"Coulomb excitation of 100Mo"
Katarzyna Wrzosek-Lipska, Heavy Ion Laboratory, University of Warsaw, Institute of Experimental Physics, University of Warsaw
(id #94)
Seminar: YesPoster: No
Invited talk: No
Molybdenum isotopes with neutron number close to 50 have a spherical shape and can be well described by shell model [1]. As the number of neutrons increases the influence of collective motion on the electromagnetic structure gets stronger, resulting in unusual features of nuclei from N=54 for 96Mo to N=58 for 100Mo.
The neighbouring 98Mo nucleus is one of the four stable even–even nuclei having the first excited state of spin and parity 0+. A very low-lying 0+ excited state, close in energy to the first excited 2+ state, was also observed in the 100Mo isotope. Such a rare structure is the first experimental indication of shape coexistence and cannot be easily interpreted.
Multiple Coulomb excitation is one of the most important experimental methods to study nuclear shapes. While lifetime measurements allow determining reduced transition probabilities, Coulomb excitation technique can bring information on relative signs of the matrix elements. Moreover it is sensitive to diagonal matrix elements via second-order effects, making it possible to extract quadrupole moments including their signs, which are the measure of the
shape associated with a given state. Low-energy Coulomb excitation is the only experimental technique that can distinguish between prolate and oblate shape of the nucleus in a short-lived excited state.
Coulomb excitation experiment of the 100Mo isotope was performed at HIL in Warsaw using the 32S beam from the U-200P cyclotron. Gamma rays depopulating Coulomb-excited states were detected by the OSIRIS-II array in coincidence with back-scattered particles [2]. The OSIRIS-II spectrometer
was a multi-detector system consisting of 12 HPGe detectors equipped with anti-compton BGO shields. The scattered projectiles were detected by 45 silicon PiN diodes, placed inside a small spherical chamber of 5 cm radius. Scattering angle coverage extended from 110 to 152 degrees with respect to the beam direction.
Twenty E2 and M1 reduced matrix elements, including three quadrupole moments, connecting eight low-lying states have been determined using the least-squares code GOSIA[3,4]. Such a rich set of reduced matrix elements makes it possible to extract, using the quadrupole sum rules approach, the shape parameters: the overall deformation parameter, as well as triaxiality in the ground and first excited 0+ states.
Experimental results concerning the shape parameters of the low-lying 0+ states in the 100Mo isotope will be presented for the first time. They will be compared to theoretical predictions based on the generalized Bohr Hamiltonian approach [5], and confronted with general trends of shape evolution in this mass region.
References:
[1] P. Singh et al, Phys. Rev. C45,2161 (1992)
[2] K. Wrzosek et al, Acta Phys. Pol. B39,513 (2008)
[3] T. Czosnyka, D. Cline, C. Y. Wu Bull Amer. Phys. Soc. 28 (1983) 745
[4] http://www.slcj.uw.edu.pl/pl/gosia/2008manual.pdf
[5] L. Próchniak, S. G. Rohoziński J. Phys. G: Nucl.
The neighbouring 98Mo nucleus is one of the four stable even–even nuclei having the first excited state of spin and parity 0+. A very low-lying 0+ excited state, close in energy to the first excited 2+ state, was also observed in the 100Mo isotope. Such a rare structure is the first experimental indication of shape coexistence and cannot be easily interpreted.
Multiple Coulomb excitation is one of the most important experimental methods to study nuclear shapes. While lifetime measurements allow determining reduced transition probabilities, Coulomb excitation technique can bring information on relative signs of the matrix elements. Moreover it is sensitive to diagonal matrix elements via second-order effects, making it possible to extract quadrupole moments including their signs, which are the measure of the
shape associated with a given state. Low-energy Coulomb excitation is the only experimental technique that can distinguish between prolate and oblate shape of the nucleus in a short-lived excited state.
Coulomb excitation experiment of the 100Mo isotope was performed at HIL in Warsaw using the 32S beam from the U-200P cyclotron. Gamma rays depopulating Coulomb-excited states were detected by the OSIRIS-II array in coincidence with back-scattered particles [2]. The OSIRIS-II spectrometer
was a multi-detector system consisting of 12 HPGe detectors equipped with anti-compton BGO shields. The scattered projectiles were detected by 45 silicon PiN diodes, placed inside a small spherical chamber of 5 cm radius. Scattering angle coverage extended from 110 to 152 degrees with respect to the beam direction.
Twenty E2 and M1 reduced matrix elements, including three quadrupole moments, connecting eight low-lying states have been determined using the least-squares code GOSIA[3,4]. Such a rich set of reduced matrix elements makes it possible to extract, using the quadrupole sum rules approach, the shape parameters: the overall deformation parameter, as well as triaxiality in the ground and first excited 0+ states.
Experimental results concerning the shape parameters of the low-lying 0+ states in the 100Mo isotope will be presented for the first time. They will be compared to theoretical predictions based on the generalized Bohr Hamiltonian approach [5], and confronted with general trends of shape evolution in this mass region.
References:
[1] P. Singh et al, Phys. Rev. C45,2161 (1992)
[2] K. Wrzosek et al, Acta Phys. Pol. B39,513 (2008)
[3] T. Czosnyka, D. Cline, C. Y. Wu Bull Amer. Phys. Soc. 28 (1983) 745
[4] http://www.slcj.uw.edu.pl/pl/gosia/2008manual.pdf
[5] L. Próchniak, S. G. Rohoziński J. Phys. G: Nucl.
