Abstract
The availability of fast radioactive beams offers the possibility for studies of E1-strength in projectiles via Coulomb excitation. Theoretical calculations predict that a significant fraction of this strength is shifted towards lower excitation energies in neutron-rich systems. At the NSCL, virtual photon scattering was used to probe the discrete structure of both 18O and 20O for levels in the region between 1 and 8 MeV. Two 1- levels at 5.35(10) and 6.85(5) MeV were observed for the first time in 20O. The observed {gamma}-ray spectrum for 20O is, in fact, dominated by transitions resulting from E1 excitations to these states. The extracted B(E1) {up_arrow} values of {approx}0.062(16) e2fm2 and {approx}0.035(9) e2fm2 for the 5.35 and 6.85 MeV levels, respectively, are larger than shell model calculations predict. Such large dipole strengths are not observed for low-lying 1- states in 18O, indicating a shift of dipole strength towards lower energies as one approaches the neutron drip-line.
Tryggestad, E;
Baumann, T;
Brown, B A;
Heckman, P;
Thoennessen, M;
[1]
Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1321 (United States)];
Aumann, T;
Bazin, D;
Blumenfeld, Y;
Chartier, M;
[1]
Beene, J R;
Lewis, T A;
Radford, D C;
Shapira, D;
Varner, R L;
[2]
Halbert, M L;
[3]
Liang, J F
[4]
- National Superconducting Cyclotron Laboratory, East Lansing, Michigan 48824-1321 (United States)
- Physics Division, Oak Ridge National Laboratory, P. O. Box 2008, Oak Ridge, TN 37831-6368 (United States)
- University of Tennessee, Department of Physics and Astronomy, Knoxville, TN 37996 (United States)
- Oak Ridge Associated Universities, Oak Ridge, TN 37831-6368 (United States)
Citation Formats
Tryggestad, E, Baumann, T, Brown, B A, Heckman, P, Thoennessen, M, Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1321 (United States)], Aumann, T, Bazin, D, Blumenfeld, Y, Chartier, M, Beene, J R, Lewis, T A, Radford, D C, Shapira, D, Varner, R L, Halbert, M L, and Liang, J F.
Low-lying dipole strength in 20O.
United States: N. p.,
2003.
Web.
doi:10.1063/1.1556656.
Tryggestad, E, Baumann, T, Brown, B A, Heckman, P, Thoennessen, M, Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1321 (United States)], Aumann, T, Bazin, D, Blumenfeld, Y, Chartier, M, Beene, J R, Lewis, T A, Radford, D C, Shapira, D, Varner, R L, Halbert, M L, & Liang, J F.
Low-lying dipole strength in 20O.
United States.
https://doi.org/10.1063/1.1556656
Tryggestad, E, Baumann, T, Brown, B A, Heckman, P, Thoennessen, M, Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1321 (United States)], Aumann, T, Bazin, D, Blumenfeld, Y, Chartier, M, Beene, J R, Lewis, T A, Radford, D C, Shapira, D, Varner, R L, Halbert, M L, and Liang, J F.
2003.
"Low-lying dipole strength in 20O."
United States.
https://doi.org/10.1063/1.1556656.
@misc{etde_20621470,
title = {Low-lying dipole strength in 20O}
author = {Tryggestad, E, Baumann, T, Brown, B A, Heckman, P, Thoennessen, M, Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1321 (United States)], Aumann, T, Bazin, D, Blumenfeld, Y, Chartier, M, Beene, J R, Lewis, T A, Radford, D C, Shapira, D, Varner, R L, Halbert, M L, and Liang, J F}
abstractNote = {The availability of fast radioactive beams offers the possibility for studies of E1-strength in projectiles via Coulomb excitation. Theoretical calculations predict that a significant fraction of this strength is shifted towards lower excitation energies in neutron-rich systems. At the NSCL, virtual photon scattering was used to probe the discrete structure of both 18O and 20O for levels in the region between 1 and 8 MeV. Two 1- levels at 5.35(10) and 6.85(5) MeV were observed for the first time in 20O. The observed {gamma}-ray spectrum for 20O is, in fact, dominated by transitions resulting from E1 excitations to these states. The extracted B(E1) {up_arrow} values of {approx}0.062(16) e2fm2 and {approx}0.035(9) e2fm2 for the 5.35 and 6.85 MeV levels, respectively, are larger than shell model calculations predict. Such large dipole strengths are not observed for low-lying 1- states in 18O, indicating a shift of dipole strength towards lower energies as one approaches the neutron drip-line.}
doi = {10.1063/1.1556656}
journal = []
issue = {1}
volume = {656}
journal type = {AC}
place = {United States}
year = {2003}
month = {Mar}
}
title = {Low-lying dipole strength in 20O}
author = {Tryggestad, E, Baumann, T, Brown, B A, Heckman, P, Thoennessen, M, Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1321 (United States)], Aumann, T, Bazin, D, Blumenfeld, Y, Chartier, M, Beene, J R, Lewis, T A, Radford, D C, Shapira, D, Varner, R L, Halbert, M L, and Liang, J F}
abstractNote = {The availability of fast radioactive beams offers the possibility for studies of E1-strength in projectiles via Coulomb excitation. Theoretical calculations predict that a significant fraction of this strength is shifted towards lower excitation energies in neutron-rich systems. At the NSCL, virtual photon scattering was used to probe the discrete structure of both 18O and 20O for levels in the region between 1 and 8 MeV. Two 1- levels at 5.35(10) and 6.85(5) MeV were observed for the first time in 20O. The observed {gamma}-ray spectrum for 20O is, in fact, dominated by transitions resulting from E1 excitations to these states. The extracted B(E1) {up_arrow} values of {approx}0.062(16) e2fm2 and {approx}0.035(9) e2fm2 for the 5.35 and 6.85 MeV levels, respectively, are larger than shell model calculations predict. Such large dipole strengths are not observed for low-lying 1- states in 18O, indicating a shift of dipole strength towards lower energies as one approaches the neutron drip-line.}
doi = {10.1063/1.1556656}
journal = []
issue = {1}
volume = {656}
journal type = {AC}
place = {United States}
year = {2003}
month = {Mar}
}