Alpha decay properties of the semi-magic nucleus 219Np

The semi-magic nucleus 219Np was produced in the fusion reaction 187Re(36Ar, 4n)219Np at the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure). A fast electronics system based on waveform digitizers was used in the data acquisition and the sampled pulses were processed by digital algorithms. The reaction products were identified using spatial and time correlations between the implants and subsequent α decays. According to the observed α-decay chain, an energy of Eα=9039(40) keV and a half-life of T1/2=0.15−0.07+0.72 ms were determined for 219Np. The deduced proton binding energy of 219Np fits well into the systematics, which gives another evidence of that there is no sub-shell closure at Z=92. The influence of the N=126 shell closure on the stability of Np isotopes is discussed within the framework of α-decay reduced widths. Keywords: N=126 shell closure, Digital algorithm, α-particle energy, Half-life, Proton drip-line