Gamow-Teller unit cross sections of the $(p,n)$ reaction at 198 and 297 MeV on medium-heavy nuclei

Gamow-Teller (GT) unit cross sections, ${\widehat{\sigma }}_{\mathrm{GT}}$, are obtained at 198 and 297 MeV by measuring the double differential cross sections at $0^{°}$ for the $(p,n)$ reaction on ${}^{58}\mathrm{Ni}$, ${}^{70}\mathrm{Zn}$, ${}^{114}\mathrm{Cd}$, ${}^{118}\mathrm{Sn}$, and ${}^{120}\mathrm{Sn}$. The mass dependence of ${\widehat{\sigma }}_{\mathrm{GT}}$ and the ratio of ${\widehat{\sigma }}_{\mathrm{GT}}$ to the Fermi unit cross section, ${\widehat{\sigma }}_{\mathrm{F}}$, $(R^2)$ are also derived in the mass region of $58⩽A⩽120$. The ${\widehat{\sigma }}_{\mathrm{GT}}$ value for ${}^{90}\mathrm{Zr}$ at 297 MeV interpolated using the $A$-dependence obtained herein agrees with that used in a previous analysis where the GT transition strength over a wide energy region up to the continuum was discussed. However, the deduced ${}^{64}\mathrm{Ni}$${\widehat{\sigma }}_{\mathrm{GT}}$ value at 198 MeV is 20% smaller than that obtained from the analysis of a previous $(n,p)$ measurement. The present $R^2$ values in the mass region heavier than ${}^{42}\mathrm{Ca}$ are larger than those in the region up to ${}^{42}\mathrm{Ca}$ and increase as a function of $A$.

Figure 1

TOF spectrum for the ${}^{\mathrm{nat}}\mathrm{C}(p,n)$ reaction at $T_p=297$ MeV. Peaks due to the ${}^{13}\mathrm{C}(p,n){}^{13}\mathrm{N}$(3.502 MeV) and ${}^{12}\mathrm{C}(p,n){}^{12}\mathrm{N}$(g.s.) reactions are fitted with Gaussians.

Figure 2

Energy-loss spectrum for the ${}^7\mathrm{Li}(p,n)$ reaction at $T_p=297$ MeV and $\theta =0^{°}$. Events between two vertical dashed lines are due to the ${}^7\mathrm{Li}(p,n){}^7\mathrm{Be}$(g.s. $+\hspace{0.5em}0.43\hspace{0.5em}\mathrm{MeV})$ reaction.

Figure 3

Double differential cross sections for the $(p,n)$ reaction at 198 MeV on ${}^{58}\mathrm{Ni}$ and ${}^{120}\mathrm{Sn}$ as a function of energy loss of the reaction.

Figure 4

Double differential cross sections for the $(p,n)$ reaction at 297 MeV on ${}^{58}\mathrm{Ni}$, ${}^{70}\mathrm{Zn}$, ${}^{114}\mathrm{Cd}$, ${}^{118}\mathrm{Sn}$, and ${}^{120}\mathrm{Sn}$ as a function of energy loss of the reaction.

Figure 5

Excitation-energy spectra for the $(p,n)$ reaction at 198 MeV on ${}^{58}\mathrm{Ni}$ and ${}^{120}\mathrm{Sn}$ with fitted curves for each individual peak for the low-lying discrete states (left windows) and IAS (right windows). In the ${}^{58}\mathrm{Ni}(p,n)$ spectrum, the shaded peak at 0 MeV is the ground state $(1^{+})$ and the neighboring peak at 203 keV is IAS.

Figure 6

Excitation-energy spectra for the $(p,n)$ reaction at 297 MeV on ${}^{58}\mathrm{Ni}$, ${}^{70}\mathrm{Zn}$, ${}^{114}\mathrm{Cd}$, ${}^{118}\mathrm{Sn}$, and ${}^{120}\mathrm{Sn}$ with fitted curves for each individual peak for the low-lying discrete states (left windows) and IAS (right windows). In the ${}^{58}\mathrm{Ni}(p,n)$ spectrum, the shaded peak at 0 MeV is the ground state $(1^{+})$ and peak at 203 MeV is IAS.

Figure 7

Angular distribution of the differential cross sections for ${}^{118}\mathrm{Sn}(p,n){}^{118}\mathrm{Sb}$(g.s.) with the results of the MD analysis. Thick curve shows the sum of the $\Delta L=0\text{−}4$ components. Angular distributions of each $\Delta L$ component are also shown.

Figure 8

Unit cross sections ${\hat{\sigma }}_{\mathrm{GT},\mathrm{F}}$ vs. $A$ at 198 MeV. Open circles are our data. Open triangles are from data by Taddeucci et al. [10]. Open square is from the datum of the $(n,p)$ reaction by Williams et al. [6]. Shaded areas show the $A$-dependences of the unit cross sections with $1\sigma$ uncertainty.

Figure 9

Unit cross sections ${\hat{\sigma }}_{\mathrm{GT},\mathrm{F}}$ vs. $A$ at 297 MeV. Filled circles are our data. Filled triangles are from data by Watson et al. [31]. Filled square is the ${\hat{\sigma }}_{\mathrm{GT}}$ value for ${}^{90}\mathrm{Zr}$ used in Ref. [5]. Shaded areas show the $A$-dependences of the unit cross sections with $1\sigma$ uncertainty. See the text for the reliability of the ${\hat{\sigma }}_{\mathrm{GT}}$ value of ${}^{114}\mathrm{Cd}$.

Figure 10

$R^2$ vs. $A$. Open circles are our data at 198 MeV. Open triangles are the previous data at 200 MeV by Taddeucci et al. [10]. Filled circles are our data (excluding ${}^{114}\mathrm{Cd}$) at 297 MeV. Filled triangles are the previous data at 300 MeV by Alford et al. [34].