Electron Capture Ratio Research Articles

Direct Measurement of the Be7 L/K Capture Ratio in Ta-Based Superconducting Tunnel Junctions

We report a high-statistics measurement of the L/K orbital electron capture ratio in ^{7}Be embedded in cryogenic Ta. The thin Ta film formed part of a high-resolution superconducting tunnel junction radiation detector that was used to identify the signals from different decay channels. The measured L/K capture ratio of 0.070(7) is significantly larger than the only previous measurement of this quantity and the theoretical predictions that include in-medium effects. This value is a uniquely sensitive probe of the 1s and 2s orbital overlaps with the nucleus and is of relevance to nuclear and atomic physics, as well as Li production in novae and other astrophysical scenarios. This is the first experiment that uses superconducting tunnel junctions for nuclear-recoil detection, opening a new experimental avenue for low-energy precision measurements with rare isotopes.

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.

Measurement of the L/K electron capture ratio of the 207Bi decay to the 1633 keV level of 207Pb with a BGO scintillating bolometer

The ROSEBUD Collaboration has dedicated several underground runs to study different types of bolometers, mainly for the search of dark matter. Some of these runs, profiting from the good energy resolution of one bolometer of BGO and the ultra-low background of the underground laboratory of Canfranc (LSC), allowed the measurement of the L/K electron capture ratio of the 207Bi decay to the 1633 keV level of 207Pb. This paper constitutes the first published measurement of this magnitude.

TerrestrialBe7decay rate andB8solar neutrino flux

The decay rate of $^{7}\mathrm{Be}$ has always been measured by either forming a beryllium compound or implanting $^{7}\mathrm{Be}$ in a medium. We can quantitatively understand the measured changes of $^{7}\mathrm{Be}$ decay rates in different environments as well as its L/K orbital electron capture ratio using tight-binding linear muffin-tin orbital method calculations. We find that $^{7}\mathrm{Be}$ loses a very substantial fraction of its $2s$ electrons in a medium. As a result of this loss of $2s$ electrons, the extracted nuclear matrix element of the $^{7}\mathrm{Be}$ electron capture reaction from terrestrial decay rate measurements should increase by 2--2.7%, thus decreasing the calculated $^{8}\mathrm{B}$ solar neutrino flux from the Standard Solar Model by 2--2.7%.

00/00007 Low-temperature oxidation of coal studied using wire-mesh reactors with body steady-state and transient methods

Gamma-ray and Kα X-ray emissions have been measured from a very pure 209Po source containing less than 0.13% 208Po activity and no detectable 210Po (≤ 2 × 10−4%). The alpha-particle emission rate for this source has previously been determined. Data are presented that confirm alpha decay to the 205Pb excited level at 262.8 keV, with an alpha-particle emission probability (±standard uncertainty) of 0.00559±0.00008. The ratio of K-shell electron capture to total electron capture for the second forbidden unique electron capture decay to the 896.6 keV level in 209Bi was determined to be 0.594±0.018. The electron capture decay fraction was found to be 0.00454±0.00007, while the probabilities per decay for the 896.6, 262.8, and 260.5 keV gamma rays and the Bi Kα and Pb Kα X-rays were measured as 0.00445±0.00007, 0.00085±0.00002, 0.00254±0.00003, 0.00202±0.00005, and 0.00136±0.00005, respectively.

Alpha-particle and electron capture decay of 209Po

Gamma-ray and Kα X-ray emissions have been measured from a very pure 209Po source containing less than 0.13% 208Po activity and no detectable 210Po (≤ 2 × 10 −4%). The alpha-particle emission rate for this source has previously been determined. Data are presented that confirm alpha decay to the 205Pb excited level at 262.8 keV, with an alpha-particle emission probability (±standard uncertainty) of 0.00559±0.00008. The ratio of K-shell electron capture to total electron capture for the second forbidden unique electron capture decay to the 896.6 keV level in 209Bi was determined to be 0.594±0.018. The electron capture decay fraction was found to be 0.00454±0.00007, while the probabilities per decay for the 896.6, 262.8, and 260.5 keV gamma rays and the Bi Kα and Pb Kα X-rays were measured as 0.00445±0.00007, 0.00085±0.00002, 0.00254±0.00003, 0.00202±0.00005, and 0.00136±0.00005, respectively.

Enhancement of charge capture from a laser-excited target by highly charged ions.

A charge-transfer experiment has been done in which 63-keV ${\mathrm{Ar}}^{7+}$ was incident on sodium in the ground and first excited states. The electron-capture ratio \ensuremath{\sigma}(Na(3p))/\ensuremath{\sigma}(Na(3s)) was experimentally determined for this system. The charge-capture cross section was observed to increase by a factor of 1.5 for the excited target.

Unsuitability of 157Tb for light-neutrino rest-mass studies.

We have measured accurately the intensity ratio of L and K x rays in the $^{157}\ensuremath{\rightarrow}^{157}$Gd electron-capture decay as 0.932\ifmmode\pm\else\textpm\fi{}0.015. From this ratio, we have deduced a value of 4.0\ifmmode\pm\else\textpm\fi{}0.2 for the electron-capture ratio ${\mathit{P}}_{\mathit{L}}$/${\mathit{P}}_{\mathit{K}}$, leading, in turn, to a decay energy of 60.0\ifmmode\pm\else\textpm\fi{}0.3 keV. This Q value is 2.9 keV lower than the currently accepted value. This decay energy rules out L capture to the daughter excited state at 54.54 keV; therefore, $^{157}\mathrm{Tb}$ is not a suitable candidate for light-neutrino rest-mass studies based on this L-capture branch.

Coral grief: K. Muzik, Technology Review, 94(3), 1991, pp 60–67

Gamma-ray and Kα X-ray emissions have been measured from a very pure 209Po source containing less than 0.13% 208Po activity and no detectable 210Po (≤ 2 × 10−4%). The alpha-particle emission rate for this source has previously been determined. Data are presented that confirm alpha decay to the 205Pb excited level at 262.8 keV, with an alpha-particle emission probability (±standard uncertainty) of 0.00559±0.00008. The ratio of K-shell electron capture to total electron capture for the second forbidden unique electron capture decay to the 896.6 keV level in 209Bi was determined to be 0.594±0.018. The electron capture decay fraction was found to be 0.00454±0.00007, while the probabilities per decay for the 896.6, 262.8, and 260.5 keV gamma rays and the Bi Kα and Pb Kα X-rays were measured as 0.00445±0.00007, 0.00085±0.00002, 0.00254±0.00003, 0.00202±0.00005, and 0.00136±0.00005, respectively.

The q-value of 157Tb

Using mass-separated and chemically purified samples, the Q-value of 157Tb has been remeasured as 62.9 ± 0.7 keV by determining electron capture ratios. The transition probability to the excited state was found to be (1.1 ± 0.1) × 10 −3, with a transition energy of 8.4 ± 0.7 keV for this branch. From the proximity to the 2s binding energy, experiments on the internal bremsstrahlung electron capture seem feasible. The half-life of 157Tb was remeasured as 99 ± 10 y.

Effects of neutrino recoil on the X-ray emission of bound electron capture atoms

Due to neutrino emission during the capture process, the nucleus experiences a recoiling motion. If one assumes that those valence charge fractions which are localised, but also bound to ligands, cannot follow the nuclear and core motion immediately, a certain electron cloud deformation takes place besides the 'normal' static chemical polarisation. This gives rise to additional X-ray transitions from the valence band to 1s for K-electron capture. For intensity reasons in connection with radioactive sources the energy dispersive version of X-ray spectrometry is mostly applied and, therefore, a Kbeta 5-type emission cannot be resolved, but it increases the relative (to Kalpha ) Kbeta intensity and enhances the chemical sensitivity of the Kbeta /Kalpha ratio. Numerical estimates for the 51Cr decay give up to 5% effects for the limiting case of absolutely fixed valence charge fractions. 'Kinetic polarisation' is proposed to explain some experimentally observable and analytically applicable aspects of the Kbeta /Kalpha ratio of electron capture (EC) nuclides.

Atomic Electron Correlation in theMCapture ofAr37

The first experimental evidence for electron correlation in nuclear electron-capture ratios is reported. The measured $\frac{M}{L}$ capture ratio of $^{37}\mathrm{Ar}$, 0.073\ifmmode\pm\else\textpm\fi{}0.007, is inconsistent with Hartree-Fock calculations, but can be explained by final-state correlation, if the disputed $3s3{p}^{6}$ assignment in Cl i is adopted. The discrepancy in the experimental $\frac{K\ensuremath{\beta}}{K\ensuremath{\alpha}}$ x-ray intensity ratio of Cl is removed, and the designation of ${L}_{23}$ x-ray and $3s$ photoemission satellites in Cl is revised.

The electron-capture decay of 196Au

The electron-capture decay of 196Au has been investigated by means of a 4π internal-source scintillation spectrometer and a Ge(Li) detector. The L/K and M/L electron-capture ratios have been measured in coincidence with the 356 keV γ-ray. The exchange and overlap corrections X L/K and X M/L have been derived from these capture ratios.

Orbital electron capture ratios in the decay of 205Pb

The M/L and N/M electron capture ratios in the decay of 205Pb have been determined by introducing the radioactive compound tetramethyllead, 205Pb(CH 3) 4, into a wall-less multiwire proportional counter as part of the counting gas mixture. The results are: P M P L = 0.525 ± 0.008 and P N P M = 0.271 ± 0.010 . These results are compared to the theory of Behrens and Bühring using the relativistic wave functions of Mann and Waber. The comparison, along with an estimate of the overlap-exchange correction factor, gives a value of Q EC = 41.4 ± 1.1 keV. The half-life of 205Pb is deduced from the results to be (1.51 ± 0.04) × 10 7 y.

The electron capture decay of 131Ba

The decay of 131Ba has been investigated by means of a 4 π internal source scintillation spectrometer and a Ge(Li) detector. The L/K. and M/L electron capture ratios of the allowed transitions to the 373, 620 and 1048 keV levels in 131Cs have been measured. From these electron capture ratios, the ifQ EC value and the exchange and overlap corrections X L/K and X M/L have been derived.

Addendum to the “correction of electron capture ratios measured by multi-wire proportional counters [1

The formulas for the calculation of the corrections of multi-wire proportional counters published in [1] are explained, simplified and corrected.

Correlation effects in L/K electron capture ratios

Correlation effects between the orbital electrons are suggested to be the origin of the discrepancy between the experimental and theoretical L/K electron capture ratios.

The L/K electron capture ratio in first-forbidden 81gKr decay

The L/K electron capture (EC) ratio of 81g Kr was measured to be 0.146±0.005 utilizing the wall-less, anticoincidence, multiwire proportional counter technique and a reactor-produced, mass separated 81g Kr source. From this value, the Q EC and log ft values were determined to be 305 −29 +38 keV and 11.6 respectively, assuming EC decay only to the ground state. If there is 4 % EC branching to a reported 276 keV level, Q EC becomes 322 −14 +31 keV from which (L/K) g.s. = 0.144 ± 0.005, log ft = 11.6 for EC to the ground state, (L/K) 276 = 0.213±0.005, and log ft = 11.4 for 4 % feeding to the 276 keV level. In order to be confident of these results, an extensive systematic comparison of experimental and theoretical L/K ratios was made for both first-forbidden non-unique and unique transitions. From this comparison, a 7 2 + ground state assignment for 81 Kr is confirmed.

The electron capture and β + decay of 132Cs

The electron capture and β + decay of 132Cs have been investigated by means of a 4π internal source scintillation spectrometer. The L/K electron capture ratio and the K/β + ratio of the first-forbidden transition to the 668 keV level of 132I have been measured: L/K = 0.136 ± 0.001 and K/ β + = 54 ± 9. The value of Q EC = 2.31 ± 0.03 MeV has been deduced from the K/β + ratio. The β + branching ratio has been measured to be (1.5 ± 0.2)%.

Nuclear matrix elements from L/K electron capture ratios in 59Ni decay

Using a recent theoretical method, the ratio of nuclear matrix elements R = ( vF 0 220−√ 3 2 AF 0 221/ vF 0 211) was determined to be either 20.50 +0.35 −0.55 or 25.22 +0.28 −0.17 in the second-forbidden nonunique decay of 8 × 10 4 y 59Ni. These values of R were obtained from a value of L 3/K = 0.008 ± 0.002 found by subtracting the theoretical ratio (L 1 + L 2) K = 0.113 (based on Q PEC = 1070 ± 8 keV) from the total ratio L/K = 0.121 ± 0.002, which was measured with a reactor-produced, doubly-mass-separated 59Ni source introduced as gaseous nickel-ocene, (C 5H 5) 2, into a wall-less, anticoincidence, multiwire proportional counter. The 854–1008 eV L and the 8.33 keV K peaks were measured simultaneously.