Analog E1 transitions and isospin mixing

We investigate whether isospin mixing can be determined in a model-independent way from the relative strength of E1 transitions in mirror nuclei. The specific examples considered are the A=31 and A=35 mirror pairs, where a serious discrepancy between the strengths of 7/2--->5/2+ transitions in the respective mirror nuclei has been observed. A theoretical analysis of the problem suggests that it ought to be possible to disentangle the isospin mixing in the initial and final states given sufficient information on experimental matrix elements. With this in mind, we obtain a lifetime for the relevant 7/2- state in 31S using the Doppler-shift attenuation method. We then collate the available information on matrix elements to examine the level of isospin mixing for both A=31 and A=35 mirror pairs

Studies of neutron-deficient nuclei near the Z=82 shell closure via cold fusion reactions

Over the last decade, we have performed in-beam experiments using Gammasphere + FMA to measure excited states in proton-rich Au, Hg, Tl and Pb isotopes. In these studies, the use of the FMA is essential in order to differentiate evaporation residues from the large fission background which dominates the reaction cross-section. In addition, we have found that using near-symmetric reactions at bombarding energies near the Coloumb barrier is beneficial in performing these studies. By keeping the bombarding energy low, fission is minimized and the reaction products are concentrated in only a few channels. New results have recently been obtained using the 90Zr+92Mo reaction to study shape co-existence in 181T1 via the lp evaporation channel. In addition, we have measured the total γ-ray energy and multiplicity associated with the surviving compund system, 179Au, following the fusion reaction, 90Zr + 89Y

High-resolution spectroscopy of decay pathways in the 12C(12C,γ) reaction

The decay branchings of a resonance in the 12C(12C,γ)24Mg reaction at Ec.m. = 8.0 MeV have been studied with high resolution using the Gammasphere array. Radiative capture residues were discriminated from scattered beam and the dominant evaporation channels using the fragment mass analyzer coupled to a multistage Parallel Grid Avalanche Counter (PGAC)/ion chamber system. The clean selection of residues has allowed the population of excited states up to 10 MeV in 24Mg to be examined in detail. Strong feeding of an excited Kπ=0- band is observed. A Jπ = 4+ assignment to the resonance is strongly favored

In-beam γ-ray spectroscopy of the proton emitter 147 69Tm using recoil-decay tagging

Gamma rays from the decay of states in the proton unstable nucleus 147Tm were observed for the first time following the 92Mo(58Ni,p2n! 147Tm reaction at 260 MeV. Prompt g rays were detected with an array of Compton-suppressed Ge detectors, placed in front of the fragment mass analyzer at the ATLAS accelerator, and were assigned to individual reaction channels on an event-by-event basis using the recoil-decay tagging method. Gamma-ray transitions were associated with both the proton decay of the ph11/2 ground state and the pd3/2 isomeric state in 147Tm, even though the cross sections for populating these states were only ' 16 mb and 2 mb, respectively. The level scheme which was constructed for 147Tm is discussed and compared with the level structures for lighter N578 isotones

High-spin states in 179Au: Spectroscopy of shape-driving orbitals beyond the neutron midshell

Multiple band structures in 179Au are established from γ-ray spectroscopic measurements with Gammasphere at the Argonne Fragment Mass Analyzer. The yrast band, based on the 13/2+ proton, confirms the predicted drop in excitation energy of the prolate deformed band head as compared to the heavier isotopes. The implications for the prolate energy minimum in odd-mass Au nuclei beyond the neutron i13/2 midshell (N<102) are discussed

Cytotoxic T Lymphocyte Responses to Transgene Product, Not Adeno-Associated Viral Capsid Protein, Limit Transgene Expression in Mice

The use of adeno-associated viral (AAV) vectors for gene replacement therapy is currently being explored in several clinical indications. However, reports have suggested that input capsid proteins from AAV-2 vector particles may result in the stimulation of cytotoxic T lymphocyte (CTL) responses that can result in a loss of transduced cells. To explore the impact of anti-AAV CTLs on AAV-mediated transgene expression, both immunocompetent C57BL/6 mice and B cell-deficient μMT mice were immunized against the AAV2 capsid protein (Cap) and were injected intravenously with an AAV-2 vector encoding α-galactosidase (α-Gal). C57BL/6 mice, which developed both CTL and neutralizing antibody responses against Cap, failed to show any detectable α-Gal expression. In contrast, serum α-Gal levels comparable to those of naive mice were observed in μMT mice despite the presence of robust CTL activity against Cap, indicating that preexisting Cap-specific CTLs did not have any effect on the magnitude and duration of transgene expression. The same strategy was used to assess the impact of CTLs against the α-Gal transgene product on AAV-mediated gene delivery and persistence of transgene expression. Preimmunization of μMT mice with an Ad/α-Gal vector induced a robust CTL response to α-Gal. When these mice were injected with AAV2/α-Gal vector, initial levels of α-Gal expression were reduced by more than 1 log and became undetectable by 2 weeks postinjection. Overall, our results indicate that CTLs against the transgene product as opposed to AAV capsid protein are more likely to interfere with AAV transgene expression

High-resolution spectroscopy of decay pathways in the C-12(C-12,gamma) reaction

The decay branchings of a resonance in the 12C(12C,γ)24Mg reaction at Ec.m. = 8.0 MeV have been studied with high resolution using the Gammasphere array. Radiative capture residues were discriminated from scattered beam and the dominant evaporation channels using the fragment mass analyzer coupled to a multistage Parallel Grid Avalanche Counter (PGAC)/ion chamber system. The clean selection of residues has allowed the population of excited states up to 10 MeV in 24Mg to be examined in detail. Strong feeding of an excited Kπ=0− band is observed. A Jπ = 4+assignment to the resonance is strongly favored

Magnetic dipole bands in 190^{190}Hg : first evidence of excitation across the Z=82 sub-shell in Hg nuclei

Matière Nucléair

Discrete line spectroscopy at the extremes of angular momentum in normal deformed 156Dy and global differential lifetime measurements in the A ∼ 130 highly-deformed region

The highest-spin discrete states (I ∼ 60ℏ and Ex ∼ 30MeV) in normal deformed nuclei have been observed in the rare-earth isotope 156Dy using the GAMMASPHERE spectrometer. The quadrupole moments for a variety of configurations, including the 9/2+[404] (g9/2) proton, 1/2+[660] (i13/2) and 1/2-[541] (f7/2, h9/2) neutron orbitals, were measured in a wide range of ∼ 130 nuclei