Electron Capture Branching Research Articles

Determination of the activity and nuclear decay data of 157Tb

Terbium-157 was radiochemically extracted from an irradiated tantalum target. Since the resulting material contained a significant impurity of 158Tb, 157Tb was isotopically purified using laser resonance ionization at the RISIKO mass separator in Mainz and then implanted on an aluminum (Al) foil. The implanted 157Tb was measured by two different calibrated gamma-ray spectrometers to determine photon emission rates. After dissolving the Al foil, a high purity 157Tb solution was obtained. The corresponding activity concentration was determined with a low relative uncertainty of 0.52% through a combination of liquid scintillation counting using the TDCR method and 4π(X,e)(LS)-(X,γ)(CeBr3) coincidence counting. By combining the results from all measurement techniques, emission intensities for K X-rays and gamma-rays were derived and found to be 16.05(31)% and 0.0064(2)%, respectively. The probability for K electron capture of the first forbidden non-unique transition to the ground state was determined to be 17.16(35)%. The probabilities for the electron-capture branch to the excited level and the ground state were found to be 0.084(4)% and 99.916(4)%, respectively. A Q+ value of 60.23(18) keV was estimated based on simplified BetaShape calculations, assuming an allowed transition.

Investigation of Electron Capture in 176Lu with a LYSO crystal scintillator

The nuclide 176Lu is one of the few naturally occurring isotopes that are potentially unstable with respect to electron capture (EC). Although experimental evidence for 176Lu EC decay is still missing, this isotope is instead well known to β− decay into 176Hf with an half-life of about 38 Gyr. Previous searches for the 176Lu EC decay were performed by using a passive Lutetium source coupled with an HP-Ge spectrometer. Our approach uses a LYSO crystal both as Lutetium source and as an active detector and the obtained 176Lu EC branching ratio limits are 7 × 10−4 and 4.4 × 10−4 for the capture of the 1s and 2s electron, respectively. Previously known limits for the EC in 176Lu are improved by a factor 3 to 15 depending on the considered EC channel.

Search for Electron-Capture Delayed Fission in the New Isotope ^{244}Md.

The electron-capture decay followed by a prompt fission process was searched for in the hitherto unknown most neutron-deficient Md isotope with mass number 244. Alpha decay with α-particle energies of 8.73-8.86MeV and with a half-life of 0.30_{-0.09}^{+0.19} s was assigned to ^{244}Md. No fission event with a similar half-life potentially originating from spontaneous fissioning of the short-lived electron-capture decay daughter ^{244}Fm was observed, which results in an upper limit of 0.14 for the electron-capture branching of ^{244}Md. Two groups of fission events with half-lives of 0.9_{-0.3}^{+0.6} ms and 5_{-2}^{+3} ms were observed. The 0.9_{-0.3}^{+0.6} ms activity was assigned to originate from the decay of ^{245}Md. The origin of eight fission events resulting in a half-life of 5_{-2}^{+3} ms could not be unambiguously identified within the present data while the possible explanation has to invoke previously unseen physics cases.

Partially monochromatic modulated neutrino beams

Recently, it was proposed to use storage rings with β+-radioactive nuclei as the sources of electron neutrino beams. If the nuclei have large electron capture branching, than such beams can have a significant monochromatic component. Under certain conditions, in particular, for hydrogen-like ions, one can modulate the monochromatic component. The selection criteria for β+-decaying nuclei, which can be used to produce intense beams of partially monochromatic and modulated electron neutrinos are proposed. It is shown that, in practice, such beams can be obtained, and they are promising for future experiments.

Development of an Ultra-Pure, Carrier-Free (209)Po Solution Standard.

Ultra-pure, carrier-free 209Po solution standards have been prepared and standardized for their massic alpha-particle emission rate. The standards, which will be disseminated by the National Institute of Standards and Technology (NIST) as Standard Reference Material SRM 4326a, have a mean mass of (5.169 ± 0.003) g of a solution of polonium in nominal 2.0 mol▪L−1 HCl (having a solution density of (1.032 ± 0.002) g▪ mL−1 at 20 °C) that are contained in 5 mL, flame-sealed, borosilicate glass ampoules. They are certified to contain a 209Po massic alpha-particle emission rate of (39.01 ± 0.18) s−1▪g−1 as of a reference time of 1200 EST, 01 December 2013. This new standard series replaces SRM 4326 that was issued by NIST in 1994. The standardization was based on 4πα liquid scintillation (LS) spectrometry with two different LS counting systems and under wide variations in measurement and counting source conditions. The methodology for the standardization, with corrections for detection of the low-energy conversion electrons from the delayed 2 keV isomeric state in 205Pb and for the radiations accompanying the small 0.45 % electron-capture branch to 209Bi, involves a unique spectral analysis procedure that is specific for the case of 209Po decay. The entire measurement protocol is similar, but revised and improved from that used for SRM 4326. Spectroscopic impurity analyses revealed that no photon-emitting or alpha-emitting radionuclidic impurities were detected. The most common impurity associated with 209Po is 208Po and the activity ratio of 208Po/209Po was < 10−7.

The TITAN in-trap decay spectroscopy facility at TRIUMF

This paper presents an upgraded in-trap decay spectroscopy apparatus which has been developed and constructed for use with TRIUMF׳s Ion Trap for Atomic and Nuclear science (TITAN). This device consists of an open-access electron-beam ion-trap (EBIT), which is surrounded radially by seven low-energy planar Si(Li) detectors. The environment of the EBIT allows for the detection of low-energy photons by providing backing-free storage of the radioactive ions, while guiding charged decay particles away from the trap centre via the strong (up to 6T) magnetic field. In addition to excellent ion confinement and storage, the EBIT also provides a venue for performing decay spectroscopy on highly charged radioactive ions. Recent technical advancements have been able to provide a significant increase in sensitivity for low-energy photon detection, towards the goal of measuring weak electron-capture branching ratios of the intermediate nuclei in the two-neutrino double beta (2νββ) decay process. The design, development, and commissioning of this apparatus are presented together with the main physics objectives. The future of the device and experimental technique are discussed.

β-decay half-life ofV50calculated by the shell model

In this work we survey the detectability of the ${\ensuremath{\beta}}^{\ensuremath{-}}$ channel of ${}_{23}^{50}\mathrm{V}$ leading to the first excited ${2}^{+}$ state in ${}_{24}^{50}\mathrm{Cr}$. The electron-capture (EC) half-life corresponding to the transition of ${}_{23}^{50}V$ to the first excited ${2}^{+}$ state in ${}_{22}^{50}\mathrm{Ti}$ had been measured earlier. Both of the mentioned transitions are 4th-forbidden non-unique. We have performed calculations of all the involved wave functions by using the nuclear shell model with the GXPF1A interaction in the full f-p shell. The computed half-life of the EC branch is in good agreement with the measured one. The predicted half-life for the ${\ensuremath{\beta}}^{\ensuremath{-}}$ branch is in the range $\ensuremath{\approx}2\ifmmode\times\else\texttimes\fi{}{10}^{19}$ yr whereas the present experimental lower limit is $1.5\ifmmode\times\else\texttimes\fi{}{10}^{18}$ yr. We discuss also the experimental lay-out needed to detect the ${\ensuremath{\beta}}^{\ensuremath{-}}$-branch decay.

In-trap spectroscopy of charge-bred radioactive ions.

In this Letter, we introduce the concept of in-trap nuclear decay spectroscopy of highly charged radioactive ions and describe its successful application as a novel spectroscopic tool. This is demonstrated by a measurement of the decay properties of radioactive mass A=124 ions (here, ^{124}In and ^{124}Cs) in the electron-beam ion trap of the TITAN facility at TRIUMF. By subjecting the trapped ions to an intense electron beam, the ions are charge bred to high charge states (i.e., equivalent to the removal of N-shell electrons), and an increase of storage times to the level of minutes without significant ion losses is achieved. The present technique opens the venue for precision spectroscopy of low branching ratios and is being developed in the context of measuring electron-capture branching ratios needed for determining the nuclear ground-state properties of the intermediate odd-odd nuclei in double-beta (ββ) decay.

Extension of the TDCR model to compute counting efficiencies for radionuclides with complex decay schemes

The triple-to-double coincidence ratio (TDCR) method is frequently used to measure the activity of radionuclides decaying by pure β emission or electron capture (EC). Some radionuclides with more complex decays have also been studied, but accurate calculations of decay branches which are accompanied by many coincident γ transitions have not yet been investigated.This paper describes recent extensions of the model to make efficiency computations for more complex decay schemes possible. In particular, the MICELLE2 program that applies a stochastic approach of the free parameter model was extended. With an improved code, efficiencies for β−, β+ and EC branches with up to seven coincident γ transitions can be calculated. Moreover, a new parametrization for the computation of electron stopping powers has been implemented to compute the ionization quenching function of 10 commercial scintillation cocktails.In order to demonstrate the capabilities of the TDCR method, the following radionuclides are discussed: 166mHo (complex β−/γ), 59Fe (complex β−/γ), 64Cu (β−, β+, EC and EC/γ) and 229Th in equilibrium with its progenies (decay chain with many α, β and complex β−/γ transitions).

Trapped-ion decay spectroscopy towards the determination of ground-state components of double-beta decay matrix elements

A new technique has been developed at TRIUMF's TITAN facility to perform in-trap decay spectroscopy. The aim of this technique is to eventually measure weak electron capture branching ratios (ECBRs) and by this to consequently determine GT matrix elements of $\beta\beta$ decaying nuclei. These branching ratios provide important input to the theoretical description of these decays. The feasibility and power of the technique is demonstrated by measuring the ECBR of $^{124}$Cs.

Electron-capture branching ratio measurements of odd-odd intermediate nuclei in double-beta decay at the TITAN facility

A novel technique to measure electron-capture branching ratios is being introduced, where the TITAN ion traps and the ISAC radioactive beam facility at TRIUMF are the central components. The technique will be applied to the intermediate odd-odd nuclei in double-beta decay. The decay properties of these nuclei will constrain theoretical models dealing with the evaluation of the nuclear matrix elements for both the 2v and the 0v mode. The present setup and its potential for measuring extremely low branching ratios at low instrumental backgrounds is described.

Decay studies for neutrino physics

Both 100Mo and 116Cd are zero-neutrino double-β-decay candidates with Jπ = 0 + and the ground states of the respective intermediate nuclei, 100Tc and 116In, have Jπ = 1 + . This makes it possible to measure these matrix elements, which turn out to provide a valuable benchmark for testing models. The electron-capture (EC) decay of 100Tc can also be used to directly determine the efficiency of a potential neutrino detector. However, the experimental determinations of the EC decay branches of interest are challenging because they are only small fractions of the main decays and co-produced radioactivities contribute significant background counts in the regions of interest. This article summarizes our work at Jyvaskyla, where we have taken advantage of the high-purity beams produced at IGISOL in combination with JYFLTRAP to achieve significant improvements in the determinations of the EC branches of 100Tc and 116In.

Design of a β-detector for TITAN-EC and the first electron-capture branching ratio measurement in a Penning trap

At TRIUMF's ion trap for atomic and nuclear science (TITAN) a new experimental technique is being developed to measure electron-capture branching ratios of intermediate nuclei in double-β decays. The key feature of this novel technique is the use of an open access Penning trap. Radioactive ions are stored inside the trap while their decays are observed. X-rays following an electron capture are detected by x-ray detectors radially installed around the trap. Electrons originating from β-decays are guided out of the trap by the Penning trap's strong magnetic field where they are then detected by a Si-detector. Detailed simulations have been performed to determine the size and characterize the efficiency of this detector. During a beam time with radioactive 107In this β-detector has been used and for the first time an electron capture branching ratio has been determined with this novel technique of in-trap decay spectroscopy.

In-trap decay spectroscopy for 2νββ decay experiments

Knowledge of 2νββ nuclear matrix elements is essential to probe the theoretical framework of 0νββ decays. At TITAN, TRIUMF’s Ion Trap for Atomic and Nuclear science, a novel technique has been developed to measure electron capture branches of virtual intermediate nuclei in ββ decays. During two experiments with radioactive 124, 126Cs isotopes the feasibility of this new method was proven.

Decay study of 246Fm at SHIP

The decay chain of 246Fm has been investigated employing the SHIP separator at GSI Darmstadt. The 246Fm nuclei were produced via the 40Ar(208Pb, 2n)246Fm fusion-evaporation reaction. Improved values of the half-life, T 1/2 = 1.54(4) s, and of the spontaneous fission branching ratio, b SF = 0.068(6) , of 246Fm were obtained. The $ \beta^{+}_{}$ /electron capture branching ratio, b EC = 0.39(3) , of 242Cf was deduced. Possible structures of high-K states in 246Fm are discussed within the framework of a model calculation based on the Woods-Saxon potential.

40Ar/ 39Ar ages of CAMP in North America: Implications for the Triassic–Jurassic boundary and the 40K decay constant bias

The Central Atlantic magmatic province (CAMP) is one of the largest igneous provinces on Earth (> 10 7 km 2), spanning four continents. Recent high-precision 40Ar/ 39Ar dating of mineral separates has provided important constraints on the age, duration, and geodynamic history of CAMP. Yet the North American CAMP is strikingly under-represented in this dating effort. Here we present 13 new statistically robust plateau, mini-plateau and isochron ages obtained on plagioclase and sericite separates from lava flows from the Fundy ( n = 10; Nova Scotia, Canada), Hartford and Deerfield ( n = 3; U.S.A.) basins. Ages mostly range from 198.6 ± 1.1 to 201.0 ± 1.4 Ma (2 σ), with 1 date substantially younger at 190.6 ± 1.0 Ma. Careful statistical regression shows that ages from the upper (199.7.0 ± 1.5 Ma) and bottom (200.1 ± 0.9 Ma) units of the lava pile in the Fundy basin are statistically indistinguishable, confirming a short duration of emplacement (≪ 1.6 Ma; ≤ 1 Ma). Three ages obtained on the Hartford (198.6 ± 2.0 Ma and 199.8 ± 1.1 Ma) and Deerfield (199.3 ± 1.2 Ma) basins were measured on sericite from the upper lava flow units. We interpret these dates as reflecting syn-emplacement hydrothermal activity within these units. Collectively, CAMP ages gathered so far suggest a short duration of the main magmatic activity (2–3 Ma), but also suggest the possibility of a temporal migration of the active magmatic centers from north to south. Such a migration challenges a plume model that would postulate a radial outward migration of the magmatism and is more compatible with other models, such as the supercontinent global warming hypothesis. When compared to the age of the Triassic–Jurassic boundary, the filtered CAMP age database suggests that the onset of the magmatic activity precedes the limit by at least few hundred thousand years, thereby suggesting a causal relationship between CAMP and the end of Triassic mass extinction. An age at 191 Ma possibly suggests a minor CAMP late tailing activity (190–194 Ma) which has been observed already for dykes and sills in Africa and Brazil. We speculate that, if genuine, this late activity can be due to a major extensional event, possibly heralding the oceanization process at ~ 190 Ma. Comparison between high quality U/Pb and 40Ar/ 39Ar ages of pegmatite lenses from the North Mountain basalts confirms a ~ 1% bias between the two chronometers. This discrepancy is likely attributed to the miscalibration of the 40K decay constants, in particular the electron capture branch.

Electron-capture branch ofTc100and tests of nuclear wave functions for double-βdecays

We present a measurement of the electron-capture branch of $^{100}\mathrm{Tc}$. Our value, $B(\mathrm{EC})=(2.6\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, implies that the $^{100}\mathrm{Mo}$ neutrino absorption cross section to the ground state of $^{100}\mathrm{Tc}$ is roughly 50% larger than previously thought. Disagreement between the experimental value and QRPA calculations relevant to double-$\ensuremath{\beta}$ decay matrix elements persists. We find agreement with previous measurements of the 539.5- and 590.8-keV $\ensuremath{\gamma}$-ray intensities.

Electron capture branching ratio measurements in an ion trap for double beta decay experiments at TITAN

Double beta decay (ββ) is a nuclear decay mode expected to appear in at least two varieties, the double-neutrino (2ν) and the zero-neutrino (0ν) mode. The 0νββ-decay is of particular interest as it requires the neutrino to be a Majorana particle. The search for such a decay is presently being carried out or planned in a number of experiments, such as EXO, MAJORANA, GERDA, CUORE, COBRA, NEMO-III and SNO+. The 0ν-decay rate depends on the neutrino mass but, unfortunately, also on a rather complex nuclear matrix element, making the extraction of the mass heavily dependent on the underlying theoretical nuclear model. However, all theoretical models can readily be tested against the 2ν mode, which, unlike its 0ν counterpart, only involves simple Gamow–Teller nuclear matrix elements. These elements can be determined experimentally either through charge-exchange reactions or, for the ground-state transition, through the electron capture (EC) or single β-decay of the intermediate odd–odd nucleus. The present program is geared towards the measurement of the EC branching ratios (BR). In most cases, these ratios are poorly known or not known at all, because EC is usually suppressed by several orders of magnitude compared to the β-decay counterpart due to energy considerations. Traditional methods for measuring these ratios have so far suffered from overwhelming background generated by these high-energy electrons. Recently, a unique background-free method for measuring EC branching ratios was proposed using the TITAN ion trap at the TRIUMF ISAC (Isotope Separator and ACcelerator) radioactive beam facility. The measurements will make use of the EBIT (Electron Beam Ion Trap) operating in Penning mode where electrons from the β−-decay will be confined by the magnetic field. K-shell X-rays from EC will be detected by seven X-ray detectors located around the trap, thus providing orders of magnitude background suppression and thus ideal low-BR measurement environment.

Electron capture branching ratios for the odd–odd intermediate nuclei in double-beta decay using the TITAN ion trap facility

We suggest a measurement of the electron capture (EC) branching ratios for the odd–odd intermediate nuclei in double-beta (β– β–) decay using the new ion trap facility TITAN at the TRIUMF radioactive beam facility. The EC branching ratios are important for evaluating the nuclear matrix elements involved in the β– β– -decay for both, the 2ν and the 0ν-decay mode. Especially the neutrinoless (0νββ) mode is presently at the center of attention, as it probes the Majorana character of the neutrino, and if observed unambiguously, knowledge of the nuclear matrix elements are the key for determining the neutrino mass. The EC branches are in most cases suppressed by several orders of magnitude relative to their β– -counterparts owing to much lower decay energies, and are, therefore, either poorly known or not known at all. Here, the traditional methods of producing the radioactive isotope through irradiation of a suitable target and then measuring the K-shell X-rays have reached a limit of sensitivity. In this note, we will describe a novel technique to measure the EC branching ratios, where the TITAN ion traps and the ISAC radioactive beam facility at TRIUMF are the central components. This approach will increase the sensitivity limit because of significantly reduced background levels. Seven cases will be discussed in detail and connections to hadronic charge-exchange reactions will be made. For most of these, the daughter isotopes are β– β– -decay nuclei that are presently under intense experimental investigations. These are [Formula: see text]PACS Nos.: 23.40.–s, 23.40.Hc, 29.30.Kv, 29.25.Rm, 14.60.Pq

Decay properties of neutron-deficient isotopes 256, 257Db, 255Rf, 252, 253Lr

Isotopes of dubnium (element 105) with mass numbers A = 256, 257, and 258 were produced by the reaction 209Bi(50Ti,xn) 259-xDb (x = 1, 2, 3) at projectile energies of (4.59-5.08) AMeV. Excitation functions were measured for the 1n, 2n and 3n evaporation channels. The same position of the excitation function was observed for the 1n channel as for the previously measured 1n channel of the reaction 208Pb(50Ti,1n)257Rf. The measured α-decay data of 257Db and its daughter products resulted in the identification of α-decaying isomeric states in 257Db and 253Lr. Two new isotopes, 256Db and 252Lr, were produced at the highest bombarding energies of 4.97 AMeV and 5.08 AMeV. They were identified by delayed α-α coincidences. The measured half-lives are (1.6+0.5 -0.3) s for 256Db and (0.36+0.11 -0.07) s for 252Lr. Besides α-decay, a spontaneous fission activity of T 1/2 = (2.3+1.1 -0.6) s was observed and attributed to an electron-capture branch of 256Db, which feeds the fissioning nucleus 256Rf. A branching ratio of 0.36±0.12 was obtained. The isotope 255Rf was produced by the reaction 207Pb(50Ti,2n)255Rf. Improved decay data have been obtained by means of α- and α-γ spectroscopy.