Hauptkomponenten unter den Vorläufern verzögerter Neutronen bei der Spaltung von Uran-235 durch thermische Neutronen

Abstract

ZusammenfassungMit schnellen radiochemischen Trennverfahren wurden die Hauptkomponenten unter den Vorläufern verzögerter Neutronen bei der Spaltung von 235 U durch thermische Neutronen ermittelt. Bestimmt wurden die Beiträge der Brom-und Jodisotope, der gesamten Nichthalogene und einiger Nichthalogenelemente, darunter Rubidium, Cäsium und Yttrium. Ein neuer Neutronenvorläufer, 0,8-sec 140 J, wurde identifiziert und ein weiterer, l,l-eec ,8 > M Y, bestätigt. Aus den relativen Häufig-keiten der Vorläufer wurden durch Normierung über die Ausbeute der 22-sec Neutronengruppe die Neutronenausbeuten der Vorläufer beim untersuchten Spaltprozeß und, durch Vergleich mit den Spaltausbeuten, ihre Neutronenemissionswahrscheinlichkeiten abgeleitet. Die Addition der Neutronenausbeuten aller bekannten Vorläufer liefert innerhalb der einzelnen Neutronengruppen Gesamtausbeuten, die mit den Gruppenausbeuten übereinstimmen. SummaryRapid radiochemical separation methods have been used to determine the main components of the delayed-neutron precursors in fission of 2S5 U by thermal neutrons. The contributions of bromine and iodine isotopes and the total contribution of the nonhalogen elements have been determined as well as the contributions of individual nonhalogen elements like rubidium, cesium, and yttrium. A new delayed-neutron precursor, 0.8 sec 110 I, has been identified and another one, 1.1 sec 98 >"Y, has been confirmed. By normalizing relative abundances of delayed-neutron precursors via the yield of the 22-sec neutron group, the neutron yields of the precursors in the fission process studied were obtained, and their neutron emission probabilities were derived by comparing neutron yields with fission yields. Summing-up the neutron yields of all known precursors within each group results within the error limits in total yields equal to the group yields.

β-decay half-lives of neutron-rich nuclides in theA=100–110mass region

“…The half-life of 99 Y has been previously measured in fission-based experiments [28][29][30][31][32], experiments using the isotope separator on-line (ISOL) technique [27], and fragmentation-based experiments [26]. The decay curve from the present work is shown in Fig.…”

Independent Fission Yields and Neutron Emission Probabilities of Short-Lived Halogen Isotopes

“…Heavy isotopes of bromine and iodine above the 50 and 82 neutron shells have been identified as (3-delayed neutron precursors contributing significantly to the delayed neutron groups in thermal neutron induced fission of 235 U [1][2][3]. The neutron branching,/^, is defined as the fraction of /3-decays of a precursor nuclide followed by the emission of a neutron.…”

Beta-delayed-neutron studies of $^{135,136}$Sb and $^{140}$I performed with trapped ions

“…5. In the direct measurements, P n was determined either from the fission yield and neutrons-per-fission of the isotope [43][44][45][46][47][48], or by counting β particles and neutrons separately [49][50][51][52][53], usually with plastic scintillators and neutron detectors (e.g., BF 3 tubes, 3 He tubes), respectively. For each isotope, there is roughly a factor of two spread among the P n results, despite the fact that in many cases, the quoted uncertainties are significantly smaller than these differences.…”