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Giant resonances and bound collective states observed in the scattering of 92.5-MeV electrons from the closed-neutron-shell nucleus Y 89 between excitation energies from 2.0 to 55 MeV

Giant resonances and bound collective states observed in the scattering of 92.5-MeV electrons... 92.5-MeV electrons were used to study in Y 89 the excitation range between 2 and 55 MeV. Above neutron threshold, broad electric resonances have been seen at 14.0 ( 63 A - 1 3 ) MeV ( E 2 , Δ T = 0 ) and 28 ( 1 2 5 A - 1 / 3 ) MeV ( E 2 , Δ T = 1 ). The total width of the isoscalar E 2 resonance is (4.5 ± 0.4) MeV and its strength (56 ± 6)% energy-weighted sum rule ( E 2 , Δ T = 0 ). For the isovector E 2 resonance only a minimal value of 7 MeV for the width can be given which is connected with (48 ± 5)% of the isovector sum rule. The strength of the E 1 resonance T < , ( 104 ± 1 0 ) % of the Thomas-Reiche-Kuhn sum rule agrees well with ( γ , n ) measurements, thus giving a check for the accuracy of the evaluating methods employed. A structure around 19-20 MeV, believed to be the T > part of the giant dipole resonance, carries (8 ± 3)% of the E 1 sum rule. In addition to these generally well known states, clustering of E 3 strength, (13 ± 2)% energy-weighted sum rule ( E 3 , Δ T = 0 ), was found at 6.75 and 8.05 MeV; the enveloping line shape of these clusters was best described by a Breit-Wigner term. Other concentrations of strength include E 3 at 2.6 MeV, (15 ± 3)% energy-weighted sum rule ( E 3 , Δ T = 0 ), E 2 at 4.0 MeV, (11 ± 3)% energy-weighted sum rule ( E 2 , Δ T = 0 ), and E 3 strength at 13.5 MeV. No resonance other than the E 1 was found around 17 MeV, thus ruling out in Y 89 the existence of a monopole state with 100% sum rule proposed for Zr 90 from ( α , α ′ ) and ( e , e ′ ) measurements. In contrast to heavy nuclei, no resonant 3 ℏ ω E 3 strength could be located. NUCLEAR REACTIONS Y 89 ( e , e ′ ) , E 0 = 92.5 MeV. Measured d 2 σ d Ω d E x , bound and continum states. Deduced multipolarity λ , reduced matrix element B ( E λ ) , radiative width Γ γ 0 , sum rule exhaustion, single particle strength, and total width of the continuum and clustered states. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review C American Physical Society (APS)

Giant resonances and bound collective states observed in the scattering of 92.5-MeV electrons from the closed-neutron-shell nucleus Y 89 between excitation energies from 2.0 to 55 MeV

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References (29)

Publisher
American Physical Society (APS)
Copyright
Copyright © 1977 The American Physical Society
ISSN
1089-490X
DOI
10.1103/PhysRevC.16.970
Publisher site
See Article on Publisher Site

Abstract

92.5-MeV electrons were used to study in Y 89 the excitation range between 2 and 55 MeV. Above neutron threshold, broad electric resonances have been seen at 14.0 ( 63 A - 1 3 ) MeV ( E 2 , Δ T = 0 ) and 28 ( 1 2 5 A - 1 / 3 ) MeV ( E 2 , Δ T = 1 ). The total width of the isoscalar E 2 resonance is (4.5 ± 0.4) MeV and its strength (56 ± 6)% energy-weighted sum rule ( E 2 , Δ T = 0 ). For the isovector E 2 resonance only a minimal value of 7 MeV for the width can be given which is connected with (48 ± 5)% of the isovector sum rule. The strength of the E 1 resonance T < , ( 104 ± 1 0 ) % of the Thomas-Reiche-Kuhn sum rule agrees well with ( γ , n ) measurements, thus giving a check for the accuracy of the evaluating methods employed. A structure around 19-20 MeV, believed to be the T > part of the giant dipole resonance, carries (8 ± 3)% of the E 1 sum rule. In addition to these generally well known states, clustering of E 3 strength, (13 ± 2)% energy-weighted sum rule ( E 3 , Δ T = 0 ), was found at 6.75 and 8.05 MeV; the enveloping line shape of these clusters was best described by a Breit-Wigner term. Other concentrations of strength include E 3 at 2.6 MeV, (15 ± 3)% energy-weighted sum rule ( E 3 , Δ T = 0 ), E 2 at 4.0 MeV, (11 ± 3)% energy-weighted sum rule ( E 2 , Δ T = 0 ), and E 3 strength at 13.5 MeV. No resonance other than the E 1 was found around 17 MeV, thus ruling out in Y 89 the existence of a monopole state with 100% sum rule proposed for Zr 90 from ( α , α ′ ) and ( e , e ′ ) measurements. In contrast to heavy nuclei, no resonant 3 ℏ ω E 3 strength could be located. NUCLEAR REACTIONS Y 89 ( e , e ′ ) , E 0 = 92.5 MeV. Measured d 2 σ d Ω d E x , bound and continum states. Deduced multipolarity λ , reduced matrix element B ( E λ ) , radiative width Γ γ 0 , sum rule exhaustion, single particle strength, and total width of the continuum and clustered states.

Journal

Physical Review C – American Physical Society (APS)

Published: Sep 1, 1977

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