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A new proton-unbound isotope 204Ac was produced in the fusion-evaporation reaction Tm(40169Ca,5n)204Ac and identified via the recoil-α correlation at the gas-filled recoiled separators SHANS2 and SHANS. The excitation function for producing 204Ac was measured and the optimal beam energy was evaluated to be 212 MeV. Nineteen ER - α1 - α2 - α3 decay chains were observed for this isotope. Based on these chains, the α-particle energy and half-life of 204Ac were determined to be 7948(15) keV and 7.4−1.4+2.2 ms, respectively. Both are consistent with the theoretical prediction. The reduced α-decay width was deduced to be 49−15+10 keV, which indicates a favored α decay for 204Ac. In addition, more precise decay properties of Eα = 7883(15) keV and T1/2 = 7.7−1.6+2.7 ms were obtained for 205Ac.

A new proton-unbound isotope 204Ac was produced in the fusion-evaporation reaction Tm ( 40 169 Ca , 5n) 204 Ac and identified via the recoil- α correlation at the gas-filled recoiled separators SHANS2 and SHANS. The excitation function for producing 204Ac was measured and the optimal beam energy was evaluated to be 212 MeV. Nineteen ER - α 1 - α 2 - α 3 decay chains were observed for this isotope. Based on these chains, the α -particle energy and half-life of 204Ac were determined to be 7948(15) keV and 7.4 − 1.4 + 2.2 ms, respectively. Both are consistent with the theoretical prediction. The reduced α -decay width was deduced to be 49 − 15 + 10 keV, which indicates a favored α decay for 204Ac. In addition, more precise decay properties of E α = 7883(15) keV and T 1 / 2 = 7.7 − 1.6 + 2.7 ms were obtained for 205Ac. [ABSTRACT FROM AUTHOR]

Results of experiments on determination of the energy of Bi α-particles for the existing lines with the intensities of 1.94 and 0.15% per decay are reported. The results were obtained by semiconductor α-ray spectrometry by comparison with the α-particle energies for the major lines of Fr and Po, known with a lower uncertainty. The experiments were designed so as to minimize and, at the same time, take into account factors affecting the deviations of the peak maxima from the true values. Special emphasis is made on the decay of recoil nuclei on the detector surface. To eliminate this effect, samples containing highly nonequilibrium systems Bi + Fr and Bi + Ac were prepared. For the measurement conditions used, the equilibrium spectra of Ac with daughter decay products were found to be unsuitable for accurate determination of the energy of the Bi major peak and can be used only for tentative estimations. The actual energies of Bi α-radiation do not coincide with the assessed reference data used today and are in the region of the upper limit of the uncertainty range for these data. The results show that the presently used energy characteristics of Bi α-radiation require refinement. [ABSTRACT FROM AUTHOR]

The decay of 218Pa was investigated by means of α and γ spectroscopy. The nucleus was produced in the fusion reaction 40Ar+182W and separated in flight by the gas-filled recoil separator SHANS (Spectrometer for Heavy Atoms and Nuclear Structure). The known α decays of 218Pa were measured with improved precision and newly assigned to be originating from the ground state, which clarified the ambiguities in their previous assignments. In addition, a new isomeric state in 218Pa decaying with α -particle energies of 9691(15) keV, 9595(21) keV and a half-life of 135 − 32 + 62 μs was identified. The spins and parities of the involved states were tentatively assigned on the basis of the systematic α -decay properties of the odd-proton N = 127 isotones and shell model calculations. [ABSTRACT FROM AUTHOR]