462 research outputs found
Reply to "comment on 'Level structure of Rh92: Implications for the two-proton decay of 94Agm'"
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Decay of the key 92-keV resonance in the 25Mg(p,γ) reaction to the ground and isomeric states of the cosmic γ-ray emitter 26Al
The 92-keV resonance in the 25Mg(p,γ)26Al reaction plays a key role in the production of 26Al at astrophysical burning temperatures of ≈100 MK in the Mg-Al cycle. However, the state can decay to feed either the ground, 26gAl, or isomeric state, 26mAl. It is the ground state that is critical as the source of cosmic γ rays. It is therefore important to precisely determine the ground-state branching fraction f0 of this resonance. Here we report on the identification of four γ-ray transitions from the 92-keV resonance, and determine the spin of the state and its ground-state branching fraction f0=0.52(2)stat(6)syst. The f0 value is the most precise reported to date, and at the lower end of the range of previously adopted values, implying a lower production rate of 26gAl and its cosmic 1809-keV γ rays.peerReviewe
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
Properties of excited states in Ge77
The nucleus Ge77 was studied through the Ge76(C13,C12)Ge77 reaction at a sub-Coulomb energy. The angular distributions of γ rays depopulating excited states in Ge77 were measured in order to constrain spin and parity assignments. Some of these assignments are of use in connection with neutrinoless double beta decay, where the population of states near the Fermi surface of Ge76 was recently explored using transfer reactions
Disruption of mouse ERCC1 results in a novel repair syndrome with growth failure, nuclear abnormalities and senescence.
BACKGROUND: The structure-specific ERCC1/XPF endonuclease complex that contains the ERCC1 and XPF subunits is implicated in the repair of two distinct types of lesions in DNA: nucleotide excision repair (NER) for ultraviolet-induced lesions and bulky chemical adducts; and recombination repair of the very genotoxic interstrand cross-links. RESULTS: Here, we present a detailed analysis of two types of mice with mutations in ERCC1, one in which the gene is 'knocked out', and one in which the encoded protein contains a seven amino-acid carboxy-terminal truncation. In addition to the previously reported symptoms of severe runting, abnormalities of liver nuclei and greatly reduced lifespan (which appeared less severe in the truncation mutant), both types of ERCC1-mutant mouse exhibited an absence of subcutaneous fat, early onset of ferritin deposition in the spleen, kidney malfunction, gross abnormalities of ploidy and cytoplasmic invaginations in nuclei of liver and kidney, and compromised NER and cross-link repair. We also found that heterozygosity for ERCC1 mutations did not appear to provide a selective advantage for chemically induced tumorigenesis. An important clue to the cause of the very severe ERCC1-mutant phenotypes is our finding that ERCC1-mutant cells undergo premature replicative senescence, unlike cells from mice with a defect only in NER. CONCLUSIONS: Our results strongly suggest that the accumulation in ERCC1-mutant mice of endogenously generated DNA interstrand cross-links, which are normally repaired by ERCC1-dependent recombination repair, underlies both the early onset of cell cycle arrest and polyploidy in the liver and kidney. Thus, our work provides an insight into the molecular basis of ageing and highlights the role of ERCC1 and interstrand DNA cross-links
Two-quasiparticle structures and isomers in Er168, Er170, and Er172
The stable and neutron-rich isotopes Er168, Er170, and Er172 have been studied with Gammasphere using inelastic excitation with energetic Xe136 beams. The previously assigned structures based on the proposed Kπ=4- isomeric intrinsic states in both Er168 and Er170 have been re-evaluated and an equivalent band identified in Er172. In Er170, the identification of a Kπ=6- band with transitions close in energy to those of the 4 - band leads to a modified interpretation, since the overlap would have compromised previous analyses. The gK-gR values for the 4- bands deduced from the in-band γ-ray intensities for the sequence of isotopes suggest a predominantly two-neutron configuration in Er168, an equally mixed two-neutron, two-proton configuration in Er170, and a two-proton configuration in Er172. A comprehensive decay scheme for the previously proposed 6+ isomer in Er172 has also been established, as well as band structures built on this isomer that closely resemble the 6+ and 7- two-neutron structures known in the isotone Yb174. The implied K hindrances are discussed. The main decay path of the 6+ isomer occurs through the newly identified 4- isomer. The measured lifetimes of the 4 - and 6+ isomers in Er172 are 57(3) and 822(90) ns, respectively. Multiquasiparticle calculations support the suggested configuration changes across the isotopic chain
Precise electromagnetic tests of ab initio calculations of light nuclei: States in Be10
In order to test ab initio calculations of light nuclei, we have remeasured lifetimes in Be10 using the Doppler shift attenuation method (DSAM) following the Li7(Li7,α)Be10 reaction at 8 and 10 MeV. The new experiments significantly reduce systematic uncertainties in the DSAM technique. The Jπ=21+ state at 3.37 MeV has τ=205±(5)stat±(7)sysfs corresponding to a B(E2) of 9.2(3)e2fm4 in broad agreement with many calculations. The Jπ=22+ state at 5.96 MeV was found to have a B(E2) of 0.11(2)e2fm4 and provides a more discriminating test of nuclear models. New Green's function Monte Carlo calculations for these states and transitions with a number of Hamiltonians are also reported and compared to experiment
Lifetime of the KÏ€=8- isomer in the neutron-rich nucleus Er174, and N=106 E1 systematics
Chopped-beam techniques and γ-ray spectroscopy with Gammasphere have been used to measure the lifetime of the 1112-keV 8- isomeric state in Er174. The value obtained of τ=5.8(4) s corresponds to a reduced hindrance of fν=98 for the 163-keV E1 transition to the 8+ state of the ground-state band, in good agreement with the systematics of the corresponding E1 strengths in the N=106 isotones. The K-mixing in the 8- states is calculated in the context of the particle-rotor model and used to extract the underlying reduced hindrances
Parity doubling in Th219 and the onset of collectivity above N=126
Excited states in Th219 have been observed for the first time in an experiment using the Mg26+Pt198 reaction and evaporation-residue-gated γ-ray spectroscopy. Two structures of interlinked alternating-parity levels with simplex quantum numbers s=±i are observed, reminiscent of similar sequences in heavier odd-mass isotopes, but only three mass units away from the N=126 neutron closed shell. The emergence of quadrupole-octupole collectivity in this mass region and the trend for parity-doublet bands are discussed
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