Photon Emission Probabilities Research Articles

Bremsstrahlung emission of high energy accompanying spontaneous fission ofCf252

The study of the bremsstrahlung photon emission accompanying fragments produced in the spontaneous fission of heavy nuclei by a fully quantum approach is presented for the first time. This kind of problem requires the knowledge of wave functions of the fissioning system leading to a wide distribution of couples of fragments that are the products of fission. With the aim of obtaining these wave functions, the interaction potential between the emitted fragment and residual nucleus is calculated by a standard approach. A new procedure was performed that allows an increase in the accuracy of calculations of radial integrals in the far asymptotic region and the achievement of the convenient convergence in calculations of the spectra. The total probability of the emitted photons in the spontaneous fission of {sup 252}Cf was calculated in such a way. We obtained good agreement between theory and experimental data up to 38 MeV for the bremsstrahlung spectrum of photons while the calculation of the total probability of photon emission accompanying fragments was performed up to an energy of 60 MeV. The analysis of contributions in the bremsstrahlung spectrum accompanying the emission of light, medium, and heavy fragments in the fission of {sup 252}Cf is presented.

Simple cases of spontaneous emission from an atom-photon cluster localized in a microcavity

The spontaneous emission from an atomic ensemble localized in a microcavity with the participation of microcavity photons and an external broadband quantized electromagnetic field at the Raman resonance of photons with an optically forbidden (two-photon) atomic transition has been studied. The average spontaneous decay intensity has been calculated for simple cases. It is shown that the dynamics of spontaneous emission from this atomic ensemble differs generally from the conventional superradiance (spontaneous emission of an atomic ensemble at a one-photon optically allowed transition from excited to the ground state. When the atomic ensemble is strongly excited, the delay times and the emission pulse shape differ significantly. The parameter ranges where the spontaneous emission from the atomic ensemble under consideration at a two-photon Raman transition can be described as conventional superradiance with renormalized parameters are found. In the case of single excitation the photon emission probability depends on the number of photons and atoms in the microcavity.

Single-photon emission via Raman scattering from the levels with partially resolved hyperfine structure

The probability of emission of a single-photon via Raman scattering of laser pulse on the three-level Λ – type atom in microcavity is studied. The duration of the pulse is considered to be short enough, so that the hyperfine structure of the upper level remains totally unresolved, while that of the lower level is totally resolved. The coherent laser pulse is assumed to be in resonance with the transition between one hyperfine-structure component of the lower atomic level and all hyperfine-structure components of the upper level, while the quantized cavity field is assumed to be in resonance with the transition between the other hyperfine-structure component of the lower level and all components of the upper one. The dependence of the photon emission probability on the mutual orientation of polarization vectors of the cavity mode and of the coherent laser pulse is analyzed. Particularly, the case is investigated, when the total electronic angular momentum of the lower atomic level equals 1/2, which is true for the ground states of alkali atoms employed in the experiments on deterministic single-photon emission. It is shown, that in this case the probability of photon emission equals zero for collinear polarizations of the photon and of the laser pulse, and the probability obtains its maximum value, when the angle between their polarizations equals 60°.

Activity standardization and decay data of 64Cu

The activity of a solution of (64)Cu was measured by 4pibeta(PC)-gamma coincidence counting and liquid scintillation counting using the CIEMAT/NIST method. In addition, 4pi ionization chambers were used to establish and preserve calibration factors for secondary standardizations and for a determination of the half-life, for which a value of 12.704(5)h was measured. The photon emission probabilities were determined using gamma-ray spectrometry, finding values of p(511 keV)=0.3512(22) and p(1346 keV)=0.00474(5). The results were checked for consistency, and an ampoule was submitted to the BIPM to have the activity result entered into the database of the International Reference System (SIR), yielding the first entry for this radionuclide.

Recovering Absolute Fret Efficiency from Single Molecules: Comparing Methods of Gamma Correction

Fluorescence resonance energy transfer is widely thought of as a “spectroscopic ruler.” Because biological processes and cellular assemblies occur on the nanometer scale, FRET is a popular tool for structural biology. In contrast to ensemble solution FRET measurements which record the entire emission spectrum, microscopy- based FRET experiments separate donor and acceptor intensity by passing the emission through a series of optical elements. Observed FRET efficiency, determined from the uncorrected donor and acceptor intensities, has been called a relative proximity ratio, which is internally consistent only if the photophysical properties and instrument remain unchanged. However, it is desirable to measure absolute distances using FRET, which requires that FRET efficiency be corrected for both instrument response and fluorophore properties. Thus, “gamma” correction adjusts for differences between the donor and acceptor dyes in their probability of photon emission upon excitation and the probability that emitted photons will be detected. Methods of gamma correction vary depending on the single molecule methodology. To test different methods for correcting FRET efficiency, we recorded smFRET distributions for protein and DNA on different instruments and with different filter sets which altered the observed FRET efficiency. Knowledge of filter set transmission allows for comparison of results between groups using different instruments. Applying empirically-derived corrections for instrument response and quantum yield was only slightly better than corrections based solely on filter set transmission data. We found that gamma correction based on single molecule photobleaching was the most effective particularly when gamma was determined for each sample or even each molecule. Variations in focus of the two colors and sub-pixel errors in image mapping affect both FRET and gamma. As such, per molecule correction affects distribution width because FRET outliers may also have anomalous gamma values.

Photon strength in spherical and deformed heavy nuclei

Information on the photon strength in heavy nuclei with mass A > 150 will be given and compared to respective data. The photon strength function is a very important ingredient for statistical model calculations – especially when these are used to describe neutron capture. Several schemes for a transmutation of radioactive waste favor nuclear reactions with fast neutrons and these also influence the performance of various reactor types proposed to deliver nuclear energy together with only small quantities of such waste. Reactions with fast neutrons are less well studied as compared to those induced by thermal neutrons. As they are not easily accessible experimentally, reference is often made to calculations using the statistical model. Photon emission probabilities are needed as input to such calculations aiming for predictions on fission to capture ratios. Results of approximate calculations for radiative neutron capture will be presented.

10.1007/s11449-008-1007-z

The data on the influence of polyelectrolytes on the photon emission probability of water-soluble CdSe/ZnS nanoparticles are obtained. The decrease in the photoluminescence quantum yield of nanoparticles occurring upon their transfer to aqueous solutions from toluene (in the course of solubilization) depends on the ionic nature of an agent applied for the replacement of trioctylphosphine oxide residues on the surface of nanoparticles. It turns out that such a cationic modifying agent as cysteamine leads to an insignificant (∼10%) decrease in the photoluminescence quantum yield of nanoparticles. The use of such an anionic agent as mercaptoacetic acid causes a significant (∼80%) decrease in the quantum yield and the average decay time of photoluminescence. For nanoparticles modified by mercaptoacetic acid (anionic nanoparticles), this decrease is partially compensated if these particles interact with polyelectrolytes whose backbone is oppositely charged (cationic polyelectrolytes), such as polyallylamine and polydiallyldimethylammonium chloride. In this case, the photoluminescence quantum yield shows a reverse increase by 40%, remaining the same within a matter of months or longer. In contrast to this, cationic nanoparticles, only slightly quenched by cysteamine at the stage of solubilization, are appreciably degraded in complexes with anionic polyelectrolytes in solutions and upon immobilization of complexes on a substrate, so that their photoluminescence quantum yield irreversible decreases to zero within a few days. Possible mechanisms of the effects observed are discussed and their consideration in polyelectrolyte-based molecular lithography.

Coherent optical spectroscopy of a single quantum dot using photon counting statistics

We present the theory of coherent optical spectroscopy for single quantum dot under the pump-probe driving. We generally study the line shapes, Mandel's $Q$ parameters, and few photon emission probabilities of single quantum dot system. The probe signals demonstrate the Autler-Townes splitting effect, and the first moment of our results confirms recent experimental results [Xu et al., Science 317, 929 (2007)]. We show that the pump and probe fields modify the emission photon statistical properties and control emission photon properties.

Origins of nonzero multiple photon emission probability from single quantum dots embedded in photonic crystal nanocavities

This work explores the origins of nonzero multiphoton emission probability for quantum dots embedded in photonic crystal nanocavities using different excitation energies to inject excitons into either the GaAs barrier or the quantum-dot excited state. The detected multiphoton events are established to arise from both the recapture of excitons and background emissions from the wetting layer tail states. The exciton emission is analyzed using rate-equation calculations, which suggest that multiphoton emission is dominated by the recapture effect.

Bremsstrahlung emission accompanying α-decay of deformed nuclei

A fully quantum model describing the angular distribution of the bremsstrahlung photon emission accompanying the α-decay of a deformed nucleus is presented for the first time. An analytical dependence of the bremsstrahlung probability on the quadrupole deformation parameter β 2 of the decaying nucleus has been found. Such a model and the detailed formalism allow us to calculate the stable spectra of the bremsstrahlung emission probability for different values of the angle between the direction of the α-particle motion and the symmetry axis of the decaying nucleus. We present the results of this new model by the calculation of the photon emission probability accompanying the α-decay of the 226Ra nucleus which has the nuclear deformation parameter β 2 = 0.151 . The results show by a clear way the role and the influence of the nuclear deformation of the decaying nucleus on the bremsstrahlung photon spectrum.

Cross-Polarized Single Photon Emission from Single Semiconductor Quantum Dots with V-Type Level Driven by Pulse Field

The statistic properties of photon emissions from single semiconductor quantum dots with V-type level driven by pulses are investigated theoretically Based on quantum regression theorem and master equations, the dynamic equations of the second-order correlation function of the photon emissions are deduced. The calculated results reveal that the efficiency of single photon emissions from two orthogonal polarization eigenstates (|x〉 and |y〉) reaches the maximum when the input pulses area is about π, and the probability of the cross-polarized single photon emission from |x〉 and |y〉 decreases with increasing of pulse width.

Towards a picosecond transform-limited nitrogen-vacancy based single photon source

We analyze a nitrogen-vacancy (NV-) colour centre based single photon source based on cavity Purcell enhancement of the zero phonon line and suppression of other transitions. Optimal performance conditions of the cavity-centre system are analyzed using Master equation and quantum trajectory methods. By coupling the centre strongly to a high-finesse optical cavity [Q approximately O(10(4) - 10(5)), V approximately lambda (3)] and using sub-picosecond optical excitation the system has striking performance, including effective lifetime of 70 ps, linewidth of 0.01 nm, near unit single photon emission probability and small [O(10(-5))] multi-photon probability.

Photon emission of a two-level atom passing through double single-mode cavity fields

A two-level atom passing through double spatially separated single-mode cavity fields is studied. We investigate the effecting factors of photon emission probabilities of the atom, which include the kinetic energy of the atom, the length of the cavity and the separation between the two cavities. The results show that in the case of ultra-cold atom, when the kinetic energy of the atom is small (k/k0k/k0>1), the length of the cavity has great effect on the photon emission probabilities. The present work shows that the photon emission probabilities may be modulated by controlling the center-of-mass motion of the atom.

Photoluminescence of water-soluble CdSe/ZnS nanoparticles in complexes with cationic and anionic polyelectrolytes

The data on the influence of polyelectrolytes on the photon emission probability of water-soluble CdSe/ZnS nanoparticles are obtained. The decrease in the photoluminescence quantum yield of nanoparticles occurring upon their transfer to aqueous solutions from toluene (in the course of solubilization) depends on the ionic nature of an agent applied for the replacement of trioctylphosphine oxide residues on the surface of nanoparticles. It turns out that such a cationic modifying agent as cysteamine leads to an insignificant (∼10%) decrease in the photoluminescence quantum yield of nanoparticles. The use of such an anionic agent as mercaptoacetic acid causes a significant (∼80%) decrease in the quantum yield and the average decay time of photoluminescence. For nanoparticles modified by mercaptoacetic acid (anionic nanoparticles), this decrease is partially compensated if these particles interact with polyelectrolytes whose backbone is oppositely charged (cationic polyelectrolytes), such as polyallylamine and polydiallyldimethylammonium chloride. In this case, the photoluminescence quantum yield shows a reverse increase by 40%, remaining the same within a matter of months or longer. In contrast to this, cationic nanoparticles, only slightly quenched by cysteamine at the stage of solubilization, are appreciably degraded in complexes with anionic polyelectrolytes in solutions and upon immobilization of complexes on a substrate, so that their photoluminescence quantum yield irreversible decreases to zero within a few days. Possible mechanisms of the effects observed are discussed and their consideration in polyelectrolyte-based molecular lithography.

Electrically induced spin resonance fluorescence. I. Theory

We calculate the fluorescence of electron spins confined to a plane and driven into resonance by a magnetic field gradient and a constant magnetic field applied at right angles to each other. We solve the equation of motion of two-dimensional electrons in the magnetic field gradient to derive the dispersion curve of spin oscillators, the amplitude of electron oscillations, the effective magnetic field sensed by the electron spin, and the rate at which electrons are injected from an electrode into spin oscillators. We then switch on the interaction between the spin magnetic dipole and the electromagnetic field to find the fluorescence power radiated by the individual spin oscillators. The rate of radiative decay is first derived, followed by the probability of sequential photon emission whereby a series of spontaneous decays occurs at random times separated by intervals during which the spin performs Rabi oscillations. The quantum correlations between random radiative decays manifest as bursts of emission at regular intervals along the wire. We integrate all multiphoton processes to obtain an exact analytical expression for the radiated electromagnetic power. The present theory obtains all parameters of the problem including magnetodipole coupling, the particle dwell time in the magnetic field gradient, and the spin polarization of the incoming current. The output power contains a fine structure arising from the anharmonicity of electron oscillations and from nonlinear optical effects which both give satellite emission peaks at odd multiples of the fundamental frequency.

Radiation output of a spherical homogeneous plasma: Analytical models of computing the spectral brightness of plasma objects with various configurations

Analytical relationships between the photon-emission probability from a surface and the optical thickness along with analytical relationships between the spectral brightness of a homogeneous plasma of spherical geometry are derived with taking into account the radiation absorption. The photon-emission probability and the spectral brightness are also obtained for a plasma of cylindrical geometry and a plasma consisting of spherical layers. The relationships are given in the integral form, while attempts to find them analytically, i.e., to calculate the integrals, failed. However, they can be computed numerically. The formula for spectral brightness is derived for the case of radiation of two flat layers, which differ by the structure, thickness, and thermodynamic and spectral characteristics. The expressions for the spherical and flat layers are compared. The ratio of the dimensions permitted to approximate the flat case by the spherical case is found. The criteria of applicability and accuracy of such approximation have been elaborated. As examples of the application of the expressions derived, the radiation spectra of the aluminum, carbon, copper, and oxygen plasmas were calculated and plotted.

Activity standardization and nuclear decay data of 109Cd

The activity of a 109Cd solution has been accurately determined without using 109Cd nuclear decay data such as emission probabilities. An ampoule containing this calibrated 109Cd solution was sent to the Bureau International des Poids et Mesures to include the activity result in the database of the International Reference System (SIR). The emission rate of conversion electrons was measured by means of pressurized proportional counters as well as by a liquid scintillation spectrometer. The combination of the results with the photon emission rate measured with the aid of γ-ray spectrometers yields the activity concentration. The measurement results were also used to deduce emission probabilities with high accuracy. For the 88 keV transition, a photon emission probability of p γ = 0.03663 ( 33 ) and a total internal conversion coefficient of α t = 26.30 ( 25 ) were determined.

Standardization and decay data determinations of 125I, 54Mn and 203Hg

The absolute 4 π– βγ coincidence counting has been used to measure the activity concentrations of 54Mn and 203Hg, and the Sum–Peak method was used for 125I. 54Mn and 125I radionuclides have been part of international key-comparisons coordinated by the Bureau International des Poids et Measures (BIPM) in 2003/2004, while 203Hg is part of the traceability programme of the National Laboratory for Ionizing Radiation Metrology (LNMRI)/Brazil. Three different detectors were used for the Sum–Peak method: 3″×3″ NaI(Tl) and 5″×5″ well NaI(Tl) scintillation detectors and a planar germanium detector. Direct measurements were made of the photon emission probabilities of the 35.5-, 834.8- and 279.2-keV γ-rays of 125I, 54Mn and 203Hg to give values of (0.0667±0.0014), (0.9997±0.0055) and (0.8161±0.0005), respectively. The half-lives of 203Hg and 54Mn were also determined by means of a 4 πγ ionization chamber ( 203Hg) and by the reference source method using a HPGe detector ( 54Mn) to give values of (46.639±0.023) days and (312.1±0.9) days, respectively.

Standardization and nuclear decay data of 65Zn

Standardization by means of 4πβ–γ coincidence counting was applied to calibrate a 65Zn solution within the scope of EUROMET project no. 721. The activity result was combined with gamma-ray spectrometry measurements to investigate the photon emission probabilities. The half-life of 65Zn was measured with improved accuracy by means of 4π ionization chamber measuring systems that were also used for secondary activity determination. In addition, we tested a new secondary standardization procedure by means of liquid scintillation counting.

Improvement of the direct optical transition probability in Si by wavefunction engineering

A model for improving the direct photon emission probability from electron-hole interaction in silicon is presented. Electron and hole wavefunctions are engineered for optimum overlap in SiGeC heterostructures by proper definition of alloy compositions, potentials and layer thickness dimensions. The direct no-phonon transition probability is increased by a factor of at least 10, compared to the non-optimized direct transition probability. The calibrated structure corresponds to a type II interband structure where photons are emitted with an energy lower than the bandgap energy of the constituent layers.