J. C. S. Bacelar

Optimal radio window for the detection of Ultra-High Energy cosmic rays and neutrinos off the moon

Abstract When high-energy cosmic rays impinge on a dense dielectric medium, radio waves are produced through the Askaryan effect. We show that at wavelengths comparable to the length of the shower produced by an Ultra-High Energy cosmic ray or neutrino, radio signals are an extremely efficient way to detect these particles. Through an example it is shown that this new approach offers, for the first time, the realistic possibility of measuring UHE neutrino fluxes below the Waxman–Bahcall limit. It is shown that in only one month of observing with the upcoming LOFAR radio telescope, cosmic-ray events can be measured beyond the GZK-limit, at a sensitivity level of two orders of magnitude below the extrapolated values.

A small-angle large-acceptance detection system for hadrons

Abstract The performance of a segmented large-acceptance detector, capable of measuring particles at small forward angles, is presented. The Small-Angle Large-Acceptance Detector (SALAD), was built to handle very high rates of particles impinging on the detector. Particles down to a few MeV can be detected with it. The position of charged particles is measured by two Multi-Wire Proportional Chambers while scintillator blocks are used to measure the energy of the detected particle. A stack of thin scintillators placed behind the energy detectors allows for a hardware rejection (veto) of high-energy particles going through the scintillator blocks.

Collective and quasiparticle excitations in 180Pt

Abstract The 144Nd(40Ar, 4n)180Pt reaction has been used to study collective and quasiparticle excitations by means of several γ and electron spectroscopic measurements. Four bands are observed in addition to the ground-state, β-, γ- and S-bands up to a maximum spin of 26+. A sharp bandcrossing is observed at k = 0.33 MeV of the g.s.b. in 180Pt with the S-band. The crossing is discussed in terms of possible v i 13 2 and π h 9 2 alignments. The observed 02+ state at Ex = 478keV can be interpreted as the head of a β-band in the rotation-vibration model, or as a somewhat oblately deformed band head.

Observation of strongly deformed shapes in 154-152Dy nuclei at medium temperatures☆

The gamma-decay of the giant dipole resonance (GDR) built on excited states of 154-152Dy nuclei is studied. The selection of GDR decay from high spin states leading to specific exit channels was made possible by triggering on high spin isomers. The deduced energy splitting of the GDR implies large deformations (\beta\ congruent-to 0.4-0.5). The resonance widths of the components are comparable to those of the GDR built on the ground state indicating small shape fluctuations.

High-spin states in 148Eu

Abstract High-spin states in the odd-odd nucleus 148 Eu, populated by a carbon-13 induced reaction on a lanthanum target, were investigated with several different tools of in-beam nuclear spectroscopy. The low-energy levels show collective excitations, interpreted as 3 − octupole-phonon couplings to multi-particle-hole states. A probable two-octupole-phonon state is identified. Otherwise most 148 Eu high-spin levels are interpreted in terms of fully aligned multi-particle-hole states rather well described both by a semi-empirical shell model and a deformed independent-particle model.

The angular-momentum dependence of the giant dipole resonance in 154Dy∗

Abstract The statistical γ-ray decay of the compound nucleus 154 Dy ∗ formed at an excitation energy of 69 MeV is studied in three angular-momentum windows 〈 J 〉 = 31,42 and 50ℏ. The GDR strength function extracted from the data indicates a constant centroid energy for the resonance E GDR = 15.2 ± 0.5 MeV, a small deformation of the nuclear shape for all spin regions and an increase in the resonance width with increasing angular momentum. The latter might indicate larger shape fluctuations at higher angular momenta. A systematical study of the dependence of the extracted strength function with different methods of analysis is presented, and their discrepancies discussed.

A fast programmable multiplicity trigger system

Abstract A fast, programmable trigger module has been designed and built. It consists of commercially available components mounted on two multilayer boards and resides in a CAMAC environment. The module has been designed to provide a first-level trigger primarily for the detection of proton pairs from proton–proton bremsstrahlung measurements. The design considerations and the performance of the module are discussed.

Dynamical effects in proton–proton bremsstrahlung for non-coplanar geometries

Abstract The proton–proton bremsstrahlung process, including both coplanar and non-coplanar kinematics, has been measured with polarized protons of 190 MeV. High-precision cross sections and analyzing powers have been obtained. Cross sections as a function of non-coplanarity angle are presented and show large variations of dynamical origin. Non-coplanar analyzing powers have been measured for the first time and are compared to theoretical predictions.

Cross sections and electromagnetic response functions for radiative proton capture in

Abstract Exclusive differential cross sections of virtual-photon radiative proton capture in pd→ 3 He +e + e − at a proton energy of 190 MeV have been measured for the first time. The leptonic-angle dependence of the measured cross section is exploited in order to determine the electromagnetic response functions in the time-like region. The data are compared to a relativistic gauge-invariant impulse approximation and a Faddeev calculation. Differences between theoretical predictions and data are discussed in terms of enhanced magnetic radiation possibly originating from virtual Δ excitations.

VISCOSITY, FISSION TIME SCALE AND DEFORMATION OF 156DY

In the fusion-fission reaction Ar-40 + Cd-116 --> Dy-156*, fission, at E-b = 216 MeV and 238 MeV, gamma-rays were measured in coincidence with fission fragments. The interpretation of the gamma-ray spectra is done with the help of a modified version of the statistical-model code CASCADE. The spectra can be reproduced with nuclear viscosities in the range 0.01 <gamma <4. The extracted fission time scale is of the order of 10(-19) s. The CASCADE analysis seems to favor a prolate deformation with beta approximate to 0.45