Location of the Neutron Dripline at Fluorine and Neon

A search for the heaviest isotopes of fluorine, neon, and sodium was conducted by fragmentation of an intense ${}^{48}\mathrm{Ca}$ beam at $345\mathrm{MeV}/\mathrm{nucleon}$ with a 20-mm-thick beryllium target and identification of isotopes in the large-acceptance separator BigRIPS at the RIKEN Radioactive Isotope Beam Factory. No events were observed for ${}^{32,33}\mathrm{F}$, ${}^{35,36}\mathrm{Ne}$, and ${}^{38}\mathrm{Na}$ and only one event for ${}^{39}\mathrm{Na}$ after extensive running. Comparison with predicted yields excludes the existence of bound states of these unobserved isotopes with high confidence levels. The present work indicates that ${}^{31}\mathrm{F}$ and ${}^{34}\mathrm{Ne}$ are the heaviest bound isotopes of fluorine and neon, respectively. The neutron dripline has thus been experimentally confirmed up to neon for the first time since ${}^{24}\mathrm{O}$ was confirmed to be the dripline nucleus nearly 20 years ago. These data provide new keys to understanding the nuclear stability at extremely neutron-rich conditions.

Figure 1

Section of the nuclear chart showing the location of the isotopes studied in this work (red dotted squares).

Figure 2

Particle identification spectra as a function of $Z$ and $A/Z$ are shown for the settings tuned for (a) ${}^{33}\mathrm{F}$ and (b) ${}^{36}\mathrm{Ne}+{}^{39}\mathrm{Na}$. See the text for details.

Figure 3

Production cross sections measured for the fragmentation of ${}^{48}\mathrm{Ca}$ at $345\mathrm{MeV}/\mathrm{nucleon}$ are shown for the neutron-rich fluorine (black solid circles) and neon (red solid squares) isotopes. Prediction from the epax 2.15 and $Q_g$ systematics are shown for the fluorine (neon) isotopes by the black (red) dashed and solid curves, respectively. Those of ${}^{35}\mathrm{Na}$ and ${}^{37}\mathrm{Na}$ (blue solid triangles) are also shown along with the epax 2.15 predictions (blue dashed curve).