Low-energy Nuclear Transitions Research Articles

Dirac–Fock internal conversion coefficients at low [formula omitted]-ray energy

Presented here are internal conversion coefficients (ICCs) for nuclear transitions of low γ-ray energies from 0.1keV to 1keV in elements with 10≤Z≤118. The low-energy nuclear transitions attract significant interest since the novel experimental technique and methods make it possible to study the transitions as well as to discover new low-lying isomers. Our ICC calculations are shown to be in excellent agreement with experimental data for the fairly low-energy nuclear transitions. The calculations are based on the Dirac–Fock method. The vacancy in the atomic shell from which an electron has been emitted is taken into account in the framework of the frozen core approximation. Experimental binding energies are used for elements Z≤95. Theoretical binding energies obtained in a good approximation are used for Z≥96. Peculiarities of the ICC behavior at low energies are considered. The resonance-like structure of ICC and the drastic decrease in magnitude as the energy increases are demonstrated to be responsible for a pronounced dependence of ICC on theoretical assumptions underlying the calculations. We discuss the influence on the low-energy ICCs of the exact taking account the exchange interaction between electrons, the inclusion of the vacancy after conversion, and a credible choice of the binding energy.

Influence of a metallic matrix on the probability of the transition of 910 eV in 154Eu nuclei

The transition of 910 eV in the 154Eu nucleus is presented as a new object of study of the influence of a matrix on the probability of low-energy nuclear transitions. The variation of this transition probability causes variations in the γ-quantum yields of 154mEu decay which are easily detected from a matrix with 154mEu nuclei. Using this approach, the probability of the transition of 910 eV occurring for 154mEu nuclei in a Sm–Sn alloy is found to be 33% lower than for 154mEu nuclei in Sm chloride or metallic Sm.

Experimental search for the low-energy nuclear transition in 229Th with undulator radiation

To search for the lowest energy nuclear isomeric transition in 229Th in solid samples, a novel adsorption technique which prepares 229Th atoms on a surface of CaF2 is developed. Adsorbed 229Th is exposed to highly intensive undulator radiation in the wavelength range between 130 and 320 nm, which includes the indirectly measured nuclear resonance wavelength 160(10) nm. After the excitation, fluorescence from the sample is detected with a VUV sensitive photomultiplier tube. No clear signal relating to the nuclear transition is observed and possible reasons are discussed.

Preparation technique of thorium films by electrochemical deposition for nuclear optical frequency standard based on thorium-229

The increase of the accuracy of optical frequency standards by means of the development of nuclear clocks a novel frequency standard based on the nuclear transition to the long-living isomer nuclear state of Th-229 with energy ~7.6 eV is of great interest. The main problem is the fact that there are no experimental data on the direct measurement of the energy of the isomeric transition in Th-229, and the above result was obtained only by indirect measurements, and has great uncertainty. Low energy ion scattering spectroscopy might be used for more precision investigations of the isomeric transition in Th-229. It is caused by the fact that ion scattering spectra exhibit the fine structure determined by the target surface electronic structure. In the case of low energy nuclear transition it can give the information about the isomer nuclear state of Th-229. To prove this supposition it is necessary to prepare high quality samples with a high thorium surface coverage. An original preparation technique of the thorium films by electrochemical deposition from thorium nitrate solution on Si(111) substrate is reported. It was found that electrochemical deposition of Th on the semiconductor substrates leads to the formation of ThSiOx island films. The origin of the observed thorium films formation and the results on the investigation of 229Th and 232Th films on Si(111) surface by X-ray photoelectron spectroscopy and low energy ion spectroscopy discussed.

Low-energy nuclear transitions in subrelativistic laser-generated plasmas

AbstractThe aim of the reported research is to contribute to investigation of new processes and methods interlinking nuclear and laser-plasma physics. With respect to requirements of nuclear experiments at medium-size high-power lasers, the selection of proper candidates for studying the excitation and decay of low-lying nuclear states is reviewed. An experimental approach to the identification of low-energy nuclear transitions is discussed, simple estimates of the 181Ta excitation yield in the laser-generated plasma provide a theoretical basis for planning future work. First tests and results of the experiments at the laser facility PALS are presented.

Internal conversion and summing effects in heavy-nuclei spectroscopy

Internal conversion of low-energy nuclear transitions occurs with a high probability in heavy nuclei. After the emission of the conversion electron, a cascade of X-rays, Auger or Coster–Krönig electrons takes place. In α-decay experiments in which the nuclei of interest are implanted into a silicon detector, these atomic processes contribute to the detected energy. To understand the distortions of the α-particle energy spectra, knowledge of the various atomic yields is required. Using state-of-the-art calculations, new atomic yields are computed in 99Es and compared to those available in the literature. Detailed simulations of the Md101251α decay are performed and compared to experimental data. Possible ways to discriminate between the available atomic yields are also discussed.

Possibility of using low-energy nuclear transitions as benchmarks for frequency stabilization

The fundamental possibility of using low-energy nuclear transitions for obtaining highly stable frequency standards is considered.

Search for low-energy nuclear transitions in laser-produced plasma

The possibility to excite low-energy nuclear states using laser induced plasma on the Prague Asterix Laser System PALS is investigated. This medium-energy high-power facility yields interaction intensities at the level of 1016 ÷ 1017 Wcm−2 thus producing subrelativistic plasmas with electron temperature of the order of 1 ÷ 10 keV. Based on a systematic survey of suitable candidate nuclei, the search for the 6.238 keV excitation and decay in 181Ta has been initiated. Tests and preliminary operation of detecting systems including active detectors are reported.

Determination of the radiation cross sections of low-energy transitions of isomeric nuclei from observation of laser-induced γ fluorescence

Theoretical estimates are given along with the first experimental results on the observation of resonance fluorescence in nuclei of rubidium isomer under conditions of laser plasma X-ray pumping of the contiguous transition with an energy of 3.4 keV. The laser plasma is prepared by irradiating a silver target by a powerful radiation of a Nd laser with a pulse duration of 600 ps. It is demonstrated how one can use the recorded number of emitted γ quanta to determine the probability of low-energy nuclear transition excited by laser plasma X rays.

Decay of the low-energy nuclear isomer229Thm(3/2+,3.5±1.0 eV)in solids (dielectrics and metals): A new scheme of experimental research

The decay channels and the half-life of the proposed anomalously low-energy nuclear isomer ${}^{229}{\mathrm{Th}}^{m}{(3/2}^{+},3.5\ifmmode\pm\else\textpm\fi{}1.0 \mathrm{eV})$ in a dielectric and in metals are discussed. The preferred decay channel in wide energy-gap dielectrics is via nuclear $\ensuremath{\gamma}$ emission in the optical range. The isomer's half-life lies in the range 10 min--1 h in ${}^{229}{\mathrm{ThO}}_{2}$ for the spectral range ${\ensuremath{\omega}}_{N}=4.5--2.5\mathrm{eV}.$ Nonradiative decay channels dominate in metals. A two-step experimental scheme is developed. The first step is the excitation of the low-energy isomeric level by synchrotron radiation via the 29- and 72-keV levels, and precise measurement of the wave length of the low-energy nuclear transition in ${}^{229}{\mathrm{ThO}}_{2}.$ The second step is the excitation of a large number of the isomeric nuclei ${}^{229}{\mathrm{Th}}^{m}{(3/2}^{+},3.5\ifmmode\pm\else\textpm\fi{}1.0 \mathrm{eV})$ from the ground state by laser radiation in thorium dioxide, and investigation of the $\ensuremath{\alpha}$ decay of the isomeric level.

Analysis of internal conversion coefficients

An extensive database has been assembled that contains the three most widely used sets of calculated internal conversion coefficients (ICC): [Hager R.S., Seltzer E.C., 1968. Internal conversion tables. K-, L-, M-shell Conversion coefficients for Z=30 to Z=103, Nucl. Data Tables A4, 1-237; Band I.M., Trzhaskovskaya M.B., 1978. Tables of gamma-ray internal conversion coefficients for the K-, L- and M-shells, 10≤ Z≤104, Special Report of Leningrad Nuclear Physics Institute; Rösel F., Fries H.M., Alder K., Pauli H.C., 1978. Internal conversion coefficients for all atomic shells, At. Data Nucl. Data Tables 21, 91-289] and also includes new Dirac–Fock calculations [Band I.M. and Trzhaskovskaya M.B., 1993. Internal conversion coefficients for low-energy nuclear transitions, At. Data Nucl. Data Tables 55, 43-61]. This database is linked to a computer program to plot ICCs and their combinations (sums and ratios) as a function of Z and energy, as well as relative deviations of ICC or their combinations for any pair of tabulated data. Examples of these analyses are presented for the K-shell and total ICCs of the gamma-ray standards [Hansen H.H., 1985. Evaluation of K-shell and total internal conversion coefficients for some selected nuclear transitions, Eur. Appl. Res. Rept. Nucl. Sci. Tech. 11.6 (4) 777–816] and for the K-shell and total ICCs of high multipolarity transitions (total, K-, L-, M-shells of E3 and M3 and K-shell of M4). Experimental data sets are also compared with the theoretical values of these specific calculations.

Internal Conversion Coefficients for Low-Energy Nuclear Transitions

Presented here are calculated internal conversion coefficients (ICCs) of gamma rays for 35 observed low-energy nuclear transitions having Eγ ⪝ 3 keV. Additionally, the ICCs for 24 high-multipole-order transitions which have been measured extensively are also given. The ICC calculations have been performed using Dirac-Fock electron wave functions, the exchange terms of the Dirac-Fock equations being included wthout any approximations both for the interaction between bound electrons and the interaction between bound and free electrons. Our previous studies have shown that the Dirac-Fock method allows ICC values to be obtained in best agreement with experimental data.

Realistic Independent-Particle Model of the Nucleus

A phenomenological central potential is explored which is characterized by a universal depth (${V}_{0}$), a universal surface extension ($d$), and an inner radius function $a={a}_{1}{A}^{\frac{1}{3}}+{a}_{0}$. The four parameters are adjusted to be in accord with experimental information obtained from low-energy neutron scattering and from neutron separation energies. The results ${V}_{0}=40$ Mev, $d=1$, ${a}_{1}=1.32$, and ${a}_{0}=\ensuremath{-}0.8$ (all in units of ${10}^{\ensuremath{-}13}$ cm), are in reasonable accord with what might be expected from other experimental and theoretical considerations. Since the experimental data used in the adjustment process bound the energy region in which the discreteness of nuclear energies is most evident, one might expect that the eigenvalues and eigenfunctions based upon this phenomenological model would furnish a highly realistic set for the theoretical study of low-energy nuclear transitions within the framework of the independent-particle model of the nucleus.The energy eigenvalues and the important parameters for the energy eigenfunctions are calculated by a procedure suitable for the restricted type of potential under consideration. A simple method is presented for handling small perturbations, particularly the Coulomb perturbation. In the latter case, it is shown that the derived proton eigenvalues agree with experimental proton separation energies, provided one introduces an anomalous attractive potential which cancels approximately one-half of the classical Coulomb potential acting upon an individual proton. The implications of these results are discussed.