了基础.     

用于浅层肿瘤重离子治疗的终端束流诊断控制系统

 设计了中国科学院近代物理研究所利用兰州重离子研究装置（HIRFL）进行浅层肿瘤临床治疗试验研究中所使用的束流诊断安全控制系统。该系统包括束流强度监测及保护、剂量测量、扫描波形监测及保护3个部分。系统基于PXI系统及LabVIEW软件,给出了该系统的各部分结构。从系统建立时的多次测试结果以及实际临床治疗试验研究时的长期运行结果来看,该束流诊断控制系统在控制辐照剂量以及安全保护方面能够满足当前重离子加速器浅层肿瘤临床治疗试验的基本要求,为试验研究的顺利进行提供了可靠的保证。     

HIRFL的辐照治癌终端

为了进行重离子束流的肿瘤治疗和生物效应的研究,HIRFL正在建造一个辐照治癌终端.主要介绍了该终端的束流制备方法和束流线的布局、性能参数和束流光学设计计算结果. A new experimental terminal is being constructed at HIRFL for research program of proton and heavy ion therapies and irradiation effects of living things . The beam preparation method and the layout, performance and beam optics calculation of the beam line are presented.     

HIRFL装置主动式点扫描束流配送系统的Monte Carlo模拟优化

为获得适用于HIRFL 装置主动式点扫描束流配送系统配送的碳离子束,利用Monte Carlo (MC) 工具SHIELD-HIT12A 研究了配送距离和微型脊形过滤器结构周期对治疗室等中心处束斑半高宽(FWHM) 和剂量平坦度的影响。模拟研究发现:束流配送距离越短,束斑FWHM越小,但剂量平坦度越差;微型脊形滤器结构周期是影响剂量平坦度的关键因素,周期越小,剂量平坦度越好。通过模拟研究得出:在HIRFL装置重离子治疗终端将真空窗设置在距等中心距离小于125 cm 时,采用结构周期为2 mm微型脊形过滤器可以满足主动式点扫描照射对束斑FWHM和剂量平坦度的要求。To obtain carbon ion beams suitable for the active spot scanning beam delivery system at the Heavy Ion Research Facility in Lanzhou (HIRFL), the Monte Carlo program SHIELD-HIT12A was used to study the influences of beam delivery distance and structure period of mini ridge filter on full width at the half maximum (FWHM) of beam spot and dose flatness at the isocenter of the treatment room. The present simulation study shows that the shorter was the beam delivery distance, the smaller was the FWHM of beam spot, but the worse was the dose flatness. The structure period of mini ridge filter was a key factor to account for the dose flatness at the isocenter. The smaller was the structure period of mini ridge filter, the better was the dose flatness. Based on the simulation results, we conclude that 2 mm structure period for a mini ridge filter statisfies the requirements on the FWHM of beam spot and dose flatness at the isocenter for the active spot scanning beam delivery system at HIRFL when the distance between the vacuum window and the isocenter is set shorter than 125 cm in the nozzle.     

用于HIRFL重离子治癌的PET成像实验研究与蒙特卡罗模拟

为了HIRFL重离子治癌的需要,使用两个位置灵敏闪烁体探测器组成了一个简单的PET成像系统.对PET成像进行了实验研究,实验测量得到了物体成像以及γ射线能谱,对于511keV全能峰处的能量分辨率为186%,峰总比为52.4%.采用GEANT3程序对该系统进行了模拟计算,并与实验进行比较,最后对该系统进行了优化设计     

Calibration of ITER Instant Power Neutron Monitors: Recommended Scenario of Experiments at the Reactor

Instant power is a key parameter of the ITER. Its monitoring with an accuracy of a few percent is an urgent and challenging aspect of neutron diagnostics. In a series of works published in Problems of Atomic Science and Technology, Series: Thermonuclear Fusion under a common title, the step-by-step neutronics analysis was given to substantiate a calibration technique for the DT and DD modes of the ITER. A Gauss quadrature scheme, optimal for processing “expensive” experiments, is used for numerical integration of ²³⁵U and ²³⁸U detector responses to the point sources of 14-MeV neutrons. This approach allows controlling the integration accuracy in relation to the number of coordinate mesh points and thus minimizing the number of irradiations at the given uncertainty of the full monitor response. In the previous works, responses of the divertor and blanket monitors to the isotropic point sources of DT and DD neutrons in the plasma profile and to the models of real sources were calculated within the ITER model using the MCNP code. The neutronics analyses have allowed formulating the basic principles of calibration that are optimal for having the maximum accuracy at the minimum duration of in situ experiments at the reactor. In this work, scenarios of the preliminary and basic experimental ITER runs are suggested on the basis of those principles. It is proposed to calibrate the monitors only with DT neutrons and use correction factors to the DT mode calibration for the DD mode. It is reasonable to perform full calibration only with ²³⁵U chambers and calibrate ²³⁸U chambers by responses of the ²³⁵U chambers during reactor operation (cross-calibration). The divertor monitor can be calibrated using both direct measurement of responses at the Gauss positions of a point source and simplified techniques based on the concepts of equivalent ring sources and inverse response distributions, which will considerably reduce the amount of measurements. It is shown that the monitor based on the average responses of the horizontal and vertical neutron chambers remains spatially stable as the source moves and can be used in addition to the staff monitor at neutron fluxes in the detectors four orders of magnitude lower than on the first wall, where staff detectors are located. Owing to low background, detectors of neutron chambers do not need calibration in the reactor because it is actually determination of the absolute detector efficiency for 14-MeV neutrons, which is a routine out-of-reactor procedure.     

碳离子治疗中分野照射技术的Monte Carlo模拟

为阐述分野照射治疗方式应用于中国科学院近代物理研究所(IMP) 肿瘤重离子临床治疗试验研究的理论基础,利用Monte Carlo (MC) 软件包Gate/Geant4 模拟计算了碳离子束分野照射分衔接处的横向剂量分布,得到了患者摆位误差±1.0 mm范围内的横向剂量分布和分野衔接处中心剂量随分野间距的变化关系,计算了分野间距5.0 mm的横向剂量分布。将分野间距5.0 mm的分野照射与整野照射的MC结果进行比较,发现:在靶区范围内两者模拟的剂量偏差在6.8% 以内,符合程度较好,并提出了在患者定位精确度较高的情况下(即患者治疗体位摆位误差在±1.0 mm范围) 解决分野衔接处剂量热点问题的可行方法,从而较大幅度地提高了分野照射时靶区范围内的剂量均匀性。To characterize the theoretical basis of eld patching technique in carbon ion beam therapy, Monte Carlo software package Gate/Geant4 was used to simulate the lateral dose distribution of matched elds. The lateral dose distribution of the matched elds within 1.0 millimeter of patient positioning error and the relationship between the central dose of the matched elds and the eld patching gap were obtained. Moreover, the lateral dose pro le of eld patching irradiation with 5.0 mm gap was simulated. While comparing the lateral dose distribution of eld patching irradiation with 5.0 mm gap with the undivided eld irradiation, a good agreement between both results with a maximum dose deviation of 6.8% was observed within the target volume.Hence a feasible method for solving the issue of dose hotspots during eld patching under the condition of higher patient positioning accuracies (patient positioning error within 1.0 millimeter) was proposed and the dose homogeneit within the target volume could be greatly improved when eld patching technique is adopted in carbon ion beam therapy.