[en] We have used the decay of ^180m Hf (t = 5.5 h) to obtain a very precise γ-ray calibration source in the 90 to 330 keV energy range. The decay of ^180m Hf to the ¹⁸⁰ Hf ground state includes a cascade of three consecutive E2 γ-ray transitions of energies 332.3, 215.4 and 93.3 keV with no other feeding to to the intermediate states. Since the total transition intensities must by the same, the relative γ-ray intensities emitted by the source are thus dependent only on the calculated E2 conversion coefficients. This provides a rather precise calibration standard. (authors)

[en] We have measured the half-life of the electron-capture (ec) decay of ⁹⁷Ru in a metallic environment, both at low temperature (19 K), and also at room temperature. We find the half-lives at both temperatures to be the same within 0.1%. This demonstrates that a recent claim that the ec decay half-life for ⁷Be changes by 0.9%±0.2% under similar circumstances certainly cannot be generalized to other ec decays. Our results for the half-life of ⁹⁷Ru, 2.8370(14) d at room temperature and 2.8382(14) d at 19 K, are consistent with, but much more precise than, previous room-temperature measurements. In addition, we have also measured the half-lives of the β^--emitters ¹⁰³Ru and ¹⁰⁵Rh at both temperatures, and found them also to be unchanged.

[en] We have measured the half-life of the β^- decay of ¹⁹⁸Au to be 2.6948(9) d, with the nuclide sited in an insulating environment. Comparing this result with the half-life we measured previously with a metallic environment, we find the half-lives in both environments to be the same within 0.04%, thus contradicting a prediction that screening from a ''plasma'' of quasifree electrons in a metal increases the half-life by as much as 7%.

No abstract available

[en] The half-life of ¹⁰C has been measured to be 19.310(4) s, a result with 0.02% precision, which is a factor of three improvement over the best previous result. Since ¹⁰C is the lightest superallowed 0⁺→0⁺ β⁺ emitter, its ft value has the greatest weight in setting an upper limit on the possible presence of scalar currents

[en] The transitional rare earth region ¹⁵⁵ Er nucleus has ΔZ = 4 and ΔN = 5 valence nucleons over the magic core ₆₄¹⁴⁶ Gd. This relatively large number of valence particles determines an irregular decay pattern above the state I^π = 43/2⁺ at E^* = 5.012 MeV, while a regular rotational pattern is observed bellow this state. The neighbouring ¹⁵⁶Er behaves as a rotor at low to moderately high spins. In ¹⁵⁴ Er nucleus a typical non-collective structure has been revealed involving at highest spins the breaking of the proton or neutron cores. The present study of ¹⁵⁵ Er nucleus aims at investigating the decay scheme of ¹⁵⁵ Er nucleus and evidencing the core breaking mechanism for the new found highest spin states following the experiment on EUROGAM phase II multidetector array. About 60 of the new γ rays were found with energies within 1-2.5 MeV, out of which 16 were placed into the level scheme of ¹⁵⁵ Er, above E^* = 12 MeV, at spins higher than 77/2 and 79/2ℎ. The preliminary analysis indicates that (some of) these high energy transitions can be explained as elementary single particle excitations over the energy gap between the magic core shell closure and the valence shell (core breaking). The calculations were done using the cranking of rotation around the symmetry axis, successfully applied to nuclei whose yrast and higher excitations reveal a very irregular dependence on spin. It was found that minimizing the sum of single-particle energies in the laboratory frame with the constraint for given angular momentum, is equivalent to including in the sum only those points that lie below a straight line: e = λ + (ℎ ω)m in the (m, e) plane (spin-projection versus energy). This so-called tilted Fermi surface method is exemplified for the neutron and proton well of ¹⁵⁵ Er, respectively. Thus, the double optimal state I^π = 79/2^- which results from the neutron I^π = 47/2^- plus proton I^π = 16⁺ configurations is made by filing the orbitals up to the tilted Fermi surface to explain both yrast and non yrast experimental high spin states. When the excitations inside the valence shell are exhausted, it may prove preferable to promote particles from the lower closed shell which explains the existence of the experimentally found very high energy transitions. Tilted Fermi surfaces corresponding to the state I^π 79/2^- at E^* = 12.304 MeV of ¹⁵⁵ Er for deformation parameters β₂ = -0.150, β₄ = -0.020 (for both neutrons and protons) are given. (authors)

[en] Recently we measured the ratio of K-shell internal conversion coefficients, α_K, for the 127.5-keV E3 transition in ¹³⁴Cs and the 661.7-keV M4 transition in ¹³⁷Ba. We here report a measurement of the 165.9-keV M1 transition in ¹³⁹La, based on which we convert our earlier ratio measurement into individual α_K values for the transitions in ¹³⁴Cs and ¹³⁷Ba. These results continue to confirm the Dirac-Fock calculations of internal conversion coefficients that incorporate the atomic K-shell vacancy

[en] We present the first study of the β decay of ²³Al undertaken with pure samples. The study was motivated by nuclear astrophysics questions. Pure samples of ²³Al were obtained from the momentum achromat recoil separator (MARS) of Texas A and M University, collected on a fast tape-transport system, and moved to a shielded location where β and β-γ coincidence measurements were made. We deduced β branching ratios and log ft values for transitions to states in ²³Mg, and from them determined unambiguously the spin and parity of the ²³Al ground state to be J^π=5/2⁺. We discuss how this excludes the large increases in the radiative proton capture cross section for the reaction ²²Mg(p,γ)²³Al at astrophysical energies, which were implied by claims that the spin and parity is J^π=1/2⁺. The log ft for the Fermi transition to its isobaric analog state (IAS) in ²³Mg is also determined for the first time. This IAS and a state 16 keV below it are observed, well separated in the same experiment for the first time. We can now solve a number of inconsistencies in the literature, exclude strong isospin mixing claimed before, and obtain a new determination of the resonance strength. Both states are resonances in the ²²Na(p,γ)²³Mg reaction at energies important in novae. The reactions ²²Mg(p,γ)²³Al and ²²Na(p,γ)²³Mg have both been suggested as possible candidates for diverting some of the flux in oxygen-neon novae explosions from the A=22 into the A=23 mass chain

[en] We have measured the ratio of K-shell internal conversion coefficients, α_K, for the 127.5-keV E3 transition in ¹³⁴Cs and the 661.7-keV M4 transition in ¹³⁷Ba. Previous measurements of these α_K values led to a ratio that differed from calculated internal conversion coefficients. Our measured result, 30.01(15), disagrees with, but is a factor of three more precise than, the previous average of all experimental results. Our new result is consistent with calculations

[en] We have measured the K-shell internal conversion coefficient, α_K, for the 346.5-keV M4 transition in ¹⁹⁷Pt to be 4.23(7). This result differs from a previous value, which disagreed significantly from theory. Our new value agrees well with Dirac-Fock calculations and removes the earlier discrepancy as a source of concern.