上海理工大学学报  2020, Vol. 42 Issue (3): 224-231 PDF

Mirror nucleui emissivity in heavy ion collisions
SUN Ke, GUO Wenjun
College of Science, University of Shanghai for Science and Technology, Shanghai 200093, China
Abstract: The mirror nucleui emissivity in medium energy heavy ion collisions was studied by using a quantum molecular dynamics model. Four stable light nuclide reaction systems (64Ge+64Ge, 64Zn+64Zn, 64Ni+64Ni, 64Fe+64Fe) and five stable heavy nuclide reaction systems (124Ba+124Ba, 124Xe+124Xe, 124Te+124Te, 124Sn+124Sn, 124Cd+124Cd) were selected to study the change of the characteristics of the mirror nucleui emissivity at different time, under different incident energy and with different system neutron-proton ratio. The results show that both the Y(n)/Y(p) ratio and the Y(3H)/Y(3He) ratio increase with the increase of the system neutron-proton ratio in both light and heavy reaction systems. Y(n)/Y(p) is the ratio of pre-equilibrium neutron yield to proton yield, Y(3H)/Y(3He) is the ratio of pre-equilibrium 3H yield to 3He yield. Compared with the Y(n)/Y(p) ratio, the isospin-dependent mean field is more sensitive to the Y(3H)/Y(3He) ratio. In the heavy reaction system and neutron deficient reaction system, the mirror nucleui emissivity Y(3H)/Y(3He) is more suitable as a sensitive probe for isospin-dependent mean field.
Key words: isospin effect     mirror nucleui emissivity     heavy ion collisions

1 理论模型

IQMD模型的相互作用势

 $\begin{split}&U(\rho ) = {U^{\rm{Sky}}} + {U^{{\rm{Coul}}}} + {U^{\rm{Sym}}} + \\ &\;\;\;\;\;\;\;{U^{\rm{Yuk}}} + {U^{\rm{MDI}}} + {U^{\rm{Pauli}}}\end{split}$ (1)

 ${U^{\rm{Sky}}} = \alpha \frac{\rho }{{{\rho _0}}} + \beta {\left( {\frac{\rho }{{{\rho _0}}}} \right)^\gamma }$ (2)

 $\begin{split} U_1^{\rm{Sym}} =& cu\delta {\tau _{\rm{z}}}, \;\;U_2^{{\rm{Sym}}} = c{u^2}\left( {\delta {\tau _z} + \frac{1}{2}{\delta ^2}} \right), \\&U_3^{\rm{Sym}} = c{u^{{\rm{1/2}}}}\left( {\delta {\tau _z}{\rm{ - }}\frac{1}{2}{\delta ^2}} \right) \end{split}$ (3)

 ${U^{{\rm{Yuk}}}} = {{{t}}_{\rm{3}}}\exp \left(\frac{{\left| {{{{r}}_1}{\rm{ - }}{{{r}}_2}} \right|}}{{m}}\Bigg/\frac{{\left| {{{{r}}_1}{\rm{ - }}{{{r}}_2}} \right|}}{{{m}}}\right)$ (4)

 $\begin{split} {U}^{\rm{MDI}} = {t_4}{\ln ^2}\left( t_5 \left( { p}_{1} - { p}_{2}\right)^2 + 1 \right){\frac{\rho}{\rho _0}} \end{split}$ (5)

 $\begin{split} {U^{{\rm{Pauli}}}} =& {V_{\rm{p}}}{\left( {\frac{\hbar }{{{q_0}{p_0}}}} \right)^3}\cdot\\ &{\rm{exp}}\left( {{\rm{ - }}\frac{{{{\left( {{{{r}}_{{i}}} - {{{r}}_j}} \right)}^2}}}{{2{{q}}_0^2}} - \frac{{{{\left( {{{ p}_{{i}}}{\rm{ - }}{{ p}_j}} \right)}^2}}}{{2{{p}}_0^2}}} \right){\delta _{{p_i}{p_{\rm{j}}}}} \end{split}$ (6)
 ${\delta _{{p_i}{p_j}}} = \left\{ \begin{array}{l} 1,\quad {\rm{n}} - {\rm{n}}{\text{或}}{\rm{p}} - {\rm{p}}\\ 0,\quad {\rm{n}} - {\rm{p}} \end{array} \right.$ (7)

 $\sigma _{\rm{NN}}^{\rm{med}} = \sigma _{\rm{NN}}^{\rm{free}}\left( {1 + \gamma \frac{\rho }{{{\rho _0}}}} \right)$ (8)

2 结果与讨论

 图 1 124Te+124Te系统发射数和发射率随时间的变化 Fig. 1 Change of emission number and emissivity with time in the 124Te+124Te system

 图 2 124Te+124Te系统在不同对称势和对称势强度系数下的发射率 Fig. 2 Emissivity under different symmetry potentials and symmetric potential intensity coefficients in the 124Te+124Te system

 图 3 不同反应系统发射率随系统中质比的变化 Fig. 3 Change of emissivity with system neutron-proton ratio in different reaction systems

 图 4 修正后的发射率随系统中质比的变化 Fig. 4 Change of emissivity with system neutron-proton radio after correction

 图 5 不同反应系统发射率随能量的变化 Fig. 5 Change of emissivity with energy in different reaction systems

 图 6 不同反应系统发射率之差随能量的变化 Fig. 6 Change of Y（3H）/Y（3He）-Y（n）/Y（p）with energy in different reaction systems
3 结　论

a. 镜像核发射率Y3H）/Y3He）和发射率Y（n）/Y（p）都依赖于同位旋相关平均场，是同位旋相关平均场的灵敏探针。镜像核发射率Y3H）/Y3He）比发射率Y（n）/Y（p）高很多，镜像核发射率Y3H）/Y3He）是较好的同位旋相关平均场的灵敏探针。

b. 镜像核发射率Y3H）/Y3He）和发射率Y（n）/Y（p）都随系统中质比的增加而增加。在缺中子反应系统中，镜像核发射率Y3H）/Y3He）作为同位旋相关平均场灵敏探针的效果更好。

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