Precision measurement of the electric quadrupole moment of 31Al and determination of the effective proton charge in the sd-shell

he electric quadrupole coupling constant of the 31Al ground state is measured to be nu_Q = |eQV_{zz}/h| = 2196(21)kHz using two different beta-NMR (Nuclear Magnetic Resonance) techniques. For the first time, a direct comparison is made between the continuous rf technique and the adiabatic fast passage method. The obtained coupling constants of both methods are in excellent agreement with each other and a precise value for the quadrupole moment of 31Al has been deduced: |Q(31Al)| = 134.0(16) mb. Comparison of this value with large-scale shell-model calculations in the sd and sdpf valence spaces suggests that the 31Al ground state is dominated by normal sd-shell configurations with a possible small contribution of intruder states. The obtained value for |Q(31Al)| and a compilation of measured quadrupole moments of odd-Z even-N isotopes in comparison with shell-model calculations shows that the proton effective charge e_p=1.1 e provides a much better description of the nuclear properties in the sd-shell than the adopted value e_p=1.3 e

Electric quadrupole moment of the neutron-rich Al-33

The nuclear electric quadrupole moment (Q moment) of the neutron-rich nucleus Al-33 (I = 5/2, T-1/2 = 41 ms) has been measured by the beta-ray detected nuclear quadrupole resonance (beta-NQR) method for the first time. The Al-33 nucleus is considered to be on the border of the island of inversion within which a significant intrusion of the pf orbits occurs across the N = 20 shell gap and the intrusion causes an anomalous enhancement of the Q moment. Polarized Al-33 nuclei were produced from S-36 (77.5MeV/u) beams through the fragmentation process and separated by LISE fragment separator at GANIL. The Al-33 nuclei were implanted into a Al2O3 single-crystal plate and the beta-NQR spectrum was successfully obtained.status: publishe

Electric quadrupole moment of the neutron-rich 33Al

Expérience GANILInternational audienceThe nuclear electric quadrupole moment (Q moment) of the neutron-rich nucleus 33Al (I = 5/2, T1/2 = 41ms) has been measured by the β-ray detected nuclear quadrupole resonance (β-NQR) method for the first time. The 33Al nucleus is considered to be on the border of the island of inversion within which a significant intrusion of the pf orbits occurs across the N = 20 shell gap and the intrusion causes an anomalous enhancement of the Q moment. Polarized 33Al nuclei were produced from 36S (77.5MeV/u) beams through the fragmentation process and separated by LISE fragment separator at GANIL. The 33Al nuclei were implanted into a Al2O3 single-crystal plate and the β-NQR spectrum was successfully obtained

Erosion of N=20 shell in Al33 investigated through the ground-state electric quadrupole moment

AbstractElectric quadrupole moment Q of the Al33 ground state has been measured by means of β-NMR spectroscopy using a spin-polarized Al33 beam produced in a projectile fragmentation reaction. The obtained Q moment, |Qexp(33Al)|=132(16) emb, shows a significant excess from the prediction of shell model calculations within the sd shell. The result indicates sizable admixing of pf intruder configurations in the ground state, demonstrating that the N=20 shell closure certainly erodes in Al33, a nucleus located on the border of the island of inversion. Comparison was made with predictions of the Monte Carlo shell model, and also a particle-vibration coupling model treating the neutron pairing correlations in the ground state of Al33. Again, a significant admixture of pf intruder configurations to the Al33 ground state was needed in both theoretical approaches to explain the observed large Q