[en] The decay data (T/sub 1/2/, Q/sub β/, < E/sub β/> and < E/sub γ/>) for fission-product nuclides are reviewed, with emphasis on those nuclides important for decay-heat calculations in the region from ∼10 sec to ∼10³ sec. Problems involved in deducing < E/sub β/> and < E/sub γ/> values for these, and hence for even more neutron-rich, nuclides are illustrated by the example of ⁸⁷Br

[en] The checking of fuel cladding integrity and uranium contamination level was performed using delayed neutron cladding rupture detection system (DRG). This checking is important for the start up procedure of the reactor. The technique of DRG depends on monitoring the delayed neutron emitters such as Br-87 (t_1/2=54.5 sec) and l-137 (t_1/2=24 sec) in the coolant of the reactor. As a requirement for the start up two tests for checking fuel cladding integrity were performed. A comparison between the obtained data and the recommended data by the vendor are tabulated. Additional data were obtained at higher power. Accordingly, it can be concluded that the activities detected were due to the uranium contamination of cladding surfaces. Results confirmed that no rupture existed on the claddings

[en] An overview is given of our activities related to the study of the beta decay of neutron rich nuclei relevant for nuclear applications. Recent results of the study of the beta decay of "8"7","8"8Br using a new segmented total absorption spectrometer are presented. The measurements were performed at the IGISOL facility using trap-assisted total absorption spectroscopy

[en] Some of the problems that arise in the evaluation of decay-schemes data to obtain values for the intensities of beta transitions are discussed. As examples of these problems, the decay schemes of ⁸⁷Br and ²³³Pa are examined. No specific solutions to these problems are offered; but by pointing out to the participants in the International Nuclear Structure and Decay Data Evaluation Network, and to others, it is hoped that a general understanding of them can be gained, which may ultimately lead to a consistent means of dealing with them. 14 refs., 2 figs

[en] Full text: Very neutron-rich nuclei can emit neutrons after β^--decay when their reaction Q-value is larger than the (one/two/three) neutron separation energy. This decay mode is called -delayed (one/two/three)-neutron emission and was discovered in 1939 by Roberts et al. [1], shortly after the discoveries of fission by Meitner, Hahn, and Strassmann in 1938, and the neutron by Chadwick in 1932. Delayed in this context means, that the neutron is emitted with the -decay half-life of the precursor ^AZ, ranging from few milliseconds for the most neutron-rich isotopes up to 55.65 s for the (up to now) longest-lived βn-precursor ⁸⁷Br. These delayed neutrons have to be distinguished from the prompt neutrons evaporated immediately (in the order of 10^-14 s) after a fission event from a neutron-rich nucleus. βn measurements are commonly carried out since many decades, especially for fission fragments. With present and future nuclear physics facilities more and more neutron-rich isotopes outside the fission region become accessible which can also emit multiple neutrons. This exotic decay mode is of special interest for the astrophysical rapid neutron capture process (r process) since it leads to a deviation of the reaction flow to lower mass chains during the freeze-out phase. The exact knowledge of the beta-delayed neutron emission probability (P_n) is required to interpret the observed solar abundance peaks and draw conclusions from this about the participating r-process progenitor isotopes and their contributions. The BELEN (BEta-deLayEd Neutron) detector with its state-of-the-art digital electronics is one of the most powerful setups for the measurement of β-delayed neutrons in the world. Its present version consists of 48 ³He-filled long counters and achieves - depending on the design - a neutron detection efficiency of up to 60%. This high efficiency is necessary for the detection of very neutron-rich n-emitters as well as for the detection of multiple neutronemitters via nn coincidences. Its flexible design allows measurements at both, ISOL labs and in-flight fragmentation facilities. It was successfully used for measurements of fission fragments at JYFL in Jyvaeskylae, Finland and for r-process isotopes at N=82 and N>126 at the FRS at GSI Darmstadt. Presently BELEN is upgraded towards its 96 counters-version for the FAIRDESPEC campaign in a few year. Until then, measurements with an intermediate version are being performed in various labs.

[en] The product of cumulative yield and probability of neutron emission is used to assess the relative importance of known delayed neutron precursors. Thirteen precursors are consistently dominant. Nonlinear fits to experimental delayed neutron decay data distinguish the decay constants of the three longest-lived dominant precursors: Br-87, I- 137, and Br-88. Sensitivity calculations based on a six-to-seven group transformation lead to a proposed seven-group formulation in which the group decay constants are those of dominant precursors: Br-87, I-137, Br-88, Rb-93, I-139, Br-91, and Rb-96. An alternative six-group formulation is obtained by using the mean of the I-137 and Br-88 decay constants for group 2. Reactivity worth and transient analyses confirm that the positive reactivity scale is preserved the transformation. A known bias in the negative reactivity scale is eliminated by forcing the half-life of the longest-lived group to be the 55.9 s half-life of Br-87. The proposed use of dominant precursor decay constants offers significant simplifications in data analysis and the analysis of fast, epithermal, and thermal reactors with multiple fissioning nuclides. (author)

[en] An automatic detection and measuring system for delayed neutron-emitting fission products in nuclear reactor coolant water during reactor operation that is described is designed for the specific determination of ⁸⁷Br and ¹³⁷I without interference. Interference from the 4.14s half-life ¹⁷N and other delayed neutron-emitting fission products is eliminated by sampling at such a flow rate that a 1 to 2 min time delay occurs between the time the coolant water leaves the reactor and passes the sensitive area of the BF₃ proportional counters. The method cannot be used to distinguish between the two isotopes

[en] Published in summary form only

[en] Some of the problems which arise in the evaluation of decay-schemes data to obtain values for the intensities of β transitions are discussed. As examples of these problems, the decay schemes of ⁸⁷Br and ²³³Pa are examined. No specific solutions to these problems are offered; but by pointing them out to the participants in the International Nuclear Structure and Decay Data Evaluation Network, it is hoped that a general understanding of them can be gained, which may ultimately lead to a consistent means of dealing with them. 14 refs., 2 figs., 1 tab

[en] By carrying out a detailed study of ⁸⁷Kr levels, we have shown that delayed neutron spectroscopy can be a viable method for studying individual levels and that a broad resonance-like structure is present in the β-strength distribution. 12 refs., 1 fig