CSRe上44V基态及其同质异能态的精确质量测量

Precision mass values of 44V ground state and 44V isomeric state can be used to deduce the exciting energy of the isomeric state. Combined with existing data, the exciting energy of the A=44, T=2 isobaric analog state in 44V can also be deduced. Therefore, new and precision experimental mass values of 44V ground and isomeric state will enable us to test the mirror symmetry in the energy levels of mirror nuclei 44V and 44Sc. The precise and new mass values of 44V will also allow us to test the predictive power of various global as well as local nuclear mass models such as isobaric multiplet mass equation (IMME), Coulomb displacement energy (CDE) mass relation, Kelson-Garvey mass relations. On the other way around, the newly measured mass data can be used to constrain the parameters of these mass models. .The current experimental mass error of 44V ground state is +80 keV and -380 keV. The asymmetric error bars are due to unsolved isomeric state in the measured 44V nuclei and therefore to which state the measured 44V mass value belongs is unknown. The exciting energy of 44V isomeric state is also unknown, and its value is inferred to be 270(100) keV from the level structure of 44Sc. The half-life of the isomeric state is about 150(3) ms, which is close to the half-life of 111(7) ms of the ground state in 44V. With this project, we plan to precisely measure the mass of 44V ground state and 44V isomeric state at the Lanzhou experimental Cooler Storage Ring CSRe employing the isochronous mass spectrometry. High mass resolving power at the level of 2.8*10^5(FWHM) is a key factor to resolve the isomeric state from its ground state in 44V on the measured revolution time spectrum. Mass error smaller than 10keV is expected to be achieved.

精确测量44V基态及其同质异能态的质量，可以获得同质异能态的激发能，结合已有实验数据可以得到44V能级中A=44，T=2同量异位核素相似态的激发能；这些精确的实验数据可以用来检验f7/2壳层镜像原子核(44V和44Sc)的能级结构对称性。精确的44V质量还可以用来检验同位旋多重态质量公式、库仑位移能质量关系等局域质量模型和全局质量模型在缺中子轻质量核区的质量预言能力。新测得的44V质量数据反过来可以用来确定质量模型的参数。44V基态寿命约111ms，基态质量的实验误差高达+80–380keV，原因是44V有一个寿命约150ms、激发能约270(100)keV的同质异能态，以往的实验无法分辨测到的44V属于基态还是同质异能态。兰州储存环CSRe等时性质谱仪的质量分辨能力可达2.8*10^5(FWHM)，我们计划在CSRe上精确测量44V基态及其同质异能态的质量，获得小于10keV的质量误差。

我们利用基于双TOF探测器的CSRe等时性质谱仪，针对44V测量了其基态和同质异能态的质量，共获得519个44V离子，质量实验误差为5keV。此实验获得的最大质量分辨为3.7e5(FWHM)，在离子回旋周期谱中清楚分开了44V的基态和同质异能态。基于新测得的质量数据，得到44V同质异能态激发能为270(6)keV；结合已知实验信息，得到44V能级中同位旋T=2，Jπ=0+的同量异位核素相似态的激发能为2675(14)keV。对照44Sc中相应的两个能级激发能分别是271.24(1)keV和2779(3)keV，由此结论镜像核44V与44Sc之间的核能级结构有很好的对称性。实验结果也表明几种质量模型对缺中子核素44V基态的质量预言在±50keV范围内一致，尤其是量子力学微扰理论框架下得到的同位旋多重态质量公式（IMME 公式，局部质量模型）的预言非常准确，预言值(误差 27keV)只比实验值小 6keV。