35MeV/u 40 Ar+197 Au反应中热核的碎裂密度

许多提取核反应过程中熵产生的方法只适用于高能核反应过程 ,而约化d的产额方法可以用于较低能量的重离子核反应中 .对于 3 5MeV/u40 Ar+ 197Au的核反应过程 ,利用这种方法所得的熵和约化带电粒子多重性提取的熵结果一致 .对于后角热核发射体系 ,实验提取的核温度为 ( 4.7± 1 .2 )MeV ,熵为S/A =2 .5± 0 .5,根据实验提取的熵和核温度可以确定其碎裂密度小于 0 .1 ρ0     

35MeV/u40Ar+197Au中的熵产生

根据量子统计模型(QSM)的计算分析,找到了一个提取核反应过程中熵产生的新的可观测量.核反应过程中约化d的产额d/(d+t+³He+⁴He)和熵有单调的函数关系,并且和体系的碎裂密度(ρ/ρ₀)及体系的N/Z都无关,可以作为提取核反应过程中熵产生的一个观测量.和目前已经有的其他方法相比,约化d产额这一提取熵方法可以用于较低能量的重离子核反应中,并且数据处理分析简单.对于35MeV/u⁴⁰Ar+¹⁹⁷Au的核反应过程所提取的熵和利用约化带电粒子多重性提取的熵结果一致.结合后角类靶热核发射体系实验提取的同位素核温度为4.7±1.2MeV及S/A=2.5±0.5,根据熵和核温度的关联关系,可以确定其Break up密度接近但小于0.1(ρ/ρ₀) 关键词： 熵 约化d产额 核温度 统计发射     

35MeV/u 40Ar+197Au反应中热核的碎裂密度

许多提取核反应过程中熵产生的方法只适用于高能核反应过程,而约化d的产额方法可以用于较低能量的重离子核反应中.对于35MeV/u ⁴⁰Ar+¹⁹⁷Au的核反应过程,利用这种方法所得的熵和约化带电粒子多重性提取的熵结果一致.对于后角热核发射体系,实验提取的核温度为(4.7±1.2)MeV,熵为S/A=2.5±0.5,根据实验提取的熵和核温度可以确定其碎裂密度小于0.1ρ₀.     

46.7MeV/u~(12)C引起的核反应中碎裂与转移的竞争

本文讨论了46.7MeV/u~(12)C引起的核反应中弹核碎裂与转移反应的共存及相互竞争,实验中提取的转移部分的约化平行动量分布宽度为44±10MeV/c,这比弹核碎裂部分的σ_0=80±10MeV/c要窄。弹核碎裂及转移反应发生的几率都与被转移结团的结构有关。     

46.7MeV/u 12C引起的核反应中碎裂与转移的竞争

本文讨论了46.7MeV/u ¹²C引起的核反应中弹核碎裂与转移反应的共存及相互竞争,实验中提取的转移部分的约化平行动量分布宽度为44±10MeV/c,这比弹核碎裂部分的σ₀=80±10MeV/c要窄.弹核碎裂及转移反应发生的几率都与被转移结团的结构有关.     

46.7MeV/u 12C引起的弹核碎裂反应

测量了46.7MeV/u ¹²C束流轰击不同靶核的核反应中前方向出射的类弹碎片,发现弹核碎裂产物的最可几能量可用Abrasion图象来解释.它们的平行动量分布宽度满足Goldhaber关系式,实验中提取的约化平行动量分布宽度σ₀=80±10MeV/c,接近于相对论情形下的值,并且σ₀对于不同的反应系统有相近的值.     

30MeV/u 40Ar+112,124Sn反应中的同位素产额比与核温度

系统研究了30MeV/u^40Ar ^112,124Sn反应中的轻粒子同位素产额比随角度和初始激发能的变化关系,对于两个反应体系,均观察到3He/^4He和^6Ni/^7Li的产额比随角度的增加而增加,^6He/^4He和^8Li/^7Li随角度的增加而减少,统计发射的运动学效应不能完全符合实验结果,各种单同位素产额比与靶核的N／Z比有关,表现出同位旋效应,而由双同位素比提取的核温度几乎没有靶核相关性。     

J/ψ→γγV(ρ,φ)衰变的实验研究

利用北京谱仪(BES)收集的7.8×10⁶ J/ψ事例,对J/ψ→γγV(ρ,φ)衰变道中的η(1430)共振态进行了分析.从J/ψ→γγρ衰变模式得到其质量及衰变宽度分别为1431±17MeV和88±28MeV,衰变分支比Br(J/ψ→γη(1430))Br(η(1430)→γρ)=(1.1±0.5±0.3)×10^－4;而从J/ψ→γγφ衰变模式得到其质量及衰变宽度分别为1424±15MeV和73±58MeV,衰变分支比Br(J/ψ→γη(1430))Br(η(1430)→γφ)=(2.0±1.0±0.6)×10^－4.     

利用GEANT4研究轻带电粒子诱发反应出射中子双微分产额

轻带电粒子诱发反应产生次级中子的研究对于加速器屏蔽设计和优化具有重要意义。利用Geant4程序结合INCL、BIC、BERT物理模型分别计算了33 MeV的d核、65 MeV的3He核和4He核轰击厚的碳、铜和铅靶在轻带电粒子诱发反应产生次级中子的研究对于加速器屏蔽设计和优化具有重要意义。利用Geant4程序结合INCL、BIC、BERT物理模型分别计算了33 MeV的d核、65 MeV的3He核和4He核轰击厚的碳、铜和铅靶在$0^{\circ}$，$15^{\circ}$，$45^{\circ}$，$75^{\circ}$和$135^{\circ}$等方向出射中子的双微分产额，并与实验数据进行了比较。研究表明，对于33 MeV的d核诱发的核反应，INCL模型的计算结果基本上再现了碳靶和铜靶的实验数据，但高估了铅靶直接过程产生的中子。BIC模型和BERT模型的计算结果没有重现弹核削裂过程对应的宽峰。对于65 MeV的3He核诱发的核反应，三个模型的计算结果均未能重现前向角弹核削裂过程产生的中子，但在$15^{\circ}$，$45^{\circ}$，$75^{\circ}$和$135^{\circ}$上三个模型的计算结果与实验数据符合较好。对于65 MeV的4He核诱发的核反应，INCL模型的计算结果与碳靶和铜靶的实验数据符合较好，但低估了铅靶的中子产额。BIC模型和BERT模型的计算结果低估了碳靶的实验数据，且在大角度上略微高估了铅靶的实验数据。     

14MeV中子引起的185Re(n,2n)184g,mRe和191Ir(n,2n)190Ir的核反应截面测量

利用活化方法测量了1?4MeV中子引起的¹⁸⁵Re(n,2n)^184gRe,¹⁸⁵Re(n,2n)^184mRe和¹⁹¹Ir(n,2n)¹⁹⁰Ir核反应的截面.中子能量E_n=(14.7±0.2)MeV时的实验结果分别为:(1817±85)mb,(390±18)mb和(2038±82)mb.并利用HFTT程序计算了中子能量在7—18MeV范围内的截面值,给出了其中两个核反应的激发函数曲线.     

Measurement of energy spectra of charged particles emitted after the absorption of stopped negative pions in carbon

Energy spectra of charged particles (protons, deuterons, tritons, ³He, ⁴He and lithium nuclei) emitted after the absorption of stopped negative pions in a thin polyethylene target of 20 mg/cm² have been measured with high accuracy from the experimental threshold energy (of about 0.5 MeV) up to the kinematical limit of about 100 MeV.     

A New Measurement of ~(11)Be(p,d) Transfer Reaction

A new11 Be(p,d) transfer reaction experiment is performed in inverse kinematics with a radioactive11 Be beam at26.9 MeV. Three low-lying states, namely the 0+ground state, the 2~+ state at E_x = 3.37 MeV, and the multiplet at around 6 MeV in10 Be, are populated by this one-neutron transfer reaction. These three states in10 Be are clearly discriminated from the -value spectrum, which is rebuilt from energies and angles of the recoil deuterons in coincidence with10 Be. A spectroscopic factor for each state is extracted by comparing the experimental differential cross sections to the theoretical calculation results using the finite range adiabatic distorted wave approximation method with different global nucleon-nucleus potentials. It is found that the newly extracted spectroscopic factors for the 0+and 2+states are consistent with the previous ones, but the factor for the multiplet is smaller than the value in the reference, and the possible reason is discussed.     

Emission order of light particles and light fragments from hot nuclei followed by binary fission

Emission orders of light charged particles and Li fragments from highly excited fissioning nuclei in the reaction of ⁴⁰Ar+¹⁹⁷Au at E _beam /A=25 MeV have been studied by measuring difference velocity distributions of two correlated particles at small relative angles in coincidence with two fission fragments. By comparing the data with three-body trajectory calculations, we found that high velocity deuterons are emitted prior to high velocity Li fragments but low velocity deuterons are emitted after low velocity Li fragments. On the other hand, no preferential emission was observed among light particles, such as protons and deuterons. Furthermore, the emission orders are found to depend only weakly on the mass asymmetry of fission fragments. Received: 3 June 1997 / Revised version: 23 July 1997     

The photodisintegration of6Li and7Li

The photodisintegration of the stable Lithium isotopes has been investigated by spectroscopy of the emitted charged particles using the Giessen bremsstrahlung facility. Protons, deuterons, tritons,³He and alpha particles were detected and identified up to 20MeV particle energy. Angular distributions were measured using γ-ray energies up toE _γ =50 MeV. They are compared with theoretical predictions and with other experiments. A remarkable low (γ, t)-cross section was found for both isotopes in disagreement to previous measurements using virtual photons. Coincidence measurements between the emitted particles were performed in order to study the manybody-breakups of⁷Li.     

Reaction filters. Charged-particle multiplicity and linear momentum transfer

The relation between charged-particle multiplicity and linear momentum transfer to heavy reaction residues has been investigated with a 4π charged-particle detector for the reactions ³⁶Ar+²³⁸U at E/A=35 MeV and ¹⁴N+²³⁸U at E/A=50 MeV. The multiplicity of charged particles at backward angles (θ > 35°) incrreases linear momentum transfer while the multiplicity of charged particles in the forward direction is almost independent of the linear momentum transfer.     

中能重离子碰撞中带电粒子多重性的同位旋效应

利用兰州4π带电粒子探测器阵列测量带电粒子多重性,研究了55MeV/u ⁴⁰Ar+^58,64Ni核反应中He和中等质量碎片的产额与反应系统同位旋的关系,以及这种同位旋效应与反应系统的碰撞参数(即碰撞的激烈程度)、系统的激发能的变化关系,对两个反应系统,观察到带电粒子多重性中He的比分随带电粒子多重性的增加而增大,带电粒子多重性中IMF的比分随带电粒子多重性的增加而先增大,后减小的规律.两个反应系统虽然具有相同的核电荷数,但轻粒子He和中等质量碎片在多重性中的比分有明显的同位旋相关性。     

The correlation functions and emission time scales for light particles and light fragments in 40Ar+197Au reactions at 25 MeV/nucleon

Two-particle correlation functions were measured for the emission of protons, deuterons, tritons, α, and lithium fragment at small relative momenta in ⁴⁰Ar-induced reactions on ¹⁹⁷Au at 25 MeV/nucleon. Based on three-body trajectory calculations the emission time scales for the particles were extracted from p-d, d-d, t-t, and lithium-lithium correlation functions. The mean emission time was found to decrease with increasing sum of the kinetic energies of the particle in a correlated pairs, indicating the emission of more energetic particles at earlier stages of the reaction than at later stages. The time scale for the emission of lithium fragments emission suggests that sequential binary disassembly occurs in ⁴⁰Ar+¹⁹⁷Au reaction at MeV/nucleon. Mean emission temperature of 3.5_−0.8^+1.3 and 3.6±0.4 MeV were also extracted from the relative populations of the excited and ground states of the respective emitted nuclides ⁸Be and ⁴He.     

Isotope Ratios of Light Charged Particles and Temperature in the Reactions 30MeV/u40Ar+112,124Sn

Coincidence measurements between residues and light charged particles (LCPs) have been made for the reactions 30MeV/u 40Ar+^112,124Sn. The LCPs were measured by 11 semi-conduct telescopes from very forward angle to backward angle. The times of flight of the residues were measured by PPACs installed concentrically around the beam at forward angle. The excitation energy of the primary hot nuclei was obtained from the velocity of residues in the frame of incomplete fusion model. The single isotope ratios, as function of observing angle and excitation energy have been studied. The ratio of ³He/⁴He and ⁶Li/⁷Li increases with angle while that of ⁶He/⁴He and ⁸Li/⁷Li decreases. The calculation of statistical theory can not reproduce the curve quantitatively, implying the existence of dynamic effect. Isospin effect of the primary hot nuclei on the single isotopic ratios is demonstrated. However, the temperature extracted from double isotope ratios is target independent.