Coulomb dissociation of ${}^{20,21}\mathrm{N}$

Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on ${}^{20,21}\mathrm{N}$ are reported. Relativistic ${}^{20,21}\mathrm{N}$ ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the ${}^{19}\mathrm{N}(n,\gamma ){}^{20}\mathrm{N}$ and ${}^{20}\mathrm{N}(n,\gamma ){}^{21}\mathrm{N}$ excitation functions and thermonuclear reaction rates have been determined. The ${}^{19}\mathrm{N}(n,\gamma ){}^{20}\mathrm{N}$ rate is up to a factor of 5 higher at $T<1\mathrm{GK}$ with respect to previous theoretical calculations, leading to a 10% decrease in the predicted fluorine abundance.

Figure 1

Incoming particle identification for the FRS setting used in this work. The charge number $Z$ is derived by energy loss measurements in the PSP and the $A/Z$ ratio by time-of-flight measurements between S8 and POS (55 m distance). The red rectangles indicate a $3\sigma$ cut for ${}^{20}\mathrm{N}$ (left) and ${}^{21}\mathrm{N}$ (right). For further details, see text.

Figure 2

Sketch (top view) of the detector setup at the LAND/R3B cave. Indicated are plastic scintillators (orange), the neutron flight path (blue line), the flight path of heavy ions (magenta line), and that of protons (red line). Distances of the detectors are to scale, while the thicknesses of the thin detectors are not to scale. See text for details.

Figure 3

Doppler corrected gamma sum spectra for outgoing nuclei (red solid line) after Coulomb breakup and a background estimation (blue dashed line). Left panel for outgoing ${}^{19}\mathrm{N}$ and right panel for ${}^{20}\mathrm{N}$. The black arrows indicate known excited states [18].

Figure 4

One-neutron emission spectrum of ${}^{20}\mathrm{N}$ impinging onto a Pb target measured with LAND (red dashed line) and corrected for the LAND efficiency (blue solid line). The kinetic energy of the neutron $T_n^{\mathrm{c}.\mathrm{m}.}$ is given in the center-of-mass frame.

Figure 5

Coulomb dissociation cross section of ${}^{20}\mathrm{N}$ as a function of the excitation energy for the total reaction (black line) and transitions into the first excited state of ${}^{19}\mathrm{N}$ at 1141 keV (red line). The error bars reflect statistical uncertainties only.

Figure 6

Coulomb dissociation cross section of ${}^{21}\mathrm{N}$ as a function of the excitation energy for the total reaction (black line) and transitions into the ground state of ${}^{20}\mathrm{N}$ (magenta line). The error bars reflect statistical uncertainties only. For the ground state transitions, the error bars were omitted for reasons of clarity as they are comparable to the ones of the total reaction.

Figure 7

Stellar reaction rate for ${}^{19}\mathrm{N}(n,\gamma ){}^{20}\mathrm{N}$ (black solid line). The red dotted line denotes contributions from the neutron capture of the ground state of ${}^{19}\mathrm{N}$ and the blue dotted-dashed line denotes contributions from the neutron capture of the first excited state of ${}^{19}\mathrm{N}$. The black dashed line denotes a theoretical curve given by [25].

Figure 8

Stellar reaction rate for ${}^{20}\mathrm{N}(n,\gamma ){}^{21}\mathrm{N}$ (black solid line). The red dotted line denotes contributions from the neutron capture of the ground state of ${}^{20}\mathrm{N}$ and the blue dotted-dashed line denotes contributions from the neutron capture of the first and second excited state of ${}^{20}\mathrm{N}$.

Figure 9

Final abundances as a function of the nucleon number derived from our network calculation with our measured reaction rates (red solid line) and solar $r$-process abundance from reference (black symbols) [29]. For details, see text.

Figure 10

Reaction flow as a function of time (and temperature) during our network calculation for ${}^{19}\mathrm{N}(n,\gamma ){}^{20}\mathrm{N}$ (black dashed line) and ${}^{20}\mathrm{N}(n,\gamma ){}^{21}\mathrm{N}$ (red solid line). The temperature is plotted as the blue dotted line.