Measurement of the stellar ${}^{58}\mathrm{Ni}(n,\gamma ){}^{59}\mathrm{Ni}$ cross section with accelerator mass spectrometry

The ${}^{58}\mathrm{Ni}(n,\gamma ){}^{59}\mathrm{Ni}$ cross section was measured with a combination of the activation technique and accelerator mass spectrometry (AMS). The neutron activations were performed at the Karlsruhe 3.7 MV Van de Graaff accelerator using the quasistellar neutron spectrum at $kT=25$ keV produced by the ${}^7\mathrm{Li}(p,n){}^7\mathrm{Be}$ reaction. The subsequent AMS measurements were carried out at the 14 MV tandem accelerator of the Maier-Leibnitz Laboratory in Garching using the gas-filled analyzing magnet system (GAMS). Three individual samples were measured, yielding a Maxwellian-averaged cross section at $kT=30$ keV of ${\langle \sigma \rangle }_{30\text{keV}}$ = 30.4 (23)${}^{\mathrm{syst}}$(9)${}^{\mathrm{stat}}$ mbarn. This value is slightly lower than two recently published measurements using the time-of-flight (TOF) method, but agrees within the uncertainties. Our new results also resolve the large discrepancy between older TOF measurements and our previous value.

Figure 1

(a) Schematic drawing of the neutron production target and position of the samples during irradiation. At $E_p=1912$ keV the neutrons are kinematically collimated in a forward cone with a ${120}^{\circ }$ opening angle. (b) Comparison of the experimental neutron spectrum with a Maxwellian energy distribution of $kT=25$ keV.

Figure 2

Schematic illustration of the GAMS setup at the MLL in Garching (not to scale). Blue and red dotted lines represent the negatively and positively charged ion beam of interest, respectively. In the GAMS magnet, the isotope of interest follows the yellow, dotted trajectory into the detector. Black and gray dotted lines in the GAMS magnet represent isobars of higher and lower element number $Z$, respectively.

Figure 3

[Left column (a)–(c)] Raw spectra of the energy loss in the second anode ($Y$ axis) versus the $X$ position of the incident particles ($X$ axis), both in arbitrary units (a.u.), recorded with about equal statistics for (a) the standard sample, (b) a blank sample, and (c) the sample ni-2, all in linear scale in arbitrary units. [Right column (d)–(f)] The same spectra after applying a complete set of one-dimensional software cuts around the region of interest for ${}^{59}\mathrm{Ni}$ on all other detector signals. Additionally, a representative example of an elliptical, two-dimensional region of interest for ${}^{59}\mathrm{Ni}$ is shown in orange. The remaining background is from the tail of ${}^{59}\mathrm{Co}$ (lower left of the ${}^{59}\mathrm{Ni}$ region).

Figure 4

Comparison of the neutron capture cross section from the evaluated libraries ENDF/B-VII.1 [32], JEFF-3.2 [35], and JENDL-4.0 [36].