Filtering contaminants from a $\gamma$-sum spectrum: Measurement of the ${}^{94}\mathrm{Mo}(p,\gamma ){}^{95}\mathrm{Tc}$ cross section

A measurement of the ${}^{94}\mathrm{Mo}$($p,\gamma$)${}^{95}\mathrm{Tc}$ cross section was performed. The cross section was measured in the energy range $E_{c.m.}=1.5–4.5$ MeV, spanning essentially the entirety of the Gamow window relevant to the astrophysical $\gamma \mathrm{process}$. The $\gamma$-summing technique was used to analyze the data. At lower energies the sum peak overlapped with peaks from the reaction ${}^{19}\mathrm{F}(p,\alpha \gamma ){}^{16}\mathrm{O}$, so a new analysis method was developed to filter out the contamination from the this reaction. The measured cross section values were compared to the non-smoker database. The measured cross sections show enhanced resonancelike features at low energies, which are not predicted in the non-smoker code. The effects of this new measurement on the reaction rate were examined. It was found that there is a significant enhancement at lower temperatures in the ($p,\gamma$) reaction rate due to the enhancements found in the cross section.

Figure 1

Schematic of the target and collimator layout within the HECTOR borehole. The beam pipe is electrically isolated from the detector and from the beam line upstream to form a Faraday cup. The collimator, target, and target holder form one conductive element to collect the charge.

Figure 2

An example of the fitting procedure used to fit the sum peaks. A combination of a Gaussian on a linear background is used. The light blue shows the linear-background-subtracted histogram that is integrated to obtain the number of counts in the sum peak.

Figure 3

An example of a sum peak that is overlapping with the peaks from the reaction ${}^{19}\mathrm{F}(p,\alpha \gamma ){}^{16}\mathrm{O}$. The sum peak of interest cannot be disentangled from the contamination peaks in this case.

Figure 4

Examples of the sum spectrum after using the filtering process. (a) shows spectra for a gold backing where only the ${}^{19}\mathrm{F}(p,\alpha \gamma ){}^{16}\mathrm{O}$ peaks are present. In the standard spectrum, blue line, the peaks are clearly visible, while in the filtered spectrum, black line, there is just a flat background present. (b) shows the effect on a data taken for the ${}^{94}\mathrm{Mo}$ target. In the standard, blue, spectrum there are three peaks, but in the filtered, black, spectrum there is just one peak left, the real sum peak of interest.

Figure 5

An example of the comparison between an experimental run (black) and all of the matching simulations (heat map) for the final set of input parameters. (a) shows the sum peak, the dashed lines indicate a gate on the sum peak used to generate (b)–(d). (b) shows the individual segment energies that correspond to the events within the gated region. (c) shows the events corresponding to the sum peak with a multiplicity of 1, and (d) shows the same for events with a multiplicity of 2.

Figure 6

An example of the comparison of the M between the same experimental run (black) as Fig. 5 and all of the matching simulations (heat map) for the final set of input parameters. (a) shows the comparison of the standard M, while (b) shows the comparison of the M of the events that make it through the filter. It both cases there is good agreement between the experimental run and the distribution from the simulations.

Figure 7

The cross sections for the ${}^{94}\mathrm{Mo}$($p,\gamma$)${}^{95}\mathrm{Tc}$ reaction using the original efficiency method developed in Ref. [9] compared to the results with the extended method. For the higher-energy runs where the filter is not used there is excellent agreement between the two methods, and these extra steps are not necessary. For the runs where the filter is used there is a systematic offset between the two methods.

Figure 8

Panel (a) shows measured cross sections (black squares) for the ${}^{94}\mathrm{Mo}$($p,\gamma$)${}^{95}\mathrm{Tc}$ reaction. Excellent agreement is seen with the previous measurements by Sauter et al. (blue triangles [16]) and Foteinou et al. (red diamonds [17]). The cross sections are also compared to theoretical Hauser Feshbach calculations done using the non-smoker code [18]. Panel (b) shows a possible analysis of the structures around 2 MeV. The yield with the underlying background curve subtracted has been fit as a series of narrow resonances. The blue curves show the total fit to the structures while the green curves show the theoretical contribution from narrow underlying resonances.

Figure 9

The astrophysical reaction rate for the ${}^{94}\mathrm{Mo}$($p,\gamma$)${}^{95}\mathrm{Tc}$ reaction. The green line is the rate given in the REACLIB [21] database. The green band is a factor of 3 uncertainty. The blue line is the result of this work and the shaded region represents the $3\sigma$ uncertainty. The bottom panel shows the ratio between this work and the REACLIB rate. It is close to 1 above 2 GK. Below 2 GK it diverges and is about a factor of 2 stronger.