The ^{12}C+^{12}C fusion reaction plays a critical role in the evolution of massive stars and also strongly impacts various explosive astrophysical scenarios. The presence of resonances in this ...reaction at energies around and below the Coulomb barrier makes it impossible to carry out a simple extrapolation down to the Gamow window-the energy regime relevant to carbon burning in massive stars. The ^{12}C+^{12}C system forms a unique laboratory for challenging the contemporary picture of deep sub-barrier fusion (possible sub-barrier hindrance) and its interplay with nuclear structure (sub-barrier resonances). Here, we show that direct measurements of the ^{12}C+^{12}C fusion cross section may be made into the Gamow window using an advanced particle-gamma coincidence technique. The sensitivity of this technique effectively removes ambiguities in existing measurements made with gamma ray or charged-particle detection alone. The present cross-section data span over 8 orders of magnitude and support the fusion-hindrance model at deep sub-barrier energies.
The effect of competing ions on the sorption behaviour of uranium onto carboxyl-functionalised graphene oxide (COOH-GO) were studied in batch experiments in comparison to graphene oxide (GO) and ...graphite. The effect of increasing the abundance of select chemical functional groups, such as carboxyl groups, on the selectivity of U sorption was investigated. In the course of the study, COOH-GO demonstrated superior performance as a sorbent material for the selective removal of uranyl ions from aqueous solution with a distribution coefficient of 3.72 ± 0.19 × 10
3
mL g
−1
in comparison to 3.97 ± 0.5 × 10
2
and 2.68 ± 0.2 × 10
2
mL g
−1
for GO and graphite, respectively.
An evaluation of the radioactivity levels associated with naturally occurring radioactive materials has been undertaken as part of a systematic study to provide a surface radiological map of the ...State of Kuwait. Soil samples from across Kuwait were collected, measured and analysed in the current work. These evaluations provided soil activity concentration levels for primordial radionuclides, specifically members of the 238U and 232Th decay chains and 40K which. The 238U and 232Th chain radionuclides and 40K activity concentration values ranged between 5.9 ↔ 32.3, 3.5 ↔ 27.3, and 74 ↔ 698 Bq/kg respectively. The evaluated average specific activity concentrations of 238U, 232Th and 40K across all of the soil samples have mean values of 18, 15 and 385 Bq/kg respectively, all falling below the worldwide mean values of 35, 40 and 400 Bq/kg respectively. The radiological risk factors are associated with a mean of 33.16 ± 2.46 nG/h and 68.5 ± 5.09 Bq/kg for the external dose rate and Radium equivalent respectively. The measured annual dose rates for all samples gives rise to a mean value of 40.8 ± 3.0 μSv/y while the internal and internal hazard indices have been found to be 0.23 ± 0.02 and 0.19 ± 0.01 respectively.
•Measurements made using high-resolution gamma-ray spectrometry for activity concentrations of 238U, 232Th and 40K involving 184 analysed soil samples.•The distribution of 40K is observed to remain rather constant across the entire region of Kuwait.•Results obtained indicate higher 238U/232Th ratio in the northern region relative to southern one.•Measured radiological risk factors across the wider Kuwait environment are below world mean values.
A network of specialist laboratories support the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) with re-measurements of radionuclide samples, including ...xenon gas. The measurement of four xenon fission product radionuclides (133Xe, 135Xe, 131mXe and 133mXe) can be used to detect an underground nuclear explosion. Laboratories use a range of techniques to measure the radionuclides, including beta-gamma (β−γ) coincidence spectrometry. These highly-sensitive measurements are capable of detecting concentrations of down to 500 atoms of 133Xe in a few cm3 of xenon. In some detector systems, detection of the metastable isomers (131mXe and 133mXe) can be more challenging due to interferences between the signatures of different radionuclides. Recent work has shown that using high-purity Germanium (HPGe) high-resolution gamma detectors, these interferences can be reduced, lowering the dependence of the detection limits on radionuclide sample isotopic composition. One downside of these detectors is the reduction in detection efficiency, which impacts the overall detection sensitivity; so assessing different detector systems is a priority for radionuclide laboratories. This work presents a coincidence detector system comprising of a plastic scintillator gas cell and a large-crystal high-purity germanium detector. The energy resolution, coincidence detection efficiency, MDA and interference factors are determined from measurements of synthetic radioxenon gas samples.
•A plastic scintillator and HPGe β−γ coincidence system has been configured for the measurement of isotopes of radioxenon•Calculations show that this type of setup can improve the detection limits compared to other systems.•High-resolution γ-detectors can separate Xe and Cs X-rays, decreasing interference.
The β decay of Hg208 into the one-proton hole, one neutron-particle Tl81208127 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
The shell structure of atomic nuclei is associated with 'magic numbers' and originates in the nearly independent motion of neutrons and protons in a mean potential generated by all nucleons. During ...b1-decay, a proton transforms into a neutron in a previously not fully occupied orbital, emitting a positron-neutrino pair with either parallel or antiparallel spins, in a Gamow-Teller or Fermi transition, respectively. The transition probability, or strength, of a Gamow-Teller transition depends sensitively on the underlying shell structure and is usually distributed among many states in the neighbouring nucleus. Here we report measurements of the half-life and decay energy for the decay of 100Sn, the heaviest doubly magic nucleus with equal numbers of protons and neutrons. In the b-decay of 100Sn, a large fraction of the strength is observable because of the large decay energy. We determine the largest Gamow-Teller strength so far measured in allowed nuclear b-decay, establishing the 'superallowed' nature of this Gamow-Teller transition. The large strength and the low-energy states in the daughter nucleus, 100In, are well reproduced by modern, large-scale shell model calculations.
Terbium-152 is one of four terbium radioisotopes that together form a potential theranostic toolbox for the personalised treatment of tumours. As 152 Tb day by positron emission it can be utilised ...for diagnostics by positron emission tomography. For use in radiopharmaceuticals and for activity measurements by an activity calibrator a high radionuclide purity of the material and an accurate and precise knowledge of the half-life is required. Mass-separation and radiochemical purification provide a production route of high purity 152Tb. In the current work, two mass-separated samples from the CERN-ISOLDE facility have been assayed at the National Physical Laboratory to investigate the radionuclide purity. These samples have been used to perform four measurements of the half-life by three independent techniques: high-purity germanium gamma-ray spectrometry, ionisation chamber measurements and liquid scintillation counting. From the four measurement campaigns a half-life of 17.8784(95) h has been determined. The reported half-life shows a significant difference to the currently evaluated half-life (ζ-score = 3.77), with a relative difference of 2.2 % and an order of magnitude improvement in the precision. This work also shows that under controlled conditions the combination of mass-separation and radiochemical separation can provide high-purity 152Tb.
•First half-life measurement of 152Tb since 1970.•Precise half-life of 152Tb determined by three independent techniques from mass-separated samples.•Presented half-life value shows a relative difference of 2.2% from current evaluated value.•Order of magnitude improvement in the precision to the current evaluated value.•Radionuclide contaminants from two mass-separated samples assessed.
The safe and cost-effective decommissioning of legacy nuclear sites relies on accurate measurement of the radioactivity content of the waste materials, so that the waste can be assigned to the most ...appropriate disposal route. Such measurements are a new challenge for the science of radionuclide metrology which was established largely to support routine measurements on operating nuclear sites and other applications such as nuclear medicine. In this paper, we provide a brief summary of the international measurement system that is established to enable nuclear site operators to demonstrate that measurements are accurate, independent and fit for purpose, and highlight some of the projects that are underway to adapt the measurement system to meet the changing demands from the industry.
•How the international measurement system operates.•The new demands from the nuclear industry.•National and international projects to meet these demands.
Monte-Carlo simulations have been utilised to determine the optimum material and thickness for a γ spectrometer to be used for the assay of radionuclides that emit radiation in the 50–300 keV energy ...range. Both HPGe and LaBr3(Ce) materials were initially considered for use, however the additional background radiation and lack of resolution in the latter drove the selection of HPGe for further optimisation. Multiple thicknesses were considered for the HPGe detector, with the aim of improving the sensitivity of the system by maximising the efficiency for low energy emissions, and reducing the probability of interaction with (and therefore the continuum from) higher energy photons. The minimum amount of material needed to achieve this was found to be 15 mm for a source that is dominated by high energy (>2.614 MeV) photons, and 20–30 mm for a typical reference source (with photons of energy 59.54 keV–2.614 MeV).
•Requirements of low-energy gamma detection system identified.•Detector materials have been evaluated, including LaBr3(Ce), and HPGe.•Monte Carlo models (GEANT4) have been developed to test different crystal sizes.•Optimum crystal thicknesses have been identified for gamma radiation <300 keV.
This paper summarises a presentation given at the IRRMA8 conference in June 2011 which reviewed briefly the topic of current research studies in the evolution of nuclear structure with changing ...proton and neutron numbers. A short review of relevant contemporary spectroscopic studies of the structure of nuclei with highly exotic N/Z ratios using projectile fragmentation and fission reactions is given, together with an overview of some of the physics research aims to be attacked using the proposed Decay Spectroscopy (DESPEC) LaBr3 Fast-Timing gamma-ray array for the NUSTAR project at the upcoming Facility for Anti-Proton and Ion Research (FAIR). Examples of recent results using both ‘isomer’ and β−-delayed gamma-ray decay measurements with the Stopped RISING hyper-pure germanium array at GSI are summarised and used to highlight some of the fundamental physics studies which are expected to become available in this area of research in the coming decade. Examples of the performance of cerium-doped LaBr3 detectors from ‘in-beam’ test experiments are presented together with initial plans for the geometry of the planned multi-detector LaBr3(Ce) array for DESPEC.
► The paper presents an overview of nuclear excitation systematics in even–even nuclei. ► The paper gives a description of the Stopped RISING gamma-ray spectrometer. ► This paper gives some of the recent scientific results in nuclear spectroscopy of exotic nuclei. ► The paper shows the use of halide scintillation detectors for gamma-ray decay studies of nuclei. ► This paper shows the use of LaBr3 detectors to nuclear excited state lifetimes in the ns regime.
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