千兆电子伏重离子加速器——兰州冷却储存环

能量达千兆电子伏的兰州重离子加速器冷却储存环HIRFL-CSR,是一个集加速、累积、电子冷却及内外靶实验于一体的多功能双冷却储存环同步加速器系统,由主环CSRm和实验环CSRe构成,并以兰州重离子回旋加速器系统HIRFL作注入器。CSR将重离子束的能量从兆电子伏提高到千兆电子伏,同时利用空心电子束冷却技术将束流的动量分散及发射度降低1~2个数量级,并提供多种类的高电荷态重离子束以及放射性次级束(RIBs),以开展更高精度的物理实验及更广范围的应用研究。兰州冷却储存环于2006年建成并投入运行,实现了剥离注入与多圈注入、空心电子束对重离子束的冷却与累积、变谐波宽能区同步加速、等时性环型谱仪、RIBs的产生与收集以及重离子束的快慢引出,并实现了高能重离子束的空心电子束冷却,使得重离子束的动量分散降低到10^-5量级,而发射度收缩到0.1πmm•mrad以下。同时,完成了短寿命近滴线核素的高分辨质量测量物理实验及高能重离子束深层治癌的临床应用实验。     

一种外LET柔顺半铰的动力学建模与分析

对一种外LET柔顺半铰进行建模与动力学特性分析。采用斜率不连续的绝对节点坐标法（ANCF）建立了该柔顺半铰系统动力学方程;对外力作用下半铰中心线和外轮廓的运动变形进行仿真,与实验结果对比,证明了绝对节点坐标法对柔顺半铰动力学建模的有效性;进一步分析了半铰外形尺寸变化对其变形规律的影响。     

半导体器件内离子有效LET值测量方法研究

提出了一种基于电荷收集测试技术的离子有效LET值测量方法.首先对半导体器件内收集电荷量与入射离子有效LET值之间的关系进行了分析,根据二者之间的关系提出通过测量电荷收集量从而测量离子有效LET值的方法;然后建立了半导体器件电荷收集测试系统,利用PN结和SRAM对测量方法进行了验证;最后成功利用该方法解释了以往单粒子效应实验中出现的数据异常.     

Radiation measured for ISS-Expedition 12 with different dosimeters

Radiation in low Earth orbit (LEO) is mainly from Galactic Cosmic Rays (GCR), solar energetic particles and particles in South Atlantic Anomaly (SAA). These particles’ radiation impact to astronauts depends strongly on the particles’ linear energy transfer (LET) and is dominated by high LET radiation. It is important to investigate the LET spectrum for the radiation field and the influence of radiation on astronauts. At present, the best active dosimeters used for all LET are the tissue equivalent proportional counter (TEPC) and silicon detectors; the best passive dosimeters are thermoluminescence dosimeters (TLDs) or optically stimulated luminescence dosimeters (OSLDs) for low LET and CR-39 plastic nuclear track detectors (PNTDs) for high LET. TEPC, CR-39 PNTDs, TLDs and OSLDs were used to investigate the radiation for space mission Expedition 12 (ISS-11S) in LEO. LET spectra and radiation quantities (fluence, absorbed dose, dose equivalent and quality factor) were measured for the mission with these different dosimeters. This paper introduces the operation principles for these dosimeters, describes the method to combine the results measured by CR-39 PNTDs and TLDs/OSLDs, presents the experimental LET spectra and the radiation quantities.     

Comparison among Methods for Evaluating Dose Equivalent in Pulsed and Mixed Radiation Field

In order to ascertain the accuracy and applicability of the method which was developed in the previous paper for evaluating the dose equivalent in a single-burst and mixed radiation field, a comparison with two other ones has been carried out. One is based on the measurement of the neutron energy spectrum with TOF system and the separate measurement of the absorbed doses with twin chambers. In the other, a tissue-equivalent proportional counter is used for measuring the LET distribution of the absorbed dose. The average quality factor has been evaluated in a pulsed and mixed field generated by an electron linear accelerator. A good agreement has been found among these methods.

A problem about the experimental determination of the dose equivalent index has also been discussed. It was pointed out that the average quality factor as a function of the depth in tissue could be regarded as characteristic of the mixed radiation field.     

Conceptual design and infrastructure for the installation of the first AGATA sub-array at LNL

The first implementation of the AGATA spectrometer consisting of five triple germanium detector clusters has been installed at Laboratori Nazionali di Legnaro, INFN. This setup has two major goals, the first one is to validate the γ-tracking concept and the second is to perform an experimental physics program using the stable beams delivered by the Tandem-PIAVE-ALPI accelerator complex. A large variety of physics topics will be addressed during this campaign, aiming to investigate both neutron and proton-rich nuclei. The setup has been designed to be coupled with the large-acceptance magnetic-spectrometer PRISMA. Therefore, the in-beam prompt γ rays detected with AGATA will be measured in coincidence with the products of multinucleon-transfer and deep-inelastic reactions measured by PRISMA. Moreover, the setup is versatile enough to host ancillary detectors, including the heavy-ion detector DANTE, the γ-ray detector array HELENA, the Cologne plunger for lifetime measurements and the Si-pad telescope TRACE. In this paper the design, characteristics and performance figures of the setup will be described.     

Bystander effect in human hepatoma HepG2 cells caused by medium transfers at different times after high-LET carbon ion irradiation

Although radiation-induced bystander effects have been well documented in a variety of biological systems, whether irradiated cells have the ability to generate bystander signaling persistently is still unclear and the clinical relevance of bystander effects in radiotherapy remains to be elucidated. This study examines tumor cellular bystander response to autologous medium from cell culture irradiated with high-linear energy transfer (LET) heavy ions at a therapeutically relevant dose in terms of clonogenic cell survival. In vitro experiments were performed using human hepatoma HepG2 cell line exposed to 100 keV/μm carbon ions at a dose of 2 Gy. Two different periods (2 and 12 h) after irradiation, irradiated cell conditioned medium (ICCM) and replenished fresh medium were harvested and then transferred to unirradiated bystander cells. Cellular bystander responses were measured with the different medium transfer protocols. Significant higher survival fractions of unirradiated cells receiving the media from the irradiated cultures at the different times post-irradiation than those of the control were observed. Even replenishing fresh medium for unirradiated cells which had been exposed to the ICCM for 12 h could not prevent the bystander cells from the increased survival fraction. These results suggest that the irradiated cells could release unidentified signal factor(s), which induced the increase in survival fraction for the unirradiated bystander cells, into the media sustainedly and the carbon ions triggered a cascade of signaling events in the irradiated cells rather than secreting the soluble signal factor(s) just at a short period after irradiation. Based on the observations in this study, the importance of bystander effect in clinical radiotherapy was discussed and incorporating the bystander effect into the current radiobiological models, which are applicable to heavy ion radiotherapy, is needed urgently.     

Time of flight (TOF) spectrometer for accurate measurement of mass and angular distribution of fission fragments in heavy ion induced fission reactions

The performance of a dual time of flight (TOF) spectrometer using two 24 cm×10 cm area X–Y position sensitive Multi-Wire Proportional Counters (MWPC) is reported. Good separation of compound nuclear fission channel from elastic, quasi-elastic and non-compound fission channels have been achieved. Time calibration of the spectrometer using a technique, dependent on the detector independence of the mass or kinetic energy distributions gave a three times better mass resolutions compared to the conventional calibration technique using elastically scattered projectiles in a heavy ion induced fission reaction. Detail experimental methods in determining fission fragment mass and angular distribution have been presented and discussed.     

Ion–solid interactions at the extremes of electronic energy loss: Examples for amorphous semiconductors and embedded nanostructures

A selection of ion–solid interactions in the swift heavy-ion irradiation regime is reviewed. We consider the effects of electronic energy loss at tens of keV/nm on both bulk material and nanostructures embedded in a matrix. Specific examples include ion track formation at low ion fluences in bulk Si and Ge and porous layer formation at high ion fluences in bulk Ge. In addition, the intriguing shape and phase transformations observable at high ion fluences in Ge and metallic nanoparticles embedded in bulk SiO₂ are examined and compared. Experiment, modelling and simulation are combined synergistically as we seek fundamental atomistic insight into these unique yet poorly understood processes operative only at the extremes of electronic energy loss.     

一种基于LET预测和转发组成员数的优化组播路由协议

本文从综合考虑ODMRP协议转发组的有效性和健壮性出发,提出了一种基于LET(Link Expiration Time)预测和转发组成员数的组播路由协议LETFG-ODMRP(Optimal Multicast Protocol with LET and FGs based on ODMRP).LETFG-ODMRP通过对网络中传输路径保持连接时间LET的预测,得知路径的稳定度,然后结合考虑转发组成员数,建立一种新的路由选择标准PathMetric.采用此种路由选择标准,LETFG-ODMRP可调节权重在候选路由集中选择稳定或有效的传输路径构成转发组.模拟仿真结果证实LETFG-ODMRP提高了组播协议健壮性、有效性及自适应能力.