Soft x-ray emissions from laser plasma of cryogenic mixture targets

Abstract

Soft x-ray spectral radiation from Xe–CO2 mixture cryogenic targets with a Xe mole fraction of 0% (pure CO2) to 100% (pure Xe) irradiated by a 1 μm pulse laser at a laser intensity IL of 0.3–1.0×1012 W/cm2 has been observed. The x-ray conversion efficiency per Xe mole fraction was found to have maximum values at the Xe fractions of 10% for IL=6.0×1011 W/cm2 and 5% for IL=1.2×1012 W/cm2, which were about five and ten times as large as that in a pure Xe target, respectively. The x-ray conversion efficiencies in the cryogenic mixture targets at Xe fractions of 10%–40% were about 1.3 %/sr/nm for λ=10.8 nm and IL=1012 W/cm2, which was as high as that in a pure Xe cryogenic target. The physical mechanism behind this enhanced emission is discussed.

A new measurement of the intruder configuration in 12Be

“…The γ-energy spectrum of these triple-coincidence events is presented in Fig.3(b), with the 0.511 MeV γ-ray peak (between 0.4 and 0.6 MeV) standing well above the background. The time distribution of these 0.511 MeV γ-rays follows approximately the exponentialdecay curve with an extracted half-life of 270 ± 120 ns, being consistent with the reported value [8] within the error bar. The source of these coincidentally observed 0.511 MeV γ-rays were checked against all possible contamina- tions, such as the random or accidental coincidences, target impurities, event mixing and so on.…”

“…A special isomer-tagging method was used to discriminate the 0 + 2 state from the broad excitation-energy peak ( Fig.2(b)). The method relies on its well-known isomeric property: a life-time of 331 ± 12 ns [8] and an E0-decay (via e + e − pair emission) branching ratio of 83 ± 2 % [7]. 12 Be(0 + 2 ) isomers were stopped in the TELE0 and the subsequently emitting γ-rays, particularly the 0.511 MeV ones from the e + -annihilations, were measured by an array of six large-size NaI(Tl) scintillation detectors surrounding or at the back of the TELE0 (Fig.1).…”

“…This neutron-rich nucleus has four particle-bound states, namely the g.s. (0 + ), and the excited states at 2.107 (2 + ), 2.251 (0 + ) and 2.710 MeV (1 − ) [8]. The relatively low energies of the latter three states imply the breakdown of the N = 8 magic number and the strong intruder from the upper sd-shell [5][6][7][8][9], leading to the growth of other non-shell-like structure in this nucleus [10,11].…”

“…(0 + ), and the excited states at 2.107 (2 + ), 2.251 (0 + ) and 2.710 MeV (1 − ) [8]. The relatively low energies of the latter three states imply the breakdown of the N = 8 magic number and the strong intruder from the upper sd-shell [5][6][7][8][9], leading to the growth of other non-shell-like structure in this nucleus [10,11]. Since Barker's early work in describing the isospin T = 2 states of the mass A = 12 nuclei with a mixed configuration [12], substantial theoretical studies have been devoted to the spectroscopic studies of the low-lying states in 12 Be.…”

Structure of13Be probed via secondary-beam reactions

“…Before attempting to interpret the 12 Be+n decay energy spectrum, the issue of bound excited states of 12 Be should be addressed. At present, 12 Be is known to have three bound excited states -the well established 2 + 1 state at 2.11 MeV [71], together with a 1 − state at 2.7 MeV [24] and an isomeric 0 + 2 level (τ 1/2 ≈300 nsec) at 2.25 MeV [72,73]. The population of any of these levels will, as alluded to in the Introduction, provide for ambiguities in the interpretation of the 12 Be+n coincidences.…”