The MUGAST-AGATA-VAMOS campaign : set-up and performance

Abstract

The MUGAST-AGATA-VAMOS set-up at GANIL combines the MUGAST highly-segmented silicon array with the state-of-the-art AGATA array and the large acceptance VAMOS spectrometer. The mechanical and electronics integration copes with the constraints of maximum efficiency for each device, in particular γ-ray transparency for the silicon array. This complete set-up offers a unique opportunity to perform exclusive measurements of direct reactions with the radioactive beams from the SPIRAL1 facility. The performance of the set-up is described through its commissioning and two examples of transfer reactions measured during the campaign. High accuracy spectroscopy of the nuclei of interest, including cross-sections and angular distributions, is achieved through the triple-coincidence measurement. In addition, the correction from Doppler effect of the γ-ray energies is improved by the detection of the light particles and the use of two-body kinematics and a full rejection of the background contributions is obtained through the identification of heavy residues. Moreover, the system can handle high intensity beams (up to 10 8 pps). The particle identification based on the measurement of the time-of-flight between MUGAST and VAMOS and the reconstruction of the trajectories is investigated.

HeCTOr: the $^3$He Cryogenic Target of Orsay for direct nuclear reactions with radioactive beams

“…All the requirements described in Section 2 have been carefully taken into account in the design. In Section 4 we will present the performance during the first in-beam experiment, where the target was coupled to the MUGAST [16] silicon array, the AGATA [17,18] γ-ray array and the VAMOS [19] large-acceptance magnetic spectrometer.…”

“…The detection set-up, shown in Fig. 4, is composed of the segmented silicon array MUGAST [16], coupled to the highresolution segmented HPGe array AGATA [17,18] and the large-acceptance magnetic spectrometer VAMOS [19], allowing for a completely exclusive measurement via triple coincidence. The MUGAST array is composed of 12 Doublesided Strips Silicon Detectors (DSSD) surrounding the target: 5 trapezoidal and one annular detector in the backward hemisphere, two square detectors close to 90 • and 4 MUST2 [23] detectors at forward angles.…”

“…In experiments where absolute cross sections are extracted via γ-particle coincidence, the γ-ray efficiency of the detection set-up plays an important role in the determination of the relevant physical quantities. While MUGAST is nearly transparent to γ radiation [16], the thick frame of the target, if intercepted by γ rays before they reach AGATA, might absorb part of them and lower the effective γ-ray efficiency. When the nucleus produced in the reaction de-excite instantaneously through the emission of γ radiation, only the usual corrections to the efficiency to account for the presence of the Havar window, the MUGAST array and the scattering chamber should be applied.…”