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We investigated decays of ^{51,52,53}K at the ISOLDE Decay Station at CERN in order to understand the mechanism of the ß-delayed neutron-emission (ßn) process. The experiment quantified neutron and γ-ray emission paths for each precursor. We used this information to test the hypothesis, first formulated by Bohr in 1939, that neutrons in the ßn process originate from the structureless "compound nucleus." The data are consistent with this postulate for most of the observed decay paths. The agreement, however, is surprising because the compound-nucleus stage should not be achieved in the studied ß decay due to insufficient excitation energy and level densities in the neutron emitter. In the ^{53}K ßn decay, we found a preferential population of the first excited state in ^{52}Ca that contradicted Bohr's hypothesis. The latter was interpreted as evidence for direct neutron emission sensitive to the structure of the neutron-unbound state. We propose that the observed nonstatistical neutron emission proceeds through the coupling with nearby doorway states that have large neutron-emission probabilities. The appearance of "compound-nucleus" decay is caused by the aggregated small contributions of multiple doorway states at higher excitation energy.
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The changes in mean-squared charge radii of neutron-deficient gold nuclei have been determined using the in-source, resonance-ionization laser spectroscopy technique, at the ISOLDE facility (CERN). From these new data, nuclear deformations are inferred, revealing a competition between deformed and spherical configurations. The isotopes ^{180,181,182}Au are observed to possess well-deformed ground states and, when moving to lighter masses, a sudden transition to near-spherical shapes is seen in the extremely neutron-deficient nuclides, ^{176,177,179}Au. A case of shape coexistence and shape staggering is identified in ^{178}Au which has a ground and isomeric state with different deformations. These new data reveal a pattern in ground-state deformation unique to the gold isotopes, whereby, when moving from the heavy to light masses, a plateau of well-deformed isotopes exists around the neutron midshell, flanked by near-spherical shapes in the heavier and lighter isotopes-a trend hitherto unseen elsewhere in the nuclear chart. The experimental charge radii are compared to those from Hartree-Fock-Bogoliubov calculations using the D1M Gogny interaction and configuration mixing between states of different deformation. The calculations are constrained by the known spins, parities, and magnetic moments of the ground states in gold nuclei and show a good agreement with the experimental results.
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The ß decays from both the ground state and a long-lived isomer of ^{133}In were studied at the ISOLDE Decay Station (IDS). With a hybrid detection system sensitive to ß, γ, and neutron spectroscopy, the comparative partial half-lives (logft) have been measured for all their dominant ß-decay channels for the first time, including a low-energy Gamow-Teller transition and several first-forbidden (FF) transitions. Uniquely for such a heavy neutron-rich nucleus, their ß decays selectively populate only a few isolated neutron unbound states in ^{133}Sn. Precise energy and branching-ratio measurements of those resonances allow us to benchmark ß-decay theories at an unprecedented level in this region of the nuclear chart. The results show good agreement with the newly developed large-scale shell model (LSSM) calculations. The experimental findings establish an archetype for the ß decay of neutron-rich nuclei southeast of ^{132}Sn and will serve as a guide for future theoretical development aiming to describe accurately the key ß decays in the rapid-neutron capture (r-) process.
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We demonstrate a new technique for obtaining fission data for nuclei away from ß stability. These types of data are pertinent to the astrophysical r process, crucial to a complete understanding of the origin of the heavy elements, and for developing a predictive model of fission. These data are also important considerations for terrestrial applications related to power generation and safeguarding. Experimentally, such data are scarce due to the difficulties in producing the actinide targets of interest. The solenoidal-spectrometer technique, commonly used to study nucleon-transfer reactions in inverse kinematics, has been applied to the case of transfer-induced fission as a means to deduce the fission-barrier height, among other variables. The fission-barrier height of ^{239}U has been determined via the ^{238}U(d,pf) reaction in inverse kinematics, the results of which are consistent with existing neutron-induced fission data indicating the validity of the technique.
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The ß-delayed one- and two-neutron emission probabilities (P_{1n} and P_{2n}) of 20 neutron-rich nuclei with N≥82 have been measured at the RIBF facility of the RIKEN Nishina Center. P_{1n} of ^{130,131}Ag, ^{133,134}Cd, ^{135,136}In, and ^{138,139}Sn were determined for the first time, and stringent upper limits were placed on P_{2n} for nearly all cases. ß-delayed two-neutron emission (ß2n) was unambiguously identified in ^{133}Cd and ^{135,136}In, and their P_{2n} were measured. Weak ß2n was also detected from ^{137,138}Sn. Our results highlight the effect of the N=82 and Z=50 shell closures on ß-delayed neutron emission probability and provide stringent benchmarks for newly developed macroscopic-microscopic and self-consistent global models with the inclusion of a statistical treatment of neutron and γ emission. The impact of our measurements on r-process nucleosynthesis was studied in a neutron star merger scenario. Our P_{1n} and P_{2n} have a direct impact on the odd-even staggering of the final abundance, improving the agreement between calculated and observed Solar System abundances. The odd isotope fraction of Ba in r-process-enhanced (r-II) stars is also better reproduced using our new data.
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Using the fusion-evaporation reaction ^{96}Ru(^{58}Ni,p4n)^{149}Lu and the MARA vacuum-mode recoil separator, a new proton-emitting isotope ^{149}Lu has been identified. The measured decay Q value of 1920(20) keV is the highest measured for a ground-state proton decay, and it naturally leads to the shortest directly measured half-life of 450_{-100}^{+170} ns for a ground-state proton emitter. The decay rate is consistent with l_{p}=5 emission, suggesting a dominant πh_{11/2} component for the wave function of the proton-emitting state. Through nonadiabatic quasiparticle calculations it was concluded that ^{149}Lu is the most oblate deformed proton emitter observed to date.
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In the few years leading up to this research, CLEAPSS noticed a small but steadily increasing number of calls from UK schools regarding a red-brown discolouration on the surface of the foil of their radium source. There were no reports of this type of discolouration on foils of other radionuclides. CLEAPSS and the University of Liverpool collaborated to investigate the nature and cause of this discolouration and the likelihood that the foils were becoming unsafe. The evidence indicates that the discolouration is principally caused by some combination of silicon, sulfur and possibly lead from within the foil diffusing into the face layer. There is no indication currently that the face layers are fragmenting on these foils, but the longer-term integrity of the discoloured foils now becomes questionable. Given the age of the foils and the radiotoxicity of radium, the recommendation from this research is that discoloured foils should be taken out of service and disposed.
Assuntos
Rádio (Elemento) , Instituições Acadêmicas , Reino UnidoRESUMO
The ß decay of ^{208}Hg into the one-proton hole, one neutron-particle _{81}^{208}Tl_{127} nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the N>126, Z<82 quadrant of neutron-rich nuclei. While both negative and positive parity states with spin 0 and 1 are expected within the Q_{ß} window, only three negative parity states are populated directly in the ß decay. The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden ß decays, essential for the understanding of the nucleosynthesis of heavy nuclei in the rapid neutron capture process. Furthermore, the observation of the parity changing 0^{+}â0^{-}ß decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators.
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An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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The nuclei below lead but with more than 126 neutrons are crucial to an understanding of the astrophysical r process in producing nuclei heavier than Aâ¼190. Despite their importance, the structure and properties of these nuclei remain experimentally untested as they are difficult to produce in nuclear reactions with stable beams. In a first exploration of the shell structure of this region, neutron excitations in ^{207}Hg have been probed using the neutron-adding (d,p) reaction in inverse kinematics. The radioactive beam of ^{206}Hg was delivered to the new ISOLDE Solenoidal Spectrometer at an energy above the Coulomb barrier. The spectroscopy of ^{207}Hg marks a first step in improving our understanding of the relevant structural properties of nuclei involved in a key part of the path of the r process.
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There is sparse direct experimental evidence that atomic nuclei can exhibit stable "pear" shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole (E3) matrix elements have been determined for transitions in ^{222,228}Ra nuclei using the method of sub-barrier, multistep Coulomb excitation. Beams of the radioactive radium isotopes were provided by the HIE-ISOLDE facility at CERN. The observed pattern of E3 matrix elements for different nuclear transitions is explained by describing ^{222}Ra as pear shaped with stable octupole deformation, while ^{228}Ra behaves like an octupole vibrator.
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There is a large body of evidence that atomic nuclei can undergo octupole distortion and assume the shape of a pear. This phenomenon is important for measurements of electric-dipole moments of atoms, which would indicate CP violation and hence probe physics beyond the Standard Model of particle physics. Isotopes of both radon and radium have been identified as candidates for such measurements. Here, we observed the low-lying quantum states in 224Rn and 226Rn by accelerating beams of these radioactive nuclei. We show that radon isotopes undergo octupole vibrations but do not possess static pear-shapes in their ground states. We conclude that radon atoms provide less favourable conditions for the enhancement of a measurable atomic electric-dipole moment.
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The ^{12}C(α,γ)^{16}O reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced α width, γ_{11}, of the bound 1^{-} level in ^{16}O is particularly important to determine the cross section. The magnitude of γ_{11} is determined via sub-Coulomb α-transfer reactions or the ß-delayed α decay of ^{16}N, but the latter approach is presently hampered by the lack of sufficiently precise data on the ß-decay branching ratios. Here we report improved branching ratios for the bound 1^{-} level [b_{ß,11}=(5.02±0.10)×10^{-2}] and for ß-delayed α emission [b_{ßα}=(1.59±0.06)×10^{-5}]. Our value for b_{ßα} is 33% larger than previously held, leading to a substantial increase in γ_{11}. Our revised value for γ_{11} is in good agreement with the value obtained in α-transfer studies and the weighted average of the two gives a robust and precise determination of γ_{11}, which provides significantly improved constraints on the ^{12}C(α,γ) cross section in the energy range relevant to hydrostatic He burning.
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BACKGROUND: RECORD-3 compared everolimus and sunitinib as first-line therapy, and the sequence of everolimus followed by sunitinib at progression compared with the opposite (standard) sequence in patients with metastatic renal cell carcinoma (mRCC). This final overall survival (OS) analysis evaluated mature data for secondary end points. PATIENTS AND METHODS: Patients received either first-line everolimus followed by second-line sunitinib at progression (n = 238) or first-line sunitinib followed by second-line everolimus (n = 233). Secondary end points were combined first- and second-line progression-free survival (PFS), OS, and safety. The impacts of neutrophil lymphocyte ratio (NLR) and baseline levels of soluble biomarkers on OS were explored. RESULTS: At final analysis, median duration of exposure was 5.6 months for everolimus and 8.3 months for sunitinib. Median combined PFS was 21.7 months [95% confidence interval (CI) 15.1-26.7] with everolimus-sunitinib and 22.2 months (95% CI 16.0-29.8) with sunitinib-everolimus [hazard ratio (HR)EVE-SUN/SUN-EVE, 1.2; 95% CI 0.9-1.6]. Median OS was 22.4 months (95% CI 18.6-33.3) for everolimus-sunitinib and 29.5 months (95% CI 22.8-33.1) for sunitinib-everolimus (HREVE-SUN/SUN-EVE, 1.1; 95% CI 0.9-1.4). The rates of grade 3 and 4 adverse events suspected to be related to second-line therapy were 47% with everolimus and 57% with sunitinib. Higher NLR and 12 soluble biomarker levels were identified as prognostic markers for poor OS with the association being largely independent of treatment sequences. CONCLUSIONS: Results of this final OS analysis support the sequence of sunitinib followed by everolimus at progression in patients with mRCC. The safety profiles of everolimus and sunitinib were consistent with those previously reported, and there were no unexpected safety signals. CLINICAL TRIALS NUMBER: ClinicalTrials.gov identifier, NCT00903175.
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Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Carcinoma de Células Renais/tratamento farmacológico , Neoplasias Renais/tratamento farmacológico , Adulto , Idoso , Idoso de 80 Anos ou mais , Estudos Cross-Over , Everolimo/administração & dosagem , Feminino , Humanos , Indóis/administração & dosagem , Masculino , Pessoa de Meia-Idade , Prognóstico , Pirróis/administração & dosagem , Sunitinibe , Análise de Sobrevida , Adulto JovemRESUMO
BACKGROUND: Lung cancer screening using low-dose CT (LDCT) was shown to reduce lung cancer mortality by 20% in the National Lung Screening Trial. METHODS: The pilot UK Lung Cancer Screening (UKLS) is a randomised controlled trial of LDCT screening for lung cancer versus usual care. A population-based questionnaire was used to identify high-risk individuals. CT screen-detected nodules were managed by a pre-specified protocol. Cost effectiveness was modelled with reference to the National Lung Cancer Screening Trial mortality reduction. RESULTS: 247â 354 individuals aged 50-75â years were approached; 30.7% expressed an interest, 8729 (11.5%) were eligible and 4055 were randomised, 2028 into the CT arm (1994 underwent a CT). Forty-two participants (2.1%) had confirmed lung cancer, 34 (1.7%) at baseline and 8 (0.4%) at the 12-month scan. 28/42 (66.7%) had stage I disease, 36/42 (85.7%) had stage I or II disease. 35/42 (83.3%) had surgical resection. 536 subjects had nodules greater than 50â mm(3) or 5â mm diameter and 41/536 were found to have lung cancer. One further cancer was detected by follow-up of nodules between 15 and 50â mm(3) at 12â months. The baseline estimate for the incremental cost-effectiveness ratio of once-only CT screening, under the UKLS protocol, was £8466 per quality adjusted life year gained (CI £5542 to £12â 569). CONCLUSIONS: The UKLS pilot trial demonstrated that it is possible to detect lung cancer at an early stage and deliver potentially curative treatment in over 80% of cases. Health economic analysis suggests that the intervention would be cost effective-this needs to be confirmed using data on observed lung cancer mortality reduction. TRIAL REGISTRATION: ISRCTN 78513845.
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Detecção Precoce de Câncer/métodos , Neoplasias Pulmonares/diagnóstico , Programas de Rastreamento/métodos , Tomografia Computadorizada por Raios X/métodos , Idoso , Feminino , Humanos , Neoplasias Pulmonares/epidemiologia , Masculino , Pessoa de Meia-Idade , Projetos Piloto , Prevalência , Prognóstico , Reprodutibilidade dos Testes , Inquéritos e Questionários , Reino Unido/epidemiologiaRESUMO
Search for a new kind of superfluidity built on collective proton-neutron pairs with aligned spin is performed studying the Gamow-Teller decay of the T=1, J(π)=0+ ground state of (62)Ge into excited states of the odd-odd N=Z nucleus (62)Ga. The experiment is performed at GSI Helmholtzzentrum für Shwerionenforshung with the (62)Ge ions selected by the fragment separator and implanted in a stack of Si-strip detectors, surrounded by the RISING Ge array. A half-life of T1/2=82.9(14) ms is measured for the (62)Ge ground state. Six excited states of (62)Ga, populated below 2.5 MeV through Gamow-Teller transitions, are identified. Individual Gamow-Teller transition strengths agree well with theoretical predictions of the interacting shell model and the quasiparticle random phase approximation. The absence of any sizable low-lying Gamow-Teller strength in the reported beta-decay experiment supports the hypothesis of a negligible role of coherent T=0 proton-neutron correlations in (62)Ga.
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Coulomb-excitation experiments to study electromagnetic properties of radioactive even-even Hg isotopes were performed with 2.85 MeV/nucleon mercury beams from REX-ISOLDE. Magnitudes and relative signs of the reduced E2 matrix elements that couple the ground state and low-lying excited states in Hg182-188 were extracted. Information on the deformation of the ground and the first excited 0+ states was deduced using the quadrupole sum rules approach. Results show that the ground state is slightly deformed and of oblate nature, while a larger deformation for the excited 0+ state was noted in Hg182,184. The results are compared to beyond mean field and interacting-boson based models and interpreted within a two-state mixing model. Partial agreement with the model calculations was obtained. The presence of two different structures in the light even-mass mercury isotopes that coexist at low excitation energy is firmly established.
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The characteristics of alpha radiation have for decades been demonstrated in UK schools using small sealed (241)Am sources. There is a small but steady number of schools who report a considerable reduction in the alpha count rate detected by an end-window GM detector compared with when the source was new. This cannot be explained by incorrect apparatus or set-up, foil surface contamination, or degradation of the GM detector. The University of Liverpool and CLEAPSS collaborated to research the cause of this performance degradation. The aim was to find what was causing the performance degradation and the ramifications for both the useful and safe service life of the sources. The research shows that these foil sources have greater energy straggling with a corresponding reduction in spectral peak energy. A likely cause for this increase in straggling is a significant diffusion of the metals over time. There was no evidence to suggest the foils have become unsafe, but precautionary checks should be made on old sources.