Search results for "Isotopes of uranium"
showing 10 items of 14 documents
New measurement of the 242Pu(n,γ) cross section at n_TOF
2016
The use of MOX fuel (mixed-oxide fuel made of UO2 and PuO2 ) in nuclear reactors allows substituting a large fraction of the enriched Uranium by Plutonium reprocessed from spent fuel. With the use of such new fuel composition rich in Pu, a better knowledge of the capture and fission cross sections of the Pu isotopes becomes very important. In particular, a new series of cross section evaluations have been recently carried out jointly by the European (JEFF) and United States (ENDF) nuclear data agencies. For the case of 242 Pu, the two only neutron capture time-of-flight measurements available, from 1973 and 1976, are not consistent with each other, which calls for a new time-of flight captu…
High-resolution triple-resonance autoionization of uranium isotopes
2005
Abstract The near-threshold autoionization (AI) spectrum of uranium has been investigated by triple-resonance excitation with single-mode continuous lasers. Spectra were recorded over the first ∼30 cm − 1 above the first ionization limit at a resolution of 3 × 10 − 4 cm − 1 using intermediate states with different J values (6, 7, 8) to assign AI level total angular momentum J AI = 5 to 9. Resonances with widths ranging from 8 MHz to 30 GHz were observed; the strongest ones have J AI = 9 and widths of ∼60 MHz. Hyperfine structures for 235 U and isotope shifts for 234, 235 U have been measured in the two intermediate levels and in the final AI level for the most favorable excitation path. T…
Alpha decay study of 218U; a search for the sub-shell closure at Z=92
2006
Neutron-deficient uranium isotopes were studied via α spectroscopic methods. A low-lying α-decaying isomeric state was found in 218U. The new isomeric state was assigned spin and parity I π = 8+. The isomer decays by α emission with an energy E = 10678(17) keV and with a half-life T 1/2 = (0.56 -0.14 +0.26 ) ms. The known alpha-decay properties of the ground state of 218U was measured with improved statistics. The ground-state α-decay has an energy E = 8612(9) keV and a half-life T 1/2 = (0.51 -0.10 +0.17 ) ms.
Uranium from German Nuclear Power Projects of the 1940s— A Nuclear Forensic Investigation
2015
Here we present a nuclear forensic study of uranium from German nuclear projects which used different geometries of metallic uranium fuel. Through measurement of the (230)Th/(234)U ratio, we could determine that the material had been produced in the period from 1940 to 1943. To determine the geographical origin of the uranium, the rare-earth-element content and the (87)Sr/(86)Sr ratio were measured. The results provide evidence that the uranium was mined in the Czech Republic. Trace amounts of (236)U and (239)Pu were detected at the level of their natural abundance, which indicates that the uranium fuel was not exposed to any major neutron fluence.
α decay studies of the nuclidesU218andU219
2007
Very neutron deficient uranium isotopes were produced in fusion evaporation reactions using $^{40}\mathrm{Ar}$ ions on $^{182}\mathrm{W}$ targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate them from the scattered beam and other reaction products. The activities were implanted into a position sensitive silicon detector after passing through a gas-counter system. The isotopes were identified using spatial and time correlations between the implants and the decays. Two $\ensuremath{\alpha}$-decaying states, with ${E}_{\ensuremath{\alpha}}=(8612\ifmmode\pm\else\textpm\fi{}9)$ keV and ${T}_{1/2}=(0.{51}_{\ensuremath{-}0.10}^{+0.17})$ ms for t…
Delayed-neutrons from arsenic isotopes 84As, 85As and 86As
1973
Abstract Short-lived arsenic isotopes were produced by thermal-neutron fission of 235U and isolated within 2·5 sec by volatilization of arsenic hydride. The existence of a strong delayed-neutron precursor of 2·05±0·05 sec half-life among the arsenic isotopes is confirmed and its assignment to 85As ascertained by milking of the daughter product 33 sec 85Se and 3·1 min 84Se, which is the final nucleus in the neutron decay branch of 85As. A delayed-neutron yield of 7·8 ± 1·2 neutrons/104 fissions was obtained for 85As. A new isotope, 0·9 ± 0·2 sec 86As, was detected by delayed-neutron counting and by following the decay of its most prominent γ-ray. The mass assignment was verified by milking o…
Mass mapping of a new area of neutron-deficient suburanium nuclides
2002
Abstract The masses of 64 short-lived neutron-deficient nuclides covering the element range from tungsten to uranium have been obtained for the first time. They have been evaluated by combining directly measured masses from Schottky mass spectrometry with linked experimental Q-values in α-decay chains. Based on these new mass data we have determined the one-proton and two-proton drip-lines as well as the size of the “littoral shallow” of the sea of instability. No evidence of a Thomas–Ehrman shift has been found in the region of the investigated heavy nuclides. A peculiar behavior of two-proton separation energies has been observed in the lead region. The predictive power of various mass mo…
New Short-Lived IsotopeU221and the Mass Surface NearN=126
2015
Two short-lived isotopes ^{221}U and ^{222}U were produced as evaporation residues in the fusion reaction ^{50}Ti+^{176}Yb at the gas-filled recoil separator TASCA. An α decay with an energy of E_{α}=9.31(5) MeV and half-life T_{1/2}=4.7(7) μs was attributed to ^{222}U. The new isotope ^{221}U was identified in α-decay chains starting with E_{α}=9.71(5) MeV and T_{1/2}=0.66(14) μs leading to known daughters. Synthesis and detection of these unstable heavy nuclei and their descendants were achieved thanks to a fast data readout system. The evolution of the N=126 shell closure and its influence on the stability of uranium isotopes are discussed within the framework of α-decay reduced widt…
Beta Decay of68–74Niand Level Structure of Neutron-Rich Cu Isotopes
1998
The isotopes ${}^{68--74}\mathrm{Ni}$, of interest both for nuclear physics and astrophysics, have been produced in proton-induced fission of ${}^{238}\mathrm{U}$ and ionized in a laser ion guide coupled to an on-line mass separator. Their $\ensuremath{\beta}$ decay was studied by means of $\ensuremath{\beta}$- $\ensuremath{\gamma}$ and $\ensuremath{\gamma}$- $\ensuremath{\gamma}$ spectroscopy. Half-lives have been determined and production cross sections extracted. A partial level scheme is presented for ${}^{73}\mathrm{Cu}$ and additional levels for ${}^{71}\mathrm{Cu}$, providing evidence for a sharply lowered position of the $\ensuremath{\pi}{1f}_{5/2}$ orbital as occupancy of the $\ens…
Production of neutron-rich isotopes in fission of uranium induced by neutrons of 20 MeV average energy
2000
In the context of a parameter study conducted by several laboratories for future European radioactive beam facilities based on fast-neutron induced fission, in particular for the SPIRAL-II project at GANIL, we have measured the yields of neutron-rich isotopes in the mass range of 88 to 144. These nuclei were obtained as fission products of natural uranium bombarded by neutrons of 20 MeV average energy emitted by a thick carbon target irradiated by 50 MeV deuterons. Yields have been measured using on-line mass separation with the ion-guide method. Compared with proton-induced fission at 25 MeV the magnitude of cross-sections, except for the symmetric region, is similar. Z-distributions of is…