Penning trap mass spectrometry for nuclear structure studies

High-precision mass measurements as performed at the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN are an important contribution to the investigation of nuclear structure. Precise nuclear masses with less than 0.1 ppm relative mass uncertainty allow stringent tests of mass models and formulae that are used to predict mass values of nuclides far from the valley of stability. Furthermore, an investigation of nuclear structure effects like shell or sub-shell closures, deformations, and halos is possible. In addition to a sophisticated experimental setup for precise mass measurements, a radioactive ion-beam facility that delivers a large variety of short-lived nuclides with sufficient yield is required. An overview of the results from the mass spectrometer ISOLTRAP is given and its limits and possibilities are described.      

Direct mass measurements of exotic nuclei at the FRS-ESR facility at GSI

An overview of direct mass measurements of exotic nuclei at the FRS-ESR facility at GSI is given. The nuclides are produced at relativistic energies by projectile fragmentation and fission, separated in-flight at the fragment separator FRS and injected into the storage ring ESR. Mass measurements are performed using Schottky and Isochronous Mass Spectrometry, which both allow for high precision measurements with single-ion sensitivity. Recent experimental developments are summarized, and examples for measurement results are given, including applications in nuclear structure physics and astrophysics, comparisons with mass predictions, and the search for new isotopes and isomers. Further research potential will be available at next-generation fragment-separator-storage-ring facilities such as the Super-FRS-CR-NESR complex at the future FAIR facility.     

原子核质量的测量和评估

质量是原子核的基本性质之一,在核物理和核天体物理中都有重要的应用。原子核质量测量是目前核物理研究的一个前沿热点课题,国际上各个核物理实验室积极发展新设备和新技术,在短寿命放射性核素测量和超高精度质量测量方面取得了重要进展,本文对此进行了总结评述。在兰州重离子加速器冷却储存环（HIRFL-CSR）上利用等时性质量谱仪测量了一些原子核的质量,本文对其在测量精度、核态最短寿命等前沿进展做了简要介绍,并介绍了正在发展的双飞行时间质量谱仪。原子质量评估收集所有与原子核质量相关的实验数据,经过评估后推荐出质量值及相应误差。原子质量评估AME2016于2017年3月发表,为科技工作者提供基准数据。Mass is a fundamental property of the atomic nucleus. Nuclear mass data play an important role in nuclear physics and nuclear astrophysics. Thanks to the developments of novel mass spectrometers and radioactive nuclear beam facilities, the experimental knowledge of nuclear masses has been continuously expanding along two main directions, including:measurements aimed at high-precision mass values and at the most exotic nuclei far from the stability. The latest progress are reviewed in the paper. In the past few years, mass measurements of short-lived nuclides were performed using isochronous mass spectrometry based on the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou(HIRFL-CSR). The progresses on the frontiers of short half-life and high precision are introduced. The Atomic Mass Evaluation (AME) is the most reliable source for the comprehensive information related to the atomic (nuclear) masses. The latest version of the AME, i.e., AME2016, was published in March, 2017, serving the research community with the benchmark data.     

Extending and refining the nuclear mass surface with ISOLTRAP and MISTRAL

Through the nuclear binding energy, the atomic mass gives us important information about nuclear structure. Viewing the ensemble of mass data over the nuclear chart, we can examine the hills and valleys that form this surface and make hypotheses about the effects of certain nuclear configurations. To unveil these effects, mass measurements of very high precision (<10⁻⁶) are required. Two experiments at ISOLDE pursue this effort of nuclear cartography: the tandem Penning trap spectrometer ISOLTRAP and the radiofrequency transmission spectrometer MISTRAL. Between them, the masses of almost 150 nuclides have been measured from stable isotopes to those with half-lives as short as 30 ms. Both experiments rely on good optical properties of a low energy ion beam and are thus well suited to the ISOLDE facility. This revised version was published online in July 2006 with corrections to the Cover Date.     

原子核质量的高精度测量

原子核的质量直接反映了核内强相互作用、电磁相互作用和弱相互作用的结果.文章简要阐述了原子核质量测量的意义、现状和主要方法,介绍了基于兰州重离子冷却储存环的原子核质量测量实验,比较了首次得到的63Ge,65As,67Se和71Kr核质量测量值与理论计算结果,探讨了65As质量对天体物理快质子俘获过程的影响,文章最后给出了今后的研究内容.中国科学院近代物理研究所在轻质量丰中子区,系统测量了从Ne到Ca核素的质量,研究了N=20和28幻数随中子数和质子数变化的演化;在丰质子区,精确测量了快质子俘获路径上关键核素的质量,为解释X射线暴等爆发性天体过程提供重要的质量数据;在中重丰中子区,系统地测量丰中子核质量,通过天体网络计算模拟超新星爆发中的快中子俘获过程.     

Toward precision mass measurements of neutron-rich nuclei relevant to r-process nucleosynthesis

The open question of where, when, and how the heavy elements beyond iron enrich our Universe has triggered a new era in nuclear physics studies. Of all the relevant nuclear physics inputs, the mass of very neutron-rich nuclides is a key quantity for revealing the origin of heavy elements beyond iron. Although the precise determination of this property is a great challenge, enormous progress has been made in recent decades, and it has contributed significantly to both nuclear structure and astrophysical nucleosynthesis studies. In this review, we first survey our present knowledge of the nuclear mass surface, emphasizing the importance of nuclear mass precision in r-process calculations. We then discuss recent progress in various methods of nuclear mass measurement with a few selected examples. For each method, we focus on recent breakthroughs and discuss possible ways of improving the weighing of r-process nuclides.     

原子核质量精密测量的研究进展

原子核质量的精密测量是原子核物理学的重要课题之一,它对探索奇特原子核的结构和性质、重元素核合成之谜等均具有重大意义.文章简要介绍了原子核质量高精度测量的两个主要设备——储存环和潘宁阱,并回顾了近年来原子核质量精密测量在核结构、元素核合成、新同核异能素等领域中的研究亮点,探讨原子核质量测量的发展趋势.     

加速器质谱测量182Hf的效率研究

182Hf是长寿命放射性核素,其半衰期约为9×106 a. 测量环境样品中的182Hf对核天体物理学和核工程的研究具有重要的意义. 加速器质谱(AMS)作为一门超高灵敏核分析技术,可以测量样品中极其微量的182 Hf. 本工作在中国原子能科学研究院HI 13串列加速器核物理国家实验室的AMS装置上对182 Hf的AMS效率进行了测量,得到了初步的测量结果.     

A Physics Case for SHIPTRAP: Measuring the Masses of Transuranium Elements

SHIPTRAP will allow direct measurement of masses of transuranium nuclides. The method of choice is a Penning trap spectrometer coupled to the SHIP (Separator for Heavy Ion Products) facility at GSI, Darmstadt. In this paper the impact of the SHIPTRAP facility, with its capability of systematic mass measurements with high precision, is explored. Rather few masses of nuclides above uranium are presently known experimentally. In the region of nuclides above Z=100 no ground state masses were measured directly. SHIPTRAP will play an important role in systematically mapping out this area. Possible candidates for direct mass measurements, even with small or very small production cross sections, are presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Precision Penning trap mass measurements of rare isotopes produced by projectile fragmentation

The low-energy beam and ion trap facility LEBIT at NSCL/MSU is at present the only facility where precision experiments are performed with stopped rare isotope beams produced by fast-beam fragmentation. LEBIT combines high-pressure-gas stopping with advanced ion manipulation techniques to provide brilliant low-energy beams. So far these beams have mainly been used for mass measurements on short-lived rare isotopes with a 9.4T Penning trap mass spectrometer. Recent examples include ^70m Br , located at the proton dripline, ³²Si and the iron isotopes ^63-65Fe . While the measurement of ³²Si helps to solve a long-standing dispute over the validity of the isobaric multiplet mass equation (IMME) for the A = 32 , T = 2 multiplet, the mass measurements of ^65m,g Fe marked the first time a nuclear isomeric state has been discovered by Penning trap mass spectrometry.     

Precision Mass Measurements of Short-lived Nuclides at the Heavy-ion Storage Ring in Lanzhou

Recent commissioning of the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou enabled us to conduct high-precision mass measurements at the Institute of Modern Physics in Lanzhou (IMP). In the past few years, mass measurements were performed using the CSRe-based isochronous mass spectrometry employing the fragmentation of the energetic beams of 58Ni, 78Kr, 86Kr, and 112Sn projectiles. Masses of short-lived nuclides on both sides of the stability valley were addressed. Relative mass precision of down to 10−6 ~ 10−7 is routinely achieved. The mass values were used as an input for dedicated nuclear structure and astrophysics studies, providing for instance new insights into the rp-process of nucleosynthesis in X-ray bursts. In this contribution, we briefly review the so far conducted experiments and the main achieved results, as well as outline the plans for future experiments.     

The TITAN mass measurement facility at TRIUMF-ISAC

The TITAN facility at TRIUMF-ISAC will use four ion traps with the primary goal of determining nuclear masses with high precision, particularly for short lived isotopes with lifetimes down to approximately 10 ms. The design value for the accuracy of the mass measurement is 1 ×10^???8. The four main components in the facility are an RF cooler/buncher (RFCT) receiving the incoming ion beam, an electron beam ion trap (EBIT) to breed the ions to higher charge states, a cooler Penning trap (CPET) to cool the highly charged ions, and finally the measurement Penning trap (MPET) for the precision mass determination. Additional goals for this system are laser spectroscopy on ions extracted from the RFCT and beta spectroscopy in the EBIT (in Penning trap mode) on ions that are purified using selective buffer gas cooling in the CPET. The physics motivation for the mass measurements are manifold, from unitarity tests of the CKM matrix to nuclear structure very far from the valley of stability, nuclear astrophysics and the study of halo-nuclei. As a first measurement the mass of ¹¹Li will be determined. With a lifetime of 8.7 ms and a demonstrated production rate of 4×10⁴ ions/sec at ISAC the goal for this measurement at TITAN is a relative uncertainty of 5×10^???8. This would check previous conflicting measurements and provide information for nuclear theory and models.     

Experimental studies at JYFLTRAP

JYFLTRAP is a Penning trap system at the accelerator laboratory in Jyväskylä, Finland that enables high-precision experiments with stored, exotic species that are produced at the IGISOL facility. On one hand, these can be performed within the trap itself, like e.g. mass spectrometry. On the other hand, the trap can be used to provide the highly purified species for further experiments, e.g. for trap-assisted nuclear decay spectroscopy. This contribution focuses on these two possible applications with the presentation of some recent results on superallowed beta decays.     

First precision mass measurements of refractory fission fragments

Atomic masses of 95-100Sr, 98-105Zr, and [corrected] 102-110Mo and have been measured with a precision of 10 keV employing a Penning trap setup at the IGISOL facility. Masses of 104,105Zr and 109,110Mo are measured for the first time. Our improved results indicate significant deviations from the previously published values deduced from beta end point measurements. The most neutron-rich studied isotopes are found to be significantly less bound (1 MeV) compared to the 2003 atomic mass evaluation. A strong correlation between nuclear deformation and the binding energy is observed in the two-neutron separation energy in all studied isotope chains.     

First use of high charge states for mass measurements of short-lived nuclides in a Penning trap

Penning trap mass measurements of short-lived nuclides have been performed for the first time with highly charged ions, using the TITAN facility at TRIUMF. Compared to singly charged ions, this provides an improvement in experimental precision that scales with the charge state q. Neutron-deficient Rb isotopes have been charge bred in an electron beam ion trap to q=8-12+ prior to injection into the Penning trap. In combination with the Ramsey excitation scheme, this unique setup creating low energy, highly charged ions at a radioactive beam facility opens the door to unrivaled precision with gains of 1-2 orders of magnitude. The method is particularly suited for short-lived nuclides such as the superallowed β emitter 74Rb (T(1/2)=65 ms). The determination of its atomic mass and an improved Q(EC) value are presented.     

ISOLTRAP: An on-line Penning trap for mass spectrometry on short-lived nuclides

ISOLTRAP is a Penning trap mass spectrometer for high-precision mass measurements on short-lived nuclides installed at the on-line isotope separator ISOLDE at CERN. The masses of close to 300 radionuclides have been determined up to now. The applicability of Penning trap mass spectrometry to mass measurements of exotic nuclei has been extended considerably at ISOLTRAP by improving and developing this double Penning trap mass spectrometer over the past two decades. The accurate determination of nuclear binding energies far from stability includes nuclei that are produced at rates less than 100 ions/s and with half-lives well below 100ms. The mass-resolving power reaches 10⁷ corresponding to 10keV for medium heavy nuclei and the uncertainty of the resulting mass values has been pushed down to below 10^-8. The article describes technical developments achieved since 1996 and the present performance of ISOLTRAP.     

Decay heat studies for nuclear energy

The energy associated with the decay of fission products plays an important role in the estimation of the amount of heat released by nuclear fuel in reactors. In this article we present results of the study of the beta decay of some refractory isotopes that were considered important contributors to the decay heat in reactors. The measurements were performed at the IGISOL facility of the University of Jyväskylä, Finland. In these studies we have combined for the first time a Penning trap (JYFLTRAP), which was used as a high resolution isobaric separator, with a total absorption spectrometer. The results of the measurements as well as their consequences for decay heat summation calculations are discussed.     

Novel isotope effects observed in polarization echo experiments in glasses

In recent years unexpected magnetic field effects have been observed in dielectric measurements on insulating glasses at very low temperatures. Polarization echo experiments have indicated that atomic tunneling systems are responsible for these effects and that the nuclear properties of the tunneling particles are of importance. Subsequently, it was suggested that the magnetic field effects are caused by tunneling systems carrying a nuclear quadrupole moment. Now we have studied the isotope effect in echo experiments on fully deuterated and ordinary glycerol clearly showing the crucial role of the nuclear quadrupole moments for the magnetic field effects. In addition, we have observed a new effect in the decay of spontaneous echoes in zero magnetic field for the deuterated samples which can be explained in terms of a quantum beating involving the quadrupole levels.