C.K. Gelbke

A time-of-flight spectrometer for heavy ions

Abstract A time-of-flight spectrometer for the identification of complex nuclei produced by nuclear reactions with heavy ions has been constructed. The transmission detector consists of a thin scintillator foil; the stop signal and the energy information are derived from a surface barrier detector. A time resolution of better than 0.3 ns has been obtained. The system is able to separate masses up to A = 40 at energies below 3 MeV/amu.

ΔE-E telescope for the identification of heavy ions at low energies with good energy resolution and optimum ΔE resolution

Abstract A ΔE - E telescope for the identification of heavy ions at low energies is described. The energy loss is measured with an ionisation chamber and the residual energy of the particles is measured with a solid-state detector. The energy resolution of the telescope is comparable to the one which is obtained with solid-state detector telescopes. The ΔE resolution is limited by the energy-loss straggling of the particles in the gas and is, therefore, close to the best resolution which can be obtained with this technique. The identification of several heavy ions at low energies is discussed.

Fission characteristics of the composite system 32S + 50Ti: (II). Energy and angular dependence

Abstract Angular distributions, mass distributions and excitation functions have been measured for the heavy fragments 35 ≦ A ≦ 60 produced in the bombardment of 50 Ti by 32 S at beam energies between 121 and 166 MeV. The angular distributions are of the form ( sinθ ) −1 for all masses, although slight deviations do occur. The mass distributions exhibit a striking energy dependence with a strong trend towards symmetric mass divisions at high energies. The excitation functions agree qualitatively with the predictions of the rotating liquid drop model.

Complete identification of heavy ions by means of a time-of-flight spectrometer with ΔE ionization chamber

Abstract A time-of-flight spectrometer with ΔE ionization chamber at the end of the flight path permits complete separation of different elements and isotopes in the region of A ≈ 16 down to energies of 1 MeV/amu.

Nuclide distributions in deep inelastic reactions

Abstract The mass and charge of fragments produced in deep inelastic reactions induced by 236 MeV 40 Ar on targets of 42, 48 Ca, 50 Ti. 50 Cr, 56 Fe and 60 Ni were identified by using a time-of-flight ΔE - E detector telescope. The measured nuclide distributions are very broad along the mass asymmetry coordinate, but narrow along the charge asymmetry coordinate. A detailed description of the variations of the mass and charge distributions as a function of target neutron excess is obtained by calculating primary distributions assuming a diffusion-like mass transfer in a two-dimensional potential energy surface determined by liquid drop energies of two touching spheres and folding this primary distribution with the secondary particle decay pattern calculated in the statistical model. Exotic nuclei are produced with comparatively large cross sections.

Response of NE 111 scintillator foil to transient 16O ions

The response of a thin NE 111 scintillator foil to transient 16O ions of energies between 15 and 60 MeV has been measured.

A sliding seal scattering chamber for time-of-flight coincidence experiments

Abstract A sliding seal scattering chamber is described which is especially designed for coincidence experiments between a time-of-flight telescope and a large solid angle particle or γ-ray detector. Using differentially pumped gaskets, a vacuum of 5×10 −7 torr is obtained.

Unexpected interference patterns observed in the 12C(14N, 13N)13C reaction at energies close to the Coulomb barrier

Abstract The reaction 12 C( 14 N, 13 N) 13 C has been measured at 28, 32, 34 and 36 MeV beam energies. The energy dependence of the measured interference pattern cannot be reproduced by DWBA calculations which take account of the interference between proton and neutron transfer. A rather strong asymmetry of the angular distributions about θ c.m. = 90° has been observed.

Core exchange symmetries in heavy ion reactions

The general symmetry properties of theT-matrix due to the exchange of identical cores in nuclear reactions between composite particles are given. For the case of direct transfer reactions an explicit expression for the cross section is derived in the distorted wave Born approximation. In this model the cross section is the coherent sum of two indistinguishable transfer processes. The relative phase between the corresponding transfer amplitudes is obtained from the Pauli principle and depends on the signs of the spectroscopic amplitudes which may, therefore, be determined experimentally.