J.F. Chemin

Improvements in the in-beam γ-ray spectroscopy provided by an ancillary detector coupled to a Ge γ-spectrometer: the DIAMANT-EUROGAM II example

For the first time the 4π γ-ray spectrometer EUROGAM II has been coupled to a 4π light charged particle detector array, DIAMANT, during a test experiment on the reaction 32S + 58Ni at 120 MeV beam energy. A very large improvement in the peak-to-background ratio of the γ-spectra has been found when EUROGAM II is triggered by DIAMANT to select an exit channel. A simple algebra has been developed which provides theoretical estimates in good agreement with these experimental results. It is demonstrated that, depending on both the γ-spectrometer and ancillary detector performances, much better peak-to-background can be obtained by such a coupling. For the same peak-to-background ratio, the use of an ancillary detector allows for a lower γ-ray coincidence level and therefore improves the statistics. Ways to select the most appropriate ancillary detector are given. The ability of the ancillary detector to provide a total Doppler shift correction is crucial for the improvement of the peak-to-background ratio.

K-Ionization probability across the 460-keV12C(p, p0) resonance

We have remeasured theK-shell vacancy production probabilityPK across the 460-keV12C(p, p0) resonance, previously investigated by Duinker et al. We are unable to confirm the large (∼70 %) variation ofPK across the resonance, found by Duinker et al. for protons elastically scattered at 125°. Our values for the ratioPK(142°)/PK(16°) are independent (within±20%) of the proton bombarding energy over the resonance region, in agreement with theoretical predictions by Blair and Anholt, Feagin and Kocbach, McVoy and Weidenmüller. Our average value for this ratio, equal to 0.88 ±0.06, agrees with the value 0.88 calculated by Amundsen and Aashamar.

The DIAMANT electronics and data acquisition system

Abstract We describe the electronics and data acquisition system of the 4π light particle multidetector array DIAMANT. This system has been conceived to be very modular with regard to both the kind and number of detectors. The whole system is designed to run either with a few additional ancillary detectors (Ge) or linked to 4π γ arrays such as EUROGAM. Part of the electronics has been designed using SMD devices; the acquisition is based on CAMAC ADCs and VME units for data acquisition, data transfer is handled via a 32 bit ECL bus (DT32) used for EUROGAM. The data acquisition, distributed on a network, is based on the VxWorks Real Time kernel and the UNIX Operating System.

Production of projectile and targetK X-rays by single and multiple electron-capture in collisions of Si14+ and Si13+ ions with argon atoms at 4.5 and 5.5 MeV/amu

Projectile and target X-ray cross-sections have been measured in collisions of bare and hydrogenlike Silicon ions with argon atoms. Projectile energies are 125 MeV and 153 MeV, i.e. the intermediate velocity region forK-shell capture. Coincidence measurements between X-ray photons and the scattered Sin+ projectiles with charge statesn-1,n-2 andn-3 have been made. The relative contribution of charge exchange and direct ionization (or excitation) of the targetK-shell has been obtained directly by this new method. DoubleK-shell electron transfer is demonstrated to be very large in the case of fully stripped Si ions. A thorough theoretical analysis of the data is carried out and multiple capture processes are evaluated using an independent electron model.

Correction method for Doppler broadened γ-ray lines using the linear momentum of the evaporated charged particles in heavy-ion induced fusion–evaporation reactions

Abstract A method based on the conservation of linear momentum is used to correct the position and the width of the γ-ray lines of the residual nucleus produced in heavy-ion induced fusion–evaporation reactions. This method implies the measurement of the total number of the emitted particles, their masses, energies and directions of emission in coincidence with the prompt γ-rays. It has been applied to the 120 MeV 32 S + 58 Ni reaction whose data have been collected using the high efficiency and large granularity 4 π light charged particle detector DIAMANT, coupled to the 4 π γ-ray spectrometer EUROGAM II.

A 4π light charged particle multidetector for reaction channel identification and discrimination

Abstract We describe a compact 4π multidetector system to detect light charged particles emitted in a fusion-evaporation nuclear reaction. It consists of 17 fast plastic scintillators closely assembled in a cubic arrangement. The detector can be enclosed in the French gamma multidetector facility: the “chateau de cristal”. The characteristics and the performance of this multidetector are discussed from the 58 Ni + 54 Fe fusion-evaporation reaction.

GoldL-shell ionization probability by 1 MeV proton at large scattering angles

The impact parameter dependence of the ionization of GoldL-subshells has been measured and compared to theoretical values calculated in the SCA framework by Aashamar et al. [17]. Special attention has been paid to large scattering angle measurements and results are obtained for0lab=30°, 45°, 65°, 90°, 110°, 130°, 153° and 166°. Taking into account the sum ofLα,Lβ,Lγ,Lα,Ll lines we conclude firstly that the experimental ionization probabilityP(b) is in good agreement with the theoretical values. Secondly, comparing experimental and theoretical intensity of (Lα+Ll) and (Lγ+Lβ) X-ray lines, we show that ionization ofLII andLIII subshells is also fairly well described by the SCA model.

Anti-compton X-ray spectrometer

Abstract An anti-Compton Si(Li) X-ray spectrometer has been developed. The spectrometer consists of four detectors working in an anticoincidence mode. The performance of the system has been measured with 109 Cd, 22 Na and 60 Co sources. An improvement of signal-to-background ratio equal to 300% is reported.