The beta decay of 18C

Studying neutron-rich 18 N in fusion-evaporation reactions

“…In ref. [2] a lifetime of > 600 ns was assigned to the first excited state at 114 keV. However, from our measurement we estimate a lifetime value of < 30 ns for this state; far shorter than the value of > 600 ns given from the beta decay experiment.…”

“…18 N was produced in the 9 Be( 11 B,2p) 18 N reaction at the 88" Cyclotron at LBNL and studied using the LIBERACE-STARS detector arrayan array of large area segmented silicon detectors (E-∆E) and six HPGe Clover detectors. This experiment was the first to use a fusion-evaporation reaction to populate 18 N. Previous information on the excited states of 18 N came from 18 C beta-decay [2] and charge-exchange reactions [3]. These are highly selective reactions and the fusion-evaporation reaction used here can provide a more comprehensive picture of the excitation spectrum.…”

Nuclear structure ofN18and the neighboringN=11isotones

“…6 (left) together with shell model calculation (right). The calculation shows overall agreement with the low-energy level structure and the spin-parity assignments [11,12,16] for the four lowest states. The reversal in the ground-state and excite-state spins, compared with experiment, is discussed above.…”

“…Previous experiments to study 18 N used beta-decay [11][12][13][14] and charge-exchange reactions [15,16]. Reference [11] also carefully examines shell model results and observed levels in 18 N. The only information on excited state transition rates came from the beta-decay study [12] that suggested, based on intensity balance arguments, a long mean lifetime for the 18 N first excited state of greater than 600 ns, in disagreement with both shell model predictions and neighboring systematic trends.…”

“…Reference [11] also carefully examines shell model results and observed levels in 18 N. The only information on excited state transition rates came from the beta-decay study [12] that suggested, based on intensity balance arguments, a long mean lifetime for the 18 N first excited state of greater than 600 ns, in disagreement with both shell model predictions and neighboring systematic trends. The use of a fusion-evaporation reaction enables a direct measurement of the lifetimes of low-lying levels from observed Doppler shifted gamma-ray energies.…”