The rapidity distributions of hydrogen isotopes emitted from central collisions of neutron-rich ¹³²Sn+¹²⁴Sn and neutron-deficient ¹⁰⁸Sn+¹¹²Sn systems at 270 MeV/nucleon were investigated at RIKEN-RIBF. The data are compared with antisymmetrized molecular dynamics (AMD) calculations and the rapidity distributions can be reproduced after adjusting the in-medium nucleon-nucleon cross sections. The double ratios between the two reaction systems taken for the relative yields of deuteron to proton ($d/p$) and triton to proton ($t/p$) are further examined in the midrapidity domain, where the adjustments in the AMD calculations do not affect much on them. The $d/p$ and $t/p$ double ratios at midrapidity agree well with the ratio of the system neutron numbers and its squared value, respectively, and the rapidity dependence of these double ratios is consistent with a picture of partial mixing of colliding nuclei. By comparing with the AMD model which shows a strong symmetry energy dependence of the $t/p$ double ratio, the experimental result in the midrapidity domain favors the calculation with a symmetry-energy slope parameter around $L=46$ MeV rather than $L=108$ MeV.

在 RIKEN-RIBF 研究了富中子¹³² Sn+ ¹²⁴ Sn 和中子缺陷¹⁰⁸ Sn+ ¹¹² Sn 系统在 270 MeV/核子的中心碰撞中释放的氢同位素的快速分布。将数据与反对称分子动力学 (AMD) 计算进行比较，在调整介质中核子 - 核子截面后，可以重现快速分布。两个反应系统之间的双倍比率表示氘与质子的相对产率（$d/磷$) 和氚到质子 ($吨/磷$) 在中速域中进一步检查，其中 AMD 计算中的调整对它们没有太大影响。这$d/磷$ 和 $吨/磷$中速下的双比分别与系统中子数及其平方值的比值吻合，这些双比的速度依赖性与碰撞核的部分混合图一致。通过与 AMD 模型进行比较，该模型显示出很强的对称能量依赖性$吨/磷$ 倍率，中速域的实验结果有利于对称-能量斜率参数的计算 $升=46$ MeV 而不是 $升=108$ 兆伏。