Domingo-Pardo, C.

Gerl, J.

Pietralla, N.

Reese, M.

GSI Repository

Status of PreSPEC Commissioning Data Analysis∗M. Reese 1, C. Domingo-Pardo 2, J. Gerl 3, N. Pietralla 1, and the PreSPEC and AGATAcollaborations1Institut fu¨r Kernphysik, Technische Universita¨t Darmstadt, D-64289 Darmstadt, Germany ; 2IFIC, CSIC-Universitat deValencia, E-46980 Paterna, Spain ; 3GSI Helmholtzzentrum fu¨r Schwerionenforschung GmbH, D-64291 Darmstadt,GermanyPreSPEC-AGATA is an experiment for in-flight γ-spectroscopy at GSI to investigate the structure of ex-otic nuclei. Two physics campaigns were done: 2012and 2014. This report is about the progress in the dataanalysis of the commissioning runs in August 2012.IntroductionThe goal of the experiment was a measurement of theperformance of the PreSPEC-AGATA [1] setup, a uniquecombination of the GSI Fragment Separator (FRS) [2], theAdvanced Gamma Tracking Array (AGATA) [3], Lund-York-Cologne CAlorimeter (LYCCA) [4], and HECTORfor in-beam γ-spectroscopy. Further details about the setupand an earlier status report about the data analysis can befound in [5]. A 80Kr beam with a kinetic energy of about150 MeV/u at the secondary target position was used todo two types of experiments: Coulomb excitation on a197Au target, and secondary fragmentation reactions on aBe target. 80Kr was chosen as projectile because of its highCoulomb excitation cross-section of σclx ≈ 550mb for the2+1 state. The challenge in the analysis of in-flight γ spec-troscopic data is the large Doppler shift of emitted γ-rays atvelocities of v/c ≈ 0.5. The data is being analyzed, usinga software framework described in [6].Coulomb ExcitationIf 197Au is the target material, the dominating excita-tion mechanism of the projectile is Coulomb excitation(Coulex), i.e. exchange of virtual photons. At relativis-tic energies, one-step Coulex is dominating and the firstexcited 2+1 state at 616.6 keV in 80Kr is populated. The ob-served yield in the γ line of the excited state can be used todetermine the B(E2) value. Because of the strong Dopplereffect at large projectile velocity, the γ-rays have to be cor-rected for the Doppler shift in energy before a discrete linein the γ spectrum can be seen. The strength of the Dopplershift depends also on the angle of observation in the labo-ratory frame, which can be seen in Fig. 1. The spectrumof γ-energy in the laboratory frame shows the emission ofthe excited target nuclei from the state 7/2+1 at 547.5 keV.Another line is the emission from electron-positron anni-hilation at 511 keV. Towards lower energies (below 500keV), the background radiation level rises very quickly be-cause of the abundant atomic radiation emitted during the∗Work supported by BMBF NuSTAR.DA - TP 6, FKZ: BMBF05P12RDFN8 (TP 6), HGS-HIReinteraction of the projectile with the target electrons. Theemission line of the 2+1 state at 616.6 keV in 80Kr can onlybe seen after Doppler correction (Fig. 1, bottom). Simul-taneous observation of emission lines from target and pro-jectile de-excitation allows for a relative measurement ofthe Coulex cross-sections and thus B(E2) value of the twoexcited states 197Au and 80Kr.Final quantitative results for total efficiency and energyresolution will be obtained after taking into account theAGATA detector efficiency at different angles and for dif-ferent γ-energies. This is difficult, because efficiency isinfluenced by the combined effects of the Doppler shift:Change in angular distribution and in the energy of theemitted radiation. 0.5 0.6 0.7 0.8 0.9 1cos(θ) 0 1 2 3 4 5 6 7 8197Au: 547 keV (decay at rest)80Kr: 616 keV (v/c = 0.5) 0 50 100]e+e- annihilation511 keV197Au  7/2+      3/2+547 keV  (100 cts.) 0 50 100 450  500  550  600  650  700  750  800  850  900  950  1000                                                 Intensity [counts / keVEγ [keV]80Kr  2+      0+616 keV  (1050 cts.)after DopplercorrectionFigure 1: Top: Detected γ energy in the laboratory sys-tem as seen from different detection angles. γ-rays emittedin-flight can be seen as curved lines. Middle: The back-ground subtracted spectrum of γ energy in the laboratorysystem, shows the decay from the excitation of the targetmaterial (197Au). Bottom: Background subtracted spec-trum of Doppler-corrected γ energy show the decay spec-trum of the projectile.GSI SCIENTIFIC REPORT 2013 NUSTAR-GS-01doi:10.15120/GR-2014-1-NUSTAR-GS-01 113Secondary FragmentationIf the secondary target is Beryllium, the cross-section forfragmentation reactions is large. Such a setup is used tostudy the decay of excited fragments. In order to assign theobserved γ-radiation to specific ion species, full identifica-tion of outgoing fragments is needed. This is done with theLYCCA device [4] that performs ∆E-E and precise time-of-flight measurement of the ejectiles. From these quan-tities, the outgoing isotopes can be identified as shown inFig. 2. In the mass region around 80Kr, Z-identificationis very good while different mass peaks are overlapping.The calibration of the LYCCA DSSSD detectors was partlydone using an automatic method described in [7].After the Doppler correction of observed γ-rays in coin-cidence with the LYCCA identification, γ-emission spectraof selected excited ejectiles can be obtained. Yrast states ofthe most abundant even-even isotopes after the target canbe seen in Fig. 3. The half-life T1/2 of the excited state hasan influence on the resolution that can be obtained. If Ttaris the time the projectile needs to travel through the targetmaterial, most de-excitation processes will happen insidethe target if T1/2 < Ttar. In this case, the particle velocityafter the target is not equal to the velocity at the moment ofγ emission and the Doppler correction will be done with awrong velocity. This results in a reduced resolution for thestates with shorter half-life as can be seen in Fig. 3 whereT1/2 is given in the label of each peak. On the other handthe observed line shape enables in principle the determina-tion of lifetimes.Furthermore, data from the 80Kr fragmentation run wasused to show the feasibility for new experimental tech-niques as described in [8].OutlookThe analysis is ongoing. Since the AGATA detector is acomplicated device, exploiting pulse-shape analysis (PSA)an γ-ray tracking, some improvements can be expectedfrom a refined preprocessing of the detected γ-rays. This ispossible, because during AGATA experiments, the pream-plifier signals of all channels are written to disk. Later im-provements in software algorithms for PSA and γ-trackingcan be used to increase both, efficiency and energy resolu-tion of the Doppler-corrected peaks.References[1] P. Boutachkov et al., GSI Report 2012 (2013) 148.[2] H. Geissel et al., Nucl. Instr. and Meth. Phys. Res. B 70, 286-297 (1992).[3] S. Akkoyun et al., Nucl. Instr. and Meth. Phys. Res. A 668,26-58 (2012).[4] P. Golubev et al., Nucl. Instr. and Meth. Phys. Res. A 723,55-66 (2013)[5] N. Pietralla et. al., EPJ Web of Conferences 66, 02083 (2014).[6] M. Reese et. al. , GSI Scientific Report 2012 (2013) 48.proton numberneutron number 31 32 33 34 35 36 37 36  38  40  42  44  46 0 50 100 150 200 250 30080Kr78Kr74Se70GeFigure 2: The charge and mass identification plot that isused to produce the gated spectra of Fig. 3. Particle chargeis determined, using the E-∆E method, while the mass isobtained from an additional time-of-flight measurement. 0 100 200 300 400 500616.6 keV 8.3 ps80Kr 2+1       0+1819.5 keV 0.76 ps80Kr 4+1       2+1 956.0 keV 0.56 ps80Kr 6+1       4+180Kr gatedatomic background 0 100 200 300455 keV 21.6 ps78Kr 2+1       0+1 664.4 keV 2.52 ps78Kr 4+1       2+1 858.3 keV 0.65 ps78Kr 6+1       4+178Kr gated 0 100 200 300634.8 keV 7.1 ps74Se 2+1       0+1728 keV 1.86 ps74Se 4+1       2+1868.2 keV 0.86 ps74Se 6+1       4+1967 keV 0.38 ps74Se 8+1       6+174Se gated 0 50 100 150 200  400  600  800  1000  1200  1400energy [keV]1039.5 keV 1.3 ps70Ge 2+1       0+1 1113.6 keV 0.8 ps70Ge 4+1       2+170Ge gatedM.Reese, AG Pietralla IKP TU-DarmstadtFigure 3: Doppler-corrected γ spectra for the strongesteven-even nuclei identified by LYCCA. Decays of the firstfew Yrast states can be clearly seen. Peak labels indicatethe γ-ray energy and the half-life of the initial state.[7] M. Reese et. al. , This report.[8] C. Stahl et. al. , This report.NUSTAR-GS-01 GSI SCIENTIFIC REPORT 2013114 doi:10.15120/GR-2014-1-NUSTAR-GS-01

Status of PreSPEC Commissionning Data Analysis

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Status of PreSPEC Commissionning Data Analysis

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