Daughter Atoms Research Articles

Структура мессбауэровских спектров примесных атомов -=SUP=-119m-=/SUP=-Sn в халькогенидах свинца в условиях радиоактивного равновесия изотопов -=SUP=-119m-=/SUP=-Te/-=SUP=-119-=/SUP=-Sn

AbstractThe method of Mössbauer emission spectroscopy with ^119 m Te and ^119Sb parent isotopes in the radioactive-equilibrium state is used to obtain information on the localization and valence state of ^119 m Sn daughter atoms formed from the ^119Sb and ^119 m Te parent atoms at cation and anion sites of the lattice of PbSe and PbTe lead chalcogenides.

K-shell ionization during the α-decay of superheavy nuclei

The probabilities of K-shell ionization in daughter atoms during the α-decay of extensively studied 84Po isotopes and superheavy 117 294 Ts, 113 286 Nh, 109 278 Mt, 105 270 Db, 102 253 No, 100 249 Fm, and 111 272 Rg nuclei are calculated. Monopole and dipole terms are considered. More accurate expressions for α-particle tunneling through the atomic Coulomb barrier are derived. The electron wave functions are calculated using the relativistic Dirac–Fock method. The results are essential for processing the spectra analyzed in combined α-, γ-, and conversion-electron spectroscopy.

Characterization of the ^{163}Ho Electron Capture Spectrum: A Step Towards the Electron Neutrino Mass Determination.

The isotope ^{163}Ho is in many ways the best candidate to perform experiments to investigate the value of the electron neutrino mass. It undergoes an electron capture process to ^{163}Dy with an energy available to the decay, Q_{EC}, of about 2.8keV. According to the present knowledge, this is the lowest Q_{EC} value for such transitions. Here we discuss a newly obtained spectrum of ^{163}Ho, taken by cryogenic metallic magnetic calorimeters with ^{163}Ho implanted in the absorbers and operated in anticoincident mode for background reduction. For the first time, the atomic deexcitation of the ^{163}Dy daughter atom following the capture of electrons from the 5s shell in ^{163}Ho, the OI line, was observed with a calorimetric measurement. The peak energy is determined to be 48eV. In addition, a precise determination of the energy available for the decay Q_{EC}=(2.858±0.010_{stat}±0.05_{syst}) keV was obtained by analyzing the intensities of the lines in the spectrum. This value is in good agreement with the measurement of the mass difference between ^{163}Ho and ^{163}Dy obtained by Penning-trap mass spectrometry, demonstrating the reliability of the calorimetric technique.

Time sequence determination of parent–daughter radionuclides using gamma-spectrometry

The acquisition of time-stamped list data provides additional information useful to gamma-spectrometry analysis. A novel technique is described that uses non-linear least-squares fitting and the Levenberg–Marquardt algorithm to simultaneously determine parent-daughter atoms from time sequence measurements of only the daughter radionuclide. This has been demonstrated for the radioactive decay of short-lived radon progeny (214Pb/214Bi, 212Pb/212Bi) described using the Bateman first-order differential equation. The calculated atoms are in excellent agreement with measured atoms, with a difference of 1.3–4.8% for parent atoms and 2.4–10.4% for daughter atoms. Measurements are also reported with reduced uncertainty. The technique has potential to redefine gamma-spectrometry analysis.

Neutrino mass, electron capture, and the shake-off contributions

Electron capture can determine the electron neutrino mass, while the beta decay of Tritium measures the electron antineutrino mass and the neutrinoless double beta decay observes the Majorana neutrino mass. Electron capture e. g. on 163Ho plus bound electron to 163Dy* plus neutrino can determine the electron neutrino mass from the upper end of the decay spectrum of the excited Dy*, which is given by the Q-Value minus the neutrino mass. The Dy* states decay by X-ray and Auger electron emissions. The total decay energy is measured in a bolometer. These excitations have been studied by Robertson and by Faessler et al.. In addition the daughter atom Dy can also be excited by moving in the capture process one electron into the continuum. The escape of these continuum electrons is automatically included in the experimental bolometer spectrum. Recently a method developed by Intemann and Pollock was used by DeRujula and Lusignoli for a rough estimate of this shake-off process for "s" wave electrons in capture on 163Ho. The purpose of the present work is to give a more reliable description of "s" wave shake-off in electron capture on Holmium. For that one needs very accurate atomic wave functions of Ho in its ground state and excited atomic wave functions of Dy* including a description of the continuum electrons. In the present approach the wave functions of Ho and Dy* are determined selfconsistently with the antisymmetrized relativistic Dirac-Hartree-Fock approach. The relativistic continuum electron wave functions for the ionized Dy* are obtained in the corresponding selfconsistent Dirac-Hartree-Fock-Potential. In this improved approach shake-off can hardly be seen after electron capture in 163Ho and thus can probably not affect the determination of the electron neutrino mass.

Local heating of a medium in the nanovicinity of the 57Co nucleus that underwent radioactive decay to 57Fe

Process of formation of the Auger blob (nanosized cloud of two or three hundred of ion–electron pairs) around a 57Co radioactive atom after E-capture followed by the emission of a cascade of Auger electrons by the daughter atom 57Fe has been considered. The effect of local temperature elevation in the Auger blob caused by energy emission during ionization slowing down of Auger electrons and the secondary electrons generated by them is discussed. Some consequences of this effect have been noted.

Detection of the barium daughter in 136Xe →136Ba+2e− by in situ single-molecule fluorescence imaging

A robust technique for rejection of all γ-ray induced backgrounds in the search for the decay 136Xe→136Ba+2e− is needed to proceed to ton-scale detection systems. Efficient detection of the barium daughter would provide a long-sought pathway toward this goal. Single-molecule fluorescent imaging may offer a new way to detect the barium daughter atom in a naturally ionized state. A doubly charged barium ion can initiate a chelation process with a non-fluorescent precursor molecule, leading to a highly fluorescent complex. Repeated photo-excitation of the complex can reveal both presence and location of a single ionized atom with high precision and selectivity. Detection would be automatic, and is accomplished within the active volume of a xenon gas Time Projection Chamber operating at high pressure.

Detecting the barium daughter in 136Xe 0-νββ decay using single-molecule fluorescence imaging techniques

Single-molecule fluorescent imaging may provide an avenue to efficiently detect the Ba++ daughter atom in the decay 136Xe → Ba + 2e−, and, unambiguously associate the birth point in space within the electron trajectories of the decay event. Chelation of doubly-charged alkaline earth elements such as calcium and barium by certain precursor molecules converts the resulting complex from a non-fluorescent to a fluorescent state. Repeated photo-excitation of a single fluorescent complex reveals both presence and location with high precision. This technique, widespread now in biochemistry, biophysics and biology, may permit a similar discriminating response in a large high-pressure xenon gas TPC for the Ba++ ion from xenon double-beta decay. The TPC measures the event time and energy of the two nascent electrons, as well as topology and position in 3-D from their trajectories in the gas. Measurement of the 2-D location of the molecular ion after arrival at the cathode plane permits an association of ion with the event. Demonstration of an efficient, highly specific detection of the barium daughter would provide a long-sought pathway to a background-free result in the search for this decay mode, of central importance for determining the nature of the neutrino.

Capture of K-shell electrons by α-particles in α-decay of superheavy nuclei: I. Charge transfer in collisions of α-particles with He+(1s) ions

We consider a process in which α-particles after α-decay ionize K-shell of daughter atoms and capture electrons. We first have performed similar calculations for collisions of α-particles with He+(1s) ions. This charge transfer process is studied for the collision energy region 0.04–400 keV. The transition amplitudes are calculated in the impact parameter approximation with the use of the close coupling equations method for a basis consisting of eight molecular states. Total and partial charge-transfer cross sections to the 1s and, for the first time, to the 2s and 2p 0, 2p ±1 states of the He+ ion are obtained. Angular differential cross sections for the elastic scattering and charge-transfer processes are calculated in the eikonal approximation for a wide range of scattering angles for the collision energy of 1 keV. Results of calculations are in an excellent agreement with experimental data.

The effect of the nuclear Coulomb field on atomic ionization at positron-electron annihilation in β+- decay

We consider the process of the annihilation of a positron emitted at β+- decay and a K-electron of the daughter atom. A part of energy during this process is passed to another K- electron and it leaves the atom. The influence of the Coulomb field on the positron and the ejected electron is considered. It was calculated the probability of this process for an atom with arbitrary Z is calculated. For the nucleus Ti the effect of the Coulomb field essentially increases the probability of the considered process.

Primary retention following nuclear recoil in β-decay: Proposed synthesis of a metastable rare gas oxide (38ArO4) from (38ClO4−) and the evolution of chemical bonding over the nuclear transmutation reaction path

Argon tetroxide (ArO4) is the last member of the N=50 e– isoelectronic and isosteric series of ions: SiO44−, PO43−, SO42−, and ClO4−. A high level computational study demonstrated that while ArO4 is kinetically stable it has a considerable positive enthalpy of formation (of ~298kcal/mol) (Lindh et al., 1999. J. Phys. Chem. A 103, pp. 8295–8302) confirming earlier predictions by Pyykkö (1990. Phys. Scr. 33, pp. 52–53). ArO4 can be expected to be difficult to synthesize by traditional chemistry due to its metastability and has not yet been synthesized at the time of writing. A computational investigation of the changes in the chemical bonding of chlorate (ClO4−) when the central chlorine atom undergoes a nuclear transmutation from the unstable artificial chlorine isotope 38Cl to the stable rare argon isotope 38Ar through β-decay, hence potentially leading to the formation of ArO4, is reported. A mathematical model is presented that allows for the prediction of yields following the recoil of a nucleus upon ejecting a β-electron. It is demonstrated that below a critical angle between the ejected β-electron and that of the accompanying antineutrino their respective linear momentums can cancel to such an extent as imparting a recoil to the daughter atom insufficient for breaking the Ar–O bond. As a result, a primary retention yield of ~1% of ArO4 is predicted following the nuclear disintegration. The study is conducted at the quadratic configuration interaction with single and double excitations [QCISD/6−311+G(3df)] level of theory followed by an analysis of the electron density by the quantum theory of atoms in molecules (QTAIM). Crossed potential energy surfaces (PES) were used to construct a PES from the metastable ArO4 ground singlet state to the Ar–O bond dissociation product ArO3+O(3P) from which the predicted barrier to dissociation is ca. 22kcal/mol and the exothermic reaction energy is ca. 28kcal/mol [(U)MP2/6–311+G(d)].

Activation of local and systemic anti-tumor immune responses by ablation of solid tumors with intratumoral electrochemical or alpha radiation treatments.

Cancer, the most devastating chronic disease affecting humankind, is treated primarily by surgery, chemotherapy, and radiation therapy. Surgery and radiotherapy are mainly used for debulking the primary tumor, while chemotherapy is the most efficient anti-metastatic treatment. To control better metastatic cancer, the host immune system should be stimulated. Yet, successful specific stimulation of the immune system against tumors was seldom achieved even in antigenic tumors. Our working hypothesis is that aggressive in situ tumor ablation can release tumor antigens and danger signals, which will enhance anti-tumor T cell responses resulting in the destruction of residual malignant cells in primary tumors and distant metastases. We developed two efficient in situ ablation treatments for solid cancer, which can be used to destroy the primary tumors and stimulate anti-tumor immune responses. The first treatment, electrochemical ablation, is applied through intratumoral electrodes, which deliver unipolar-pulsed electric currents. The second treatment, diffusing alpha-emitters radiation therapy (DaRT), is based on intratumoral (224)Ra-loaded wire(s) that release by recoil its daughter atoms. These short-lived alpha-emitting atoms spread in the tumor and spray it with lethal alpha particles. It was confirmed that these treatments effectively destroy various malignant animal and human primary solid tumors. As a consequence of such tumor ablation, tumor-derived antigenic material was released and provoked systemic T cell-dependent anti-tumor immunological reactions. These reactions conferred protection against a secondary tumor challenge and destroyed remaining malignant cells in the primary tumor as well as in distant metastases. Such anti-tumor immune responses could be further amplified by the immune adjuvant, CpG. Electrochemical ablation or DaRT together with chemotherapy and immunostimulatory agents can serve as treatment protocols for solid metastatic tumors and can be applied instead of or in combination with surgery.

$Q$ Spectroscopy With Superconducting Sensor Microcalorimeters

The total reaction energy (Q) of individual nuclear decays was measured using microcalorimeters with transition-edge-sensor (TES) thermometers. For alpha-decaying actinides (e.g., U-235, Pu-239, Np-237, Am-241), Q is in the 4-6 MeV range. Nearly all of this energy goes into the relatively light alpha particle, and approximately 100 keV is left over for the much heavier, recoiling daughter atom. Alpha-particle energy spectroscopy with TES-microcalorimeters has shown the ability to simultaneously resolve peaks that overlap in conventional alpha spectroscopy, with resolution now less than 1 keV full-width-at-half-maximum (FWHM) at 5.3 MeV. For total reaction energy spectroscopy, we use the same TES design as our alpha detectors, but embed a small radioactive sample (of about 1 Bq) directly inside an absorber designed to capture all the emitted particles (alpha, recoil nucleus, electrons, X-rays) with near 100% efficiency. We have measured Q-spectra of alpha-decaying isotopes with spectral resolution of 2-3 keV FWHM. For some actinide analytical problems, the Q -spectrum is simpler than the alpha-spectrum: fewer peaks, further apart, and easier to quantify. We will discuss sensor design, methods for embedding radionuclides, and spectral data.

Tin U −-centers formed through nuclear transformations in vitreous arsenic sulfides and selenides

It has been shown using the Mossbauer emission spectroscopy for isotope 119Sn that impurity tin atoms formed after the radioactive decay of 119Sb atoms in vitreous arsenic sulfide and selenide are localized in arsenic sites and play the role of two-electron centers with negative correlation energy. The most of daughter 119mSn atoms formed after the radioactive decay of the 119mTe atoms in glasses are arranged in chalcogen sites; they are electrically inactive. Considerable recoil energy of daughter atoms in the case of decay of 119mTe leads to the appearance of 119mSn atoms shifted from chalcogen sites.

Study of charge transport mechanisms in 125I-induced DNA damage at various temperatures

Purpose: Iodine-125 decay induces localized DNA damage by three major mechanisms: (1) Direct damage by the emitted Auger electrons, (2) indirect damage by diffusible free radicals, and (3) charge neutralization of the residual, highly positively charged, tellurium daughter atom by stripping electrons from neighboring residues. The charge neutralization mechanism of 125I-induced DNA damage is poorly understood. Charge transport along a DNA molecules can occur by either a hopping mechanism initiated by charge injection into DNA and propagated by charge migration through DNA bases along the DNA length, or by a tunneling mechanism in which charge transfers directly from a donor to an acceptor residue. In the first case additional damage in DNA nucleotides can be inflicted by the traveling charge; therefore, it is important to learn if charge hopping plays a role in 125I-decay-induced DNA damage. In our previous work, we determined that at 193K the charge hopping mechanism was not an appreciable component of the mechanism of 125I-induced DNA damage. However, the question whether this is also the case at higher temperatures remained open.Methods: In the current study we used a well-known chemical barrier for charge hopping, 8-oxo-7, 8,-dihydroguanine (8-oxo-G), to assess the role of this mechanism in 125I-decay-induced DNA damage at the following temperatures: 198, 253, 277 and 298 K.Results: We found that varying the temperature had little effect on the distribution of 125I-induced DNA breaks, as well as on the breaks found at the 8-oxo-G probe both with and without piperidine treatment.Conclusions: We thus conclude that charge transport by the hopping mechanism is not a major factor in 125I-decay-induced DNA damage at biologically relevant temperatures.

Recoil and conversion electron implications to be taken into account in the design of therapeutic radiopharmaceuticals utilising in vivo generators

The use of radionuclides as potential therapeutic radiopharmaceuticals is increasingly investigated. An important aspect is the delivery of the radionuclide to the target, in which the radionuclide is not lost from the chelating agent. For in vivo generators, not only the log K of complexation between the metal ion and the chelator is important but also whether the daughter radionuclide stays inside the chelator after decay of the parent radionuclide. In our previous work, we showed that the classical recoil effect for β‐decay only applies to decays with a Q value higher than 0.6 MeV (for the atomic mass range around 100). However, the published result for 140Nd/140Pr (Q = 0.222 MeV) indicated that >95% of the daughter (140Pr) was lost by a DOTA chelator upon decay of 140Nd. The experiment was repeated with the 166Dy/166Ho generator (Q = 0.486 MeV) and the 90Sr/90Y generator (Q = 0.546 MeV), which resembles an in vivo chelator system where the transition via the Auger process is absent. It was found that 72% of the daughter (166Ho) was liberated from the DOTA chelator, in contrast to our recoil calculations. It was also found that this ratio of the 166Ho released corresponds to the ratio of transition of holmium atoms via the Auger process (immediately after decay of 166Dy). For the pure β 90Sr/90Y generator, a 1% release from the DOTA chelator was recorded. On theoretical grounds, an electron ejected with an energy above 0.36 MeV (for atomic number = 90) is expected to cause recoil of the daughter atom out of a DOTA chelator, if the chemical bond is 3 eV. From the β‐continuum spectrum of 90Sr, an estimated 10.2% of β particles have an energy exceeding 0.36 MeV. For the 166Dy/166Ho generator, the matching ratio of experimental release versus Auger transition is explained by the fragmentation of the chelator by Auger electron thereby releasing the holmium atoms. For the 90Sr/90Y generator, the calculated and measured percentage release is in the same order of magnitude, proving the equation suitable to describe the classical recoil effect for pure β emission. The discrepancy between the experimental and theoretically calculated release can be explained by a correction of the chemical bond energy to 4.4 eV. Copyright © 2012 John Wiley & Sons, Ltd.

Radon induced background processes in the KATRIN pre-spectrometer

The KArlsruhe TRItium Neutrino (KATRIN) experiment is a next generation, model independent, large scale tritium β-decay experiment to determine the effective electron anti-neutrino mass by investigating the kinematics of tritium β-decay with a sensitivity of 200 meV/c 2 using the MAC-E filter technique. In order to reach this sensitivity, a low background level of 10 −2 counts per second (cps) is required. This paper describes how the decay of radon in a MAC-E filter generates background events, based on measurements performed at the KATRIN pre-spectrometer test setup. Radon (Rn) atoms, which emanate from materials inside the vacuum region of the KATRIN spectrometers, are able to penetrate deep into the magnetic flux tube so that the α-decay of Rn contributes to the background. Of particular importance are electrons emitted in processes accompanying the Rn α-decay, such as shake-off, internal conversion of excited levels in the Rn daughter atoms and Auger electrons. While low-energy electrons (<100 eV) directly contribute to the background in the signal region, higher energy electrons can be stored magnetically inside the volume of the spectrometer. Depending on their initial energy, they are able to create thousands of secondary electrons via subsequent ionization processes with residual gas molecules and, since the detector is not able to distinguish these secondary electrons from the signal electrons, an increased background rate over an extended period of time is generated.

Resonance enhancement of neutrinoless double electron capture

The process of neutrinoless double electron ( 0 ν ECEC ) capture is revisited for those cases where the two participating atoms are nearly degenerate in mass. The theoretical framework is the formalism of an oscillation of two atoms with different total lepton number (and parity), one of which can be in an excited state so that mass degeneracy is realized. In such a case and assuming light Majorana neutrinos, the two atoms will be in a mixed configuration with respect to the weak interaction. A resonant enhancement of transitions between such pairs of atoms will occur, which could be detected by the subsequent electromagnetic de-excitation of the excited state of the daughter atom and nucleus. Available data of atomic masses, as well as nuclear and atomic excitations are used to select the most likely candidates for the resonant transitions. Assuming an effective mass for the Majorana neutrino of 1 eV, some half-lives are predicted to be as low as 10 22 years in the unitary limit. It is argued that, in order to obtain more accurate predictions for the 0 ν ECEC half-lives, precision mass measurements of the atoms involved are necessary, which can readily be accomplished by todayʼs high precision Penning traps. Further advancements also require a better understanding of high-lying excited states of the final nuclei (i.e. excitation energy, angular momentum and parity) and the calculation of the nuclear matrix elements.

Evidence for As lattice location and Ge bound exciton luminescence in ZnO implanted withAs73andGe73

The results of photoluminescence (PL) measurements performed on high quality single crystal ZnO implanted with radioactive $^{73}\mathrm{Ga}$ and $^{73}\mathrm{As}$, both of which decay to stable $^{73}\mathrm{Ge}$, are presented. Identical effects are observed in the two cases, with a sharp line at 3.3225(5) eV found to grow in intensity in accordance with the growth rate of the Ge daughter atom populations. On the strength of the well-established result that Ga occupies Zn sites, we conclude from the identical outcomes for $^{73}\mathrm{Ga}$ and $^{73}\mathrm{As}$ implantations that implanted As also preferentially occupies Zn sites. This result supports the findings of others that As preferentially occupies the Zn rather than the O site in ZnO. The thermal quenching energy of the 3.3225(5) eV line is found to be only 2.9(1) meV in contrast to its large spectral shift of 53.4(1) meV with respect to the lowest energy free exciton. The PL is attributed to exciton recombination at neutral Ge double donors on Zn sites involving transitions that leave the donor in an excited state.

Neutrinoless double-beta decay and double-electron capture

The fundamental importance of searching for neutrinoless double-beta decay is widely recognized. Observation of the decay would tell us that the total lepton number is not conserved and that, consequently, neutrinos are massive Majorana fermions. The same statement could be made in the case of observing neutrinoless double-electron capture. We address the question of the sensitivity of the 0 ν ε ε decay to the effective mass of the Majorana neutrino. According to our estimates, in the case of 152Gd and 164Er the sensitivity can be comparable to the favored 0 ν β β decays of nuclei. The main uncertainty in the prediction of half-lives of the 0 ν ε ε decay stems from the lack of sufficient precision in measuring the mass difference between the parent and daughter atoms. More accurate measurements can be accomplished using the modern high-precision ion traps.