S. M. Lukyanov

Evidence for particle stability of 31 F and particle instability of 25 N and 28 O

Abstract The neutron drip line up to fluorine has been investigated by the projectile fragmentation of a 94.1A MeV 40 Ar beam at the fragment separator RIPS at RIKEN. A new neutron-rich isotope, 31 F, has been observed for the first time while clear evidence for the particle instability of 24,25 N, 27,28 O and 30 F has been obtained. The sudden change in stability from oxygen to fluorine may demonstrate the onset of deformation for the neutron-rich fluorine isotopes.

New mass measurements of neutron-rich nuclei near N= 20

Abstract The masses of 39 neutron-rich nuclei in the mass range 17–37 have been measured using a direct time-of-flight technique following the fragmentation of a 48 Ca beam at 55 MeV/nucleon. The masses of 29,30 Ne, 34,35 Mg and 36,37 Al are reported for the first time. The very neutron-rich nuclei, 31–33 Na, are found to be 2–4 MeV less bound than previously believed. A comparison is made with recently available large scale shell model calculations encompassing the deformed A ∼32 nuclei. Conclusions are drawn regarding the extent of the region of deformation, which is found to include 30 Ne.

Search for 28O and study of neutron-rich nuclei near the N = 20 shell closure

Abstract A search for 28 O with a 78 AMeV beam of the neutron-rich isotope 36 S has been performed for the first time. Evidence for the unbound character of 28 O was obtained. In the same experiment the half-lives of the very neutron-rich isotopes 27,29 F and 30 Ne were measured and those for 28,29 Ne and 30,31 Na reexamined. The results are compared to shell-model predictions and conclusions drawn regarding the extent of the region of deformation around N = 20.

Identification of the doubly-magic nucleus 100Sn in the reaction 112Sn+natNi at 63 MeV/nucleon

Abstract We report on the production of the doubly-magic nucleus 100 Sn and other proton-rich nuclei in the A ∼ 100 region in the reaction 112 Sn + nat Ni at 63 MeV/nucleon. The experiment was carried out using the high acceptance device SISSI and the Alpha and LISE3 spectrometers at GANIL. The identification of the reaction products ( A , Z and Q ) was made using the measurements of time-of-flight, energy-loss and kinetic energy.

Experimental evidence for the particle stability of 34Ne and 37Na

The neutron drip line in a neon–magnesium region has been explored by the projectile fragmentation of a 59.8 A MeV 48Ca beam using the new fragment separator LISE 2000 at GANIL. New neutron-rich isotopes, 34Ne and 37Na, have been observed together with some evidence for the particle instability of 33Ne and 36Na.

β-Delayed neutron emission of the isotopes 20C, 40,41,42P, 43,44S☆

Abstract Very neutron-rich isotopes have been produced by the fragmentation of 55 MeV/u 48 Ca projectiles from GANIL onto a 181 Ta target. The nuclei were separated by means of the doubly achromatic spectrometer LISE and implanted into a semiconductor telescope for identification in Z and A . Their β-delayed neutron radioactivity is observed by means of a 4π β -n coincidence detector. The results include first measurements of the half-life T 1 2 and the neutron emission probability P n for the isotopes 20 C, 40,41,42 p and 43,44 S. They are compared to current theoretical predictions.

Identification of μs-isomers produced in the fragmentation of a 112Sn beam

Abstract Decays of over forty short-lived ( T 1 2 from ≈ 50 ns to 70 μs) isomeric states including a new isomer 66mAs produced in the fragmentation of a 112Sn beam (58 A·MeV, 63 A·MeV) on a natNi target were observed at the final focus of the LISE3 spectrometer at GANIL. Their detection, based on the slow (≈ 10 μs) time correlation of identified ions with the characteristic γ-radiation, represents a novel method to search for new isomers and can be used for unambiguous isotope identification for projectile fragment separator experiments. Isomeric yields and isomer-to-total production ratios were determined.

Determination of the astrophysical S factor of the 8B(p,γ)9C capture reaction from the d(8B,9C)n reaction

The asymptotic normalization coefficients for the virtual decay 9 C → 8 B + p have been determined by measuring the crosssection of the 8 B(d, n) 9 C reaction in inverse kinematics at 14.4 MeV/u, using the RIPS facility. The deduced astrophysical S factor S18 of the 8 B(p ,γ ) 9 C capture reaction in the center of mass energy range 1–100 keV is S18 = 45 ± 13 eV b.  2001

Single neutron emission following 11Li β-decay

Abstract The spectrum of neutrons emitted after the β-decay of 11 Li has been measured with a large time-of-flight array. The spectrum exhibits six peaks corresponding to neutron emission from known states in the 11 Be daughter nucleus. The measured branching ratios indicate significant feeding to states over a broad energy range. The energies and parities of the states are in very good agreement with the previous results of the 9 Be(t,p) reaction. Comparison of the present results with shell model calculations indicate the effect of the two neutron halo in 11 Li. The beta-delayed neutron spectrum of 8 He was determined in order to remove contributions from beam contamination.

Isospin diffusion and equilibration for Sn+Sn collisions at E/A=35 MeV

Equilibration and equilibration rates have been measured by colliding Sn nuclei with different isospin asymmetries at beam energies of E/A=35 MeV. Using the yields of mirror nuclei of {sup 7}Li and {sup 7}Be, we have studied the diffusion of isospin asymmetry by combining data from asymmetric {sup 112}Sn+{sup 124}Sn and {sup 124}Sn+{sup 112}Sn collisions with those from symmetric {sup 112}Sn+{sup 112}Sn and {sup 124}Sn+{sup 124}Sn collisions. We use these measurements to probe isospin equilibration in central collisions where nucleon-nucleon collisions are strongly blocked by the Pauli exclusion principle. The results are consistent with transport theoretical calculations that predict a degree of transparency in these collisions, but inconsistent with the emission of intermediate mass fragments by a single chemically equilibrated source. Comparisons with quantum molecular dynamics calculations are consistent with results obtained at higher incident energies that provide constraints on the density dependence of the symmetry energy.