天然气水合物开发多物理场特征及耦合渗流研究进展与建议

天然气水合物作为一种非常规的清洁能源,在全球分布广、资源量大.自20世纪90年代以来,加拿大、美国、日本、中国已经先后进行了陆域及海域的水合物试采,但发现出砂、单井日产气量低、稳产时间短等问题,试采产量远不能满足商业化开发的需求,其中核心问题是对水合物开发过程中的相变、多相多组分多场耦合渗流特征的认识不够明晰.本文根据天然气水合物开发过程中涉及的渗流场、温度场、化学场、力学场等多场耦合特征,重点综述水合物生成/分解对各物理场主要特征参数的影响,包括水合物储层的孔隙度、水合物饱和度、渗透率、相对渗透率等基础物性参数及其动态演变,天然气水合物的导热系数、比热容、热扩散系数以及水合物生成/分解热等热力学参数,天然气水合物生成、分解动力学特征,纯水合物以及含水合物沉积物的力学性质等,最后阐述了天然气水合物开发渗流中的多场耦合关系及相互作用,提出了今后水合物开发多物理场特征及耦合渗流的科学研究、技术开发的有关建议.     

Dipole bands in nucleus ~(139)Pm

High-spin states in nucleus 139Pm have been studied using the reaction 116Cd(27Al,4n)139Pm.Two dipole cascades have been found.Spin and parity assignments were based on the Directional Correlation of Oriented Nuclei(DCO) ratios and systematic behavior in neighboring odd-proton nuclei.The level structures of 139Pm are compared with those of the N =78 isotone 141Eu in which two dipole bands have been confirmed as magnetic rotational bands.The close similarity between them suggests that the dipole bands in 139...     

活性靶技术熔合截面测量极限研究

天体环境中丰中子核素熔合反应率对研究中子星表面超级暴现象的点火机制有重要意义。由于次级束流强过低,无法使用传统固体靶实验技术测量垒下熔合反应截面。活性靶技术的发展为垒下丰中子核素熔合反应截面的测量提供了可行的途径。基于Geant4模拟详细地分析了多重采样电离室（MUSIC）与时间投影室（TPC）两种活性靶探测器中熔合反应与弹性散射的运动学性质,给出了4种熔合反应鉴别判据,并且计算了由这些判据误判引起的熔合截面系统误差。在E_cm=13.6 MeV时,MUSIC与TPC的弹性散射误判截面分别为0.5 mb和2.9×10-3 mb,都远小于此时熔合截面（877 mb）。在垒下,MSUIC的熔合截面系统误差已经超出实验测量要求,而TPC能够进行实验测量的能量可以降低至E_cm=4.7 MeV。Reaction rates of fusion reactions among neutron-rich nuclei in the astrophysical environment are of great significance to understand the ignition of superbursts on neutron stars. Since beam intensity is rather low for radioactive ion beams, it is extremely difficult to operate a direct measurement for cross sections of such fusion reactions below the Coulomb barrier using thick target technique. In this case, a novel technique, active target technique, has been developed recently. To study the energy limit for measurement below Coulomb barrier, the kinematics of elastic scattering and fusion reaction in MUSIC and TPC are discussed with Geant4 simulation. Four identification methods are used and uncertainties of cross sections resulted from misjudgments are calculated. With E_cm=13.6 MeV, the uncertainties of cross sections for MUSIC and TPC are 0.5 mb and 2.9×10-3 mb, respectively. The uncertainties for MUSIC become far beyond measurement when below coulomb barrier, while TPC remains to be a suitable detector for measuring fusion cross sections until E_cm=4.7 MeV.     

天然气水合物开发多物理场特征及耦合渗流研究进展与建议

天然气水合物作为一种非常规的清洁能源, 在全球分布广、资源量大. 自20世纪90年代以来, 加拿大、美国、日本、中国已经先后进行了陆域及海域的水合物试采, 但发现出砂、单井日产气量低、稳产时间短等问题, 试采产量远不能满足商业化开发的需求, 其中核心问题是对水合物开发过程中的相变、多相多组分多场耦合渗流特征的认识不够明晰. 本文根据天然气水合物开发过程中涉及的渗流场、温度场、化学场、力学场等多场耦合特征, 重点综述水合物生成/分解对各物理场主要特征参数的影响, 包括水合物储层的孔隙度、水合物饱和度、渗透率、相对渗透率等基础物性参数及其动态演变, 天然气水合物的导热系数、比热容、热扩散系数以及水合物生成/分解热等热力学参数, 天然气水合物生成、分解动力学特征, 纯水合物以及含水合物沉积物的力学性质等, 最后阐述了天然气水合物开发渗流中的多场耦合关系及相互作用, 提出了今后水合物开发多物理场特征及耦合渗流的科学研究、技术开发的有关建议.      

用于核天体物理实验的活性靶时间投影室

发生在中子星壳层内的丰中子熔合反应对中子星演化以及X射线超级爆等现象均会产生影响。受限于放射性束流强度和反应机制的复杂性，实验数据极其缺乏，难以有效约束理论模型。基于活性靶技术的时间投影室(Time Projection Chamber，TPC)将工作气体作为反应靶，具备近4$\pi$立体角接受度和三维径迹重建能力，能够实现对反应事件的全记录，显著提高了探测效率，大幅降低了熔合反应截面测量对束流强度的要求。我们研制了240路信号读出的TPC，并使用放射性束流16N对探测器进行了测试，探索了该实验方法的可行性和有效性。为了得到更加精确的反应产物径迹，对反应事件做出更好的筛选，进一步发展了1 024路信号读出TPC，并开展了12C+12C库仑位垒附近熔合反应截面测量实验，初步实验结果与已有实验数据符合较好。     

Electric-dipole transitions in ^165Er

High-spin states of ^165Er were studied using the ^160Gd（^9Be, 4n）reaction at beam energies of 42 and 45 MeV. The previously known bands based on the ν5/2^-[523] and ν5/2^＋[642] configurations have been extended to high-spin states. Electric-dipole transitions linking these two opposite parity bands were observed. Relatively large B（E1） values have been extracted experimentally and were attributed to octupole softness.     

锦屏深地核天体物理实验(JUNA)地面实验进展

锦屏深地核天体物理(JUNA)实验项目将利用中国锦屏深地实验室(CJPL)的良好条件，在天体物理伽莫夫能量窗口开展核天体关键反应$^{25}{\rm{Mg}}({\rm{p}},{\rm{\gamma}})^{26}{\rm{Al}}$、$^{19}{\rm{F}}({\rm{p}},\alpha)^{16}{\rm{O}}$、$^{13}{\rm{C}}(\alpha, {\rm{n}})^{16}{\rm{O}}$和$^{12}{\rm{C}}(\alpha,{\rm{\gamma}})^{16}{\rm{O}}$的直接测量，为理解恒星演化和元素起源提供新的数据。目前，已经在地面上对加速器装置、束流稳定性、靶、探测器以及电子学进行了系统的测试。地面实验内容包括高纯锗探测器效率刻度，$^{25}{\rm{Mg}}({\rm{p}}, {\rm{\gamma}})^{26}{\rm{Al}}$在304 keV的共振强度测量，$^{19}{\rm{F}}({\rm{p}}, \alpha)^{16}{\rm{O}}$的截面测量，聚乙烯作为慢化体的中子探测器的设计、加工和效率刻度，靶的设计和稳定性检测等。JUNA项目整体进展顺利，地面实验已取得一系列关键进展和初步成果。在不远的将来，JUNA项目将有序开展地下实验，完成设定目标，也将促进更广泛的国际合作，助力于天体演化中的若干重大科学问题的解决。     

低能加速器质子束流性质的测量(英文)

中国锦屏地下实验室（CJPL）坐落于四川省锦屏山中,利用水电站修建的隧道建成。由于其本底环境极低,非常适合开展低本底实验测量。一台基于ECR源的400 kV强流加速器将安装在CJPL中,其可以为核天体物理实验提供流强为12 emA的质子束流,6 emA的He+束流和2.5 emA的He2+束流。拟通过非共振反应12C（p,γ）13N以及一系列的共振反应27Al（p,γ）28Si等,对加速器的束流能量进行精确刻度,对束流的能量展宽以及长期稳定性进行测量。由于该加速器正在中国原子能科学研究院进行地面调试,我们利用中国科学院近代物理研究所的320 kV研究平台,进行了12C（p,γ）13N和27Al（p,γ）28Si反应的测试实验。测量结果表明,在质子束流能量为224 keV时,束流的能量展宽约为1.0 keV,束流能量在连续4小时的测量期间,其晃动幅度远小于±200 eV。China JinPing underground Laboratory (CJPL) was established inside the tunnels piercing Jinping Mountain in Sichuan Province, China, which can provide an ideal environment for low background experiment. A new 400 kV accelerator, with high current based on an ECR source, will be placed at this underground laboratory for nuclear astrophysics experiment. The beam characteristics of this accelerator, like absolute energy, energy spread, and long-term energy stability, will be determined by several wellknown resonance and non-resonance reactions. Due to the new accelerator still being under construction, the resonance reaction of 27Al(p, γ)28Si and non-resonance 12C(p, γ)13N were studied at the 320 kV highvoltage platform in Institute Modern Physics of CAS in Lanzhou. The energy spread of proton beam is about 1.0 keV at proton energy E_p=224 keV and the long-term energy stability of proton beam is much better than 200 eV during 4 hours measurement.     

12C+13C熔合截面测量中统计模型引入的系统误差研究(英文)

在本工作中,我们分别采用薄靶和厚靶实验技术,测量了12C+13C反应在质心系能量4~6 MeV的熔合截面。实验得到了12C+13C反应的在线γ产额和离线的24Na活度,利用TALYS统计模型给出的反应道分支比,导出了熔合反应的总截面。通过对比不同实验得到的总截面,定量研究了统计模型修正所带来的系统误差:在线γ分支比修正引入的系统误差为14%;由离线24Na活度测量得到总截面时,24Na分支比修正带来的系统误差也为14%。     

Dipole bands in nucleus ^139Pm

High-spin states in nucleus ^139Pm have been studied using the reaction ^116Cd（^27Al, 4n）^139Pm. Two dipole cascades have been found. Spin and parity assignments were based on the Directional Correlation of Oriented Nuclei （DCO） ratios and systematic behavior in neighboring odd-proton nuclei. The level structures of ^139Pm are compared with those of the N = 78 isotone ^141Eu in which two dipole bands have been confirmed as magnetic rotational bands. The close similarity between them suggests that the dipole bands in ^139Pm may be magnetic rotational bands.