Ultraviolet spectroscopy of 233 U and 232 U, in the form of uranium oxide dissolved in 3M nitric acid, has revealed a number of spectral lines with widths of less than 6 nm from the 233 U source but no detectable narrow lines from the 232 U source. These lines could possibly be attributed to the decay of the 229 Th isomeric state at an energy of around 4.0 eV. [S0031-9007(98) PACS numbers: 23.20.Lv, 27.90. + b, 32.30.Jc In 1994 Helmer and Reich [1] determined the separation of the ground and first excited nuclear states in 229 Th to be 3.5 61.0 eV. Recently the direct decay from this state may have been observed at higher resolution [2]. This is then the lowest excitation energy for a nuclear first excited state yet found and the first to be on a similar energy scale to atomic valence electrons. Such a small energy separation provides the potential to examine a regime of nucleus-atom interactions not previously observable. The value for the excitation energy was obtained by applying the Ritz combination principle to groups of g-ray energies of several tens to hundreds of keV. Using energies of 4-5 orders of magnitude larger than the energy under investigation makes it difficult to increase the accuracy of the measured energy separation by this method.The spins and parities of the ground and first excited states together with the small excitation energy suggest that the excited state should be a long lived isomeric state [3]. A photon emitted by the direct decay of the first excited state to the ground state would have a wavelength in the blue-ultraviolet region of the electromagnetic spectrum, i.e., between 270 and 500 nm, with 3.5 eV corresponding to 350 nm. Thus conventional UV spectroscopy is an ideal tool for increasing the accuracy to which the separation is known. A recent experiment [2] used UV spectroscopy of two solid sources of 233 U to look for the 229 Th-isomer deexcitation following the a decay of the 233 U. The results show a broad spectral feature at ϳ2.5 eV, with a set of spectral lines centered at approximately 3.5 eV.In the current work a 233 U source was also used; however, the radioactive isotope was in the form of uranium oxide dissolved in 3M nitric acid, producing an equilibrium in which uranyl nitrate ions dominate (UO 2 NO 1 3 ). The source activity was 4 MBq and its volume of 0.25 ml was contained in a 6 mm internal diameter quartz tube. 233 U has an a-decay half-life of 1.7 3 10 5 years, which ensures the activity will be essentially constant throughout the course of the experiment. It has been estimated that about (1-2)% of the total a decays of the uranium feed into the 229 Th first excited state [4,5]. Because both 233 U and 229 Th have long half-lives it was not considered necessary to remove the daughters produced since the production of the 233 U source in 1992.A control source, with 232 U as the main active element, was also made. The half life of 232 U is 72 yr, which, while adequate for the duration of the measurements means that a substantially smaller quantity of the isot...
Using a frequency-doubled diode laser system, we have measured the hyperfine splitting in the (6s 2 7s)7S 1/2 excited state of the two naturally occurring thallium isotopes. For 205 Tl and 203 Tl we find frequency intervals of 12294.5͑1.5͒ and 12180.5͑1.8͒ MHz, respectively. This measurement addresses an earlier discrepancy in measured values for these intervals. At the same time, we have measured, with a factor of 50 improved precision, the 205 Tl-203 Tl isotope shift within the 378-nm 6 P 1/2 -7S 1/2 transition.
An isomer has been detected in 171 Hf with a half-life of T 1/2 = 29.5(9) s. The state was populated in the 170 Yb(α,3n) 171m Hf reaction at a beam energy of E α = 50 MeV in an on-line ion guide isotope separator. The isomeric 171m Hf + beam was extracted from the ion guide, mass-analysed and implanted in the surface of a microchannel-plate. The half-life of the collected activity was measured from the decay of the microchannel-plate count rate. We associate the isomer with the first excited state in 171 Hf with spin 1/2 − at an excitation energy of 22(2) keV.
The first successful application of an ion-guide separator (IGISOL) for collinear laser spectroscopy of radioisotopes has achieved an efficiency comparable with the best obtained with catcher-ionizer facilities. The ion beam energy spread was determined to be less than 6 eV, allowing laser fluorescence resonance signals for the radioisotopes to be detected with high resolution and sensitivity. Applications of this technique to measuring nuclear properties of refractory elements and short lived isomers promises to be particularly advantageous.
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