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M1 and E2 transition rates from core-excited states in semi-magic Ru-94
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.ORCID iD: 0000-0003-1771-2656
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.ORCID iD: 0000-0002-1406-5695
KTH, School of Engineering Sciences (SCI), Physics.
Show others and affiliations
2018 (English)In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 54, no 9, article id 145Article in journal (Refereed) Published
Abstract [en]

Lifetimes of high-spin states have been measured in the semi-magic (N = 50) nucleus Ru-94. Excited states in Ru-94 were populated in the Ni-58(Ca-40, 4p)Ru-94* fusion-evaporation reaction at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from gamma-rays emitted while the residual nuclei were slowing down in a thick 6 mg/cm(2) metallic Ni-58 target. In total eight excited-state lifetimes in the angular momentum range I = (13-20)h have been measured, five of which were determined for the first time. The corresponding B(M1) and B(E2) reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.

Place, publisher, year, edition, pages
Springer, 2018. Vol. 54, no 9, article id 145
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:kth:diva-234570DOI: 10.1140/epja/i2018-12581-7ISI: 000443091000003Scopus ID: 2-s2.0-85052645166OAI: oai:DiVA.org:kth-234570DiVA, id: diva2:1249510
Funder
Swedish Research Council, 621-2014-5558Swedish Research Council, 621-2012-3805Swedish Research Council, 621-2013-4323Göran Gustafsson Foundation for Research in Natural Sciences and Medicine
Note

QC 20180917

Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2020-04-07Bibliographically approved
In thesis
1. Experimental Studies of the Neutron Deficient Atomic Nuclei 94Ru, 95Rh and 172Pt via their Electromagnetic Properties: Du som saknar dator/datorvana kan kontakta Pär Olsson, polsson@kth.se för information
Open this publication in new window or tab >>Experimental Studies of the Neutron Deficient Atomic Nuclei 94Ru, 95Rh and 172Pt via their Electromagnetic Properties: Du som saknar dator/datorvana kan kontakta Pär Olsson, polsson@kth.se för information
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis reports new results obtained from studies of the neutron deficient atomic nuclei 94Ru, 95Rh and 172Pt using two different experimental set-ups. In the first part, lifetimes of highly excited states in nuclei near the N=50 closed-shell (94Ru and 95Rh) were deduced from an analysis of the Doppler broadened transition lineshapes measured following the 58Ni(40Ca,4p) and 58Ni(40Ca,3p) fusion-evaporation reactions at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex situated in Caen, France. Doppler Shift Attenuation Method (DSAM) lifetime analysis was performed on the Doppler broadened peaks in energy spectra from γ-rays emitted from excited states in the nuclei of interest while they were slowing down in a thick 6 mg/cm2 metallic 58Ni target. For 94Ru, eight excited-state lifetimes in the angular momentum range I= (13-20)h have been measured in total, five of which were determined for the first time. For the lifetime analysis of 95Rh, three lifetime values have been obtained. One of them, the lifetime of the 39/21- excited state, has been measured for the first time. In the other cases, the lifetimes of the previously measured 29/22- and 37/21- excited states have been obtained. The corresponding B(M1) and B(E2) reduced transition strengths have been deduced and are discussed within the framework of large-scale shell model (LSSM) calculations. In the second part, the extremely neutron deficient 172Pt nucleus has been studied. Excited states in 172Pt were populated using the 96Ru(78Kr,2p) and 92Mo(83Kr,3n) reactions at the Accelerator Laboratory of the University of Jyväskylä (JYFL), Finland. Prompt γ-rays were detected using the JUROGAM high-purity germanium detector array at the target position while the identification and decay spectroscopy of 172Pt was performed using the RITU gas-filled separator in conjunction with the GREAT spectrometer. The Recoil Decay Tagging (RDT) technique was used for the selection of prompt γ-rays. The known positive-parity band has been extended and the negative-parity structure has been established on top of the lowest member of the negative parity band which has now been firmly assigned as spin-parity 3-. Moreover, the newly observed E3 transition provides a link between the negative parity band with the ground state. The observations of this E3 transition together with several E1 transitions connecting the negative-parity structure with the ground-state band is consistent with the presence of octupole collectivity in 172Pt. Furthermore, this is the first observation of an E3 transition connecting the negative parity band with the ground-state band in the Pt-Os-W region. The experimental results were interpreted in terms of LSSM and total routhian surface calculations. With the support of these theoretical calculations, evidence for octupole collectivity in 172Pt is proposed.

Abstract [sv]

Denna avhandling beskriver resultat från studier av de neutronfattiga isotoperna rutenium-94 (94Ru), rodium-95 (95Rh) och platina-172 (172Pt). Den första delen av avhandlingen behandlar livstidsmätningar för högt exciterade tillstånd i kärnorna 94Ru och 95Rh med antalat neutroner, N, = 50 vilket motsvarar ett slutet skal i den modell för atomkärnors struktur som benämns skalmodellen. Livstider för 94Ru och 95Rh härleddes från en analys av Dopplerbreddade övergångslinjer uppmätta efter det att kärnorna skapats i fusion mellan jonstrålar av kalcium-40 och strålmål bestående av nickel-58. Experimentet utfördes vid den franska acceleratoranläggningen Grand Accelerateur National d'Ions Lourds (GANIL). Gammastrålning uppmättes med germaniumdetektorsystemet EXOGAM medan elektriskt laddade partiklar och neutroner som utsändes i anslutning till fusionsreaktionerna registrerades i CsI-detektorsystemet DIAMANT respektive neutron detektorsystemet Neutron Wall. För 94Ru har livstider uppmätts för åtta exciterade tillstånd med spinn i intervallet I= 13-20h. För fem av dessa bestämdes livstiden för första gången. För 95Rh har tre livstidsvärden erhållits. För ett av dem, 39/21-, har livstiden uppmättts för första gången i detta arbete. I de tvä andra fallen (37/21- och 29/22-) var livstiden känd sedan tidigare men har nu uppmätts med högre precision. De reducerade övergångssannolikheterna för magnetiska dipolövergångar och elektriska kvadrupolövergångar (B(M1) respektive B(E2)) från dessa tillstånd har härletts från de uppmätta livstiderna samt förgreningsförhållanden för de relevanta elektromagnetiska övergångarna. Dessa jämförs med och diskuteras inom ramen för storskaliga skalmodellsberäkningar (LSSM). I den andra delen av avhandlingsarbetet har den extremt neutronfattiga atomkärnan 172Pt studerats. Exciterade tillstånd i 172Pt populerades i fusionsreaktionerna 96Ru(78Kr, 2p)172Pt* och 92Mo(83Kr, 3n)172Pt* mellan jonstrålar av kryptonisotoperna med masstal 78 och 83 och strålmål bestående av tunna folier av rutenium-96 respektive molybden-92. Dessa experiment utfördes vid Acceleratorlaboratoriet vid universitetet i Jyväskylä (JYFL), Finland. Prompt gammastrålning detekterades med germaniumdetektorsystemet JUROGAM vilket var placerat i anslutning till strålmålet. Sönderfallsspektroskopi av 172Pt och andra neutronfattiga fusionsprodukter utfördes i fördröjd koincidens mellan JUROGAM och spektrometern för radioaktiva sönderfall, GREAT efter att de hade passerat den gasfyllda elektromagnetiska rekylseparatorn RITU. Den s.k. Recoil Decay Tagging (RDT)-tekniken användes för identifiering av de sällsynta 172Pt-kärnorna. På detta sätt kunde den kända strukturen av exciterade tillstånd i 172Pt och elektromagnetiska övergångar mellan dessa tillstånd och till grundtillståndet utökas. I synnerhet har ett lågt liggande tillstånd med spin-paritet 3- fastställts och sönderfallet mellan detta tillstånd och grundtillståndet observerats. Bl.a. egenskaperna hos denna gammaövergång med multipolaritet E3 stöder teoretiska förutsägelser om att atomkärnan 172Pt uppvisar oktupolkollektivitet dvs. kan exciteras från grundtillståndet till ett oktupolvibrationellt tillstånd.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2020. p. 60
Series
TRITA-SCI-FOU ; 2020:07
National Category
Physical Sciences
Research subject
Physics, Atomic, Subatomic and Astrophysics
Identifiers
urn:nbn:se:kth:diva-271771 (URN)978-91-7873-484-9 (ISBN)
Public defence
2020-04-23, Via Zoom: https://kth-se.zoom.us/webinar/register/WN_ZIbDpWsxSSql98O0C4TBxA, 14:00 (English)
Opponent
Supervisors
Available from: 2020-04-07 Created: 2020-04-07 Last updated: 2020-04-21Bibliographically approved

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