Experimental study of pionic fusion 4He(3He,π0)7Be

doctoral thesis

• Title (croatian): Eksperimentalno proučavanje pionske fuzije 4He(3He, π0)7Be
• Author: Igor Gašparić
• Mentor: Roman Čaplar (mentor)
• Committee member: Matko Milin (predsjednik povjerenstva)
• Committee member: Nils Paar (član povjerenstva)
• Committee member: Herbert Loehner (član povjerenstva); strani drzavljanin: Nije dostupno
• Committee member: Roman Čaplar (član povjerenstva)
• Committee member: Dubravko Klabučar (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2011-06-28, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

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.

Abstract (croatian)

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.

• Keywords: pionic fusion; subthreshold pion production; CsI(Tl) scintillator; phoswich; magnetic spectrometer
• Keywords (croatian): pionska fuzija; stvaranje piona ispod praga; CsI (Tl) scintilator; phoswich; magnetski spektrometar
• Language: english
• URN:NBN: urn:nbn:hr:217:671706
• Study programme: Title: Physics; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika (doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika)
• Type of resource: Text
• Extent: XXXV, 121, III str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-23 11:45:25