For the first time a comprehensive level and decay scheme has been obtained for a T=(5)/(2) nucle... more For the first time a comprehensive level and decay scheme has been obtained for a T=(5)/(2) nucleus in the s-d shell (27Na) by using a radioactive beam and target. Particle-gamma and p-gamma-gamma coincidences were measured following the 14C(14C,pgamma)27Na reaction at Elab=22MeV. The results do not support an inversion of the 2s1/2 and 1d5/2 orbitals, as previously proposed for Tz>~3, but they do suggest an increased N=16 gap between the 2s1/2 and 1d3/2 orbitals due to the neutron excess. A consistent interpretation of the level scheme in terms of the s-d shell model using the USD Hamiltonian is possible below 4 MeV, but differences increase at higher excitation energies. Another interpretation is that the influences of both the p1/2 and f7/2 intruder orbitals increase simultaneously with increasing T, an effect not included in the USD Hamiltonian.
The b-unstable nuclei 32,34,36,38 Si have been produced by projectile fragmentation and studied b... more The b-unstable nuclei 32,34,36,38 Si have been produced by projectile fragmentation and studied by inbeam Coulomb excitation. Excited states at 1399 6 25 keV and 1084 6 20 keV have been identified for the first time in 36 Si and 38 Si, respectively, and tentatively assigned J p 2 1. The B͑E2; 0 1 1 ! 2 1 1 ͒ values leading to these states and the previously identified 2 1 1 states in 32,34 Si have been measured, and are compared to shell model calculations. Our results indicate that the 2 1 1 state in 34 Si has a large fp-shell intruder component, and that the 2 1 1 states in the N. 20 silicon isotopes can be reproduced assuming an N 20 shell closure. [S0031-9007(98)05530-6]
One-neutron knockout reactions from the deeply bound N = 16 isotones with Z = 16, 17, and 18 have... more One-neutron knockout reactions from the deeply bound N = 16 isotones with Z = 16, 17, and 18 have been studied in inverse kinematics with intermediate-energy beams. ␥-ray spectroscopy in coincidence with the detection of knockout residues allowed for an investigation of the one-neutron removal leading to individual excited states. Spectroscopic factors are deduced in the framework of the sudden and eikonal approximations and are compared to USD shell-model predictions. The momentum distributions observed in the experiment are used to identify the angular momentum l carried by the knockedout neutron by comparing with calculations based on a black-disk reaction model. The systematics of reduced single-particle occupancies attributed to the effect of short-range correlations, observed so far for stable and near-magic nuclei in ͑e , eЈp͒ and ͑d , 3 He͒ reactions and in one-nucleon knockout on light deeply bound systems, are extended in this work.
Excited states in the neutron-rich doubly-odd nucleus 78As have been identified for the first tim... more Excited states in the neutron-rich doubly-odd nucleus 78As have been identified for the first time by proton-), and 3,-3, coincidence measurements via the 76Ge(a,pn) reaction at 32, 36, and 40 MeV beam energy. Four levels have been found to decay with lifetimes in the nanosecond region. The 5 (+) to (10 +) states are ascribed to the (Trg9/2 ® v99/2) intruder two-quasiparticle configuration with some collective components in the 9 (+) and (10 +) states.
Particle-gamma-ray angular correlations have been performed using the 12C(12C, pgamma)23Na reacti... more Particle-gamma-ray angular correlations have been performed using the 12C(12C, pgamma)23Na reaction at the resonant laboratory energy of 38.82 MeV. Branching ratios, mixing ratios, and lifetimes are determined for the gamma decay of states up to 13 MeV excitation energy in 23Na. These results are combined with the 12C(12C, 8Be)16O, 12C(12C, d)22Na, and 12C(12C, p)23Na reaction analyses to produce the following
High-spin states in As have been studied via the Ge(,{ital p}2{ital n}) reaction. Proton-gated ex... more High-spin states in As have been studied via the Ge(,{ital p}2{ital n}) reaction. Proton-gated excitation functions extracted from measured -ray yields at beam energies of 32, 36, and 40 MeV and an additional - coincidence measurement at 40 MeV have been used to assign new -ray decay sequences to As. In particular, a positive-parity sequence up to spin 25/2 and
The MoNA project is a 10 college and university collaboration to construct a highly efficient lar... more The MoNA project is a 10 college and university collaboration to construct a highly efficient large-area detector for high-energy neutrons, to be used in experiments with fast rare isotopes at the National Superconducting Cyclotron Laboratory. Undergraduate participation is central to the MoNA project, both in the construction and in the use of the detector. The detector covers an area of
The 9 Be 32 Ar; 31 ArX reaction, leading to the 5 2 ground state of a nucleus at the proton drip ... more The 9 Be 32 Ar; 31 ArX reaction, leading to the 5 2 ground state of a nucleus at the proton drip line, has a cross section of 10.4(13) mb at a beam energy of 65:1 MeV=nucleon. This translates into a spectroscopic factor that is only 24(3)% of that predicted by the many-body shell-model theory. We introduce refinements to the eikonal reaction theory used to extract the spectroscopic factor to clarify that this very strong reduction represents an effect of nuclear structure. We suggest that it reflects correlation effects linked to the high neutron separation energy (22.0 MeV) for this state.
The asymptotic D - to S -state ratio η for the {l_angle}dαthinsp{vert_bar} â¶Li{r_angle} bound... more The asymptotic D - to S -state ratio η for the {l_angle}dαthinsp{vert_bar} â¶Li{r_angle} bound-state overlap is determined from measurements of the tensor analyzing powers for (â¶Li,thinspd ) reactions on medium-heavy targets. The reactions are described by the distorted-wave Born approximation assuming a direct α -particle transfer reaction mechanism. The calculations provide good agreement with cross section and vector analyzing power
Fragmentation reactions with intermediate-energy heavy-ion beams exhibit a wide range of reaction... more Fragmentation reactions with intermediate-energy heavy-ion beams exhibit a wide range of reaction mechanisms, ranging from direct reactions to statistical processes. We examine this transition by measuring the relative population of excited states in several sd-shell nuclei produced by fragmentation with the number of removed nucleons ranging from two to sixteen. The two-nucleon removal is consistent with a non-dissipative process whereas the removal of more than five nucleons appears to be mainly statistical.
ABSTRACT Intermediate-energy Coulomb excitation has been used to study excited states in the radi... more ABSTRACT Intermediate-energy Coulomb excitation has been used to study excited states in the radioactive N=19 nuclei 33Si and 34P, which are neutron-rich spherical nuclei located along the boundary of the ``island of inversion.'' The present results for the 1010 keV state in 33Si and states up to 2.2 MeV excitation energy in 34P can be understood in terms of 0ħω (nonintruder) configurations. This suggests that the energy differences between 0ħω and 2ħω configurations are large enough in 33Si and 34P that the low-lying 0ħω states are not significantly perturbed.
Neutron hole states in the exotic N = 27 isotope 44 Cl have been populated using the intermediate... more Neutron hole states in the exotic N = 27 isotope 44 Cl have been populated using the intermediate-energy single-neutron knockout reaction 9 Be(45 Cl, 44 Cl)X. The momentum distribution of the residual 44 Cl nuclei after direct population of the ground state is consistent with removal of an l = 1 neutron. This observation and comparison with a shell-model calculation imply that p 3/2 neutrons from above the N = 28 major shell closure play important roles in the ground states of both 44 Cl and 45 Cl. The present result is significant because 44 Cl is even closer to the valley of stability than 43 S, where a similar result was recently obtained using a g-factor measurement.
It is proposed that certain states of undetermined spin and parity observed in previously reporte... more It is proposed that certain states of undetermined spin and parity observed in previously reported ¹â¹â¸Pt(p,p'/gamma/) and /sup 194,196,198/Pt(p,p') experiments are 3â» states and contain a significant amount of octupole strength. These results show that the octupole strength is fragmented in the Pt isotopes. The predictions of Engel for the distribution of octupole strength in Pt isotopes are compared to
For the first time a comprehensive level and decay scheme has been obtained for a T=(5)/(2) nucle... more For the first time a comprehensive level and decay scheme has been obtained for a T=(5)/(2) nucleus in the s-d shell (27Na) by using a radioactive beam and target. Particle-gamma and p-gamma-gamma coincidences were measured following the 14C(14C,pgamma)27Na reaction at Elab=22MeV. The results do not support an inversion of the 2s1/2 and 1d5/2 orbitals, as previously proposed for Tz>~3, but they do suggest an increased N=16 gap between the 2s1/2 and 1d3/2 orbitals due to the neutron excess. A consistent interpretation of the level scheme in terms of the s-d shell model using the USD Hamiltonian is possible below 4 MeV, but differences increase at higher excitation energies. Another interpretation is that the influences of both the p1/2 and f7/2 intruder orbitals increase simultaneously with increasing T, an effect not included in the USD Hamiltonian.
The b-unstable nuclei 32,34,36,38 Si have been produced by projectile fragmentation and studied b... more The b-unstable nuclei 32,34,36,38 Si have been produced by projectile fragmentation and studied by inbeam Coulomb excitation. Excited states at 1399 6 25 keV and 1084 6 20 keV have been identified for the first time in 36 Si and 38 Si, respectively, and tentatively assigned J p 2 1. The B͑E2; 0 1 1 ! 2 1 1 ͒ values leading to these states and the previously identified 2 1 1 states in 32,34 Si have been measured, and are compared to shell model calculations. Our results indicate that the 2 1 1 state in 34 Si has a large fp-shell intruder component, and that the 2 1 1 states in the N. 20 silicon isotopes can be reproduced assuming an N 20 shell closure. [S0031-9007(98)05530-6]
One-neutron knockout reactions from the deeply bound N = 16 isotones with Z = 16, 17, and 18 have... more One-neutron knockout reactions from the deeply bound N = 16 isotones with Z = 16, 17, and 18 have been studied in inverse kinematics with intermediate-energy beams. ␥-ray spectroscopy in coincidence with the detection of knockout residues allowed for an investigation of the one-neutron removal leading to individual excited states. Spectroscopic factors are deduced in the framework of the sudden and eikonal approximations and are compared to USD shell-model predictions. The momentum distributions observed in the experiment are used to identify the angular momentum l carried by the knockedout neutron by comparing with calculations based on a black-disk reaction model. The systematics of reduced single-particle occupancies attributed to the effect of short-range correlations, observed so far for stable and near-magic nuclei in ͑e , eЈp͒ and ͑d , 3 He͒ reactions and in one-nucleon knockout on light deeply bound systems, are extended in this work.
Excited states in the neutron-rich doubly-odd nucleus 78As have been identified for the first tim... more Excited states in the neutron-rich doubly-odd nucleus 78As have been identified for the first time by proton-), and 3,-3, coincidence measurements via the 76Ge(a,pn) reaction at 32, 36, and 40 MeV beam energy. Four levels have been found to decay with lifetimes in the nanosecond region. The 5 (+) to (10 +) states are ascribed to the (Trg9/2 ® v99/2) intruder two-quasiparticle configuration with some collective components in the 9 (+) and (10 +) states.
Particle-gamma-ray angular correlations have been performed using the 12C(12C, pgamma)23Na reacti... more Particle-gamma-ray angular correlations have been performed using the 12C(12C, pgamma)23Na reaction at the resonant laboratory energy of 38.82 MeV. Branching ratios, mixing ratios, and lifetimes are determined for the gamma decay of states up to 13 MeV excitation energy in 23Na. These results are combined with the 12C(12C, 8Be)16O, 12C(12C, d)22Na, and 12C(12C, p)23Na reaction analyses to produce the following
High-spin states in As have been studied via the Ge(,{ital p}2{ital n}) reaction. Proton-gated ex... more High-spin states in As have been studied via the Ge(,{ital p}2{ital n}) reaction. Proton-gated excitation functions extracted from measured -ray yields at beam energies of 32, 36, and 40 MeV and an additional - coincidence measurement at 40 MeV have been used to assign new -ray decay sequences to As. In particular, a positive-parity sequence up to spin 25/2 and
The MoNA project is a 10 college and university collaboration to construct a highly efficient lar... more The MoNA project is a 10 college and university collaboration to construct a highly efficient large-area detector for high-energy neutrons, to be used in experiments with fast rare isotopes at the National Superconducting Cyclotron Laboratory. Undergraduate participation is central to the MoNA project, both in the construction and in the use of the detector. The detector covers an area of
The 9 Be 32 Ar; 31 ArX reaction, leading to the 5 2 ground state of a nucleus at the proton drip ... more The 9 Be 32 Ar; 31 ArX reaction, leading to the 5 2 ground state of a nucleus at the proton drip line, has a cross section of 10.4(13) mb at a beam energy of 65:1 MeV=nucleon. This translates into a spectroscopic factor that is only 24(3)% of that predicted by the many-body shell-model theory. We introduce refinements to the eikonal reaction theory used to extract the spectroscopic factor to clarify that this very strong reduction represents an effect of nuclear structure. We suggest that it reflects correlation effects linked to the high neutron separation energy (22.0 MeV) for this state.
The asymptotic D - to S -state ratio η for the {l_angle}dαthinsp{vert_bar} â¶Li{r_angle} bound... more The asymptotic D - to S -state ratio η for the {l_angle}dαthinsp{vert_bar} â¶Li{r_angle} bound-state overlap is determined from measurements of the tensor analyzing powers for (â¶Li,thinspd ) reactions on medium-heavy targets. The reactions are described by the distorted-wave Born approximation assuming a direct α -particle transfer reaction mechanism. The calculations provide good agreement with cross section and vector analyzing power
Fragmentation reactions with intermediate-energy heavy-ion beams exhibit a wide range of reaction... more Fragmentation reactions with intermediate-energy heavy-ion beams exhibit a wide range of reaction mechanisms, ranging from direct reactions to statistical processes. We examine this transition by measuring the relative population of excited states in several sd-shell nuclei produced by fragmentation with the number of removed nucleons ranging from two to sixteen. The two-nucleon removal is consistent with a non-dissipative process whereas the removal of more than five nucleons appears to be mainly statistical.
ABSTRACT Intermediate-energy Coulomb excitation has been used to study excited states in the radi... more ABSTRACT Intermediate-energy Coulomb excitation has been used to study excited states in the radioactive N=19 nuclei 33Si and 34P, which are neutron-rich spherical nuclei located along the boundary of the ``island of inversion.'' The present results for the 1010 keV state in 33Si and states up to 2.2 MeV excitation energy in 34P can be understood in terms of 0ħω (nonintruder) configurations. This suggests that the energy differences between 0ħω and 2ħω configurations are large enough in 33Si and 34P that the low-lying 0ħω states are not significantly perturbed.
Neutron hole states in the exotic N = 27 isotope 44 Cl have been populated using the intermediate... more Neutron hole states in the exotic N = 27 isotope 44 Cl have been populated using the intermediate-energy single-neutron knockout reaction 9 Be(45 Cl, 44 Cl)X. The momentum distribution of the residual 44 Cl nuclei after direct population of the ground state is consistent with removal of an l = 1 neutron. This observation and comparison with a shell-model calculation imply that p 3/2 neutrons from above the N = 28 major shell closure play important roles in the ground states of both 44 Cl and 45 Cl. The present result is significant because 44 Cl is even closer to the valley of stability than 43 S, where a similar result was recently obtained using a g-factor measurement.
It is proposed that certain states of undetermined spin and parity observed in previously reporte... more It is proposed that certain states of undetermined spin and parity observed in previously reported ¹â¹â¸Pt(p,p'/gamma/) and /sup 194,196,198/Pt(p,p') experiments are 3â» states and contain a significant amount of octupole strength. These results show that the octupole strength is fragmented in the Pt isotopes. The predictions of Engel for the distribution of octupole strength in Pt isotopes are compared to
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