A rotating target wheel with thin targets for heavy ion beams of high current densities

The production of fermium isotopes was attempted by complete fusion of different targets and projectiles spanning a wide range of effective entrance channel fissilities below and above the predicted threshold value Xef fthr~(l'/-v... For the most asymmetric systems where fusion is expected to occur without dynamical hindrance we investigate to what extent the expected amount of sub-barrier fusion contributes to the production of fermium evaporation residues. For increasingly symmetric systems the experimental fusion barriers are found to exceed the fusion barriers predicted by the proximity formalism. The barrier heights are discussed in the framework of both the extra-push model and the surface friction model.

Section: Methodsmentioning

confidence: 99%

Probing sub-barrier fusion and extra-push by measuring fermium evaporation residues in different heavy ion reactions

G�ggeler¹,

Sikkeland²,

Wirth³

et al. 1984

“…The thicknesses of the 2~ targets were (470-530) gg/cm 2. The melting point of Bi is 544 K. To withstand the high beam currents, the targets were covered with (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) ~tg/cm 2 carbon films for radiative cooling and mounted on a rotating wheel [11]. The wheel that supported 9 targets was synchronized with the UNILAC beam pulsing, which has a repetition rate of 50 cps and a duty factor of 25 %.…”

Section: Methodsmentioning

confidence: 99%

Evidence for element 109 from one correlated decay sequence following the fusion of58Fe with209Bi

Münzenberg¹,

Reisdorf²,

Hofmann³

et al. 1984

Self Cite

An experiment to synthesize element 109 is presented. Decay patterns characteristic of complete fusion products were searched for in an irradiation of 2~ targets with SaFe projectiles at specific incident energies of 4.95, 5.05, and 5.15 MeV/u. A total dose of 7 X 1017 particles was obtained. The experimental method involves in-flight separation of forward peaked reaction products with a static-field velocity filter, their passage through a time-of-flight device and their final implantation into position sensitive solid state detectors to measure their kinetic energy, approximate mass and their time and position of incidence. The subsequent decay of the narrowly localised reaction products by cascades of alpha particles and/or spontaneous fission is also registered in terms of the energies and times of all the emitted particles. One outstanding decay sequence that started with the emission of two alpha particles within subsequent time intervals of 5 ms and 22 ms and ended with spontaneous fission after 13 s was found at 5.15 MeV/u. The first alpha particle had a kinetic energy of (11.10_+0.04) MeV. A detailed analysis of all the alternative interpretations of this observation, such as a purely random correlation of signals, the decay of a product from a transfer reaction or of any of the various energetically possible evaporation residues, shows that the isotope with mass 266 of element 109, i.e. the one neutron evaporation channel after complete fusion, is the statistically most significant assignment. The outlook for new element synthesis is also briefly discussed.

“…The current has been measured by a Faraday cup. To withstand high beam intensities, the targets are covered with carbon films of 0.03mg/cm 2 to improve radiative cooling [6] and are mounted on a rotating target wheel [7]. The UNILAC beam provides a macro-pulse structure with beam bursts of 5 ms duration followed by intervals of 15 ms.…”

Section: Methodsmentioning

confidence: 99%

“…The halflive evaluated by the maximum likelihood method ( +_1.7) is 2.9 1.2 s. Four decays were observed at (7,889 _+25)keV, two of them correlated as daughter decays with times distances of 6s and 17s, respectively. The daughter decays fit to 243Es, which has a decay energy of (7,890_+ 20) keV and an average lifetime of 30s [19].…”

Section: Irradiation Of 2~mentioning

confidence: 99%

The new isotopes247Md,243Fm,239Cf, and investigation of the evaporation residues from fusion of206Pb,208Pb, and209Bi with40Ar

Münzenberg¹,

Hofmann²,

Faust³

et al. 1981

Self Cite

The evaporation residues produced in heavy ion fusion reactions between 4~ and z~ Z~ and 2~ respectively, were investigated. They were separated in-flight using a velocity filter (SHIP) and identified after implantation into an array of position sensitive surface barrier detectors by measuring their decay characteristics.Three new e-emitting isotopes were found: 247Md, 243Fm, and 239Cf. Z~TMd was identified by correlation to its known daughter decay 243Es, and 243Fm and 239Cf were observed as correlated decays. Moreover, all previously known deexcitation channels, characterized by spontaneous fission or by ~ decay, could be observed for the first time in one experimental setup. Our results for formation cross sections and decay characteristics are in agreement with known data.