Search for isomers in 254Rf

Zeitschrift f�r Physik A Atoms and Nuclei, 1985

Evaporation residues from the heavy-ion fusion reaction 5~ on 2~ were investigated. They were separated from the projectile beam by the velocity filter SHIP and identified after implantation into an array of position-sensitive surface-barrier detectors by analyzing their a-decay chains. Spontaneous fission was also observed. A A+0.9 S), 257105 = Four new ~ emitters, 258105 (T1/2 ..... 0.6 (T1/2 =1"4-+~ S), 254Lr (T1/2 13_ +3 s), and 253Lr +0.6 (T1/2 = 1.3 0.3 s) could be identified. For the isotope 257105 we obtained a spontaneous-fission branch of about 20%. A spontaneous-fission activity with a halflife comparable to that for the e decay of 258105 was explained as fission of 258104, formed by electron capture from 258105. An excitation function for evaporation-residue production was measured for bombarding energies in the range of EcM= 184.4 MeV to EcM= 196.6 MeV. Nearly all evaporation residues we observed, could be attributed to the In and 2n deexcitation channels. The maximum cross sections were ~r(1 n) = c/2.9_+ 0.3) nbarn, and a(2n) = c/2.1 _ 0.8) nbarn, respectively. We could measure the total kinetic energy of the fission fragments of 258104 to be TKE = (220+_ 15)MeV, a value that fits into empirical systematics based on a Z2/A ~/3 dependence.

Journal of the Physical Society of Japan, 2008

Nuclear Physics A, 2019

The neutron-deficient isotopes 254,255 Rf were produced in the fusion-evaporation reaction 50 Ti + 206 Pb at the gas-filled recoil separator TASCA. Decay properties of these nuclei were investigated by applying fast digital electronics. A search for isomeric states in both isotopes was performed by using the accompanying conversion electron emissions. Isomeric states with half-lives of 4(1) µs and >30 µs were measured for 254 Rf and 255 Rf, respectively, which confirm the findings at different separators. The present experimental results demonstrate the great potential of fast digital electronics for measurements of isomeric states in the heaviest nuclei, which are only producible in small quantities.

The decay properties of the new isotope 282 113 and its daughter nuclei have been measured in the 237 Np( 48 Ca, 3n) 282 113 reaction. During an irradiation with a beam dose of 1.1 × 10 19 244-MeV 48 Ca projectiles, two decay chains originating from the odd-odd isotope 282 113 (E α = 10.63 ± 0.08 MeV, T α = 73 +134 −29 ms) were produced in the complete fusion reaction with a cross section of 0.9 +1.6 −0.6 pb; these properties are all in agreement with expectations based on the results of previous experiments.

Physical Review C, 2011

The fission fragment mass angle correlations and mass ratio distributions have been investigated for the two systems 16 O + 197 Au and 27 Al + 186 W, leading to the same compound nucleus 213 Fr around the Coulomb barrier energies. Systematic analysis of the variance of the mass distributions as a function of temperature and angular momentum suggests true compound nuclear fission for both the reactions, indicating the absence of nonequilibrium fission processes.

2012

A search for isomeric γ-decays among fission fragments from 345 MeV/nucleon 238 U has been performed at the RIKEN Nishina Center RI Beam Factory. Fission fragments were selected and identified using the superconducting in-flight separator BigRIPS and were implanted in an aluminum stopper. Delayed γ-rays were detected using three clover-type high-purity germanium detectors located at the focal plane within a time window of 20 μs following the implantation. We identified a total of 54 microsecond isomers with half-lives of ~ 0.1-10 μs, including discovery of 18 new isomers in very neutron-rich nuclei:

Physical Review C, 2004

Excited states in 210 Ra and 209 Ra were populated using the 184 W͑ 30 Si, xn͒ reaction at 148 MeV beam energy. Fusion evaporation recoils were selected using the gas-filled spectrometer, SASSYER. Prompt ␥ rays were detected using Compton-suppressed Ge detectors from the YRAST Ball array surrounding the target. Delayed ␥ rays, following isomeric decays, were detected at the focal plane of SASSYER with a smaller array of Ge detectors. The decay energy and lifetime for the 8 + ͑h 9/2 ͒ n isomer of 210 Ra were determined; values for the yrast B͑E2;8 + → 6 + ͒ in 210 Ra and neighboring nuclei are interpreted within the seniority scheme. This isomer was also used to select ␥-rays deexciting levels above the isomeric state in 210 Ra. In addition, transitions in 209 Ra were identified for the first time. Two high-spin isomers are suggested to exist in this isotope.

Dynamical Aspects of Nuclear Fission - Proceedings of the 5th International Conference, 2002

European Physical Journal A, 2007

With a view to study complete-and incomplete-fusion components in 159 Tb, 169 Tm( 16 O, x) reactions, experiments have been carried out at the Inter-University Accelerator Center, New Delhi, India using the 15UD Pelletron accelerator facilities. The forward mean recoil ranges for some radio-nuclides; 168m Lu, 167 Lu, 167 Yb, 166 Tm produced in the 16 O + 159 Tb system at ≈ 90 MeV, and 179 Re, 177 Re, 177 W, 178 Ta and 177 Hf produced in the 16 O + 169 Tm system at ≈ 87 MeV have been measured. The recoilcatcher activation technique followed by off-line γ-spectrometry has been employed in the present work. The analysis of forward mean ranges for different radio-nuclides has been done in the framework of the degree of linear momentum transfer from projectile to target nucleus by adopting break-up fusion model considerations. Different complete-and incomplete-fusion components, which may be attributed to the fusion of 16 O and/or 12 C and 8 Be transfer from the 16 O projectile to the target nucleus have been observed. An attempt has also been made to separate out the relative percentage contributions of complete-and incomplete-fusion components using experimentally measured forward recoil ranges. The complete-fusion contributions deduced from recoil range distribution are found to be consistent with the prediction of the theoretical model code PACE. The analysis of data indicates the complete-and incomplete-fusion competition for both the systems at the given energies.

Physical Review C, 2008

Isotopes of rutherfordium (258-261 Rf) were produced in irradiations of 238 U targets with 26 Mg beams. Excitation functions were measured for the 4n, 5n, and 6n exit channels. Production of 261 Rf in the 3n exit channel with a cross section of 28 +92 −26 pb was observed. α-decay of 258 Rf was observed for the first time with an α-particle energy of 9.05 ± 0.03 MeV and an α/total-decay branching ratio of 0.31 ± 0.11. In 259 Rf, the electron capture/total-decay branching ratio was measured to be 0.15 ± 0.04. The measured half-lives for 258 Rf, 259 Rf, and 260 Rf were 14.7 +1.2 −1.0 ms, 2.5 +0.4 −0.3 s, and 22.2 +3.0 −2.4 ms, respectively, in agreement with literature data. The systematics of the α-decay Q-values and of the partial spontaneous fission half-lives were evaluated for even-even nuclides in the region of the N = 152, Z = 100 deformed shell. The influence of the N = 152 shell on the α-decay Q-values for rutherfordium was observed to be similar to that of the lighter elements (96 Z 102). However, the N = 152 shell does not stabilize the rutherfordium isotopes against spontaneous fission, as it does in the lighter elements (96 Z 102).