Weak-coupling Core-excitation Model Research Articles

Excited stategfactors inTe125

The transient-field technique has been used to measure, with considerably improved precision, the $g$ factors of the $3/{2}^{+}$ and $5/{2}^{+}$ states in $^{125}\mathrm{Te}$ at 444 and 463 keV, respectively, relative to the $g$ factor of the first excited state in $^{126}\mathrm{Te}$. Together with shell model and weak-coupling core-excitation model calculations, the $g$-factor measurements provide insight into the orbital occupation of the odd neutron for the low-excitation states in $^{125}\mathrm{Te}$. A new $9/{2}^{+}$ level at 1029 keV, together with a firm $7/{2}^{+}$ spin assignment for the level at 1018 keV, identifies candidate states for the coupling of the ${s}_{1/2}$ neutron to the ${4}^{+}$ core excitation.

Measured gyromagnetic ratios and the low-excitation spectroscopy of 197Au

Transient-field precessions were measured for levels in 197Au and 182,184,186W as their ions simultaneously traversed polarized Gd hosts. Gyromagnetic ratios were inferred for the positiveparity levels between, and including, the lowest 5 2 + and 11 2 + states in 197Au. Lifetimes of several levels were determined using the Doppler-broadened lineshape technique, and multipole mixing ratios of a number of transitions were deduced from measured particle-γ-ray angular correlations. The measured static and dynamic electromagnetic moments are compared with the predictions of the weak-coupling core-excitation model and with those of the interacting boson-fermion model (IBFM), including its Spin(6) supersymmetry limit.

Negative parity levels in195Pt via [Coulomb excitation

Low lying negative parity levels in195Pt were Coulomb excited with 4.0–5.5 MeV protons to test the weak coupling core-excitation model. A Ge(Li) detector was used to measure gamma ray yields and angular distributions. The levels at 449.6 and 793 keV were Coulomb excited repeatedly. The results of the gamma-ray angular distributions not only confirmed the assignment of 3/2 spin to the 199 keV level but also established 5/2, 5/2, and 3/2 spins for the levels at 389.6, 449.6 and 793 keV, respectively. The E2 and M1 transition probabilities for the 389.6, 449.6 and 793 keV transitions were found for the first time. The 211.2, 239.2, 389.6 and 793 keV states have electromagnetic magnetic properties consistent with the interpretation of coupling of a P1/2 neutron to the 2 1 + and 2 2 + core-states.

Study of negative parity levels in 63Cu

Low-lying negative parity levels in 63Cu were Coulomb excited with 3.25 to 4.25 MeV protons to test the weak coupling core-excitation model. A Ge(Li) detector was used to measure the gamma-ray yields. The 1412, 1547, and 1861 keV levels in 63Cu were Coulomb excited for the first time. Gamma-ray angular distributions were measured at 4.25 MeV proton energy in deducing multipole mixing ratios and spin values. The E2 and M1 reduced transition probabilities were determined for the six states. The 669.6, 962, 1327, and 1547 keV levels have properties consistent with the interpretation of coupling a 2p3/2 proton to the first 2+core state. The present results were compared with the available particle–core and particle–phonon model calculations.

Coulomb excitation of low-energy levels in 45Sc

Low-lying negative parity levels in 45Sc were Coulomb excited with 2.5 to 3.5 MeV protons and 4 to 5 MeV 4He ions to test the weak coupling core-excitation model. A Ge(Li) detector was used to measure the gamma-ray yields. The 543, 976, 1408, and 1662 keV levels in 45Sc were Coulomb excited for the first time. Gamma-ray angular distributions were measured at 3.0 MeV proton energy in deducing multipole mixing ratios and spin values. Energy level measurements (in units of kiloelectronvolts) and spin values obtained are as follows: 976, 5/2, 7/2 and 1408, 7/2. The E2 and M1 reduced transition probabilities were determined for the six states. The 376, 720, 1237, 1408, and 1662 keV levels have properties consistent with the interpretation of coupling a 1f7/2 proton to the first 2+ core state.

Measured lifetimes of states in 197Au and a critical comparison with the weak-coupling core-excitation model

The lifetimes of five excited states in 197Au up to an excitation energy of 885 keV were measured by the recoil-distance method (RDM). These levels were populated by Coulomb excitation using both 90 MeV 20Ne and 120 MeV 35Cl ion beams. The experimentally determined spectroscopy of the low-lying levels 3 2 + (ground state) and 1 2 + , 3 2 2 + , 5 2 + , and 7 2 + at 77.3, 268.8, 278.9, and 547.5 keV excitation energy, respectively, has been critically compared with the detailed predictions of the de-Shalit weak-coupling core-excitation model. When the model is taken to represent the case of a d 3 2 proton hole coupled to a 198Hg core, the model parameters obtained are in accord with the criteria implicit for weak core coupling and, at the same time, are in remarkably good agreement with virtually all measured E2 and M1 transition rates.

(p, t) Reactions on odd-a nuclei and the weak-coupling core-excitation model

Excited 7 2 − states to which enhanced L = 0 (p, t) transitions are observed have been identified in 41Ca at 2958 keV and in 57Co at 2611 keV. A comparison of these (p, t) transitions with those to the 0 + states in 40Ca at 3353 keV and in 58Ni at 2940 keV leads to the conclusion that these states are obtained by weak-coupling of a f 7 2 particle and hole, respectively, to the excited 0 + states of the doubly even cores. It is suggested that these cases are examples of a rather general weak-coupling phenomenon.

Negative parity levels in 103Rh via coulomb excitation

Low-lying negative parity levels in 103Rh were Coulomb excited with 7–10 MeV 4He ions and 36–45 MeV 16O ions to test the weak-coupling core excitation model for two-quadrupole phononcore states. A Ge(Li) detector was used to observe the de-excitation γ-rays in singles and 16O-γ coincident spectra. Gamma-ray angular distribution measurements taken during 4He ion bombardment established spin values of 5 2 and 3 2 for the 880 and 1277 keV states, respectively. The 848, 880, 920 and 1107 keV levels have properties consistent with the interpretation of coupling a 2p 1 2 proton to the 4 + and second 2 + core states. Our spectra give some indication of a level at 803 keV previously seen in inelastic proton-scattering work which could be a state arising from coupling to the two- phonon 0 + core state.

Coulomb Excitation of Levels inPd105

The low-lying excited states of ${\mathrm{Pd}}^{105}$ were investigated by means of Coulomb excitation using 4.4-8.0-MeV $\ensuremath{\alpha}$-particle projectiles. The $\ensuremath{\gamma}$-ray spectrum resulting from the deexcitation of these levels was recorded at each bombarding energy with the aid of a large-volume high-resolution Ge(Li) detector. Thirteen transitions were observed that result from direct $E2$ excitation of 10 excited states up to an excitation energy of 782 keV. The $B(E2\ensuremath{\uparrow})$ values from the ground state to each of these 10 levels was determined. Several $E2$ transitions were found to be strongly enhanced over estimates of single-particle speed, a pattern suggestive of collective behavior. The measured $B(E2)$ values, together with some inferred $M1$ transition speeds, are compared with predictions of a weak-coupling core-excitation model.

Inelastic Alpha-Particle Scattering on Copper 65 at 29 MeV

The excited states of 65 Cu have been studied by inelastic scattering of 29-MeV alpha particles. The over-all energy resolution of about 70 keV in this experiment enabled to resolve six quadrupole and eight octupole states. Transition strengths were extracted for these states using the DWBA method. The results were compared with the weak-coupling core-excitation model and with the theoretical calculation of Thankappan and True.

A study of the 28Si(d, 3He) 27Al reaction

Spectroscopic factors have been measured for all the levels in 27Al up to 3 MeV from the reaction 28Si(d, 3He) 27Al. The level at 3.00 MeV with J π 9 2 + is excited much more strongly than that at 2.98 MeV with J π = 3 2 + , although it does not show either an l = 2 or an l = 4 pick-up distribution. The results are not in agreement with the collective rotational model. Better, but still not very good, agreement is found with the weak-coupling core-excitation model. Occupation numbers are obtained for protons in d 5 2 , d 3 2 and d 1 2 orbits for the ground state wave function of 28Si. These are compared with the neutron occupation numbers.