Fission of highly excited fragments from collisions of 750 A.MeV 238U-ions on 208Pb

Fragments of relativistic 750 A.MeV U-projectiles were investigated by using the fragment separator FRS for magnetic selection of reaction products including ray-tracing and ΔE-ToF techniques. For elements between Ge and Sb, measurements of isotopic yield distributions and velocities revealed three processes: fragmentation, low-energy fission, and high-energy fission. The last of these regimes is presently reported. First and second moments of distributions of mass numbers, atomic numbers and velocities of the corresponding fragments allowed us to identify ¹⁰¹ ₄₃Tc₅₆ as the most probable fragment of a high energy symmetric fission reaction. Moreover, we could deduce a hypothetical mean fissioning fragmentation product ²⁰⁸Rn and its highly excited pre-fragmentation parent ²²⁷Ra produced in a primary abrasion reaction at an excitation energy of about 290 MeV. Received: 26 January 1998 / Revised version: 16 March 1998     

ON THE PHOTOIONIZATION ENERGY THRESHOLD OF TRYPTOPHAN IN AQUEOUS SOLUTIONS

Abstract— To investigate the existence and energy position of a photoionization threshold. tryptophan (Trp) has been photoionized in desecrated neutral aqueous or alcoholic solution under monochromatic light of variable frequency, in presence of N₂O to scavenge the photoelectron.
Present findings and some literature data converge to show the existence of a threshold for the one photon ionization process. This threshold is located at 4.5 ± 0.1 eV and 4.85 ± 0.1 cV for Trp in aqueous and ethanol solutions. respectively, which corresponds to a lowering with respect to the gas phase ionization potential of 3.4 and 3.0 eV.
The photoionization quantum yields for Trp is found about 4 times greater at 250 nm than at Λ_cx= 265 nm, where φe^-_4M=0.080±0.025. In such spectral range. at most one photoelectron out of 4–5 escaping geminate recombination would lead to Trp photodegradation in acrated solutions.
These results also point out that the neutral radical Trp. which has been previously observed for Λ_cx > 275 nm, i.e. below the ionization threshold energy—would not necessarily derive from Trp ⁺ deprotonation or cation-electron dissociative recombination. Similarly, the opening of the indole ring with formylkynurenine (FK) formation which is observed under aerobic conditions and Λ_cx >, 280 nm would not imply an electron attachment on O₂ but reactions such as Trp +³O₂ or Trp*+³O₂ or else
     

Decay studies of neutron-rich isotopes of manganese,iron, cobalt,nickel, copper and zinc

A 46 mg/cm² thick ^natW target was irradiated with an 11.5 MeV/u ⁸²Se beam. On-line massseparated samples of projectile-like neutron-rich products from multi-nucleon transfer reactions were investigated by βγ spectroscopy in the mass region A = 52–79. Decay properties of the nuclei ⁶¹Mn (0.71 s), ⁶⁴Fe (2.0 s), ⁶⁵Co (1.25 s), ⁶⁹Ni (10 s) and ^73mZn (5.8 s) were measured for the first time. For ⁶⁷Ni a decay scheme could be constructed using information from new γ-transitions. The known decay schemes of ⁶⁰Mn, ⁶³Fe, ⁶³Co and ⁶⁹Cu were extended. New half-life values of neutron-rich isotopes are compared with theoretical predictions.     

First study of the (14C, 12C) reaction: Selectivity of the reaction and the energy levels of 28Mg and 30Si

The first measurements are reported for (¹⁴C, ¹²C) two-neutron stripping reactions. Energy spectra up to an excitation energy of 12 MeV have been measured at 69 MeV for the ²⁶Mg(¹⁴C, ¹²C) and ²⁸Si(¹⁴C, ¹²C) reactions. A strong selectivity of this reaction is observed. Using this selectivity, the comparison of the spectra suggests J^π assignments for several ³⁰Si and ²⁸Mg states. The results from the other two-neutron stripping reactions, (t, p) and (¹⁸O, ¹⁶O) are compared with those of the (¹⁴C, ¹²C) reaction.     

On the neutralization luminescence in γ-irradiated pure or alkaline ices

The origin of the stimulated luminescence (SL) observed at 380 nm from γ-irradiated pure and alkaline ices at 77 K is discussed. From the observed life-time of the emission, it seems that OH^- is not responsible for the SL. Energy considerations lead also to disregard H^- as the emitting species.     

Production and identification of new neutron-rich fragments from 33 MeV/u86Kr beam in the 18≦Z≦27 region

The new nuclei⁴⁷Ar,⁵⁷Ti,^59,60V,^61,62Cr,^64,65Mn,^66,67,68Fe,^68,69,70Co haye been produced by fragmentation of a⁸⁶Kr beam and identified through time of flight andΔE×E measurements. The tentative observation of⁵⁶Ti,^57,58V,⁶⁰Cr and⁶⁵Fe by other groups is confirmed.     

Production and identification of heavy Ni isotopes: evidence for the doubly magic nucleus 28 78 Ni

We report the first observation of the doubly magic nucleus⁷⁸Ni₅₀ and the heavy isotopes⁷⁷Ni,^73,74,75Co,⁸⁰Cu. The isotopes were produced by nuclear fission in collisions of 750 A·MeV projectiles of²³⁸U on Be target nuclei. The fully-stripped fission products were separated in-flight by the fragment separator FRS and identified event-by-event by measuring the magnetic rigidity, the trajectory, the energy deposit, and the time of flight. Production cross-sections and fission yields for the new Ni-isotopes are given.The authors would like to thank K.-H. Behr, A. Brünle, K. Burkard, L. Petizon, H. J. Schött, the accelerator staff, and the GSI target laboratory for their valuable support. We acknowledge the financial support from the IN2P3-GSI contract.