S.M. Polikanov

Excitation energy of spontaneously fissioning isomer 242mAm

Abstract The excitation function for the reaction 243 Am(n, 2n) 242 Am leading to the formation of a spontaneously fissioning isomer has been studied. The mono-energetic 8–14.4 MeV. neutrons were obtaained from the reaction D(d, n) 3 He using a gaseous deuterium target. The excitation function has a distinct threshold character. The neutron energy corresponding to the reaction threshold is found to be 9.2±0.3 MeV in the c.m. system. The difference between this value and the threshold of the reaction leading to the ground state, equal to 2.9±0.4 MeV, is considered as the excitation energy of the spontaneously fissioning state of 242 Am.

Fission of 232Th, 238U and 235U induced by negative muons

Abstract The absolute yields of prompt and delayed fission induced by negative muons in 232 Th, 238 U and 235 U have been measured. The delayed fission yields are much lower than could be predicted from Γ n / Γ f systematics for 15–20 MeV nuclear excitation. The systematics of prompt fission yields are compared with recently obtained photofission data. It is suggested that prompt fission can be used for investigating the channel structure of the fission barrier.

A study of the spontaneously-fissioning isomer of 242Am through the 241Am(n,γ) reaction

Abstract The excitation function for the 241 Am(n,γ) 242m Am reaction leading to the excitation of the 14 ms, spontaneously fissioning isomer has been studied in the range 0–6.5 MeV. The experimental results can be well explained taking into account the hypothesis of Strutinsky concerning the “shape isomerism”.

On the nuclear properties of the isotopes 256103 and 257103

Abstract The isotopes 256 103 and 257 103 were synthesized by bombarding 243 Am with 18 O ions. The assignment was based on the excitation functions of the reactions 243 Am( 18 O, 5n) 256 103 and 243 Am( 18 O, 4n) 257 103. The isotope 256 103 has a complicated alpha spectrum in the range 8.35 ≦ E α ≦ 8.60 MeV. An intense group of alpha particles has E α = 8.42 MeV. The measured half-life for 256 103 is about 35 sec. The obtained experimental data permit as to conclude that 257 103 has T 1 2 ≈ 35 sec and 8.5 ≦ E α ≦ 8.6 MeV . The experiments were performed on the external beam of the 310 cm cyclotron of the Laboratory of Nuclear Reactions, JINR.

Muon induced fission of 237Np, 239Pu and 242Pu

Abstract The absolute yields for prompt and delayed fission induced by negative muons in 237 Np, 239 Pu and 242 Pu have been measured and compared with photofission data.

Population of the spontaneously fissioning isomer 244mfAm through the (n, γ) reaction

Abstract The excitation function of the 0.6 ms spontaneously fissioning isomer 244mf Am obtained in the reaction 243 Am(n,γ) 244mf Am was measured in the neutron energy range 0.3–4 MeV and compared to the results obtained for the spontaneously fissioning isomer 242mf Am.

The muon capture rate in 232Th and 238U studied in the fission mode

Abstract The muon lifetime has been measured in the fission mode for muons captured in natural thorium and uranium. The results obtained are the following: τ μ ( 232 Th )= 77.3 ± 0.3 ns and τ μ ( 238 U )=(77.1 ± 0.2) ns . The results agree within the errors with values previously reported for the fission mode.

The formation of a spontaneously fissioning isomer in the capture of neutrons by Am

Abstract The formation of a spontaneously fissioning isomer (T 1 2 = 13.1±0.1 msec ) was observed during the irradiation of Am243 with 14 MeV neutrons. The cross-section for the Am243 (n, 2n) Am242 reaction is about 0.15 mb. The results of this work together with the data previously obtained lead to the conclusion that an isotope of Am242 in an isomeric state undergoes spontaneous fission.

Fission of muonic 232Th and 238U

Abstract Muon-induced prompt fission of 232 Th and 238 U, interpreted usually as being caused by muonic radiationless transitions, was observed in delayed coincidence with the decay electrons from muons bound to fission fragments. The measured lifetime indicates that the muon is captured preferentially by the heavy fragments. Muon conversion from highly excited fission fragments was also observed.

Negative pion capture in mercury, gold and platinum nuclei

Abstract The results of the irradiation of natural mercury, gold and platinum targets with stopped negative pions are reported. The product nuclei distributions indicate that the (π−, xn) reaction dominates over reactions with charged particle emission. The neutron multiplicity after pion capture can be as large as x = 16. Furthermore, the preferential population of high-spin isomeric states is observed. The extracted isomeric ratios are compared with those from other reactions.