Nuclear Charge Distributions in the Isobars 92 to 100 Resulting from Thermal Neutron Fission of Uranium-235

Abstract

The nuclear charge distribution of fission products from 235 U(w th ,/) is determined for the isobaric chains 92 to 100. The results were obtained from the energy loss of monoisobaric and monoenergetic fission products in a AE Si surface-barrier detector. The odd-even effect is found also in the mass chains reported here for the first time, revealing an approximately sinusoidal variation of the charge distribution width with mass.The fission products separated by "LOHENtheir nuclear charge; therefore, the method is in-GRIN" 1 according to mass and kinetic energy prodependent of any chemical or decay properties vide a unique means to measure the nuclear of the selected fission products. The efficiency charge distribution in fission, which is only known of this detector does not depend on the nuclear incompletely. The energy loss of these separated charge. With an 8-Lim-thick AE silicon detector fission products in a AE detector depends only on the achieved nuclear-charge resolving power Z/ TABLE I. The fractional independent fission yields and the average nuclear charge Z p for fission products of the isobaric chains 92 to 100 from 235 U(« th ,/). The yields in brackets are the FIY values (Ref. 3) Mass 92 93 94 95 96 97 98 99 35 Br 1.8±0.8 ( ) 0.7±0.5 ( o ) 36 K ' 28.7±1.5 ( ) 33.5±2.0 ( ) 15.0±2.2 ( ) 6.2±1.2 ( ) 39 Y 1.2±0.7 ( ) 2.1±0.7 (1.6±0.2) 5.9±0.8 (6.0±2.0) 14.8±1.5 (13.0±6.0) 31.6±2.5 ( ) : 50.3±2.0 ( ) 37.7+3.0 ( ) 35.5±2.5 ( • ) 40 Zr 0.9±0.7 ( .) 1.1±0.7 ( ) 0.8±0.5 ( ) 1.6±0.8 ( ) 3.5±0.8 ( ) 11.4±1.5 ( ) 43.4±3.0 ( ) 52.2±2.5 ( )41 Nb 1.1±0.8 ( ) 1.3±0.6 ( ) 3.Oil.5 ( ) 4.7±1.2 ( ) 42 Mo l.3±n. ( Z P 36.87 (36.79) 37.34 (37.41) 37.74 (37.79) 38.03 (38.03) 38.36 (38.35) 38.73 ( ) 39.33 ( ) .6 39.59 ) ( ) 100 0.9+0.5 7.9±1.2 84.6±3.0 5.7i0.9 0.9+0.5 39.98 ( ) ( ) ( ' ) ( ) ( ) ( ) 1034

Systematics study of the ZP model for the 235U + n fission

“…The discrete parameters and their errors were obtained based upon these measured data in the way mentioned above. Figure 1 was an instance of the fit of measured data, it showed on chain A = 99, the present fit yields were consistent with the measured data except those from Siegert et al (1975) [13], which were too high compared to the others. The systematics parameters ∆Z P (A ), σ(A ), F Z (A ) and F N (A ) and their errors, were reached by spline fitting the discrete parameters and resulted with reduced χ 2 s about 4, 1, 70 and 70, respectively, indicating that the fit for the ∆Z P is acceptable, for the σ is quite well, but for the F Z and F N are not satisfied, as shown in figures 2-4.…”

“…1), the present systematics yields are well consistent with the measured data except those at Z = 38 and Z = 42 from ref. [13] (1975), which were too obsolete. While the yield in ENDF/B7-FPY and JEF-3.0/FPY at Z = 42 should be updated with the newer data from ref.…”

The β-decay of98Y and the level scheme of98Zr

“…The intensity vs Bp distribution of the 1590.7 keV transition is composite and shows that some of the nuclei leading to this transition passed the separator as 9Sy and others as 9SSr. The full curve is a fit through the experimental points according to a calculation [20] which takes into consideration the fission yields [21] and half-lives of 98Sr [-18, 19] and 9sy as well as the timing conditions of the tape [11]. The good agreement shows that both the 98Sr and9Sy nuclei contribute with their full (> 90 %) fission yields to the feeding of this isomeric state.…”

“…The uncertainty includes the uncertainty of the absolute intensity of the 787.7 keV reference transition [17] as well as experimental errors. The fission yields were taken from [21], the feeding of the first excited 0~-state of 98Zr is given in [6]. The ground state feeding has also been determined from the analysis of the intensity versus Bpdistributions.…”

The influence of pairing and nuclear structure on the thermal-neutron-induced fission of235U

“…In addition, new physical methods to determine the nuclear charge of mass separated fission products have been developed [4,5]. Some results on nuclear charge distributions have been reported recently [6,7]. In Ref.…”