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The characteristics and performance of an annular parallel plate avalanche counter (APPAC) developed for performing heavy ion nuclear physics experiments are presented. The main motive of developing this detector system is to perform Coulomb excitation (Coulex) experiments using particle– γ coincidence technique. The Coulex measurements are performed with APPAC and clover germanium detectors. The APPAC has a two electrode geometry and provides information about the scattering angles of the reaction products, which along with their velocity and/or energy information is used for correcting Doppler energy shift of γ -ray events coming from the in-flight decay of reaction products. The detector has an active area of ∼ 410 cm2 and provides scattering angle information in two coordinates namely polar angle θ and azimuthal angle ϕ . The ϕ resolution is fixed at 22.5°, and the θ resolution for the present experimental configuration is about 0.6°. Average rise times of the signals after amplification was observed to be 5 ns. During the experiments, the detector could handle heavy ion count rates of about 25 x 104 pps without any deterioration in the quality of signals.

An investigation of Empirical Mode Decomposition (EMD) based noise filtering algorithm has been carried out on a mirror signal from a two fold germanium clover detector. EMD technique can decompose linear as well as nonlinear and chaotic signals with a precise frequency resolution. It allows to decompose the preamplifier signal (charge pulse) on an event-by-event basis. The filtering algorithm provides the information about the Intrinsic Mode Functions (IMFs) mainly dominated by the noise. It preserves the signal information and separates the overriding noise oscillations from the signals. The identification of noise structure is based on the frequency distributions of different IMFs. The preamplifier noise components which distort the azimuthal co-ordinates information have been extracted on the basis of the correlation between the different IMFs and the mirror signal. The correlation studies have been carried out both in frequency and time domain. The extracted correlation coefficient provides an important information regarding the pulse shape of the γ-ray interaction in the detector. A comparison between the EMD based and state-of-the-art wavelet based denoising techniques has also been made and discussed. It has been observed that the fractional noise strength distribution varies with the position of the collimated gamma-ray source. Above trend has been reproduced by both the denoising techniques.

The main objective of the Advanced GAmma Tracking Array (AGATA) is the investigation of the structure of exotic nuclei at the new generation of RIB facilities. As part of the preparatory phase for FAIR-NUSTAR, AGATA is going to be installed at the FRS fragmentation facility of the GSI centre for an experimental campaign to be performed in 2012 and 2013. Owing to its γ - ray tracking capabilities and the envisaged enhancement in resolving power, a series of in-flight γ - ray spectroscopy experiments are being planned. The present work describes the conceptual design of this first implementation of AGATA at GSI-FRS, and provides information about the expected performance figures. According to the characteristics of each particular experiment, it is foreseen that the target–array distance is adjusted in order to achieve the optimum compromise between detection efficiency and energy resolution, or to cover an specific angular range of the emitted electromagnetic radiation. Thus, a comprehensive Monte Carlo study of the detection sensitivity in terms of photopeak efficiency, resolution and peak-to-total ratio, as a function of the target–array distance is presented. Several configurations have been investigated, and MC-calculations indicate that a remarkable enhancement in resolving power can be achieved when double-cluster AGATA detectors are developed and implemented. Several experimental effects are also investigated. This concerns the impact of passive materials between the target and the array, the angular distribution of the detection efficiency and the influence of target thickness effects and transition lifetimes in the attainable detection sensitivity. A short overview on half-life measurements via lineshape effects utilizing AGATA is also presented.

The design, R&D, and testing of a new plastic-scintillator detector for Time-of-Flight measurements with relativistic heavy-ion beams are presented. A design approach using 32 independent precise timing measurements of the same physical event is followed. This is different from the conventional scheme, which aims at two or four high-precision measurements. A circular, 27 cm in diameter, BC-420 plastic-scintillator sheet is read-out by 32 photomultiplier tubes in order to achieve an intrinsic detector resolution on the order of 10 ps root mean square.

The lineshapes and peak position of Doppler corrected γ -ray spectra from in-beam experiments at relativistic energies are investigated with respect to the intrinsic energy resolution of the employed detectors, the particles’ velocities, and the photons’ emission angle uncertainties at the moment of γ -ray emission. The uncertainties in velocity and photon emission angle are dependent on the lifetime of the excited state. The impact of these two observables on the lineshape and energy resolution are studied for the RISING γ -spectrometer by means of simulations and experimental results from a two-step fragmentation experiment at ≈ 200 MeV / u . Potential use of the distinct lineshape for lifetime determination is demonstrated for measured γ -ray transitions.

An active stopper for the RISING project at GSI has been developed for beta-decay studies and conversion electron spectroscopy following projectile fragmentation/fission reactions. This system employs six double-sided silicon strip detectors in the final focal plane of the GSI FRagment Separator (FRS) to detect both the fragment implantations and their subsequent charged-particle (alpha, beta, p) decays. The wide range of energy response required (150keV up to several GeVs) was covered by the use of a logarithmic preamplifier. Measurements with a Bi-207 conversion electron source yielded an energy resolution of 20 keV at electron energies of similar to 1 MeV and a detection threshold of 150 keV. The response to the implantation of 400 AMeV Xe-136 ions in the active stopper is also discussed in the present paper. (c) 2008 Elsevier B.V. All rights reserved., This work is supported by EPRSC (UK) and EURONS (EU Contract number 506065). Work partially supported by Spanish MEC, Grants FPA2005-03993 and FPA2005-00732. A.A. recognizes partial support of the Ramon y Cajal program.

A novel Calorimeter Telescope (CATE) is employed in the fast beam Rare Isotope Investigations at GSI (RISING) g-campaign with relativistic energies at the Fragment Separator (FRS) at GSI. CATE consists of nine modular Si2CsIðTlÞ detector telescopes for position

The Rare ISotopes INvestigation at GSI project combines the former EUROBALL Ge-Cluster detectors, the MINIBALL Ge detectors, BaF2--HECTOR detectors, and the fragment separator at GSI for high-resolution in-beam gamma-ray spectroscopy measurements with radioactive beams. These secondary beams produced at relativistic energies are used for Coulomb excitation or secondary fragmentation experiments in order to explore the nuclear structure of the projectiles or projectile like nuclei by measuring de-excitation photons. The newly designed detector array is described and the performance characteristics are given. Moreover, particularities of the experimental technique are discussed.

A program for simulating pulse shapes of HPGe detectors has been developed taking into account the closed-ended geometry as well as multiple interactions of γ-rays. Good agreement between simulated and experimentally determined pulse shapes is achieved. From a detailed investigation of risetime distributions a method to determine the radial coordinate of the first point of interaction has been substantiated. For a large Ge detector with 70 mm diameter a radial resolution of 4 to 8 mm has been obtained. This method, combined with segmentation of the detector, reduces the Doppler broadening of γ-lines significantly.

The response of an array of 7 hexagonal BGO detectors each 7.5 cm long (6.7 radiation lengths) with 3.6 cm side-to-side distance was measured using monochromatic photons from the tagged-photon facility at the electron accelerator MAMI A at Mainz. The experimental spectra of the deposited energy for a single detector and for the array of seven modules compare very well with the predictions of Monte Carlo shower simulations using the code GEANT3. Significant improvement of the energy resolution is observed for the summed energy spectra compared to the resolution of a single module. This improvement deteriorates at higher photon energies because the length of the detector is not sufficient to absorb the forward component of the electromagnetic shower.

We present design studies, results of test measurements, and Monte Carlo simulations which served as a basis for the realization of a large area neutron detector (LAND). It has a front area of 2m×2m and a depth of 1 m, and features a multilayer structure of passive converter and active scintillator material. The detector is subdivided in independently operating paddles which allow time-of-flight and position measurement. An energy resolution of ΔT n / T n =5.3% for a flight path of 15 m and an overall detection efficiency of ϵ ≈ 1 is anticipated for neutrons with T n ≈ 1 GeV. The operation of LAND at the SIS facility of GSI is described.

BaF 2 detectors of 20 cm length (10 radiation lengths) and hexagonal cross section (diameter 5.2 cm) were tested using monochromatic photons from the tagged-photon facility at the electron accelerator MAMIA at Mainz. The experimental spectra the deposited energy for a single detector and for an array of seven modules compare very well with the predictions of Monte Carlo shower simulations using the code GEANT3. At high photon energies a significant improvement (more than a factor 2) of the energy resolution is observed for the summed energy spectra as compared to the resolution of one single module.

A γ-spectrometer consisting of one planar and two large volume coaxial germanium crystals, closely packed in a common cryostat, and of a cylindrically symmetric bismuth germanate shield has been built. The system can simultaneously be operated in various escape suppressed modes as well as in a pair spectrometer mode, choosing appropriate coincidence and anticoincidence conditions. This unique feature of the system gives rise to both an exceptional wide dynamical range in γ-ray energies and a good background suppression. The performance of the system has been measured in an energy range between 120 keV and 3.4 MeV using standard radioactive sources.

The performance of germanium detectors and Compton suppression spectrometers is calculated using the Monte Carlo method in the energy range that is of interest for nuclear γ-ray spectroscopy. The calculated properties are: intrinsic peak efficiencies, peak/total and peak/Compton ratios as well as the Compton suppression factor for single γ-rays and high multiplicity γ cascades. The reliability of the calculation is checked by comparison with the observed properties of existing devices. Then, response functions are predicted for new spectrometers. In particular, a new symmetric Compton suppression configuration using three germanium crystals, which is capable of achieving an excellent performance, is proposed. This detector has been constructed and the experimental results are compared with the calculation.