Gamma-Ray Transitions Induced in Nuclear Spin Isomers by X-Rays

Because of the high density of energy storage and the large cross section for its release, nuclear spin isomers have attracted considerable recent interest. The triggering of induced gamma emission from them has encouraged efforts to develop intense sources of short-wavelength radiation. One of the more interesting examples is the 16⁺ 4-qp isomer of ¹⁷⁸Hf which stores 2.445 MeV for a half-life of 31 years meaning that as a material, such isomeric ¹⁷⁸Hf would store 1.3 GJ/g. Recently, a sample containing 6.3×10¹⁴ nuclei of the isomer of ¹⁷⁸Hf was irradiated with X-ray pulses derived from a device operated at 15 mA to produce bremsstrahlung radiation with end point energies set to values between 60 and 90 keV. Emission of gamma radiation from the sample was increased by 1–2% above the quiescent value of spontaneous emission. Such an accelerated decay of the ¹⁷⁸Hf isomer is consistent with an integrated cross section of 2.2×10⁻²² cm² keV if the resonant absorption of the X-rays takes place below 20 keV as indicated by the use of selective absorbing filters in the irradiating beam. The work reported here describes the current experimental focus and results recently obtained with the use of coincident detection of emitted gamma photons by several detectors. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Gamma Resonance Problem of Long-Lived Nuclear Isomers

A review is given of the studies relating to the problem of γ-resonant (Mössbauer) excitation of long-lived nuclear isomers. The theoretical estimates of possible γ-line broadening are presented. Earlier experiments are described with ^107mAg and ^109mAg isomers using polycrystalline samples of pure Ag and Ag-Pd alloys. The results of these experiments did not contradict the theoretical predictions. The series of papers using Ag single-crystal γ-sources is reviewed. Their results were interpreted as indications of a rather small ^109mAg γ-line broadening, which cannot be explained by modern theory. The results of the last experiments by ITEP group with ^109mAg are also presented. These data may be coordinated with results of other research, if one takes into account the Zeeman splitting of the γ-spectra by Earth's magnetic field.     

Non-Linear Excitation and Decay of Low-Energy Nuclear Isomers Produced under Femtosecond Laser–Plasma Interaction

The properties of internal electronic conversion of nucleus excited in hot dense laser plasma are considered. The important role of dynamics of plasma charge state in residual gas is shown. We are also considering the role of multi-quanta photoexcitation of low-energy nuclear levels in this plasma. This revised version was published online in August 2006 with corrections to the Cover Date.     

三自旋体系长寿命核自旋单重态的制备

长寿命核自旋单重态的寿命（T_S）可以长于常规的纵向弛豫时间（T₁）,基于这个独特的优势,长寿命核自旋单重态具有较好的应用价值.本文对已有脉冲序列进行了改进,给出了适用于任意三自旋弱耦合体系长寿命核自旋单重态制备的参数计算方法,发现在同一个三自旋体系内核自旋单重态具有多种不同比例系数组合的形式,并以丙烯酸为例制备出了两种长寿命核自旋单重态,实验上观察到不同的核自旋单重态的寿命存在差异,另外我们还探究了温度对丙烯酸核自旋单重态寿命的影响.     

Review of Induced Gamma Emission and Gamma-Ray Laser Research

Induced gamma emission with the potential for substantial energy gain is an exciting area of research. This paper reviews related work done internationally, including some that has potential for a gamma-ray laser. This revised version was published online in August 2006 with corrections to the Cover Date.     

原子数据库在研究同核异能态诱发辐射中的应用

如何人为地诱发同核异能态辐射,从而利用储存在其中的巨大能量,是个备受关注的交叉学科课题。利用原子物理过程进行触发是目前较为可行的方案,原子物理参数将在里面起到关键作用。介绍了一套高效率的原子数据库,目前该数据库可对原子序数小于96的元素所有电离度离子的能级结构信息进行快速扫描,从而筛选出一些可能通过原子过程触发的同核异能态体系。通过在197Au元素电子跃迁诱导核激发过程和178Hf元素电子俘获诱导核激发过程中的应用,展示了该数据库对寻找合适同核异能态体系的作用。     

核破裂中的激发能的作用

在晶格气体模型的框架中研究了¹²⁹Xe系统在破裂过程中的热力学性质和轻粒子发射性质随核温度和系统的冻结密度的变化规律.计算发现在不同的冻结密度下,¹²⁹Xe破裂过程的物理观测量呈现了不同的温度相关性.在这种情况下,核物质液气相变发生时的临界温度强烈地依赖于系统的冻结密度.当激发能代替温度作为一个自变量时,临界激发能将不再灵敏地依赖于系统的冻结密度.除此之外,由于不同冻结密度而引起的不同粒子发射产额的温度相关性,也随着激发能的应用,出现了几乎一致的激发能依赖性.从这些结果中可以认为,激发能可以作为一个控制核破裂的基本物理量和标度量.     

原子数据库在研究同核异能态诱发辐射中的应用

 如何人为地诱发同核异能态辐射,从而利用储存在其中的巨大能量,是个备受关注的交叉学科课题。利用原子物理过程进行触发是目前较为可行的方案,原子物理参数将在里面起到关键作用。介绍了一套高效率的原子数据库,目前该数据库可对原子序数小于96的元素所有电离度离子的能级结构信息进行快速扫描,从而筛选出一些可能通过原子过程触发的同核异能态体系。通过在¹⁹⁷Au元素电子跃迁诱导核激发过程和¹⁷⁸Hf元素电子俘获诱导核激发过程中的应用,展示了该数据库对寻找合适同核异能态体系的作用。     

The Linear Optical Susceptibilities of Five Ci8 hllerene Isomers

Using the extended Sn-Schrieffer-Heeger (SSH) model, we have calculated the linear polarizability α for five different C₇₈ fullerene isomers. Our numerical calculation results indicate that both symmetry and shape of the isomers have great effect on their finear optical properties.     

Proposal for a nuclear light source

This study considers a principal possibility of creating a nuclear light source of the vacuum ultra violet (VUV) range based on the \begin{document}$ ^{229} $\end{document}Th nucleus. This nuclear light source can help solve two main problems — excitation of the low-lying \begin{document}$ ^{229m} $\end{document}Th isomer and precision measurement of the nuclear isomeric transition energy. The thorium nuclear light source is based on the nuclei implanted in a thin dielectric film with a large bandgap. While passing an electric current through the sample, the \begin{document}$ ^{229} $\end{document}Th nuclei are excited to the low energy isomeric state \begin{document}$ 3/2^+(8.19\pm0.12 $\end{document} eV) through the process of inelastic scattering of conduction electrons. The subsequent spontaneous decay of \begin{document}$ ^{229m} $\end{document}Th is followed by the emission of γ quanta in the VUV range. The luminosity of the thorium nuclear light source is approximately \begin{document}$ 10^5 $\end{document} photons/s per 1 A of current, per 1 ng of \begin{document}$ ^{229} $\end{document}Th. The suggested scheme to obtain γ radiation from the \begin{document}$ ^{229m} $\end{document}Th isomer can be considered as a type of nuclear analogue of the optical radiation from the usual metal-insulator-semiconductor (MIS) junction.     

The Linear Optical Polarizability Spectra of Five C78 Isomers

Effects of anisotropy, symmetry, atom arrangement and Coulomb interaction on the linear optical polarizability spectra of five C₇₈ isomers are theoretically studied by using the extended Su-Schrieffer-Heeger model with and without Coulomb interaction. The main results are as follows. 1) The spectra become anisotropic with respect to the direction of the electric field of light. The property is common in the niorlel with and without Coulomb interaction. 2) The symmetry and atom arrangement have grcat effects on the peak positions, strengths, and number. 3) The Coulomb interaction tends to shift peaks to higher energies and enhances the oscillator strengths at higher energies.     

6 MeV/u 的19F+27Al 反应碎片的发射机制

重离子核反应中的碎片发射机制是近年来人们十分关注的研究课题。利用ΔE-E 探测器,测量了~6 MeV/u 的19F+27Al 反应中核电荷数Z = 2 ~13 的出射碎片。对产物的能谱、角分布、激发函数及能量自关联函数的分析表明,出射产物主要来自弹靶核深部非弹性碰撞所形成的转动的双核系统。In recent years, extensive studies have been made to understand the fragment emission mechanisms in low energy light heavy-ion reactions. These fragments are found to be emitted from quasielastic/projectile breakup, deep-inelastic and fusion-fission processes. Fragments of Z = 2~13 induced by the collision of 19F+27Al have been measured by ΔE-E telescope. The analysis of the energy spectra, angular distributions, excitation functions and energy auto-correlation functions of these fragments shows that the emission of fragments is coming from a rotational dinuclear system formed in the dissipative collision of the projectile and target nuclei.     

35MeV/u 40Ar+197Au反应中热核的统计发射研究

利用硅半导体+CsI(T1)闪烁体望远镜测量35MeV/u ⁴⁰Ar+¹⁹⁷Au中发射的轻带电粒子,用能谱斜率方法和双同位素产额比方法提取了核温度参量.研究了热核发射过程中的统计发射规律.     

Photoacoustic Spectroscopic Study on a Pair of Hydrate Isomers for Dinuclear Copper(II) Complexes

Photoacoustic spectroscopy has been used to measure the optical absorption of a pair of hydrate isomers of dinuclear copper (II) complexes with 26-membered hexa-aza-macrocycle. It is found that the absorptions of both isomers in the visible region are quite different, which indicates the diversity of their crystal structures. It is also shows that the difference on absorption properties of the studied isomers is difficult to distinguish by using other conventional spectroscopies.     

Initial Search for Triggered Gamma Emission from 178Hfm2 Using the YSU Miniball Array

Experiments with the long-lived, high-K isomer ¹⁷⁸Hf^m2 have been recognized as intriguing tests of multi-quasiparticle state structures and their interactions with external radiation. A triggered release of the energy stored by this isomer, 2.5 MeV per nucleus or 1.2 GJ/gram, in the form of a gamma-ray burst might prove valuable for numerous applications. The observation of “accelerated” decay of ¹⁷⁸Hf^m2 during irradiation by 90-keV bremsstrahlung has already been reported, but with poor statistical accuracy due to the experimental approach. That approach employed single Ge detectors to seek increases in the areas of peaks at energies corresponding to transitions in the spontaneous decay of the isomer. The need for better quality data to confirm those results has motivated the development of improved detection concepts. One such concept was utilized here to perform an initial search for low-energy (<20 keV) triggered gamma emission from ¹⁷⁸Hf^m2 using the YSU miniball detector array. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nuclear dissociation after the O 1s $\rightarrow (^4\Sigma_\text{u}^-)$3sσ excitation in O$_2$ molecules

We investigate the dissociation dynamics of core-excited $\mathrm{O}_2$ molecules using a high-resolution energy-resolved electron-ion coincidence experimental setup. The excited cationic states with two valence holes and one Rydberg electron are created after spectator Auger decay induced by $\mathrm{O}$ 1s $\rightarrow (^4\Sigma_{\rm u}^-)3{\rm s}\sigma$ core excitation in $\mathrm{O}_2$. From the energy correlation between the kinetic energy of the Auger electron and the ion kinetic energy release, we distinguish several dissociation channels. Rather complex dissociation channels of the spectator Auger final states are disclosed, which can be explained by the increased number of the crossing point due to the existence of Rydberg electron. The quantum system will evolve into different dissociation limits at each crossing point between the potential energy curves.     

驱动堆中长寿命核废料碘的嬗变研究

利用理论模拟和实验手段对加速器驱动的快中子堆消除常规反应堆排放的核废料碘进行了研究.实验中,利用加速器加速质子使其能量达到1.0GeV,并轰击重金属铅靶,利用靶中产生的次级中子诱发核废料¹²⁹I的嬗变,使其嬗变为稳定同位素¹³⁰Xe.对实验嬗变效率进行了理论模拟验证,进而拓宽到研究的驱动堆体系中.堆芯区的核燃料为乏燃料铀和钚,靶和初级热交换剂为液态铅.     

原子核同核异能态诱发辐射研究进展

介绍了同核异能态的特点和诱发同核异能态的几种机制,如直接光激发、电子跃迁诱导核激发(NEET)和电子俘获诱导核激发(NEEC)。同核异能态的诱发辐射研究目前在国际上竞争激烈,尤其是对最近提出的NEEC的研究。同时探讨了在我国开展这些研究的可能性。     

相位可控的核四极矩共振激励脉冲发生器设计

在核四极矩共振（NQR）领域,射频激励脉冲信号的优劣对NQR响应信号有重要影响.针对常规方法中射频激励脉冲参数不可控的问题,本文基于32位闪存微型控制器STM32和直接数字频率合成（DDS）芯片AD9910设计了一种相位可控激励脉冲发生器.采用STM32控制AD9910产生波形参数（脉冲宽度、脉冲间隔、脉冲个数和共振频率等）可控的射频激励脉冲,利用LabVIEW软件平台设计脉冲参数设置界面,并建立计算机与微控制器通信,实现波形参数的精确优化控制.实验结果表明,该方法实现了相位可控的NQR激励脉冲序列,可为后续NQR信号检测提供有效激励源.     

The NUBASE2020 evaluation of nuclear physics properties

The NUBASE2020 evaluation contains the recommended values of the main nuclear physics properties for all nuclei in their ground and excited,isomeric(T1/2≥100 ns)states.It encompasses all experimental data published in primary(journal articles)and secondary(mainly laboratory reports and conference proceedings)references,together with the corresponding bibliographical information.In cases where no experimental data were available for a particular nuclide,trends in the behavior of specific properties in neighboring nuclei were examined and estimated values are proposed.Evaluation procedures and policies that were used during the development of this evaluated nuclear data library are presented,together with a detailed table of recommended values and their uncertainties.