MONSTER: a TOF Spectrometer for β-delayed Neutron Spectroscopy

Development of a Reference Database for Beta-Delayed Neutron Emission

“…This is true for all fissioning system and all energies, suggesting that the long-lived precursors, such as 87 Br and 91 Rb, are well identified and their data are well known. The CRP+ENDF/B-VIII.0 database gives a slightly smaller a 1 than ENDF/B-VIII.0, because the P n of 91 Rb has been set to zero. The reason is that its Q βn happens to be very small and experimental values are still preliminary (see Table XXIII).…”

“…The fifth abundance which includes precursors 94 Rb, 139 I, 85 As and 98m Y, is systematically overestimated with the exception of some isolated cases ( 238 U f and 232 Th f ). On the other hand, the seventh abundance, which involves 91 Br and 95 Rb, is systematically underestimated, with the exception of 236 U f and 237 Np f . The sixth and eight abundances do not follow any specific pattern.…”

“…The difference between the CRP contribution and JEFF-3.1.1 is considerably larger (over 100%) due to the relatively lower value of P n = 22(3)% adopted in JEFF-3.1.1 [30]. 91 Br is among the top 20 contributors in the CRP list with P n = 29.8(8)%, which is similar to the JEFF-3.1.1 value P n = 20(2)% taken from [30] and JENDL/DDF-2015 P n = 20(3) taken from ENSDF. In ENDF/B-VIII.0, however, this precursor does not have a delayed-neutron decay branch, therefore it does not contribute to the delayed neutron activity.…”

“…The currently operational TOF arrays for decay studies are VANDLE [87,88] (used at various facilities in the USA, at CERN, and at RIKEN), DESCANT [89,90] at TRIUMF/ISAC in Vancouver (Canada), and MON-STER which has been built for FAIR and already used at ISOLDE and at the IGISOL facility in Jyväskyä [91].…”

“…The fact that, when considering all the precursors, such a difference decreases to +6.4×10 −4 , means that there is a compensation due to the underestimation of less important precursors in the CRP P n tables with respect to the ENDF/B-VIII.0 decay library. From a comparison of the individual isotopes, it appears that the largest ∆ν d,i belongs to 137 I and 91 Br. The latter precursor in particular, has P n = 0 in ENDF/B-VIII.0, whereas in the previous version ENDF/B-VII.1 [24] it had a non-zero P n value.…”