丰质子核统计平衡
Proton-Rich Nuclear Statistical Equilibrium
摘要：
处于核统计平衡状态的富质子物质是核合成研究最少的领域之一。原因之一是氢燃烧后，恒星演化是在中子和质子数相等或中子丰度稍高的条件下进行的。恒星中的富质子核合成只有在吸积到白矮星或中子星上的富氢物质爆炸时，或者在核合成之前或期间，来自新生原中子星或中子星盘的风中的中微子相互作用驱动物质富质子时才会发生。在本文中，我们解决了NSE方程的范围内的质子丰富的热力学条件。我们表明，冷质子丰富的NSE是从中子丰富的NSE质的不同。代替由具有最大的每个核子的结合能的Fe峰核（其具有接近规定的电子分数的质子与核子比）主导，用于接近冻结温度的富含质子的材料的NSE主要由Ni 56和自由质子组成。以前的核反应网络计算结果依赖于这种非直观的高质子丰度，本文将对此进行解释。我们展示了如何的差异，特别是大部分的自由质子所产生的自由能的最小化作为一个微妙的竞争之间的熵和核结合能的结果。
英文摘要：
Proton-rich material in a state of nuclear statistical equilibrium (NSE) is one of the least studied regimes of nucleosynthesis. One reason for this is that after hydrogen burning, stellar evolution proceeds at conditions of equal number of neutrons and protons or at a slight degree of neutron-richness. Proton-rich nucleosynthesis in stars tends to occur only when hydrogen-rich material that accretes onto a white dwarf or neutron star explodes, or when neutrino interactions in the winds from a nascent proto-neutron star or collapsar-disk drive the matter proton-rich prior to or during the nucleosynthesis. In this paper we solve the NSE equations for a range of proton-rich thermodynamic conditions. We show that cold proton-rich NSE is qualitatively different from neutron-rich NSE. Instead of being dominated by the Fe-peak nuclei with the largest binding energy per nucleon that have a proton to nucleon ratio close to the prescribed electron fraction, NSE for proton-rich material near freeze-out temperature is mainly composed of Ni56 and free protons. Previous results of nuclear reaction network calculations rely on this non-intuitive high proton abundance, which this paper will explain. We show how the differences and especially the large fraction of free protons arises from the minimization of the free energy as a result of a delicate competition between the entropy and the nuclear binding energy.
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