β−decay of the neutron-rich isotope215Pb

Abstract

This Brief Report reports on the first observation of the β − -delayed γ decay of 215 Pb, feeding states in 215 Bi. The 215 Pb beam was produced using resonant laser ionization and mass separated at the ISOLDE-CERN on-line mass separator. This ensured clean identification of the γ rays as belonging to the decay of 215 Pb or its β-decay daughters. A half-life of 147 (12) Despite the wealth of experimental data available for the doubly magic nucleus 208 Pb (Z = 82,N = 126) and its closest neighbors, the more neutron-rich lead isotopes remain poorly explored. The reason for the limited spectroscopic information lies in the experimental difficulties to access this region of the nuclear chart. Indeed the high N/Z ratio of these isotopes rules out heavy-ion fusion-evaporation reactions to produce the nuclei of interest and spallation reactions suffer from high contamination levels from more abundantly produced isobars.However for which data were collected during the same experimental campaign have been reported elsewhere.The β − decay of 215 Pb has been observed at ISOLDE in a high-energy proton induced spallation reaction. A 1.4 GeV pulsed proton beam bombarded a thick (50 g/cm 2 ) UC x target. The proton beam, with an intensity of 3.1 × 10 13 particles per pulse was delivered by the PS booster, during a 16.8 s long supercycle, made of 14 equidistant pulses, 1.2 μs long each. Out of these 14 pulses, seven were sent to the ISOLDE target. After diffusion out of the target, the spallation products were selectively ionized in the resonance ionization laser ion source [10,11]. The element-selective laser ionization of the lead isotopes in the hot niobium cavity (2100 • C, 3 mm diameter, 30 mm length) was achieved in three steps: after doubling of the fundamental frequency in a nonlinear BBO (β barium borate) crystal, a tunable pulsed dye laser delivered a photon beam with a wavelength λ = 283.305 nm to raise a valence electron out of the 6p 2 (1/2,1/2) 0 ground state to a first excited atomic state 6p7s(1/2,1/2) 1 . For the second step, the wavelength of the second dye laser was tuned to 600.186 nm, thus exciting the atoms to a 6p8p(1/2,3/2) 2 state. The copper-vapor lasers, pumping the dye lasers, simultaneously provided the necessary energy for the final ionizing step.Subsequently, the ions were extracted by a 60 kV extraction voltage and mass separated by the ISOLDE-GPS separator. After every proton impact, the beam-gate was closed for 100 ms reducing the isobaric contamination, lowering the amount of 067303-1 0556-2813/2013/87(6)/067303(5)

Current Status of r-Process Nucleosynthesis

“…Spectroscopy of this nucleus also found a high Q value of 8.34 MeV for this decay, which agrees with recent mass models that include shell quenching effects. Additional measurements for the neutron-rich nuclei near the r-process path with an implantation tape include half-lives of 216 Bi [240], nuclear spectroscopy of 133 Sn [241], half-lives and spectroscopy of 130−132 Cd [242,243], β-decay half-lives and β-delayed neutron emission, P n , for the neutron-rich isotopes 94−99 Kr and 142−147 Xe [244], decay lifetimes and spectroscopy of 215,217,218 Bi [245,246,247], decay half-life and spectroscopy of 215 Pb [248].…”

In-Source Laser Spectroscopy with the Laser Ion Source and Trap: First Direct Study of the Ground-State Properties ofPo217,219

“…The introduction of the resonance laser-ionization technique has increased the element selectivity of the ionization process [8], which has enabled a large research program to be undertaken, among others, in the lead region; see, e.g., Refs. [9][10][11][12][13][14][15][16][17]. Alternative production routes are found in the combination of in-flight fusion-evaporation or fragmentation facilities with a gas catcher [18][19][20].…”

“…However, the elements with a low ionization energy (IE) (e.g., 87 Fr, 88 Ra) are surface ionized at the walls of the hot cavity alongside the laser-ionization process. Attempts to suppress the surface ions through the use of low-work-function cavity materials [22] or the pulsed-release technique [23] have been successfully applied in cases where only moderate selectivity enhancement is sufficient (e.g., for 215 ≤ A ≤ 218 [9][10][11][12][13]). In the case of 219 Po, however, the RILIS-ionized polonium beam is typically contaminated with 10 5 times more francium if ionization takes place inside a surface-ion-source cavity.…”

Isomeric decay spectroscopy of theBi217isotope

“…Besides 211 Bi, the only other known isomeric state in the neutron-rich odd-even bismuth isotopes is in 215 Bi, six neutrons above N = 126, which was populated with a spallation reaction at ISOLDE [10]. Such reactions at ISOLDE were also successfully employed for the production of 215 Pb [11] and 218 Bi [12]. Recent improvements in experimental devices and beam intensities presently allow exploring more extensively the exotic neutron-rich nuclei in this region, via fragmentation reactions from a 238 U beam [13].…”