Olaf Scholten

Interacting boson model of collective nuclear states III. The transition from SU(5) to SU(3)

Abstract We study the transition from the vibrational, SU(5), to the rotational, SU(3), limit of the interacting boson model. We show how this model can be used to calculate energies, electromagnetic transitions, multipole moments, nuclear radii, and two-nucleon transfer intensities in transitional nuclei.

Collective quadrupole states of Xe, Ba and Ce in the interacting boson model

Abstract We present the results of a calculation of the collective quadrupole states of the Xe, Ba and Ce isotopes within the framework of the proton-neutron interacting boson model.

A macroscopic description of coherent geo-magnetic radiation from cosmic-ray air showers

Abstract We have developed a macroscopic description of coherent electromagnetic radiation from air showers initiated by ultra-high-energy cosmic rays due to the presence of the geo-magnetic field. This description offers a simple and direct insight in the relation between the properties of the air shower and the time structure of the radio pulse.

On shapes and shape phase transitions in the interacting boson model

Abstract The algorithm developed by Gilmore and Feng for the construction of classical limits of quantum operators belonging to a compact Lie algebra is applied to the SU(6) hamiltonian of the interacting boson model for the description of collective nuclear properties. It is shown that the three limiting cases (dynamical symmetries) that appear in the IBA model correspond to different shape phases. The study of the shape phase transitions between the extreme cases shows that the nature of the phase transition is different for each of the three transitional regions.

Polarized radio emission from extensive air showers measured with LOFAR

We present LOFAR measurements of radio emission from extensive air showers. We find that this emission is strongly polarized, with a median degree of polarization of nearly 99%, and that the angle between the polarization direction of the electric field and the Lorentz force acting on the particles, depends on the observer location in the shower plane. This can be understood as a superposition of the radially polarized charge-excess emission mechanism, first proposed by Askaryan and the geomagnetic emission mechanism proposed by Kahn and Lerche. We calculate the relative strengths of both contributions, as quantified by the charge-excess fraction, for 163 individual air showers. We find that the measured charge-excess fraction is higher for air showers arriving from closer to the zenith. Furthermore, the measured charge-excess fraction also increases with increasing observer distance from the air shower symmetry axis. The measured values range from (3.3± 1.0)% for very inclined air showers at 25 m to (20.3± 1.3)% for almost vertical showers at 225 m. Both dependencies are in qualitative agreement with theoretical predictions.

Method for high precision reconstruction of air shower Xmax using two-dimensional radio intensity profiles

The mass composition of cosmic rays contains important clues about their origin. Accurate measurements are needed to resolve longstanding issues such as the transition from Galactic to extra-Galact ...

Macroscopic treatment of radio emission from cosmic ray air showers based on shower simulations

Abstract We present a macroscopic calculation of coherent electro-magnetic radiation from air showers initiated by ultra-high energy cosmic rays, based on currents obtained from Monte Carlo simulations of air showers in a realistic geo-magnetic field. We can clearly relate the time signal to the time dependence of the currents. We find that the most important contribution to the pulse is related to the time variation of the currents. For showers forming a sufficiently large angle with the magnetic field, the contribution due to the currents induced by the geo-magnetic field is dominant, but neither the charge excess nor the dipole contribution can be neglected. We find a characteristic bipolar signal. In our calculations, we take into account a realistic index of refraction, whose importance depends on the impact parameter and the inclination. Also very important is the role of the positive ions.

A realistic treatment of geomagnetic Cherenkov radiation from cosmic ray air showers

We present a macroscopic calculation of coherent electro-magnetic radiation from air showers initiated by ultra-high energy cosmic rays, based on currents obtained from three-dimensional Monte Carlo simulations of air showers in a realistic geo-magnetic field. We discuss the importance of a correct treatment of the index of refraction in air, given by the law of Gladstone and Dale, which affects the pulses enormously for certain configurations, compared to a simplified treatment using a constant index. We predict in particular a geomagnetic Cherenkov radiation, which provides strong signals at high frequencies (GHz), for certain geometries together with “normal radiation” from the shower maximum, leading to a double peak structure in the frequency spectrum. We also provide some information about the numerical procedures referred to as EVA 1.0.

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.

The 116Sn(d, t)115Sn reaction and the investigation of deeply bound hole states in the odd-A tin isotopes

Abstract Single-neutron pick-up via the (d, t) reaction was studied at E d = 50 MeV on all stable, even- A tin isotopes with an emphasis on the pick-up from the first major shell below the valence shell. The deeply bound hole states thus observed exhibit themselves as a gross structure phenomenon with a systematic variation of its width as a function of neutron number. The most extensive study was done for the 116 Sn(d, t) 115 Sn reaction for which angular distributions were obtained not only for the deeply bound hole states but also for the pick-up of valence nucleons, and for the excitation of the isobaric analogue states. A DWBA analysis yielded the full sum-rule strength for the pick-up of the valence nucleons. It located in the gross structure about 45% of the combined 1g 9 2 , 2p 1 2 , 2p 3 2 and 1f 5 2 strength. Additional strength may be found in the continuous “background” on which the gross structure peaks are riding. A systematic study of the gross structure shapes and cross sections in all odd- A tin isotopes is presented. The observed variation in the spreading of the 1g 9 2 hole strength as a function of neutron number is compared with recent calculations.