Fission in238U+238U collisions below the Coulomb barrier

Abstract

Integral fission cross sections in the system z3su + 238U were measured at beam energies below the interaction barrier Vc. Scattering angle dependent probabilities and integral cross sections for Coulomb fission were calculated. It is concluded that earlier observed discrepancies between measured and calculated angular distributions for the one-neutron transfer product z39U cannot be explained by sequential fission. Multi-nucleon transfer induced fission is observed down to energies (0.90 + 0.02) x V c.

Cross sections for nuclear reactions in collisions of238U+238U and238U +197Au near and below the coulomb barrier

“…Figure 2 shows that these multi-nucleon transfer products are observed down to 0.90 Vc. This is consistent with the above mentioned analysis of the fission measurements in the system 238U+ 238U, where transfer processes (followed by fission) different fiom the one-neutron transfer were claimed to set in at 0.90 Vc [16]. Damped reaction products at low energies have also been seen in lighter systems such as 58Ni+t24Sn down to 0.96 Vc [2].…”

“…The two-neutron transfer to 24~ and the exchange of one proton and one neutron to 238Np, are still quasi-elastic transfer products because their cross sections follow the semiclassical expectations, as we will show below. Further important processes in the interaction between very heavy ions include fission which has been investigated previously [16], and Coulomb excitation which is not measured with the present method. Coulomb excitation calculations show that practically all colliding nuclei are excited at the distances of closest approach where mass transfer is observed.…”

“…The occurence of more complex transfer channels below the barrier was also concluded from the analysis of the fission excitation function in the 238U-~238U system [16]. The high fission cross sections exceeding the expected cross sections for Coulomb fission for bombarding energies above 0.90 Vc were tentatively attributed to sequential fission following multi-nucleon transfer.…”

“…Coulomb fission is induced over very large distances and can therefore, like one-neutron transfer, not be taken as experimental signal for nuclear contact. At incident energies above 0.9 Vc, the cross sections for the transfer-induced fission component rises steeply [16] and indicates the opening, below the barrier, of more complex transfer channels. Due to finite fission widths the corresponding survivors should be observable.…”

“…Another important reaction channel in the system 238U+23SU is fission [16]. Experimental fission cross sections are composed of the transfer-induced sequential fission and Coulomb fission, the latter being the dominant fission component at very low energies.…”