Juhani K. Peltonen

Response of BGO and CsI(Tl) scintillators to heavy ions

Abstract Response of BGO and CSI(Tl) scintillators to ions heavier than helium has been studied at energies below 30 MeV/n. An argon beam was scattered from gold target. The reaction products, covering ions from lithium to argon, were identified by using the conventional ΔE - E method. A thin silicon surface barrier detector was used as an energy loss detector and a scintillator as a residual energy detector. The energies of incident nuclei were determined by using the signals from the calibrated ΔE detector, and the light yield of the scintillators was obtained from the observed pulse heights. Telescope consisting of a silicon transmission detector and either BGO of CsI(Tl) scintillators as a residual energy detector were found to have similar identification capabilities of heavy ions. The light output of BGO was found to be linear at all energies observed, except for the lightest nuclei, where some nonlinearity was apparent below about 6–7 MeV/n. The response of CsI(Tl) was linear for all ions above 6 MeV/n.

Energetic and relativistic nuclei and electron experiment of the SOHO mission

Abstract The design of the ERNE experiment of the ESA and NASA collaborative SOHO mission is described. ERNE will investigate the sun by measuring energetic particles. Starting from the design objectives, as determined by the scientific goals of the experiment, and from the adopted basic solutions, the design and structure of the instrument are presented in detail. The fundamental technical aspects encountered in building a space instrument are briefly considered. The methods of implementation of scientifically the most important parts of the instrument, the sensors for measuring energetic particles and the associated electronics, are thoroughly explained. Both hardware and software are examined. The pre-flight calibrations of the instrument are described and the performance of the instrument in space is demonstrated.

Cosmic-ray spectra as calculated from atmospheric hadron cascades

A Monte-Carlo model has been developed for the calculation of the intensities of hadrons and muons emerging from particle cascades initiated by primary cosmic rays in the atmosphere. Special attenuation is paid to the energy spectra of the particles reaching sea level. Vertical energy spectra were obtained for neutrons, protons, muons and pions at sea level in the energy range 0.1-100 GeV. The predictions show overall agreement with experimental results in all four cases. This indicates that the general features of the atmospheric hadron cascades are satisfactorily understood in the energy range 0.1-10000 GeV.

Composition and spectra of cosmic-ray hadrons at sea level

Energy spectra of neutrons, protons and pions were measured at sea level using a cosmic-ray hadron spectrometer consisting of a double neutron monitor and scintillation counters. All the hadron spectra were determined simultaneously. The analysis of the observed neutron multiplicity distributions was based on computer simulations of hadron cascades in the spectrometer. The neutron spectrum was determined in the range 0.05-1000 GeV. The proton-to-neutron ratio was estimated below 2 GeV, where the contribution of pions is of minor importance. Assuming a smooth rise of the p/n ratio above 2 GeV to a constant value at 5 GeV, the pion spectrum was determined between 2 and 50 GeV. At higher energies, where accompanied hadrons distort the measured spectra, upper bounds of the pion intensities were estimated. The composition of the hadron flux at sea level is discussed on the basis of the present and previous experimental and theoretical results.

Interplanetary propagation of relativistic solar protons

Particle fluxes and pitch angle distributions of relativistic solar protons at Earths orbit have been determined by Monte Carlo calculations. The analysis covers two hours after the release of the particles from the Sun and total of 8 × 106 particle trajectories were simulated. The pitch angle scattering was assumed to be isotropic and the scattering mean free path was varied from 0.1 to 4 AU.The intensity-time profiles after a delta-like injection from the Sun show that the interplanetary propagation is clearly non-diffusive at scattering mean-free paths above 0.5 AU. All pitch angle distributions have a steady minimum at 90 °, and they become similar about 20 min after the arrival of first particles.As an application, the solar injection profile and the interplanetary scattering mean-free path of particles that gave rise to the GLE on 7 May, 1978 were determined. In contrast to the values of 3–5 AU published by other authors, the average scattering mean-free path was found to be about 1 AU.

Solar intensity X-ray spectrometer (SIXS) ASIC for a large dynamic range onboard BepiColombo ESA mission to Mercury

The SIXS instrument is designed for detecting and measuring solar X-rays and solar energetic particles in a Mercury orbit onboard BepiColombo. The particle detector consists of a CsI(Tl) core detector and 5 GaAs surface detectors. The front-end electronics of the particle detector is implemented as an ASIC which requires a large dynamic range of 2,000e- to 1,500,000e- and an integral non-linearity (INL) < 3% for a temperature range of -30deg C to +55deg C. The SIXS ASIC test structure has been manufactured to determine performance of differential vs. single-ended designs for noise, power supply rejection and current consumption. The ASIC has 8 channels, each of which consists of a preamplifier, a CR-RC shaper, a peak hold, a comparator and a buffer, all designed using enclosed geometry transistors. There are 6 channels for GaAs detectors with 3 different preamplifier types consisting of a single-ended with pole zero compensation; single-ended without pole zero compensation and a differential configuration. There are 2 channels for Csl detectors with single- ended and differential preamplifier designs. This ASIC has been manufactured in a 0.35 mum CMOS process. The ASIC architecture and design flow are described including simulated and measured results.

Accompanied hadrons in sea-level detectors

The coincidences of cosmic-ray particles in sea-level detectors were investigated theoretically. The object of the work was to clarify the role of accompanied particles in the measurement of the spectrum of hadrons. The calculations were based on a Monte-Carlo model of atmospheric hadron cascades. The counting rates and energy spectra of hadrons with different numbers of accompanied charged hadrons were calculated by using the area of the detector as a parameter. The effect of accompanied hadrons on the measured spectra was found to be appreciable at total energies above 500 GeV.

Spectra of cosmic-ray hadrons in the range 0.1–1000 GeV

The energy spectra of cosmic-ray neutrons, protons, and pions were determined at sea level in the range 0.1 – 1000 GeV. The results are based on the measurements of the neutron-multiplicity distributions produced by cosmic hadrons in the Turku spectrometer. Below 0.5 GeV, the values γ = 1.47 ± 0.04 and 0.8 ± 0.1 were obtained for the slopes of the neutron and proton spectra. At 1000 GeV, the nucleon spectra are much steeper with γ = 2.79 ± 0.06. The pion spectrum was found to obey the power law with γ = 1.41 ± 0.05 in the low-energy region up to 30 GeV. Above 500 GeV, the spectrum of pions, containing an admixture of accompanied particles, was found to reach the high energy limit with γ = 2.92 ± 0.06.

Solar Intensity X-Ray Spectrometer (SIXS) ASIC onboard the ESA BepiColombo mission to Mercury

The new SIXS prototype ASIC has been designed for detecting and measuring solar X-rays in a Mercury orbit onboard BepiColombo. The SIXS detector consists of a CsI(Tl) core detector and 5 Silicon surface detectors. This new ASIC has undergone major modifications and has a new differential charge preamplifier without any pole zero cancellation and has a large dynamic range of 2,000e- to 1,500,000e-. The ASIC has 8 channels, each of which consists of a preamplifier, a CR-RC shaper, a peak detect hold, a comparator, a buffer, and a new 8 bit resistor string DAC which sets the programmable threshold for the comparator There are 6 channels for Si detectors with a shaping time of 1 ¿s and 2 channels for CsI detector with a shaping time of 3 ¿s, one of which has twice the gain to accommodate for low output efficiency of the detector. The channels are multiplexed to a single 10/11 bit SAR ADC which runs at a 10 MHz clock and additional on chip programmable phase shifted clocks and programmable Upper and Lower threshold voltages. This ASIC has been manufactured in a 0.35 ¿m CMOS process using enclosed geometry transistors. All digital logic in the ASIC including control and ADC logic use voting logic flipflops for SEU prevention.

Specialized detector techniques and electronics of the ERNE instrument onboard SOHO

ERNE is designed to study the composition and energy spectra of particles encountered in interplanetary space in the energy range from 1 MeV/n to well beyond 500 MeV/n. Several innovative ideas had to be incorporated in the design of the instrument in order to fulfill the scientific requirements. Position-sensitive strip detectors are used in the High Energy Detector (HED) for determining particle trajectories. Integrated interstrip capacitances were designed to allow for a very simple read-out technique from the two edges of each detector. The event recognition, signal multiplexing and control of the pulse height analysis are based on a gate array technique. The versatility of the gate array also allowed an elegant realization of a number of other functions and instrument control tasks. By using the gate array a very compact structure of the digital control electronics was achieved.