Decay Of 7Be Research Articles

Monte Carlo Simulations of Superconducting Tunnel Junction Quantum Sensors for the BeEST Experiment

Superconducting Tunnel Junctions (STJs) are used as high-resolution quantum sensors to search for evidence of sterile neutrinos in the electron capture decay of 7Be. We are developing spatially resolved Monte Carlo simulations of the energy relaxation in superconductors to understand electron escape after the 7Be decay and distinguish details in the STJ response function from a possible sterile neutrino signal. Simulations of the charge generation and the Fano factor for different materials agree with the literature values. Initial simulations of the escape tail are consistent with observations and contain fine structure in the line shape. The line shape will be refined as better experimental data become available.

Meteoritic evidence of a late superflare as source of 7Be in the early Solar System

Fossil meteoritic records of short-lived, now-extinct radionuclides provide crucial high-resolution temporal information about the events, processes and activity of the Sun during the early phases of Solar System formation1. The proposed genesis of one such radionuclide,10Be, by spallation reactions of carbon and oxygen2–5 led to the hypothesis of enhanced irradiation in the early Solar System6–8. An alternative scenario of production of 10Be (half-life t1/2 = 1.386 ± 0.016 million years9) by a neutrino process in a supernova arising from the core collapse of a low-mass star (11.8 solar masses, M⊙) has recently been suggested10 and can explain the observed abundance of 10Be in the early Solar System. Here, we report well-resolved excesses in 7Li/6Li of up to ~21.5% in a calcium- and aluminium-rich inclusion (CAI) from the Efremovka meteorite that correlate with 9Be/6Li, suggestive of in situ decay of 7Be. The in situ decay of 7Be to 7Li, with a characteristic half-life of 53.12 ± 0.07 days11, entails multiple episodes of enhanced irradiation in the early Solar System, which have been observed recently in other Sun-like stars12,13. The short half-life of 7Be limits its production by interaction of solar energetic particles (SEPs) with the nebular gas and solids, and provides constraints on the genealogy and chronology of CAIs. Irradiation of the solid and gaseous precursors of CAIs of solar composition by a superflare (X-ray luminosity approximately 1032 erg s−1) during the terminal phase of class I or II of the pre-main-sequence stages of the Sun explains the isotopic properties, distinctive petrographic features and diffusivity constraints in the CAI. Li and Be isotopic measurements of calcium–aluminium inclusions (CAIs) in the Efremovka meteorite suggest that the solid and gaseous precursors of CAIs were irradiated by a superflare during the last stages of the pre-main-sequence evolution of the Sun.

Early Solar System Solar Wind Implantation of 7Be into Calcium-Alumimum Rich Inclusions in Primitive Meteortites

The one time presence of short-lived radionuclides (SLRs) in Calcium-Aluminum Rich inclusions (CAIs) in primitive meteorites has been detected. The solar wind implantation model (SWIM) is one possible model that attempts to explain the catalogue of SLRs found in primitive meteorites. In the SWIM, solar energetic particle (SEP) nuclear interactions with gas in the proto-solar atmosphere of young stellar objects (YSOs) give rise to daughter nuclei, including SLRs. These daughter nuclei then may become entrained in the solar wind via magnetic field lines. Subsequently, the nuclei, including SLRs, may be implanted into CAI precursors that have fallen from the main accretion flow which had been destined for the proto-star. This mode of implanting SLRs in the solar system is viable, and is exemplified by the impregnation of the lunar surface with solar wind particles, including SLRs. X-ray luminosities have been measured to be 100,000 times more energetic in YSOs, including T-Tauri stars, than present-day solar luminosities. The SWIM scales the production rate of SLRs to nascent SEP activity in T-Tauri stars. Here, we model the implantation of 7Be into CAIs in the SWIM, utilizing the enhanced SEP fluxes and the rate of refractory mass inflowing at the X-region, 0.06 AU from the proto-Sun. Taking into account the radioactive decay of 7Be and spectral flare variations, the 7Be/9Be initial isotopic ratio is found to range from 1 × 10−5 to 5 × 10−5.

Search for resonant states in 10C and 11C and their impact on the primordial 7Li abundance

The cosmological 7Li problem arises from the significant discrepancy of about a factor 3 between the predicted primordial 7Li abundance and the observed one. The main process for the production of 7Li during Big-Bang nucleosynthesis is the decay of 7Be. Many key nuclear reactions involved in the production and destruction of 7Be were investigated in attempt to explain the 7Li deficit but none of them led to successful conclusions. However, some authors suggested recently the possibility that the destruction of 7Be by 3He and 4He may reconcile the predictions and observations if missing resonant states in the compound nuclei 10C and 11C exist. Hence, a search of these missing resonant states in 10C and 11C was investigated at the Orsay Tandem-Alto facility through 10B(3He,t)10C and 11B(3He,t)11C charge-exchange reactions respectively. After a short overview of the cosmological 7Li problem from a nuclear physics point of view, a description of the Orsay experiment will be given as well as the obtained results and their impact on the 7Li problem.

Astrophysical S-factor of the [formula omitted] reaction in the Big-Bang nucleosynthesis

In the present work, we have studied the properties of the 23He(α,γ)47Be reaction. The direct radiative capture nuclear reactions in the Big-Bang nucleosynthesis mainly, are done in the external areas of inter-nuclear interaction range and play an essential role in nuclear astrophysics. Among of these reactions, the 23He(α,γ)47Be reaction with Q = 1.586 MeV is the main part of the Big-Bang nucleosynthesis chain reactions. This reaction can be used to understand the physical and chemical properties of the sun as well as can be justified the lake of the observed solar neutrino in the detector of the Earth. Since product neutrino fluxes are predicated in the center of the sun by the decay of 7Be and 8B, and almost are proportional to the astrophysical S-factor for the 23He(α,γ)47Be reaction, S34. The 23He(α,γ)47Be reaction is considered the key to solve the solar neutrino puzzle. Finally, we have astrophysical S-factor obtained for the ground S1,3/2-, first excited S1,1/2-and total S34 states by modern nucleon-nucleon two-body local potential models. We have also compared the obtained S-factor with experimental data and other theoretical works.

Estimating short-term soil erosion rates after single and multiple rainfall events by modelling the vertical distribution of cosmogenic 7Be in soils

The 7Be method is a promising tool for estimating soil erosion rates at time scales of days to months. However, so far its applicability is limited to steady state concentrations of the tracer. In this paper a diffusion-sorption model is presented, which takes into account atmospheric input rates, transport down the soil column and radioactive decay of 7Be. It allows simulation of the non-steady-state 7Be inventories and depth distributions in soil and their modification by discrete erosion events as well as by tillage. This model is used to quantify erosion rates for 12 individual heavy rainfall events over a period of two years at an agricultural study site in Germany. Comparisons of soil collected at the bottom of our study site with predictions made using our proposed radioberyllium technique generally show good to excellent agreement even for multiple erosion events.

Optimisation of beryllium-7 gamma analysis following BCR sequential extraction

The application of cosmogenic 7Be as a sediment tracer at the catchment-scale requires an understanding of its geochemical associations in soil to underpin the assumption of irreversible adsorption. Sequential extractions offer a readily accessible means of determining the associations of 7Be with operationally defined soil phases. However, the subdivision of the low activity concentrations of fallout 7Be in soils into geochemical fractions can introduce high gamma counting uncertainties. Extending analysis time significantly is not always an option for batches of samples, owing to the on-going decay of 7Be (t1/2=53.3 days).Here, three different methods of preparing and quantifying 7Be extracted using the optimised BCR three-step scheme have been evaluated and compared with a focus on reducing analytical uncertainties. The optimal method involved carrying out the BCR extraction in triplicate, sub-sampling each set of triplicates for stable Be analysis before combining each set and coprecipitating the 7Be with metal oxyhydroxides to produce a thin source for gamma analysis. This method was applied to BCR extractions of natural 7Be in four agricultural soils. The approach gave good counting statistics from a 24h analysis period (∼10% (2σ) where extract activity >40% of total activity) and generated statistically useful sequential extraction profiles. Total recoveries of 7Be fell between 84 and 112%. The stable Be data demonstrated that the extraction procedure had a high reproducibility (<1% RSD), thus gamma counting uncertainties dominated the overall uncertainty.In addition, extractions of soil equilibrated with stable Be at a concentration below the Cation Exchange Capacity (CEC) of the soil demonstrated that doubling the soil:solution ratio to enhance the mass of soil used in a sequential extraction scheme affects the apparent distribution of approximately 10% of the total Be. At high concentration, stable Be was found to be a poor proxy for 7Be fallout in sequential extractions.

Search for Decay Rate Variation of 7Be in Pt and A1

The decay rate variation of 7Be implanted into platinum and aluminum host materials has been measured via detecting the 478 keV γ-rays from the first excited state of 7Li populated in the electron capture decay of 7Be. The result (λPt – λA1)/λ0 = (–0.17 ± 0.13)% is obtained. It is smaller than the theoretical estimate from the TB-LMTO calculation (0.38%). This is quite different from our previous study which showed a larger decay rate variation ((0.8 ± 0.2)%) than the TB-LMTO calculation (0.30%) of 7Be in palladium and gold. It is suggested that the effective quasi-free electron density near the implanted ions in different metal host materials may play an important role in 7Be EC decay rate variation in addition to the electronic affinity and crystal structure of different host materials.

Comment on “Li and Be isotopic variations in an Allende CAI: Evidence for the in situ decay of short-lived 10Be and for the possible presence of the short-lived nuclide 7Be in the early solar system,” by M. Chaussidon, F. Robert, and K.D. McKeegan

Recently Chaussidon et al. reported isotopic measurements of the Allende meteorite Ca, Al-rich inclusion (CAI) 3529-41 that they claim as evidence that live 7Be was incorporated into this CAI at the time of its formation [Chaussidon, M., Robert, F., McKeegan, K.D., 2006. Li and Be isotopic variations in an Allende CAI: evidence for the in situ decay of short-lived 10Be and for the possible presence of the short-lived nuclide 7Be in the early solar system. Geochim. Cosmochim. Acta 70, 224–245]. They claim their data show excesses of 7Li/ 6Li above the chondritic value, and that the 7Li/ 6Li excesses correlate linearly with 9Be/ 6Li, implying that the excess 7Li arose from the decay of 7Be ( t 1/2 = 53 days). In this Comment we dispute this claim. We show that the authors did not statistically analyze their data correctly, and that a linear correlation between 7Li/ 6Li and 9Be/ 6Li can in fact be ruled out. We show that the authors over-corrected for the effects of spallogenic Li, and in fact no statistically significant excesses of 7Li above chondritic ratios exist. Finally, we show that many of the spots in Allende 3529-41 that the authors counted as isotopically undisturbed show evidence of isotopic disturbance. We demonstrate that while their data support the late addition of isotopically light Li in spots with low Be/Li, their data are otherwise consistent with constant 7Li/ 6Li at near-chondritic levels. The data do not provide support for live 7Be in the early Solar System.

Li and B isotopic variations in an Allende CAI: Evidence for the in situ decay of short-lived 10Be and for the possible presence of the short-lived nuclide 7Be in the early solar system

The concentrations and isotopic compositions of lithium, beryllium, and boron, analyzed in situ by ion microprobe in 66 spots of a type B1 Ca–Al-rich inclusion (CAI 3529-41) from the Allende meteorite, are reported. Large variations are observed for both the Li and the B isotopic ratios with 7Li/ 6Li ranging from 9.2 ± 0.22 to 12.22 ± 0.43 (a ≈250‰ range in δ 7Li values) and 10B/ 11B ranging from 0.2468 ± 0.0057 to 0.4189 ± 0.0493 (a 410‰ range in δ 11B values). The very low Li concentrations (<1 ppb) observed in several anorthite and fassaite grains require that a correction for the contribution of spallogenic Li produced during irradiation of the Allende meteoroid by galactic cosmic rays (GCR) be made (after this correction 7Li/ 6Li ranges from 9.2 ± 0.22 to 13.44 ± 0.56, i.e., a ≈350‰ range in δ 7Li values). In 3529-41, the 10B/ 11B ratios are positively correlated with 9Be/ 11B in a manner indicating the in situ decay of short-lived 10Be (half-life = 1.5 Ma) with a 10Be/ 9Be ratio at the time of formation of the CAI of 8.8 ± 0.6 × 10 −4, which is in agreement with previous findings [McKeegan, K.D., Chaussidon, M., Robert, F., 2000. Incorporation of short-lived 10Be in a calcium–aluminum-rich inclusion from the Allende meteorite. Science 289, 1334–1337]. The present detailed investigation demonstrates that only minor perturbations of the 10Be– 10B system are present in 3529-41, contrary to the 26Al/ 26Mg system for which numerous examples of isotopic redistribution following crystallization were observed [Podosek, F.A., Zinner, E.K., MacPherson, G.J., Lundberg, L.L., Brannon, J.C., Fahey, A.J., 1991. Correlated study of initial 87Sr/ 86Sr and Al–Mg systematics and petrologic properties in a suite of refractory inclusions from the Allende meteorite. Geochim. Cosmochim. Acta 55, 1083–1110]. Petrographically based criteria were developed to identify within the 66 analyzed spots in 3529-41, those where post-magmatic perturbation of the Li and Be distributions occurred. Li and Be concentrations measured in different analytical spots are compared with those predicted by using experimentally determined partition coefficients according to a model of closed-system crystallization of the CAI melt. These criteria show that 56% of the spots in melilite, 38% in anorthite, and 8% in fassaite suffered post-crystallization perturbations of Li and/or Be distributions. In the remaining spots, which do not show obvious indication of redistribution of Li or Be, the 7Li/ 6Li isotopic variations (corrected for GCR exposure) are positively correlated with 9Be/ 6Li suggesting the in situ decay of now-extinct 7Be. The derived isochron implies that at the time of its formation, the CAI melt had a 7Be/ 9Be ratio of 0.0061 ± 0.0013 and a 7Li/ 6Li ratio of 11.49 ± 0.13. In contrast, all the spots in 3529-41, which do show evidence for post-magmatic redistribution of Li and Be, have relatively constant 7Li/ 6Li, averaging 11.72 ± 0.56, which is consistent with mass balance calculations for Li isotopic homogenization in the CAI after the decay of 7Be. The incorporation of live 7Be in 3529-41 requires, because of the very short half-life of this nuclide (53 days), that it be produced essentially contemporaneously with the formation of the CAI. Therefore, the irradiation processes responsible for production of 7Be must have occurred within the solar accretion disk. Calculations developed in the framework of the x-wind model [Gounelle, M., Shu, F.H., Shang, H., Glassgold, A.E., Rehm, E.K., Lee, T., 2004. The origin of short-lived radionuclides and early Solar System irradiation (abstract). Lunar Planet. Sci. 35, 1829] reproduce the 7Be and 10Be abundances observed in 3529-41. The correlated presence of 7Be and 10Be in 3529-41 is thus a strong argument that 10Be, which is observed rather ubiquitously in CAIs, is also a product of irradiation in the early solar system, as might be a significant fraction of other short-lived radionuclides observed in early solar system materials.

Decay of 7Be in metallic environment

The electron capture half life of 7Be implanted into different metals has been measured with high precision in order to search for a possible dependence of the decay rate on the electron configuration around the 7Be atoms. In order to reduce systematic errors, the half life in different metals is measured by three laboratories simultaneously using different experimental setups. The measurements and data analysis are in progress, preliminary results are presented.

Destruction of 7Li and 7Be in astrophysical environments

The destruction of 7Li and 7Be in astrophysical environments is essential for understanding several stellar and cosmological processes and is not well understood, though earlier 7Li + 3He experiments have been performed [1]. The primordial abundance of 7Li after Big Bang Nucleosynthesis (BBN) plays a major role in our understanding of the early universe [2]. The value of the baryon to photon ratio (η) deduced from BBN combined with measurements of the cosmic microwave background provide some of the strongest and earliest evidence for the existance of non-baryonic dark matter [2]. The destruction of 7Be during the hot-pp cycle may alter our conclusions on the production of carbon in this process, which is thought to compete with the triple-α process for the production of 12C, as the reaction 7Be( 3He, 2α)2p competes with 7Be( 4He, γ) 11C and may reduce carbon production [3]. These stellar and cosmological environments involve high temperatures, and thus, effective burning energies (Gamow windows) that are quite high. Experiments using 7Be targets inevitably involve interactions with 7Li as background due to the 7Li daughters from the beta decay of 7Be. The experiments were performed at the Weizmann Institute VDG Laboratory using 3He beams from 390 keV to 1130 keV on 7LiF foil targets and 7Be implanted targets. Results from measurements using 10 μg 7LiF foil targets will be discussed.

10Be/7Be tracer of atmospheric transport and stratosphere‐troposphere exchange

The 10Be/7Be ratio is a sensitive tracer of atmospheric transport and stratosphere‐troposphere exchange (STE). Data from five NASA aircraft field missions (PEM: West A and B, Tropics A; SONEX; and SUCCESS) have been assembled to produce the largest data set of 10Be, 7Be, and their ratio collected to date (&gt;300 samples). Ratios near 0.60 are indicative of tropospheric air with little stratospheric influence, while higher ratios are found in stratospheric air. Samples from the lower stratosphere were all collected within 2.5 km of the tropopause and had ratios &gt;1.27. Of these lower stratosphere samples only 16% had ratios in excess of 3.0, suggesting that higher ratio air resides away from the tropopause. Seasonality observed in the 10Be/7Be ratios results from the downwelling of air with elevated ratios from higher in the stratosphere in the spring and summer (midlatitudes) and from the decay of 7Be during descent in the winter polar vortex (high latitudes). Our results illustrate the complexity of STE and some of the mechanisms through which it occurs, including tropopause folding, mixing associated with subtropical jets, and the effect of synoptic systems such as hurricanes and northeasters. The 10Be/7Be ratio provides important information beyond that which can be derived from studies that rely on chemical mixing ratios alone.

The branching ratio in the decay of 7Be

A measurement of the branching ratio for electron capture (EC) decay of 7Be to the 478-keV level in 7Li is reported. The reaction 10B(p, α)7Be was used and the 7Be recoils were detected and stopped in a particle detector thin enough to transmit the protons. The absolute γ-ray emission rate of 478-keV γ rays from the implanted detector was determined with a well-shielded intrinsic Ge detector. The absolute efficiency of the Ge detector was established with 22Na, 137Cs, and 88Y standard sources. A value of 11.4 ± 0.7% was obtained for the EC branch to the 478-keV state. Calculations suggest that the axial vector coupling constant GA must be reduced by a factor of 0.94 ± 0.02 to obtain agreement with the experimental result.

Branching ratios for EC decay of 7Be and 51Cr

The branching ratio for the EC decay of 7Be to 7Li has been measured by counting the total number of neutrons produced in the 7Li(p, n) 7Be reaction and subsequently counting the yield of 478 keV γ-rays from the activated targets. Six targets were measured with particular attention given to monitoring migration or loss of 7Be during and after activation. The branching ratio for the EC decay of 51Cr to 51V (320 keV γ-ray) was also measured using the same technique. The resulting branching ratios to the first excited states in 7Li and 51V are (10.61 ± 0.17)% and (10.30 ± 0.19)% respectively.

Measurement of the 7Be branching ratio

The branching ratio in the electron-capture decay of 7Be to the 478 keV and ground states of 7Li has been measured employing an activation technique. Three 7Li targets were bombarded with a proton beam and the neutrons resulting from the 7Li(p, n) 7Be reaction were counted in 4π geometry. After bombardment, the 478 keV γ-activity was determined. To calibrate neutron-detection efficiency, two 89Y targets were bombarded, and the resulting neutrons and ensuing 909 keV γ-activity counted. Comparison of the neutron yields with the γ-activities results in a 7Be branch of (10.49 ± 0.07)% to the 478 keV state of 7Li.

The branching ratio in the decay of beryllium-7

The branching ratio for the decay of 7Be to the 477-keV level in 7Li has been determined from measurements of the absolute disintegration rate and γ-quanta emission rate for each of ten mass separated sources. The absolute disintegration-rate measurements were carried out using the 4 πβ− γ coincidence technique and the γ-quanta emission rates were obtained in a calibrated sodium iodide well-crystal. A value of 0.1035 was obtained with a standard error of 0.0001 (nine degrees of freedom) and a systematic uncertainty of ±0.0008.

The branching ratios of 7Be and 65Zn

The branching ratios of the electron-capture transitions in the decay of 7Be and 65Zn were measured to be 0.1042 ± 0.0018 and 0.493 ± 0.0008 at the 68 per cent confidence level, respectively. They were obtained by measuring the neutron yields from the reactions 7 Li(p, n) 7 Be and 65 Cu(p, n) 65 Zn and the gammay-ray activities of the residual nuclei. Neutron emission was determined with a calibrated vanadium bath surrounding the target, and the gamma-ray activity measured with a sodium iodide detector calibrated against standard radioactivity sources. Results are compared with previously published data.