Elsevier

Nuclear Physics A

Volume 247, Issue 2, 4 August 1975, Pages 359-376
Nuclear Physics A

The Pn values of the 235U(nth, f) produced precursors in the mass chains 90, 91, 93–95, 99, 134 and 137–139

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Abstract

The first results are reported on the Pn values obtained with the recoil focussing parabolatype mass separator for unslowed fission products Lohengrin installed at the Grenoble high flux reactor. The mass chains studied were 90, 91, 93, 94, 95, 99, 134, 137, 138 and 139. Both the neutron and the β activities were measured simultaneously. The technique used to measure the neutron and the β activities and the method of analyzing the experimental data are discussed in detail. The present work led to: (i) three new periods corresponding to the new isotopes of selenium (91Se, T12 = 0.27±0.05 sec), strontium (99Sr, 0.6±0.2 sec) and telurium (138Te, 1.3±0.3 sec); (ii) accurate periods of 99Y(T12 = 1.45±0.22 sec) and 134Sn (0.7±0.2 sec); (iii) four new delayed neutron precursors consisting of 91Se, 94Kr, 99Sr and 138Te; (iv) six new Pn values corresponding to the precursors 91Se (Pn = (21±10)%), 94Kr ((5.7±2.2)%), 99Sr ((3.4±2.4)%), 99Y ((1.2±0.8)%), 134Sn ((17±13)%) and 138Te ((6.3±2.1)%); (v) a precise Pn value of the precursor 137Te ((2.5±0.5)%); (vi) a redetermination of the Pn values of the precursors 90, 91Br, 93Kr, 93, 94, 95Rb and 137, 138, 139I. The results of this work are discussed and compared with the existing data. The low level sensitivity of the present detection system is determined to be Pn(m)Yq(m) ⪆ 0.4 × 10−6 n/f (where Yq(m) is the cumulative yield for the mass m and the ionic charge q).

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    This work forms a part of the Thèse de Docteur-Ingenieur of J. P. Gautheron, submitted to the University of Grenoble, 1974.

    ††

    Dápartment de Recherche Fondamentale, CEN Grenoble, France.

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