The probability of prompt and delayed fission of muonic237Np

Abstract

Fission fragments from the reaction 237Np(p ,y f) have been measured in coincidence with muonic X-rays. The efficiency of the fission fragment detector is determined from (p , 7f)-data of the same experiment. The total fission probability per p-stop Pt has been measured as well as the fission probabilities Pf of the non-radiative muonic (3d~ ls)-and (2p~ls)-transitions; the latter has been divided into two parts leading to different mean excitation energies E: Pt=(54_+17)%, Pf(3d--*ls)=(41__21)%, Pf(2p--~ls, E= 6.218 MeV) = (61 _+ 19)%, andPf(2p~ls, E = 6.525 MeV) = (57 _+ 18)%. The influence of the muon on the fission barrier is discussed. The fission probability after muon capture is compared with a calculated value using a distribution of nuclear excitation energies following muon capture and the fission probability as measured in a a38U (3He, ~f)-reaction.

The study of prompt and delayed muon induced fission

“…The amount of prompt events is given by the difference between this integral and the sum of events with t < r 0. [19] a, [20] [191" [8] a The result is depending on the data evaluation procedure applied a The error is essentially due to the error given in Table 5a. The results obtained by this procedure are confirmed by the conventional way of fitting, but the errors are smaller.…”

“…From the fission probabilities determined relative to each other for the series of isotopes 233U, 234U, 235U, 236[J, 238U, 237Np ' 242pu ' and 24apu, the probabilities of prompt (Pfp) and delayed (Pfd) fission per muon stop have been deduced by using the value of the total fission probability (Pf~) of 237Np published in [8]. The present analysis has been performed with the aim of obtaining more reliable and more accurate data.…”

“…The emission of one nucleon with an energy of about 80 MeV occurs in this process with a high probability [24]. Absolute values of the fission probabilities per deduced from the value for 237Np [8] excitation energy. Absolute values of the fission probabilities per deduced from the value for 237Np [8] excitation energy.…”

“…Because the data analysis is very sensitive to the target thickness, this effect might reflect the uncertainty of the specified target thicknesses and indicate a possible systematical error of 10%-20%. In contrast to (p-, f)-measurements, (71-, yf)coincidence experiments offer the possibility of a direct determination of the fission fragment detection efficiency by regarding the muonic transitions (6~5) or (5~4) as a signal for a muon stop [8,11]. Table4b contains the results of this measurement.…”

Delayed muon induced fission of209Bi and the role of meson-exchange currents

“…The pion contamination of the beam was less than 10 -4. The set-up, similar to previous experiments [27][28][29], is sketched in Fig. 2.…”