Shape Changes in the Mirror Nuclei

We studied the proton-rich T_{z}=-1 nucleus ^{70}Kr through inelastic scattering at intermediate energies in order to extract the reduced transition probability, B(E2;0^{+}→2^{+}). Comparison with the other members of the A=70 isospin triplet, ^{70}Br and ^{70}Se, studied in the same experiment, shows a 3σ deviation from the expected linearity of the electromagnetic matrix elements as a function of T_{z}. At present, no established nuclear structure theory can describe this observed deviation quantitatively. This is the first violation of isospin symmetry at this level observed in the transition matrix elements. A heuristic approach may explain the anomaly by a shape change between the mirror nuclei ^{70}Kr and ^{70}Se contrary to the model predictions.

Establishing the Maximum Collectivity in Highly Deformed N=Z Nuclei.

The lifetimes of the first excited 2^{+} states in the N=Z nuclei ^{80}Zr, ^{78}Y, and ^{76}Sr have been measured using the γ-ray line shape method following population via nucleon-knockout reactions from intermediate-energy rare-isotope beams. The extracted reduced electromagnetic transition strengths yield new information on where the collectivity is maximized and provide evidence for a significant, and as yet unexplained, odd-odd vs even-even staggering in the observed values. The experimental results are analyzed in the context of state-of-the-art nuclear density-functional model calculations.

Isospin Properties of Nuclear Pair Correlations from the Level Structure of the Self-Conjugate Nucleus

The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N=Z) nuclide _{44}^{88}Ru_{44} has been measured using the combination of the Advanced Gamma Tracking Array (AGATA) spectrometer, the NEDA and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in ^{88}Ru were populated via the ^{54}Fe(^{36}Ar,2nγ)^{88}Ru^{*} fusion-evaporation reaction at the Grand Accélérateur National d'Ions Lourds (GANIL) accelerator complex. The observed γ-ray cascade is assigned to ^{88}Ru using clean prompt γ-γ-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring N>Z nuclides. The direct observation of such a "delayed" rotational alignment in a deformed N=Z nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.

Experimental Evidence for Transverse Wobbling in

New rotational bands built on the ν(h_{11/2}) configuration have been identified in ^{105}Pd. Two bands built on this configuration show the characteristics of transverse wobbling: the ΔI=1 transitions between them have a predominant E2 component and the wobbling energy decreases with increasing spin. The properties of the observed wobbling bands are in good agreement with theoretical results obtained using constrained triaxial covariant density functional theory and quantum particle rotor model calculations. This provides the first experimental evidence for transverse wobbling bands based on a one-neutron configuration, and also represents the first observation of wobbling motion in the A∼100 mass region.

Discovery of

In this Letter, the observation of two previously unknown isotopes is presented for the first time: ^{72}Rb with 14 observed events and ^{77}Zr with one observed event. From the nonobservation of the less proton-rich nucleus ^{73}Rb, we derive an upper limit for the ground-state half-life of 81 ns, consistent with the previous upper limit of 30 ns. For ^{72}Rb, we have measured a half-life of 103(22) ns. This observation of a relatively long-lived odd-odd nucleus, ^{72}Rb, with a less exotic odd-even neighbor, ^{73}Rb, being unbound shows the diffuseness of the proton drip line and the possibility of sandbanks to exist beyond it. The ^{72}Rb half-life is consistent with a 5^{+}→5/2^{-} proton decay with an energy of 800-900 keV, in agreement with the atomic mass evaluation proton-separation energy as well as results from the finite-range droplet model and shell model calculations using the GXPF1A interaction. However, we cannot explicitly exclude the possibility of a proton transition between 9^{+}(^{72}Rb)→9/2^{+}(^{71}Kr) isomeric states with a broken mirror symmetry. These results imply that ^{72}Kr is a strong waiting point in x-ray burst rp-process scenarios.

Evolution of collectivity in 72Kr: evidence for rapid shape transition.

The transition rates from the yrast 2+ and 4+ states in the self-conjugate 72Kr nucleus were studied via lifetime measurements employing the GRETINA array with a novel application of the recoil-distance method. The large collectivity observed for the 4+→2+ transition suggests a prolate character of the excited states. The reduced collectivity previously reported for the 2+→0+ transition was confirmed. The irregular behavior of collectivity points to the occurrence of a rapid oblate-prolate shape transition in 72Kr, providing stringent tests for advanced theories to describe the shape coexistence and its evolution.

16+ spin-gap isomer in 96Cd.

A ß-decaying high-spin isomer in (96)Cd, with a half-life T(1/2)=0.29(-0.10)(+0.11) s, has been established in a stopped beam rare isotope spectroscopic investigations at GSI (RISING) experiment. The nuclei were produced using the fragmentation of a primary beam of (124)Xe on a (9)Be target. From the half-life and the observed γ decays in the daughter nucleus, (96)Ag, we conclude that the ß-decaying state is the long predicted 16(+) "spin-gap" isomer. Shell-model calculations, using the Gross-Frenkel interaction and the πν(p(1/2),g(9/2)) model space, show that the isoscalar component of the neutron-proton interaction is essential to explain the origin of the isomer. Core excitations across the N=Z=50 gaps and the Gamow-Teller strength, B(GT) distributions have been studied via large-scale shell-model calculations using the πν(g,d,s) model space to compare with the experimental B(GT) value obtained from the half-life of the isomer.

Long-term mercury dynamics in UK soils.

A model assuming first-order losses by evasion and leaching was used to evaluate Hg dynamics in UK soils since 1850. Temporal deposition patterns of Hg were constructed from literature information. Inverse modelling indicated that 30% of 898 rural sites receive Hg only from the global circulation, while in 51% of cases local deposition exceeds global. Average estimated deposition is 16 µg Hg m(-2) a(-1) to rural soils, 19 µg Hg m(-2) a(-1) to rural and non-rural soils combined. UK soils currently hold 2490 tonnes of reactive Hg, of which 2140 tonnes are due to anthropogenic deposition, mostly local in origin. Topsoil currently releases 5.1 tonnes of Hg(0) per annum to the atmosphere, about 50% more than the anthropogenic flux. Sorptive retention of Hg in the lower soil exerts a strong control on surface water Hg concentrations. Following decreases in inputs, soil Hg concentrations are predicted to decline over hundreds of years.

Mercury in United Kingdom topsoils; concentrations, pools, and Critical Limit exceedances.

The median total mercury concentration in 898 UK rural topsoils, sampled between 1998 and 2008, was 0.095 µg g(-1). Approximate adjustment for unreactive metal produced an estimate of 0.052 µg g(-1) for reactive Hg. The highest concentrations were in the north and west, where organic-rich soils with low bulk densities dominate, but the spatial pattern was quite different if soil Hg pools (mg m(-2)) were considered, the highest values being near to the industrial north of England and London. Possible toxic effects of Hg were best evaluated by comparison with soil Critical Limits expressed as ratios of Hg to soil organic matter, or soil solution Hg(2+) concentrations, estimated by chemical speciation modelling. Only a few percent of the rural UK soils showed exceedance, and this also applied to rural soils from the whole of Europe. UK urban and industrial soils had higher Hg concentrations and more cases of exceedance.

Nanoparticulate delivery can improve peroral bioavailability of cyclosporine and match Neoral Cmax sparing the kidney from damage.

Cyclosporine (CsA) as an immunosuppressant has demonstrated immense potential in the field of organ transplantation and autoimmune disorders, despite the nephrotoxicity. The present investigation is an attempt to develop biodegradable nanoparticles entrapping CsA that can match Cmax of Neora, the most potent formulation available to date. The Cmax and AUC0-72 of CsA administered as nanoparticles demonstrated an increase with increase in the dose administered, however the relative bioavailability decreased. The Cmax and AUC0-72 increased from 682 to 1073 ng/ml and 34854 to 55322 ng . h/ml, respectively whereas, the relative bioavailability decreased from 120 to 64%. On the other hand, the increase in initial CsA loading (10-30% w/w of polymer) recorded a proportional increase in Cmax and AUC0-72, from 494 to 1101 ng/ml and 17774 to 51763 ng . h/ml, respectively. The relative bioavailability also increased from 31 to 89%. The CsA nanoparticles at 30% CsA loading w/w of polymer and at 30 mg/Kg single dose demonstrated comparable Cmax of Neoral at 15 mg/Kg, which upon chronic administration over a period of 30 days daily dosing showed low nephrotoxicity to that exhibited by Neoral. The reduced toxicity of nanoparticulate CsA indicated by lower blood urea nitrogen, plasma creatinine and glomerular damage, was due to delay in Tmax as result of slow release of the CsA from the nanoparticles. The investigation unlocks the potential of polymeric nanoparticles in oral delivery of CsA.

Peroxynitrite stimulates pulmonary artery endothelial and smooth muscle cell proliferation: involvement of ERK and PKC.

BACKGROUND: There is evidence that peroxynitrite is generated in pulmonary hypertension and we have therefore investigated whether peroxynitrite can cause proliferation of pulmonary artery cells. METHODS: Bovine pulmonary artery endothelial (PAEC) and smooth muscle cells (PASMC) were exposed to peroxynitrite solution or to the peroxynitrite generating compound, 3-morpholinosydnonimine (SIN-1). Vascular cell proliferation was determined by cell count and (3)H-thymidine incorporation. Protein biochemistry was by western blot analysis. RESULTS: Transient exposure to peroxynitrite stimulated the proliferation of PASMC (peroxynitrite 0.2 nM-2 µM) and PAEC (peroxynitrite 0.2 µM). Peroxynitrite 0.2 µM stimulated DNA synthesis in PASMC cell by 200 ± 22% and in PAEC by 137 ± 4%. DNA synthesis in PAEC and PASMC was also stimulated by the peroxynitrite generator SIN-1 2 µM. Cell proliferation was accompanied by activation of ERK, which peaked at 15 min and remained elevated for 12 h in PASMC. However peroxynitrite at the concentrations used in this study did not activate the stress pathways p38 mitogen activated protein kinase (MAPK) or Jun N-terminal kinase (JNK). Peroxynitrite-induced proliferation and ERK phosphorylation in PASMC were abolished by the peroxynitrite scavenger ebselen 5 µM. Peroxynitrite-induced proliferation and extracellular signal-regulated kinase (ERK) phosphorylation in PASMC was prevented by selective inhibitors of MAP kinase kinase (MEK) (U0126 5 µM, PD98059 50 µM), Raf-1 (Raf-1 kinase inhibitor 10 µM), Ras (FPT II and FPT III 10 µM) and protein kinase C (PKC) (GF109203X 10 µM). Inhibition of EGF or PDGF receptor signaling using AG-1296, AG-1478 or imatinib prevented peroxynitrite-induced cell proliferation and ERK phosphorylation in PASMC. CONCLUSION: Peroxynitrite can stimulate proliferation of pulmonary artery cells, involving ERK, PKC and EGF or PDGF receptors.

Evidence for a spin-aligned neutron-proton paired phase from the level structure of (92)Pd.

Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work that introduced a strong spin-orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron-proton pairing, in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus (92)Pd. Gamma rays emitted following the (58)Ni((36)Ar,2n)(92)Pd fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution γ-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction. We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron-proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis.

Background wet deposition of mercury in Great Britain.

Precipitation samples have been collected on a monthly basis from a network of 10 sites in Great Britain (GB) in order to estimate background mercury (Hg) deposition in the rural environment. Collection started in February 2005 and results presented here cover the period up to June 2009. The annual volume-weighted mean (AVWM) Hg concentrations range from 1.0 ng L(-1) at Cockley Beck in the Lake District in 2006 to 8.8 ng L(-1) at Heigham Holmes on the Norfolk Coast England in 2008. The largest validated solution concentrations were 33.7 ng L(-1) Hg measured at Cockley Beck in May 2008. The large difference in rainfall amount between sites means that the remote site at Cockley Beck has both the lowest long-term AVWM concentration (1.6 ng L(-1)) and the greatest annual flux is greatest at 43 mg ha(-1) yr(-1). Predicted deposition tends to be much greater in western Britain where the greater rainfall occurs. Because some observations are very close to the analytical detection limit (1.0 ng L(-1)), rigorous cleaning procedures, the use of replicate samplers to monitor contamination, and the inclusion of 'bottle blanks' are required to obtain valid measurements of Hg in the bulk deposition. Deposition in rural sites is equivalent to about 10% of the estimated magnitude of known emissions in GB.

Two-particle separation energy trends in the superdeformed well.

A measurement of the energy and spin of superdeformed states in 190Hg, obtained through the observation of transitions directly linking superdeformed and normal states, expands the number of isotopes in which binding energies at superdeformation are known. Comparison with neighboring nuclei shows that two-proton separation energies are higher in the superdeformed state than in the normal state, despite the lower Coulomb barrier and lower total binding energy. This unexpected result provides a critical test for nuclear models.

Coherent contributions to isospin mixing in the mirror pair 67As and 67Se.

Isospin symmetry breaking has been investigated in mass A=67 mirror nuclei through the experimental determination of the E1 strengths of analog electromagnetic transitions. Lifetimes of excited states have been measured in (67)Se and (67)As with the centroid shift method. Through the comparison of the B(E1) strengths of the mirror 9/2(+)-->7/2(-) transitions, the isovector and the isoscalar components of the electromagnetic transition amplitude were extracted. The presence of a large isoscalar component provides evidence for coherent contributions to isospin mixing, probably involving the isovector giant monopole resonance.

Prostacyclin analogues: the next drug-eluting stent?

Recent concern over existing drug-eluting stents, for the treatment of myocardial ischaemia, has led to the development of approaches that seek to inhibit restenosis while promoting the recovery of a functional endothelium. Prostacyclin analogues may be worthy candidates for use within a drug-eluting stent by virtue of their wide profile of vasoprotective effects. This article reviews recent developments in this area, and in so doing, reveals the future challenges for the further development of this technology.

Identification of excited states in the T(z) = 1 nucleus (110)Xe: evidence for enhanced collectivity near the N=Z=50 double shell closure.

Gamma-ray transitions have been identified for the first time in the extremely neutron-deficient (N=Z+2) nucleus (110)Xe, and the energies of the three lowest excited states in the ground-state band have been deduced. The results establish a breaking of the normal trend of increasing first excited 2(+) and 4(+) level energies as a function of the decreasing neutron number as the N=50 major shell gap is approached for the neutron-deficient Xe isotopes. This unusual feature is suggested to be an effect of enhanced collectivity, possibly arising from isoscalar n-p interactions becoming increasingly important close to the N=Z line.

Estimating uncertainty in terrestrial critical loads and their exceedances at four sites in the UK.

Critical loads are the basis for policies controlling emissions of acidic substances in Europe and elsewhere. They are assessed by several elaborate and ingenious models, each of which requires many parameters, and have to be applied on a spatially-distributed basis. Often the values of the input parameters are poorly known, calling into question the validity of the calculated critical loads. This paper attempts to quantify the uncertainty in the critical loads due to this "parameter uncertainty", using examples from the UK. Models used for calculating critical loads for deposition of acidity and nitrogen in forest and heathland ecosystems were tested at four contrasting sites. Uncertainty was assessed by Monte Carlo methods. Each input parameter or variable was assigned a value, range and distribution in an objective a fashion as possible. Each model was run 5000 times at each site using parameters sampled from these input distributions. Output distributions of various critical load parameters were calculated. The results were surprising. Confidence limits of the calculated critical loads were typically considerably narrower than those of most of the input parameters. This may be due to a "compensation of errors" mechanism. The range of possible critical load values at a given site is however rather wide, and the tails of the distributions are typically long. The deposition reductions required for a high level of confidence that the critical load is not exceeded are thus likely to be large. The implication for pollutant regulation is that requiring a high probability of non-exceedance is likely to carry high costs. The relative contribution of the input variables to critical load uncertainty varied from site to site: any input variable could be important, and thus it was not possible to identify variables as likely targets for research into narrowing uncertainties. Sites where a number of good measurements of input parameters were available had lower uncertainties, so use of in situ measurement could be a valuable way of reducing critical load uncertainty at particularly valuable or disputed sites. From a restricted number of samples, uncertainties in heathland critical loads appear comparable to those of coniferous forest, and nutrient nitrogen critical loads to those of acidity. It was important to include correlations between input variables in the Monte Carlo analysis, but choice of statistical distribution type was of lesser importance. Overall, the analysis provided objective support for the continued use of critical loads in policy development.