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Studies of collective phenomena in neutron deficient nuclei: by means of lifetime measurements, angular correlation measurements and the recoil-decay tagging technique
KTH, School of Engineering Sciences (SCI), Physics.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The nucleus is a mesoscopic system that retains features from both the quantum and macroscopic worlds. A basic property of a macroscopic body is its shape. Nuclear shapes can be deduced from experimental data as they influence the excitation mode of the nucleus and hence the energies and lifetimes of its excited levels. Various short-lived nuclei were created in fusion-evaporation experiments performed at international heavy-ion accelerator facilities. The emitted γ rays and, in some experiments, also the charged particles and neutrons emitted in the reactions were detected. The studied neutron-deficient isotopes were either selected by the type and number of particles emitted in the reactions, or by using their characteristic decays. The excited states of the different isotopes were extracted from the γ-ray analyses. Spectroscopic properties, such as the lifetimes of the excited states or the angular distribution of the emitted γ rays were measured when possible. The experimentally obtained level schemes together with the other spectroscopic information were used to deduce the excitation modes and the shapes of the studied nuclei. The detector systems are described in the first chapter and in the second chapter some techniques used to extract information from the experimental data are explained. Finally, a brief theoretical overview on the nuclear models which were used to interpret the experimental results is given.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , x, 57 p.
Series
Trita-FYS, ISSN 0280-316X ; 2008:15
Keyword [en]
heavy-ion reactions, multi-detector arrays, recoil separator, in-beam gamma-ray spectroscopy, high spin states, lifetime measurements, recoil-decay tagging, nuclear shape
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:kth:diva-4693ISBN: 978-91-7178-929-7 (print)OAI: oai:DiVA.org:kth-4693DiVA: diva2:13472
Public defence
2008-04-28, FA32, AlbaNova, 10691 Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100621Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-08-20Bibliographically approved
List of papers
1. Excited states in the neutron-deficient nuclei Rn-197,Rn-199,Rn-201
Open this publication in new window or tab >>Excited states in the neutron-deficient nuclei Rn-197,Rn-199,Rn-201
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2008 (English)In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 77, no 5, 054303-1-054303-7 p.Article in journal (Refereed) Published
Abstract [en]

Excited states of the extremely neutron-deficient radon isotopes with N = 111, 113, 115 have been studied for the first time in a series of in-beam experiments performed at the Accelerator Laboratory of the University of Jyvaskyla. The reactions used were: Sn-118(Kr-82, 3n)Rn-197, Sn-120(Kr-82, 3n)Rn-199, Sm-150(Cr-52, 3n)Rn-199, and Sn-122(Kr-82, 3n)Rn-201. The gamma rays emitted from excited states in the different isotopes were identified using the recoil-alpha-decay tagging technique. The estimated cross section for the production of Rn-197(m) was 7(3) nb, which is the lowest cross section reported so far for an in-beam study. The energies of the (17/2(+)) levels built on the isomeric (13/2(+)) states in Rn-197,Rn-199,Rn-201 indicate a transition from an anharmonic vibrational structure toward a rotational structure at low spins for these nuclei. However, the transition is not as sharp as predicted by theory.

Keyword
EVEN-EVEN NUCLEI; GAMMA-RAY SPECTROSCOPY; ALPHA-DECAY; MEAN-FIELD; ISOTOPES; RN-198
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8208 (URN)10.1103/PhysRevC.77.054303 (DOI)000256885600013 ()2-s2.0-43449092879 (Scopus ID)
Note
QC 20100620Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-08-20Bibliographically approved
2. gamma-ray spectroscopy of At-197
Open this publication in new window or tab >>gamma-ray spectroscopy of At-197
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2008 (English)In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 78, no 4, 044328-1-044328-8 p.Article in journal (Refereed) Published
Abstract [en]

Excited states of the extremely neutron-deficient nucleus At-197 have been studied in an in-beam experiment using the fusion-evaporation reaction Sn-118(Kr-82,p2n)At-197. gamma rays belonging to At-197 feeding the I-pi=(9/2(-)) ground state, as well as gamma rays feeding the 311-keV I-pi=(13/2(+)) isomer, decaying via the emission of gamma rays, and the 52-keV I-pi=(1/2(+)) alpha-decaying isomer have been identified using the recoil-alpha-decay tagging technique. Total Routhian surface calculations predict a near-spherical shape for the (9/2(-)) ground state and oblate shapes with beta(2) around -0.2 for the (1/2(+)) and the (13/2(+)) states. These predictions agree with our experimental findings.

Keyword
HIGH-SPIN STATES, ALPHA-DECAY, BI-187, BI-189 ISOTOPES, EXCITED-STATES, MEAN-FIELD, NUCLEI, IDENTIFICATION, DEFORMATION, BEHAVIOR
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-8209 (URN)10.1103/PhysRevC.78.044328 (DOI)000260574700043 ()2-s2.0-55849132529 (Scopus ID)
Note
QC 20100621Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-08-20Bibliographically approved
3. Low-spin collective behavior in the transitional nuclei Mo-86,Mo-88
Open this publication in new window or tab >>Low-spin collective behavior in the transitional nuclei Mo-86,Mo-88
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2007 (English)In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 76, no 1, 014307-1-014307-9 p.Article in journal (Refereed) Published
Abstract [en]

Low-spin structures in Mo-86,Mo-88 were populated using the Ni-58(Ar-36, x alpha yp) heavy-ion fusion-evaporation reaction at a beam energy of 111 MeV. Charged particles and gamma rays were emitted in the reactions and detected by the DIAMANT CsI ball and the EXOGAM Ge array, respectively. In addition to the previously reported low-to-medium spin states in these nuclei, new low-spin structures were observed. Angular correlation and linear polarization measurements were performed in order to unambiguously determine the spins and parities of intensely populated states in Mo-88. Quasiparticle Random Phase Approximation (QRPA) calculations were performed for the first and second excited 2(+) states in Mo-86 and Mo-88. The results are in qualitative agreement with the experimental results, supporting a collective interpretation of the low-spin states for these transitional nuclei.

Keyword
STATES; MO-90; ZR-86; MO-88; SPECTROSCOPY; STRENGTHS; ENERGIES; SHAPES; BANDS
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-8210 (URN)10.1103/PhysRevC.76.014307 (DOI)000248542400026 ()2-s2.0-34547659038 (Scopus ID)
Note
QC 20100621Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-08-20Bibliographically approved
4. Lifetime measurements of normal deformed states in Lu-165(71)
Open this publication in new window or tab >>Lifetime measurements of normal deformed states in Lu-165(71)
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2005 (English)In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 71, no 1, 121-127 p.Article in journal (Refereed) Published
Abstract [en]

Picosecond lifetimes of medium spin states in Lu-165 were measured for the first time. The reaction used to populate the nucleus of interest was La-139(Si-30,4n)Lu-165 at a beam energy of 135 MeV. The beam was provided by the XTU-tandem accelerator of Laboratori Nazionali di Legnaro, Italy. By using the differential decay curve method, lifetimes of 19 states in four different rotational bands were obtained. Therefrom the B(E2) values and the transitional quadrupole moments were deduced. The obtained Q(t) for the different bands are compared with total Routhian surface (TRS) calculations and particle-rotor-model calculations. The TRS calculations predict different axial symmetric shapes for the bands built on the 9/2(-)[514], 9/2(+)[404], and 1/2(-)[541] configurations, with a gamma softness for the 9/2(-)[514] configuration. This band has also been studied using the particle-rotor model, the results of which, however, are consistent with a triaxial shape with a gamma value of -15(p).

Keyword
DECAY CURVE METHOD; MEAN-FIELD; NUCLEI; CONFIGURATION; BANDS
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-8211 (URN)10.1103/PhysRevC.71.014312 (DOI)000226701900018 ()2-s2.0-18244405559 (Scopus ID)
Note
QC 20100621Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-06-28Bibliographically approved
5. RDM lifetime measurements in 107Cd
Open this publication in new window or tab >>RDM lifetime measurements in 107Cd
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2005 (English)In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 31, no 10, S1563-S1568 p.Article in journal (Refereed) Published
Abstract [en]

Lifetimes for decays linking near-yrast states in Cd-107 have been measured using the recoil distance method (RDM). The nucleus of interest was populated via the (MO)-M-98(C-12,3n)(107) Cd fusion-evaporation reaction at an incident beam energy of 60 MeV. From the measured lifetimes, transition probabilities have been deduced and compared with the theoretical B(E2) values for limiting cases of harmonic vibrational and axially deformed rotational systems. Our initial results suggest a rotor-like behaviour for the structure based on the unnatural-parity, h(11/2) orbital in Cd-107, providing further evidence for the role of this 'shape-polanzing' orbital in stabilizing the nuclear deformation in the A similar to 100 transitional region.

Keyword
DECAY CURVE METHOD; ROTATIONAL BANDS; STATES; ISOTOPES; MOMENTS; NUCLEI
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-6506 (URN)10.1088/0954-3899/31/10/033 (DOI)000232575600035 ()2-s2.0-25444462530 (Scopus ID)
Note
QC 20100621Available from: 2006-12-06 Created: 2006-12-06 Last updated: 2010-06-28Bibliographically approved

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