Dipole strength in ${}^{80}\mathrm{Se}$ for $s$ process and nuclear transmutation of ${}^{79}\mathrm{Se}$

The dipole strength distribution of ${}^{80}\mathrm{Se}$ was studied in a photon-scattering experiment by using bremsstrahlung produced with an electron beam of energy 11.5 MeV at the linear accelerator ELBE. We identified $180\gamma$ transitions up to an energy of 9.6 MeV, and analyzed the strength in the quasicontinuum of the spectrum. Simulations of statistical $\gamma$-ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section below the neutron-separation energy derived in this way was combined with the photoabsorption cross section obtained from an earlier $(\gamma ,n)$ experiment and used as an input for the calculation of ${}^{79}\mathrm{Se}(n,\gamma )$ reaction rates on the basis of the statistical reaction model.

Figure 1

Spectrum of $\gamma$ rays scattered from ${}^{80}\mathrm{Se}$ combined with ${}^{11}\mathrm{B}$, measured during the irradiation with bremsstrahlung produced by electrons of an energy of $E_e^{\mathrm{kin}}=11.5$ MeV. This spectrum is the sum of the spectra measured with the two detectors placed at ${127}^{\circ }$ relative to the beam.

Figure 2

Absolute photon flux at the target deduced from intensities of four known transitions in ${}^{11}\mathrm{B}$ (circles) using the detector efficiency calculated with geant4 and the relative flux calculated as described in the text (solid line).

Figure 3

Response-corrected spectrum of the two detectors placed at ${127}^{\circ }$, simulated spectrum of photons scattered from the target to the detectors by atomic processes, and the difference between the two.

Figure 4

Uncorrected photoabsorption cross section (black solid line), TLO (dashed line), input (blue solid line), and output (red circles with error bars) of the 8. (i.e., last) iteration step in the simulation of $\gamma$-ray cascades.

Figure 5

Photoabsorption cross sections deduced from the present measurement (red circles) in comparison with $(\gamma ,n)$ data from Ref. [36] (blue triangles) and Ref. [59] (green squares), and with the TLO (black dashed curve).

Figure 6

Cross-section data used for the construction of the EPACS input strength function (black circles) and ${}^{80}\mathrm{Se}(\gamma ,\mathrm{abs})$ cross sections as a function of $\gamma$-ray energy based on various models used as input for calculations using the code talys.

Figure 7

Same as Fig. 6, but showing the data relative to the TLO.

Figure 8

${}^{79}\mathrm{Se}(\mathrm{n},\gamma )$ cross sections as functions of neutron energy calculated by using the code talys with various modes for the input strength function. The uncertainty of the EPACS due to level density model is shown as a blue (gray) band. Recent results of $\gamma$ strength method obtained from the $\gamma \mathrm{SF}$ above neutron threshold [38] are also shown as black points (see text).

Figure 9

${}^{79}\mathrm{Se}(n,\gamma )$ Maxwellian-averaged cross sections calculated by using the code talys with various models for the input strength function compared with KADoNiS (version 0.3) (black circles). The uncertainty of the EPACS shown as a blue band results from the use of various nuclear level density models.

Figure 10

${}^{79}\mathrm{Se}(\mathrm{n},\gamma )$ reaction rates as a function of temperature, calculated by using the code talys with various models for the input strength function. The uncertainty of the EPACS shown as a blue band results from the use of various nuclear level density models.

Figure 11

${}^{80}\mathrm{Se}(\gamma ,\mathrm{n})$ reaction rates as a function of temperature, calculated by using the code talys with various models for the input strength function. The uncertainty of the EPACS shown as a blue band results from the use of various nuclear level density models.