Search for a Neutron Dark Decay in

Neutron dark decays have been suggested as a solution to the discrepancy between bottle and beam experiments, providing a dark matter candidate that can be searched for in halo nuclei. The free neutron in the final state following the decay of ^{6}He into ^{4}He+n+χ provides an exceptionally clean detection signature when combined with a high efficiency neutron detector. Using a high-intensity ^{6}He^{+} beam at Grand Accélérateur National d'Ions Lourds, a search for a coincident neutron signal resulted in an upper limit on a dark decay branching ratio of Br_{χ}≤4.0×10^{-10} (95% C.L.). Using the dark neutron decay model proposed originally by Fornal and Grinstein, we translate this into an upper bound on a dark neutron branching ratio of O(10^{-5}), improving over global constraints by one to several orders of magnitude depending on m_{χ}.

Impact of Nuclear Deformation and Pairing on the Charge Radii of Palladium Isotopes.

The impact of nuclear deformation can been seen in the systematics of nuclear charge radii, with radii generally expanding with increasing deformation. In this Letter, we present a detailed analysis of the precise relationship between nuclear quadrupole deformation and the nuclear size. Our approach combines the first measurements of the changes in the mean-square charge radii of well-deformed palladium isotopes between A=98 and A=118 with nuclear density functional calculations using Fayans functionals, specifically Fy(std) and Fy(Δr,HFB), and the UNEDF2 functional. The changes in mean-square charge radii are extracted from collinear laser spectroscopy measurements on the 4d^{9}5s ^{3}D_{3}→4d^{9}5p ^{3}P_{2} atomic transition. The analysis of the Fayans functional calculations reveals a clear link between a good reproduction of the charge radii for the neutron-rich Pd isotopes and the overestimated odd-even staggering: Both aspects can be attributed to the strength of the pairing correlations in the particular functional which we employ.

Repellent and Attractive Effects of α-, ß-, and Dihydro-ß- Ionone to Generalist and Specialist Herbivores.

In plants, the oxidative cleavage of carotenoid substrates produces volatile apocarotenoids, including α-ionone, ß-ionone, and dihydro-ß-ionone, compounds that are important in herbivore-plant communication. For example, ß-ionone is part of an induced defense in canola, Brassica napus, and is released following wounding by herbivores. The objectives of the research were to evaluate whether these volatile compounds would: 1) be released in higher quantities from plants through the over-expression of the carotenoid cleavage dioxygenase1 (CCD1) gene and 2) cause herbivores to be repelled or attracted to over-expressing plants relative to the wild-type. In vivo dynamic headspace collection of volatiles coupled with gas chromatography-mass spectrometry was used to determine volatile organic compounds (VOC) in the headspace of the Arabidopsis thaliana ecotype Columbia-0 (L.) over-expressing the AtCCD1 gene. The analytical method allowed the detection of ß-ionone in the Arabidopsis headspace where emission rates ranged between 2 and 5-fold higher compared to the wild type, thus corroborating the in vivo enhancement of gene expression. A two chamber choice test between wild type and AtCCD1 plants revealed that crucifer flea beetle Phyllotreta cruciferae (Goeze) adults were repelled by the AtCCD1 plants with the highest transcription and ß-ionone levels. α-Ionone and dihydro-ß-ionone were not found in the headspace analysis, but solutions of the three compounds were tested in the concentration range of ß-ionone found in the Arabidopsis headspace (0.05 to 0.5 ng/µl) in order to assess their biological activity with crucifer flea beetle, two spotted spider mite Tetranychus urticae (Koch), and silverleaf whiteflies Bemisia tabaci (Gennadius). Choice bioassays demonstrated that ß-ionone has a strong repellent effect toward both the flea beetle and the spider mite, and significant oviposition deterrence to whiteflies. In contrast, dihydro-ß-ionone had attractant properties, especially to the crucifer flea beetle, while α-ionone did not show any significant activity. These findings demonstrate how regulating genes of the carotenoid pathway can increase herbivore deterrent volatiles, a novel tool for insect pest management.

Observation of the ß-delayed γ-proton decay of (56)Zn and its impact on the Gamow-Teller strength evaluation.

We report the observation of a very exotic decay mode at the proton drip line, the ß-delayed γ-proton decay, clearly seen in the ß decay of the T_{z}=-2 nucleus ^{56}Zn. Three γ-proton sequences have been observed after the ß decay. Here this decay mode, already observed in the sd shell, is seen for the first time in the fp shell. Both γ and proton decays have been taken into account in the estimation of the Fermi and Gamow-Teller strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.

Measurement of the isoscalar monopole response in the neutron-rich nucleus 68Ni.

The isoscalar monopole response has been measured in the unstable nucleus (68)Ni using inelastic alpha scattering at 50A MeV in inverse kinematics with the active target MAYA at GANIL. The isoscalar giant monopole resonance (ISGMR) centroid was determined to be 21.1 ± 1.9 MeV and indications for a soft monopole mode are provided for the first time at 12.9 ± 1.0 MeV. Analysis of the corresponding angular distributions using distorted-wave-born approximation with random-phase approximation transition densities indicates that the L = 0 multipolarity dominates the cross section for the ISGMR and significantly contributes to the low-energy mode. The L=0 part of this low-energy mode, the soft monopole mode, is dominated by neutron excitations. This demonstrates the relevance of inelastic alpha scattering in inverse kinematics in order to probe both the ISGMR and isoscalar soft modes in neutron-rich nuclei.

Experimental study of the two-body spin-orbit force in nuclei.

Energies and spectroscopic factors of the first 7/2-, 3/2-, 1/2-, and 5/2- states in the (35)Si21 nucleus were determined by means of the (d, p) transfer reaction in inverse kinematics at GANIL using the MUST2 and EXOGAM detectors. By comparing the spectroscopic information on the Si35 and S37 isotones, a reduction of the p3/2-p1/2 spin-orbit splitting by about 25% is proposed, while the f7/2-f5/2 spin-orbit splitting seems to remain constant. These features, derived after having unfolded nuclear correlations using shell model calculations, have been attributed to the properties of the two-body spin-orbit interaction, the amplitude of which is derived for the first time in an atomic nucleus. The present results, remarkably well reproduced by using several realistic nucleon-nucleon forces, provide a unique touchstone for the modeling of the spin-orbit interaction in atomic nuclei.

Half-life systematics across the N=126 shell closure: role of first-forbidden transitions in the ß decay of heavy neutron-rich nuclei.

This Letter reports on a systematic study of ß-decay half-lives of neutron-rich nuclei around doubly magic (208)Pb. The lifetimes of the 126-neutron shell isotone (204)Pt and the neighboring (200-202)Ir, (203)Pt, (204)Au are presented together with other 19 half-lives measured during the "stopped beam" campaign of the rare isotope investigations at GSI collaboration. The results constrain the main nuclear theories used in calculations of r-process nucleosynthesis. Predictions based on a statistical macroscopic description of the first-forbidden ß strength reveal significant deviations for most of the nuclei with N<126. In contrast, theories including a fully microscopic treatment of allowed and first-forbidden transitions reproduce more satisfactorily the trend in the measured half-lives for the nuclei in this region, where the r-process pathway passes through during ß decay back to stability.

Hindered Gamow-Teller decay to the odd-odd N=Z (62)Ga: absence of proton-neutron T=0 condensate in A=62.

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.

Spectroscopy of 26F to probe proton-neutron forces close to the drip line.

A long-lived J(π) = 4(1)(+) isomer, T(1/2) = 2.2(1) ms, has been discovered at 643.4(1) keV in the weakly bound (9)(26)F nucleus. It was populated at Grand Accélérateur National d'Ions Lourds in the fragmentation of a (36)S beam. It decays by an internal transition to the J(π) = 1(1)(+) ground state [82(14)%], by ß decay to (26)Ne, or ß-delayed neutron emission to (25)Ne. From the ß-decay studies of the J(π) =1(1)(+) and J(π) = 4(1)(+) states, new excited states have been discovered in (25,26)Ne. Gathering the measured binding energies of the J(π) = 1(1)(+) -4(1)(+) multiplet in (9)(26)F, we find that the proton-neutron π0d(5/2)ν0d(3/2) effective force used in shell-model calculations should be reduced to properly account for the weak binding of (9)(26)F. Microscopic coupled cluster theory calculations using interactions derived from chiral effective field theory are in very good agreement with the energy of the low-lying 1(1)(+), 2(1)(+), 4(1)(+) states in (26)F. Including three-body forces and coupling to the continuum effects improve the agreement between experiment and theory as compared to the use of two-body forces only.

Direct observation of long-lived isomers in 212Bi.

Long-lived isomers in (212)Bi have been studied following (238)U projectile fragmentation at 670 MeV per nucleon. The fragmentation products were injected as highly charged ions into a storage ring, giving access to masses and half-lives. While the excitation energy of the first isomer of (212)Bi was confirmed, the second isomer was observed at 1478(30) keV, in contrast to the previously accepted value of >1910 keV. It was also found to have an extended Lorentz-corrected in-ring half-life >30 min, compared to 7.0(3) min for the neutral atom. Both the energy and half-life differences can be understood as being due a substantial, though previously unrecognized, internal decay branch for neutral atoms. Earlier shell-model calculations are now found to give good agreement with the isomer excitation energy. Furthermore, these and new calculations predict the existence of states at slightly higher energy that could facilitate isomer deexcitation studies.

The Atacama Rover Astrobiology Drilling Studies (ARADS) Project.

With advances in commercial space launch capabilities and reduced costs to orbit, humans may arrive on Mars within a decade. Both to preserve any signs of past (and extant) martian life and to protect the health of human crews (and Earth's biosphere), it will be necessary to assess the risk of cross-contamination on the surface, in blown dust, and into the near-subsurface (where exploration and resource-harvesting can be reasonably anticipated). Thus, evaluating for the presence of life and biosignatures may become a critical-path Mars exploration precursor in the not-so-far future, circa 2030. This Special Collection of papers from the Atacama Rover Astrobiology Drilling Studies (ARADS) project describes many of the scientific, technological, and operational issues associated with searching for and identifying biosignatures in an extreme hyperarid region in Chile's Atacama Desert, a well-studied terrestrial Mars analog environment. This paper provides an overview of the ARADS project and discusses in context the five other papers in the ARADS Special Collection, as well as prior ARADS project results.

Unveiling the intruder deformed 02(+) state in 34Si.

The 02(+) state in 34Si has been populated at the GANIL-LISE3 facility through the ß decay of a newly discovered 1(+) isomer in 34Al of 26(1) ms half-life. The simultaneous detection of e(+)e(-) pairs allowed the determination of the excitation energy E(02(+))=2719(3) keV and the half-life T(1/2)=19.4(7) ns, from which an electric monopole strength of ρ(2)(E0)=13.0(0.9)×10(-3) was deduced. The 2(1)(+) state is observed to decay both to the 0(1)(+) ground state and to the newly observed 0(2)(+) state [via a 607(2) keV transition] with a ratio R(2(1)(+)→0(1)(+)/2(1)(+)→0(2)(+))=1380(717). Gathering all information, a weak mixing with the 0(1)(+) and a large deformation parameter of ß=0.29(4) are found for the 0(2)(+) state, in good agreement with shell model calculations using a new SDPF-U-MIX interaction allowing np-nh excitations across the N=20 shell gap.

Well developed deformation in 42Si.

Excited states in (38,40,42) Si nuclei have been studied via in-beam γ-ray spectroscopy with multinucleon removal reactions. Intense radioactive beams of ^{40}S and (44)S provided at the new facility of the RIKEN Radioactive Isotope Beam Factory enabled γ-γ coincidence measurements. A prominent γ line observed with an energy of 742(8) keV in (42) Si confirms the 2(+) state reported in an earlier study. Among the γ lines observed in coincidence with the 2^{+} → 0+ transition, the most probable candidate for the transition from the yrast 4(+) state was identified, leading to a 4(1)+) energy of 2173(14) keV. The energy ratio of 2.93(5) between the 2(1)+ and 4(1)(+) states indicates well-developed deformation in (42) Si at N = 28 and Z = 14. Also for 38,40)Si energy ratios with values of 2.09(5) and 2.56(5) were obtained. Together with the ratio for (42)Si, the results show a rapid deformation development of Si isotopes from N = 24 to N = 28.

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.

4D-imaging of drip-line radioactivity by detecting proton emission from 54mNi pictured with ACTAR TPC.

Proton radioactivity was discovered exactly 50 years ago. First, this nuclear decay mode sets the limit of existence on the nuclear landscape on the neutron-deficient side. Second, it comprises fundamental aspects of both quantum tunnelling as well as the coupling of (quasi)bound quantum states with the continuum in mesoscopic systems such as the atomic nucleus. Theoretical approaches can start either from bound-state nuclear shell-model theory or from resonance scattering. Thus, proton-radioactivity guides merging these types of theoretical approaches, which is of broader relevance for any few-body quantum system. Here, we report experimental measurements of proton-emission branches from an isomeric state in 54mNi, which were visualized in four dimensions in a newly developed detector. We show that these decays, which carry an unusually high angular momentum, ℓ = 5 and ℓ = 7, respectively, can be approximated theoretically with a potential model for the proton barrier penetration and a shell-model calculation for the overlap of the initial and final wave functions.

Prolate-spherical shape coexistence at N=28 in 44S.

The structure of 44S has been studied by using delayed γ and electron spectroscopy. The decay rates of the 02+ isomeric state to the 2(1)+ and 0(1)+ states, measured for the first time, lead to a reduced transition probability B(E2: 2(1)+→0(2)+)=8.4(26) e(2) fm4 and a monopole strength ρ2(E0: 0(2)+→0(1)+)=8.7(7)×10(-3). Comparisons to shell model calculations point towards prolate-spherical shape coexistence, and a two-level mixing model is used to extract a weak mixing between the two configurations.

Outbreak of 2009 pandemic influenza A(H1N1), Los Lagos, Chile, April-June 2009.

On 17 May 2009, the first two cases of 2009 pandemic influenza A(H1N1) were confirmed in the Metropolitan region (Santiago, Chile). On 6 June 2009, Chile reported 500 confirmed cases, seven severe and two fatal. Because six of the severe cases and the two deaths occurred in the region of Los Lagos in southern Chile, a retrospective study was conducted using data on emergency room visits as well as laboratory viral surveillance, during the period from 1 April to 31 May, in order to establish the date of the beginning of the outbreak. From 1 to 27 June, data were collected in real time, to establish the real magnitude of the outbreak, describe its transmission, clinical severity and secondary attack rates. Confirmed cases, their household contacts and healthcare workers were interviewed. This analysis showed that the outbreak in Los Lagos started on 28 April. By 27 June, a total of 14.559 clinical cases were identified, affecting mostly 5-19 year-olds. The effective reproduction number during the initial phase (20 days) was 1.8 (1.6-2.0). Of the 190 confirmed cases with severe acute respiratory infection, 71 (37.4%) presented a risk condition or underlying illness.

Phase I clinical trial in healthy adults of a nasal vaccine candidate containing recombinant hepatitis B surface and core antigens.

BACKGROUND: The nasal vaccine candidate (NASVAC), comprising hepatitis B virus (HBV) surface (HBsAg) and core antigens (HBcAg), has been shown to be highly immunogenic in animal models. METHODS: A phase I double-blinded, placebo-controlled randomized clinical trial was carried out in 19 healthy male adults with no serologic markers of immunity/infection to HBV. This study was aimed at exploring the safety and immunogenic profile of nasal co-administration of both HBV recombinant antigens. The trial was performed according to Good Clinical Practice guidelines. Participants ranged in age from 18 to 45 years and were randomly allocated to receive a mixture of 50 microg HBsAg and 50 microg HBcAg or 0.9% physiologic saline solution, as a placebo, via nasal spray in a five-dose schedule at 0, 7, 15, 30, and 60 days. A total volume of 0.5 ml was administered in two dosages of 125 microl per nostril. Adverse events were actively recorded 1 h, 6 h, 12 h, 24 h, 48 h, 72 h, 7 days and 30 days after each dose. Anti-HBs and anti-HBc titers were evaluated using corresponding ELISA kits at days 30 and 90. RESULTS: The vaccine candidate was safe and well tolerated. Adverse reactions included sneezing (34.1%), rhinorrhea (12.2%), nasal stuffiness (9.8%), palate itching (9.8%), headache (9.8%), and general malaise (7.3%). These reactions were all self-limiting and mild in intensity. No severe or unexpected events were recorded during the trial. The vaccine elicited anti-HBc seroconversion in 100% of subjects as early as day 30 of the immunization schedule, while a seroprotective anti-HBs titer (>or=10 IU/l) was at a maximum at day 90 (75%). All subjects in the placebo group remained seronegative during the trial. CONCLUSION: The HBsAg-HBcAg vaccine candidate was safe, well tolerated and immunogenic in this phase I study in healthy adults. To our knowledge, this is the first demonstration of safety and immunogenicity for a nasal vaccine candidate comprising HBV antigens.

Una vista a la tasa de mortalidad por enfermedad de alzheimer en Chile en el periodo de 2017 a 2021 / A view of the mortality rate due to alzheimer's disease in Chile in the period from 2017 to 2021

Introducción: La enfermedad de Alzheimer (EA) es la principal causa de demencia, caracterizada por pérdida progresiva de memoria. Principal fuente de morbimortalidad en mayores de 65 años. En los últimos 20 años las muertes por EA han aumentado un 145% en el mundo. En Chile no hay estudios actuales que describan mortalidad por EA. El objetivo del presente trabajo es analizar y comparar las tasas de mortalidad (TM) por EA según sexo y grupo etario en Chile entre 2017-2021. Materiales y métodos: Estudio descriptivo, ecológico, sobre defunciones por EA entre 2017-2021 en Chile según sexo y grupo etario (n=10.223). Información obtenida de la base de datos del Departamento de Estadísticas e Información de Salud. Se realizó estadística descriptiva y cálculo de TM. No se requiere comité de ética. Resultados: La máxima TM del periodo fue 11,74 por cada 100.000 habitantes en 2021. El sexo femenino logró la mayor TM en este periodo. El grupo etario con mayor cantidad de defunciones fue el de 81 o más años con 76.6% (7.829) de las defunciones totales. Discusión: Se evidenció mantención y luego ascenso de TM por EA, podría deberse al aumento en la esperanza de vida. La mayor frecuencia de defunciones según sexo y edad, podría explicarse por mayor vulnerabilidad femenina a desarrollar EA y a cambios fisiológicos del envejecimiento. En conclusión, la TM por EA en Chile ha aumentado, probablemente secundario al aumento en la esperanza de vida. Se hace un llamado a continuar el estudio de la patología.

Introduction: Alzheimer's disease (AD) is the most common cause of dementia, characterized by progressive memory loss. It is the main source of morbidity and mortality in individuals over 65 years of age, with age being its primary non-modifiable risk factor. In the last 20 years, deaths from AD have increased by 145% worldwide. However, there are no current studies in Chile that describe mortality from AD. The objective of this study is to analyze and compare mortality rates due to AD according to sex and age group in the Chilean population during the years 2017-2021. Material and Methods: Descriptive, ecological study on deaths from AD between 2017-2021 in Chile, categorized by sex and age group (n=10,223). The database was obtained from the Department of Health Statistics and Information. Descriptive statistics and mortality rate calculations were performed. No ethics committee approval was required. Results: The maximum mortality rate (MR) was observed in 2021 with a value of 11.74 per 100,000 inhabitants. Women had the highest MR in this period. The age group with the highest number of deaths was 81 years or older, accounting for 76.6% (7,829) of the total deaths. Discussion: A plateau and subsequent increase in MR due to AD were observed, possibly explained by the increase in life expectancy. The higher frequency of deaths in women and specific age groups may be attributed to the higher vulnerability of women to developing AD and physiological changes related to aging. In conclusion, the MR from AD has increased in Chile, likely due to the rise in life expectancy, emphasizing the importance of continued research on this pathology.