Temperature dependence of spreading width of giant dipole resonance

The quasiparticle-phonon nuclear model extended to finite temperature within the framework of thermofield dynamics is applied to calculate a temperature dependence of the spreading width ${\Gamma }^{\downarrow }$ of a giant dipole resonance. Numerical calculations are made for ${}^{120}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$ nuclei. It is found that ${\Gamma }^{\downarrow }$ increases with $T$. The reason for this effect is discussed as well as a relation of the present approach to other ones existing in the literature.

Figure 1

Temperature dependence of the centroids of $E1$ strength functions in ${}^{120}\mathrm{Sn}$ (solid line) and ${}^{208}\mathrm{Pb}$ (dashed line).

Figure 2

The model $\mathrm{EWSR}$ in ${}^{120}\mathrm{Sn}$ at different $T$ (dashed line). Solid horizontal line, the value of the model independent energy weighted sum rule $S_1$.

Figure 3

The model $\mathrm{EWSR}$ in ${}^{208}\mathrm{Pb}$ at different $T$ (dashed line). Solid horizontal line, the value of the model independent energy weighted sum rule $S_1$.

Figure 4

The total photoabsorption cross section in ${}^{208}\mathrm{Pb}$ calculated with the theoretical $E1$ strength functions at $T=0$ (solid line) and $T=1\mathrm{MeV}$ (dashed line). Experimental data (full circles with error bars) are taken from Ref. 37).

Figure 5

Temperature dependence of the variance of the theoretical $E1$ strength function ${\sigma }_{\mathrm{th}}$ and the experimental $\mathrm{GDR}$ width ${\Gamma }_{\exp }$ in ${}^{120}\mathrm{Sn}$. Full diamonds, the revised experimental data from Ref. 6; full circle, the data from Ref. 11; open diamond, the data from Ref. 38 (see also Ref. 39).

Figure 6

Temperature dependence of the variance of the theoretical $E1$ strength function ${\sigma }_{\mathrm{th}}$ and the experimental $\mathrm{GDR}$ width ${\Gamma }_{\exp }$ in ${}^{208}\mathrm{Pb}$. Full diamonds, the revised experimental data from Ref. 6; open diamond, the data from Ref. 38 (see also Ref. 39).

Figure 7

Temperature dependence of ${\sigma }_{\mathrm{th}}$ in ${}^{208}\mathrm{Pb}$ calculated with different two-phonon model spaces: dashed line, $B=50\%$; solid line, $B=60\%$ (see the text for comprehensive explanations).