Spectroscopy of exotic reflection-asymmetric atomic nuclei

原子核可以根据它们所拥有的中子和质子的数量而呈现出不同的形状。许多原子核是球形的，但有些细胞核的形状是变形的，比如橄榄球(拉伸的球体)或南瓜(挤压的球体)。在某些情况下，原子核可以变成反射不对称的或梨形的。这发生在核图的某些局部区域，在那里，中子和质子占据着特定的轨道，这些轨道驱动着反射形状。具体地说，感兴趣的轨道在轨道角动量和总角动量上都有3 hbar的差异。占据这些轨道的核子可以通过八极相互作用相互作用，从而产生反射不对称或八极变形的形状。在核图上，这发生在34、56、88和126号核子附近。任何具有这样数量的核子的核都容易受到八极关联的影响，在极端情况下还会发生永久的八极形变。具有最强八极关联的核具有接近88的质子数Z和接近126的中子数N，这是轻鳗系元素区域。该区域包括贫中子氡(Z=86)、镭(Z=88)、钍(Z=90)和铀(Z=92)核。在过去的几十年里，许多这样的核已经被实验研究，它们展示了八极形变的光谱特征，如低位负宇称态，相反奇偶的交错带，以及强烈的电偶极跃迁。最近的计算表明，轻鳗系元素区的八极形变区域可能比之前认为的更大--即可能包括缺乏中子的钚(Z=94)和钚(Z=96)同位素。到目前为止，这些奇特的原子核还不在实验研究的范围之内，但新的实验技术正在使这些原子核变得可用。这个PHD项目将涉及到研究轻鳗系元素区域中的奇特原子核，该区域位于Z值大于94的区域的上侧。PHD项目将使用不同的技术来研究这些原子核，例如，包括衰变光谱，即在重离子聚变-蒸发反应中，在阿尔法衰变之后，激发态被填充。这些实验将使用芬兰Jyväskylä大学加速器实验室Ritu反冲质谱仪焦平面上的辐射探测器阵列进行。其他实验也将使用最先进的伽马射线光谱仪，如芝加哥附近Argonne国家实验室的Digital-Gammasphere，以及意大利帕多瓦附近的Legnaro国家实验室的新Agata伽马射线跟踪光谱仪。在这个博士项目中进行的工作将包括一个或多个这样的实验，包括用模拟和建模来规划实验，建立和运行实验，以及数据分析。PHD项目的结果将有助于更好地理解原子核中奇异反射-不对称形变的发展和演化。

Atomic nuclei can assume different shapes depending on the numbers of neutrons and protons that they possess. Many nuclei are spherical but some take on shapes that are deformed like a rugby ball (stretched sphere) or a pumpkin (squashed sphere). In some cases atomic nuclei can become reflection-asymmetric or pear shaped. This occurs in certain localized regions of the nuclear chart, where the neutrons and protons occupy specific orbitals which drive towards a reflection shape. Specifically the orbitals of interest have a difference in both orbital and total angular momentum of 3 hbar. Nucleons occupying these orbitals can interact by the octupole interaction which gives rise to a reflection-asymmetric or octupole-deformed shape. On the nuclear chart, this occurs close to nucleon numbers 34, 56, 88, and 126. Any nucleus with these numbers of nucleons is susceptible to octupole correlations and in extreme cases permanent octupole deformation. The nuclei that possess the strongest octupole correlations have proton number Z close to 88 and neutron number N close to 126, which are the light actinide region. This region includes the neutron deficient radon (Z=86), radium (Z=88), thorium (Z=90), and uranium (z=92) nuclei. Over the past few decades a number of these nuclei have been studied in experiments and they have demonstrated the spectroscopic features of octupole deformation such as low-lying negative-parity states, interleaving bands with opposite parities, and strong electric-dipole transitions. Recent calculations have shown that the region of octupole deformation in the light-actinide region maybe more extended than previously thought - that is, it may include the neutron-deficient plutonium (Z=94) and curium (Z=96) isotopes. To date, these exotic nuclei have been out of the reach of experimental investigation, but new experimental techniques are making these nuclei accessible.This PhD project will involve the study of exotic atomic nuclei in the light actinide region with Z values on the upper side of the region with Z values greater than about 94. The PhD project will use different techniques to study these nuclei, for example including decay spectroscopy where excited states are populated following alpha decay in heavy-ion fusion-evaporation reactions. Such experiments will be performed using an array of radiation detectors at the focal plane of the RITU recoil mass spectrometer at the University of Jyväskylä Accelerator Laboratory in Finland. Other experiments will also be performed using state-of-the-art gamma-ray spectrometers such as Digital-Gammasphere at Argonne National Laboratory near Chicago and using the new AGATA gamma-ray tracking spectrometer at the Legnaro National Laboratory near Padova in Italy. The work undertake in this PhD project will include one or more such experiments, including planning for the experiment with simulations and modelling, setting up and running the experiment, and analysis of data. The results of the PhD project will lead to a better understanding of the development and evolution of exotic reflection-asymmetric deformations in atomic nuclei.