Eksperimentalno proučavanje pionske fuzije 4He(3He, π0)7Be

Pionic fusion reactions where two nuclei fuse into a new one by emitting a pion need a highly coherent mechanism and therefore give an insight into the collective motion of nucleons in nuclei. The reaction 4He(3He,π0)7Be has been studied experimentally at beam energies about 10 MeV above the coherent production threshold. The experiment was performed at KVI, Groningen using the AGOR accelerator facility. The created nuclei were detected in a phoswich detector array in the focal plane of the Big-Bite Spectrometer in coincidence with the photons from neutral pion decay which were detected in the Plastic Ball detector. The Plastic Ball contains 552 phoswich detectors covering polar laboratory angles 50◦<0<160◦ in almost the full azimuthal range. To improve the photon detection efficiency an active inner shell of 64 CsI(Tl) crystals is put inside the Plastic Ball. The fused nuclei are identied by a pulse-shape analysis and a time-of- flight measurement. They are clearly correlated with two photons detected in the Plastic Ball at mutually large opening angles corresponding to pion decay. The event selection yields approximately 500 background-free pionic fusion events. The pion angular distribution is corrected for the acceptance and the eciency obtained from Monte Carlo simulations and normalized with the beam current. The measured differential cross section is compared to available theoretical calculations. The Legendre polynomial fit gives the total cross section σ=(53±9) nb.Reakcija pionske fuzije u kojoj se dvije jezgre fuzioniraju u novu emitirajući pritom pion, zahtijeva veoma koherentni mehanizam i stoga pruža uvid u kolektivno gibanje nukleona u jezgri. Reakcija 4He(3He,π0)7Be je eksperimentalno proučavana na energiji snopa od oko 10 MeV iznad praga. Eksperiment je izveden na KVI-u, u Groningenu na akceleratoru AGOR. Stvorene jezgre su opažene pomoću niza phoswich detektora u fokalnoj ravnini Big-Bite spektrometra istovremeno s fotonima proizašlim iz raspada neutralnog piona i detektiranima u Plastic Ball detektoru. Plastic Ball sadrži 552 phoswich detektora koji pokrivaju laboratorijske polarne kuteve 50◦<0<160◦ u gotovo cijelom azimutalnom rasponu. Da bi se poboljšala efikasnost detekcije fotona unutar Plastic Ball detektora postavljena su 64 kristala CsI(Tl). Složene jezgre su identicirane analizom oblika signala i mjerenjem vremena proleta. One su korelirane s dva fotona opažena u Plastic Ball detektoru s velikim kutem između njihovih smjerova što odgovara raspadu piona. Izborom događaja dobije se oko 500 događaja pionske fuzije bez pozadine. Kutna raspodjela piona je korigirana prema akceptanciji i ekasnosti koje su dobivene iz simulacija i normalizirane prema struji snopa. Mjereni diferencijalni udarni presjek uspoređen je s postojećim teorijskim proračunima. Prilagodba na red Legendreovih polinoma daje za ukupni udarni presjek σ=(53±9) nb

Eksperimentalno proučavanje pionske fuzije 4He(3He, π0)7Be

Pionic fusion reactions where two nuclei fuse into a new one by emitting a pion need a highly coherent mechanism and therefore give an insight into the collective motion of nucleons in nuclei. The reaction 4He(3He,π0)7Be has been studied experimentally at beam energies about 10 MeV above the coherent production threshold. The experiment was performed at KVI, Groningen using the AGOR accelerator facility. The created nuclei were detected in a phoswich detector array in the focal plane of the Big-Bite Spectrometer in coincidence with the photons from neutral pion decay which were detected in the Plastic Ball detector. The Plastic Ball contains 552 phoswich detectors covering polar laboratory angles 50◦<0<160◦ in almost the full azimuthal range. To improve the photon detection efficiency an active inner shell of 64 CsI(Tl) crystals is put inside the Plastic Ball. The fused nuclei are identied by a pulse-shape analysis and a time-of- flight measurement. They are clearly correlated with two photons detected in the Plastic Ball at mutually large opening angles corresponding to pion decay. The event selection yields approximately 500 background-free pionic fusion events. The pion angular distribution is corrected for the acceptance and the eciency obtained from Monte Carlo simulations and normalized with the beam current. The measured differential cross section is compared to available theoretical calculations. The Legendre polynomial fit gives the total cross section σ=(53±9) nb.Reakcija pionske fuzije u kojoj se dvije jezgre fuzioniraju u novu emitirajući pritom pion, zahtijeva veoma koherentni mehanizam i stoga pruža uvid u kolektivno gibanje nukleona u jezgri. Reakcija 4He(3He,π0)7Be je eksperimentalno proučavana na energiji snopa od oko 10 MeV iznad praga. Eksperiment je izveden na KVI-u, u Groningenu na akceleratoru AGOR. Stvorene jezgre su opažene pomoću niza phoswich detektora u fokalnoj ravnini Big-Bite spektrometra istovremeno s fotonima proizašlim iz raspada neutralnog piona i detektiranima u Plastic Ball detektoru. Plastic Ball sadrži 552 phoswich detektora koji pokrivaju laboratorijske polarne kuteve 50◦<0<160◦ u gotovo cijelom azimutalnom rasponu. Da bi se poboljšala efikasnost detekcije fotona unutar Plastic Ball detektora postavljena su 64 kristala CsI(Tl). Složene jezgre su identicirane analizom oblika signala i mjerenjem vremena proleta. One su korelirane s dva fotona opažena u Plastic Ball detektoru s velikim kutem između njihovih smjerova što odgovara raspadu piona. Izborom događaja dobije se oko 500 događaja pionske fuzije bez pozadine. Kutna raspodjela piona je korigirana prema akceptanciji i ekasnosti koje su dobivene iz simulacija i normalizirane prema struji snopa. Mjereni diferencijalni udarni presjek uspoređen je s postojećim teorijskim proračunima. Prilagodba na red Legendreovih polinoma daje za ukupni udarni presjek σ=(53±9) nb

Coulomb dissociation of ¹⁶O into ⁴He and ¹²C

We measured the Coulomb dissociation of ¹⁶O into ⁴He and ¹²C at the R³B setup in a first campaign within FAIR Phase 0 at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The goal was to improve the accuracy of the experimental data for the ¹²C(α,γ)¹⁶O fusion reaction and to reach lower center-ofmass energies than measured so far. The experiment required beam intensities of 10⁹ ¹⁶O ions per second at an energy of 500 MeV/nucleon. The rare case of Coulomb breakup into ¹²C and ⁴He posed another challenge: The magnetic rigidities of the particles are so close because of the same mass-to-charge-number ratio A/Z = 2 for ¹⁶O, ¹²C and ⁴He. Hence, radical changes of the R³B setup were necessary. All detectors had slits to allow the passage of the unreacted ¹⁶O ions, while ⁴He and ¹²C would hit the detectors’ active areas depending on the scattering angle and their relative energies. We developed and built detectors based on organic scintillators to track and identify the reaction products with sufficient precision