Delayed-neutron emission probabilities of separated isotopes of Br, Rb, I, and Cs

Abstract

Delayed-neutron emission probabilities (P") were measured for 16 isotopes of Br, Rb, I, and Cs. Sources of chemically and mass separated nuclides were obtained from an on-line mass spectrometer facility. Neutrons were counted in a multitube polyethylene-moderated detector. The total number of precursor atoms was determined by direct counting of ions deposited on the first dynode of an electron multiplier. The P"values from this work generally agree with earlier measurements for the longer-lived precursors but are consistently higher for the shorter-lived precursors. A log-log plot of P"versus the reduced energy window (Q& -B")l(Q& -C) gives a straight line with a slope of 6.0~1.4 in agreement with simplified theoretical predictions. Half-lives of Rb and Cs nuclides measured by neutron decay curves are given. P", T&~2, on-line mass separation, polyethylene-moderated neutron counter.

Half-lives andP n values of delayed-neutron precursors in the mass chains 85?87, 92, 135, 136 and 145

“…Its P,-value was determined via method 3 using a fractional independent fission yield of y)4s =0.0226 +0.003 [21,22,25]. Our value of (12.5 _+3.0) ~o is in agreement with those given by Roeckl et al [17] and Ristori et al [18], but it is nearly a factor of two lower than that recently presented by Reeder et al [8].…”

“…The result of this fit is in agreement with previous applications of the same systematics using all fission product precursors [23] or certain isotope sequences [13,17]. In a very recent publication [8], a log-log plot of 16 experimental P,-values of halogen and alkaline precursors is given with a slope of 6 as expected from Equation (2). However, applying our computer programm [36] to these data, a slope of m=4.1 _+0.2 was obtained which is in better agreement with previous results.…”

“…Neutron emission probabilities given in literature (Table 2) have been obtained with quite different experimental methods: simultaneous neutron-and flcounting using 27c [17] or 4n [1,18] geometry for the latter, simultaneous detection of neutrons and ions [8], or determination of absolute neutron and fission yields [7,15]. Besides those completely experimental values, calculated values are also given using measured neutron abundances and estimated fission yields [I0, 11,13,20] obtained from different yield systematics.…”

Half-lives and delayed neutron emission probabilities of short-lived Rb and Cs precursors

“…After a small delay to remove the tape and carry away the remaining /?-activity, the cycling was repeated until adequate satistics had been obtained. With this method corrections for buildup of long-lived activities [12,13] are circumvented. By simultaneously counting neutron-and /?-activity, the neutron emission probability P, can directly be determined from the ratio of the two absolute intensities.…”

Measurement of {sup 235}U content and flow of UF{sub 6} using delayed neutrons or gamma rays following induced fission

“…The neutron detector array (Reeder et al 1977) consists of 42 3He tubes (4 atm., 2.5 cm diameter, 36 cm length) embedded in polyethylene around the pipe. The individual tubes are parallel to the pipe and arranged in concentric circles in holes in the polyethylene.…”