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重离子核反应余核温度的测量方法和结果
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12月1日凌晨1点,接到编辑部发了的邮件通知,我们关于重离子核反应中余核温度的工作已经在线发表.文章从7月开始构思并逐步开展,第一稿在7月底写完,与合作者讨论后9月份投到PhysRevC,11月接受并在11月的最后一天在网上刊出.从时间进度来看,还是比较快的.相比我们另外一个在PhysRevC被折磨的死去活来的文章,这个快速的过程真的让我很高兴.
文章主要讨论重离子核反应中产生的余核的温度的测量方法问题.重离子核反应中测量到的余核由于温度不为零,熵对结合能有贡献,这部分贡献影响了结合能的大小,以及其中各分能项(体积能/对称能/表面能以及库伦能等)的大小.对称能依赖于核物质的温度和密度,研究其温度依赖是比较重要的.
余核的产额和温度,余核的自由能相关.余核的自由能等于余核在该温度下的结合能,即包含熵的贡献.研究结合能在较低温对温度的依赖,对于理解丰中子核的形成等具有重要意义.我们利用等量异位素产额比方法,利用零温度的结合能差代替低温余核的结合能差,提取了丰中子核的温度和与反应体系相关的中子质子化学势能差.同时利用统计擦碎模型研究了退激发过程对提取温度的影响.
结果显示:
1.重质量余核的温度与轻核温度不同,温度较低,约为1-3MeV.与轻核产额比的温度相同,重余核温度在反应系统中有炮弹同位旋大小依赖.
2.中子质子化学势能差与温度比依赖与体系的N/Z,并有简单的线性关系.
3.退激发过程影响了余核温度,实际上退激发过程决定了重余核的温度,并使他们在不同的反应(入射能量等)中温度趋于一致.
详细的方法可见PRC86,054611(2012).
-------------abstract-----------------------
Background: Temperature (T ) in heavy-ion collisions is an important parameter. Previously, many works
have focused on the temperature of the hot emitting source. But there are few systematic studies of the
temperature among heavy fragments in peripheral collisions with incident energies near the Fermi energy
to a few A GeV, though it is very important to study the property of neutron-rich nucleus in heavy-ion
collisions.
Purpose: This work focuses on the study of temperature associated with the final heavy fragments in reactions
induced by both the neutron-proton symmetric and the neutron-rich projectiles, and with incident energy ranges
from 60A MeV to 1A GeV.
Methods: Isobaric yield ratio (IYR) is used to determine the temperature of heavy fragments. Cross sections of
measured fragments in reactions are analyzed, and a modified statistical abrasion-ablation (SAA) model is used
to calculate the yield of fragment in 140A MeV 64Ni+9Be and 1A GeV 136Xe+208Pb reactions.
Results: Relatively low T of heavy fragments are obtained in different reactions (T ranges from 1 to 3 MeV).
T is also found to depend on the neutron richness of the projectile. The incident energy affects T very little. μ/T (the ratio of the difference between the chemical potential of neutron and proton to temperature) is found
to increase linearly as N/Z of projectile increases. It is found that T of the 48Ca reaction, for which IYRs
are A < 50 isobars, is affected greatly by the temperature-corrected B(T ). But T of reactions using IYRs of
heavier fragments are only slightly affected by the temperature-corrected B(T ). The SAA model analysis gives
a consistent overview of the results extracted in this work.
Conclusions: T from IYR, which is for secondary fragments, is different from that of the hot emitting source. T and μ are essentially governed by the sequential decay process.
have focused on the temperature of the hot emitting source. But there are few systematic studies of the
temperature among heavy fragments in peripheral collisions with incident energies near the Fermi energy
to a few A GeV, though it is very important to study the property of neutron-rich nucleus in heavy-ion
collisions.
Purpose: This work focuses on the study of temperature associated with the final heavy fragments in reactions
induced by both the neutron-proton symmetric and the neutron-rich projectiles, and with incident energy ranges
from 60A MeV to 1A GeV.
Methods: Isobaric yield ratio (IYR) is used to determine the temperature of heavy fragments. Cross sections of
measured fragments in reactions are analyzed, and a modified statistical abrasion-ablation (SAA) model is used
to calculate the yield of fragment in 140A MeV 64Ni+9Be and 1A GeV 136Xe+208Pb reactions.
Results: Relatively low T of heavy fragments are obtained in different reactions (T ranges from 1 to 3 MeV).
T is also found to depend on the neutron richness of the projectile. The incident energy affects T very little. μ/T (the ratio of the difference between the chemical potential of neutron and proton to temperature) is found
to increase linearly as N/Z of projectile increases. It is found that T of the 48Ca reaction, for which IYRs
are A < 50 isobars, is affected greatly by the temperature-corrected B(T ). But T of reactions using IYRs of
heavier fragments are only slightly affected by the temperature-corrected B(T ). The SAA model analysis gives
a consistent overview of the results extracted in this work.
Conclusions: T from IYR, which is for secondary fragments, is different from that of the hot emitting source. T and μ are essentially governed by the sequential decay process.
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