Nanosecond-Scale Proton Emission from Strongly Oblate-Deformed

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.

Solving the Puzzles of the Decay of the Heaviest Known Proton-Emitting Nucleus

Two long-standing puzzles in the decay of ^{185}Bi, the heaviest known proton-emitting nucleus are revisited. These are the nonobservation of the 9/2^{-} state, which is the ground state of all heavier odd-A Bi isotopes, and the hindered nature of proton and α decays of its presumed 60-µs 1/2^{+} ground state. The ^{185}Bi nucleus has now been studied with the ^{95}Mo(^{93}Nb,3n) reaction in complementary experiments using the Fragment Mass Analyzer and Argonne Gas-Filled Analyzer at Argonne National Laboratory's ATLAS facility. The experiments have established the existence of two states in ^{185}Bi; the short-lived T_{1/2}=2.8_{-1.0}^{+2.3} µs, proton- and α-decaying ground state, and a 58(2)-µs γ-decaying isomer, the half-life of which was previously attributed to the ground state. The reassignment of the ground-state lifetime results in a proton-decay spectroscopic factor close to unity and represents the only known example of a ground-state proton decay to a daughter nucleus (^{184}Pb) with a major shell closure. The data also demonstrate that the ordering of low- and high-spin states in ^{185}Bi is reversed relative to the heavier odd-A Bi isotopes, with the intruder-based 1/2^{+} configuration becoming the ground, similar to the lightest At nuclides.

Search for Nova Presolar Grains: γ-Ray Spectroscopy of

The discovery of presolar grains in primitive meteorites has initiated a new era of research in the study of stellar nucleosynthesis. However, the accurate classification of presolar grains as being of specific stellar origins is particularly challenging. Recently, it has been suggested that sulfur isotopic abundances may hold the key to definitively identifying presolar grains with being of nova origins and, in this regard, the astrophysical ^{33}Cl(p,γ)^{34}Ar reaction is expected to play a decisive role. As such, we have performed a detailed γ-ray spectroscopy study of ^{34}Ar. Excitation energies have been measured with high precision and spin-parity assignments for resonant states, located above the proton threshold in ^{34}Ar, have been made for the first time. Uncertainties in the ^{33}Cl(p,γ) reaction have been dramatically reduced and the results indicate that a newly identified ℓ=0 resonance at E_{r}=396.9(13) keV dominates the entire rate for T=0.25-0.40 GK. Furthermore, nova hydrodynamic simulations based on the present work indicate an ejected ^{32}S/^{33}S abundance ratio distinctive from type-II supernovae and potentially compatible with recent measurements of a presolar grain.

Shape Coexistence at Zero Spin in

The low-spin structure of the semimagic ^{64}Ni nucleus has been considerably expanded: combining four experiments, several 0^{+} and 2^{+} excited states were identified below 4.5 MeV, and their properties established. The Monte Carlo shell model accounts for the results and unveils an unexpectedly complex landscape of coexisting shapes: a prolate 0^{+} excitation is located at a surprisingly high energy (3463 keV), with a collective 2^{+} state 286 keV above it, the first such observation in Ni isotopes. The evolution in excitation energy of the prolate minimum across the neutron N=40 subshell gap highlights the impact of the monopole interaction and its variation in strength with N.

Evidence for Rigid Triaxial Deformation in

An extensive, model-independent analysis of the nature of triaxial deformation in ^{76}Ge, a candidate for neutrinoless double-beta (0νßß) decay, was carried out following multistep Coulomb excitation. Shape parameters deduced on the basis of a rotational-invariant sum-rule analysis provided considerable insight into the underlying collectivity of the ground-state and γ bands. Both sequences were determined to be characterized by the same ß and γ deformation parameter values. In addition, compelling evidence for low-spin, rigid triaxial deformation in ^{76}Ge was obtained for the first time from the analysis of the statistical fluctuations of the quadrupole asymmetry deduced from the measured E2 matrix elements. These newly determined shape parameters are important input and constraints for calculations aimed at providing, with suitable accuracy, the nuclear matrix elements relevant to 0νßß.

Probing the Single-Particle Character of Rotational States in

A beam containing a substantial component of both the J^{π}=5^{+}, T_{1/2}=162 ns isomeric state of ^{18}F and its 1^{+}, 109.77-min ground state is utilized to study members of the ground-state rotational band in ^{19}F through the neutron transfer reaction (d,p) in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2^{+} band-terminating state. The agreement between shell-model calculations using an interaction constructed within the sd shell, and our experimental results reinforces the idea of a single-particle-collective duality in the descriptions of the structure of atomic nuclei.

Superallowed α Decay to Doubly Magic

We report the first observation of the ^{108}Xe→^{104}Te→^{100}Sn α-decay chain. The α emitters, ^{108}Xe [E_{α}=4.4(2) MeV, T_{1/2}=58_{-23}^{+106} µs] and ^{104}Te [E_{α}=4.9(2) MeV, T_{1/2}<18 ns], decaying into doubly magic ^{100}Sn were produced using a fusion-evaporation reaction ^{54}Fe(^{58}Ni,4n)^{108}Xe, and identified with a recoil mass separator and an implantation-decay correlation technique. This is the first time α radioactivity has been observed to a heavy self-conjugate nucleus. A previous benchmark for study of this fundamental decay mode has been the decay of ^{212}Po into doubly magic ^{208}Pb. Enhanced proton-neutron interactions in the N=Z parent nuclei may result in superallowed α decays with reduced α-decay widths significantly greater than that for ^{212}Po. From the decay chain, we deduce that the α-reduced width for ^{108}Xe or ^{104}Te is more than a factor of 5 larger than that for ^{212}Po.

Estimating the burden of A(H1N1)pdm09 influenza in Finland during two seasons.

In Finland, the pandemic influenza virus A(H1N1)pdm09 was the dominant influenza strain during the pandemic season in 2009/2010 and presented alongside other influenza types during the 2010/2011 season. The true number of infected individuals is unknown, as surveillance missed a large portion of mild infections. We applied Bayesian evidence synthesis, combining available data from the national infectious disease registry with an ascertainment model and prior information on A(H1N1)pdm09 influenza and the surveillance system, to estimate the total incidence and hospitalization rate of A(H1N1)pdm09 infection. The estimated numbers of A(H1N1)pdm09 infections in Finland were 211 000 (4% of the population) in the 2009/2010 pandemic season and 53 000 (1% of the population) during the 2010/2011 season. Altogether, 1·1% of infected individuals were hospitalized. Only 1 infection per 25 was ascertained.

Modelling multi-type transmission of pneumococcal carriage in Bangladeshi families.

The burden of pneumococcal carriage is largest in developing countries from which, however, detailed studies on pneumococcal transmission are missing. In this study we followed nasopharyngeal carriage in Bangladeshi infants (n=99) from birth, with 2-week sampling intervals until age 4 months, and monthly thereafter until age 1 year, and also their family members at the same intervals. We assessed the dependence of pneumococcal acquisition rates on age, serotype, serotype-specific exposure (i.e. transmission) and current state of carriage (yes/no). A statistical model of pneumococcal transmission, taking into account incompletely observed data, was applied to estimate rates of acquisition and clearance for a large number of serotypes at the same time. Serotypes that were common in the study population were more often acquired from the community than rarer serotypes. However, when conditioning on serotype-specific exposure within the family, transmission rates were similar between different serotypes. Exposure within families signified more than tenfold increase in the rate of acquisition.

Modelling the impact of varicella vaccination on varicella and zoster.

It has been suggested that the incidence of herpes zoster may increase due to lack of natural boosting under large-scale vaccination with the varicella vaccine. To study the possibility and magnitude of such negative consequences of mass vaccination, we built a mathematical model of varicella and zoster epidemiology in the Finnish population. The model was based on serological data on varicella infection, case-notification data on zoster, and new knowledge about close contacts relevant to transmission of infection. According to the analysis, a childhood programme against varicella will increase the incidence of zoster by one to more than two thirds in the next 50 years. This will be due to increase in case numbers in the 35 years age groups. However, high vaccine coverage and a two-dose programme will be very effective in stopping varicella transmission in the population.

Pneumococcal carriage in children during their first two years: important role of family exposure.

BACKGROUND: Close family and day-care contacts have been identified as risk factors for pneumococcal (Pnc) carriage. This study addresses the risk of Pnc carriage by infants 2 to 24 months of age in terms of simultaneous carriage of pneumococcus by family members. METHODS: Nasopharyngeal swabs were collected from 100 Finnish infants and their family members on 10 scheduled visits (when infant was 2, 3, 4, 5, 6, 9, 12, 15, 18 and 24 months of age). The 7 most common pneumococcal serogroups (4, 6, 9, 14, 18, 19, 23), also represented in the new heptavalent Pnc conjugate vaccine, were analyzed. Marginal logistic regression analyses were performed to assess the relative importance of different predictors for carriage. RESULTS: The carriage of the studied Pnc serogroups increased with age, being highest at the age of 18 months (28%). Among children older than 6 months of age, the strongest predictor of carriage was simultaneous carriage of the same serogroup by another family member (odds ratio, 3.8; 95% confidence interval, 2.1 to 6.9). At the age of 6 months or younger, carriage was rare and was not significantly associated with a family carriage. CONCLUSIONS: Young infants (< or =6 months old) were largely protected from pneumococcal carriage. After this age family transmission seemed very important despite the small family size. Contrary to some earlier studies communal day care was not associated with an increased risk of Pnc carriage. This could be partly because of the long parental leave in Finland and thus the late age of starting organized day care.

The effect of a pneumococcal conjugate vaccine on the risk of otitis media with effusion at 7 and 24 months of age.

OBJECTIVE: To explore the effect of a pneumococcal conjugate vaccine on the risk of otitis media with effusion and to search for subgroups in which the vaccine had a higher or lower effect. METHODS: Analyses were performed on data from the Finnish Otitis Media Vaccine Trial, a randomised controlled double-blind trial to evaluate the efficacy of pneumococcal conjugate vaccination against acute otitis media. Data on the vaccination effect against otitis media with effusion were obtained by means of symptom interview and pneumatic otoscopy during pre-scheduled follow-up visits at the age of 7 and 24 months. Two endpoint definitions were considered: otitis media/tube (otitis media or tympanostomy tube in situ (OM/T)) as the primary endpoint and otitis media with effusion as the secondary endpoint. No evidence was found of an age-dependent association with vaccination effect. Therefore, the final marginal logistic regression analyses were performed on the combined data from the two follow-up visits. RESULTS: The risk of otitis media tended to be lower in the pneumococcal vaccine group. The odds ratio for otitis media/tube was 0.94 (95% confidence interval 0.77-1.14) and the odds ratio for otitis media with effusion was 0.90 (95% confidence interval 0.69-1.19). Presence of older siblings increased the risk of otitis media/tube and otitis media with effusion at 7 months of age. In addition, it appeared that children without older siblings and attending day-care at 24 months of age tended to benefit more from the pneumococcal conjugate vaccine. In this subgroup, the odds ratio for otitis media/tube was 0.81 (95% confidence interval 0.55-1.20) and for otitis media with effusion the odds ratio was 0.43 (95% confidence interval 0.22-0.86). CONCLUSION: The effect of pneumococcal conjugate vaccination on the risk of otitis media with effusion was concordant with the efficacy seen against acute otitis media, although not distinguishable from no effect in the overall analysis. In children without older siblings, vaccination appeared to reduce the point prevalence of otitis media with effusion; this effect was not apparent in children with older siblings.

High tetanus and diphtheria antitoxin concentrations in Finnish adults--time for new booster recommendations?

The tetanus and diphtheria vaccination programme in Finland has been running for 50 years. After primary doses, tetanus boosters have been offered to men in military service and decennial boosters recommended for all through the adult life. For 30 years a diphtheria booster was only offered to men in the military service. Not until 1989 diphtheria-tetanus (dT) and diphtheria (d) booster vaccines for adolescence and adults were introduced. In this study serum samples of 990 subjects from 30 years of age, participating in a population survey in 2000-2001, were used to assess the tetanus and diphtheria antitoxin concentrations. More than 70% of the adults up to 50 years of age were fully protected (antitoxin concentrations >0.1 IU mL) against tetanus and diphtheria. Of these adults more that 76% had antitoxin concentrations >1 IU/mL against tetanus, indicating long-term protection but also an increased risk for hyperimmunisation. A comparison of this study and two immunogenicity studies conducted in Finland in 1987-1988 and 1995-1996 shows the impact of an active decennial dT adult booster programme in a country with a high primary tetanus and diphtheria vaccination coverage in infants since the 1950s. Recommendations for limited decennial boosters by increase the time interval between dT boosters up to 20 years as suggested by this study and also studies performed, e.g., in Denmark and Portugal should be considered. Finnish adults born before 1930 should, however, still be vaccinated with decennial boosters, especially against tetanus.

Back-calculating the age-specific incidence of recurrent subclinical Haemophilus influenzae type b infection.

We consider the estimation of an age-specific incidence rate of a subclinical Haemophilus influenzae type b (Hib) infection from data recording the ages of children with a clinical Hib infection (Hib disease). The model is based on the assumption that the probability of being immune to clinical infection is determined by the time of the previous immunization caused by a subclinical infection, and by the distribution of the duration of immunity. We use a non-parametric Bayesian intensity model to arrive at smooth estimates of incidence rates. The estimated age-specific incidence rate of subclinical Hib infection is almost constant which indicates that the observed age-specific pattern of clinical Hib infection incidence is mainly due to immunity by either maternally derived antibodies or by immunizing subclinical infections. The estimated rate is relatively high, corresponding to one immunizing subclinical infection in less than two years.

Replication in genetic studies of complex traits.

Disappointments in replicating initial findings in gene mapping for complex traits are often attributed to small sample sizes and inadequate techniques to determine the threshold value. This is clearly not the whole truth. More fundamental reasons lie in the inherent heterogeneity related to disease, including genetic heterogeneity, differences in allele frequencies, and context-dependency in genetic architecture. There are also other reasons related to the data collection and analysis. Replication may remain a source of frustration unless more emphasis is put on controlling these sources of heterogeneity between studies.

The influence of competition and vaccination on the coexistence of two pneumococcal serotypes.

Streptococcus pneumoniae (pneumococcus) is one of the most important bacterial pathogens and a leading cause of mucosal infections (e.g. otitis media) and various forms of serious diseases (e.g. pneumonia, meningitis, bacteraemia) in developing and developed countries. Based on the polysaccharide capsule, there are at least 90 different pneumococcal serotypes, which may compete with each other to colonize the nasopharynx. Newly developed protein-polysaccharide conjugated vaccines have been shown to provide protection against disease caused by the serotypes included in the vaccine, and also against colonization (carriage). It is feared that yet uncommon, but nonetheless pathogenic serotypes which have been suppressed by competition, may become more prevalent in carriage and disease after large-scale use of conjugate vaccines. In this paper, we use transmission models of pneumococcal carriage to study how competition and vaccination influence the coexistence of two serotypes. According to our results, direct (physical) competition between two pneumococcal serotypes only influences colonization if the duration of naturally acquired immunity is short. By contrast, indirect (antibody-mediated) competition is of influence only if naturally acquired immunity is long lasting. Vaccination reduces the prevalence of the target serotype--an effect that is enforced by the presence of directly competing bacteria. The emergence of a non-target serotype after vaccination is only observed if bacteria compete directly. These results emphasize the importance of studying whether bacteria compete directly or indirectly and for how long people are protected in order to assess the long-term effects of sero-competition.

A statistical model of transmission of Hib bacteria in a family.

The simultaneous estimation of family and community transmission rates as well as cure rates from panel data in a recurrent Hib (Haemophilus influenzae type b bacteria) infection is considered. An individual-based stationary Markov process model with constant hazards in two age groups is applied to describe recurrent asymptomatic Hib infection in a family with small children. The problem of estimation is solved in terms of the Bayesian posterior of the model parameters. The model is used to predict prevalence and incidence of Hib carriage in families as a function of the family size and age structure.

Modelling transmission, immunity and disease of Haemophilus influenzae type b in a structured population.

An individual-based stochastic simulation model was constructed to study the epidemiology of Haemophilus influenzae type b (Hib) transmission, immunity and invasive disease. Embedded in a demographic model, the transmission model of Hib carriage employs the most important social mixing patterns with three types of contact sites (family, day-care group, and school class). The model includes immunity against invasive Hib disease, initiated and boosted by Hib carriage and cross-reactive bacterial encounters. The model reproduces the observed age patterns in Hib carriage and disease in Finland before large-scale use of the Hib conjugate vaccines. The model was used to investigate characteristics of Hib transmission. The analysis emphasizes transmission between children and adults in families while pointing out the importance of pre-school and school-aged children in maintaining Hib circulation. Carriage in these age groups is thus identified as being essential to target for sustained effects of interventions by vaccination.

Indirect protection obtained by Haemophilus influenzae type b vaccination: analysis in a structured population model.

We used a structured population model to study factors determining the magnitude of indirect protection in Haemophilus influenzae type b (Hib) vaccination. On a simulation platform mimicking the population of Finland, a Hib transmission and immunity model, including cross-reactive bacterial encounters, was formulated. Utilizing different vaccination coverages and vaccine types we could study how fast the incidence of Hib disease declined due to direct and indirect vaccination effects. With the Finnish vaccination schedule we could reproduce the observed disappearance of Hib cases. Our results show that an indirect effect was already significant with a relatively low vaccine coverage, even with a vaccine only partly reducing carriage acquisition. This suggests that the vaccination schedule and vaccine to be used should be chosen to result, in addition to immunological memory, in high antibody concentrations, sufficient to reduce carriage, the latter being the main factor behind successful elimination of transmission and disease.

Dynamics of natural immunity caused by subclinical infections, case study on Haemophilus influenzae type b (Hib).

Natural immunity to Haemophilus influenzae type b (Hib) is based primarily on antibodies that are thought to develop in response to subclinical infections. Wide use of conjugated Hib vaccines could lead to decreases in circulating Hib bacteria, thereby diminishing antibody levels in the unvaccinated. We applied a statistical model to estimate the duration of natural immunity to Hib under different forces of infection. Prior to the introduction of conjugated Hib vaccines, new Hib infections were estimated to occur once in 4 years and the antibody concentration to stabilize at a level around 1 microg/ml. In the absence of new stimuli, i.e. infection, 57% of the unvaccinated population would become susceptible to invasive disease (antibody levels < 0.15 microg/ml) in 10 years. Due to an interaction between the force of infection and the duration of immunity, in some situations numbers of invasive infections could increase in unvaccinated cohorts. This theoretical scenario has yet to be observed in practice.