Photon Emission Probabilities Research Articles

Structural Characterization and Absolute Luminescence Efficiency Evaluation of Gd2O2S High Packing Density Ceramic Screens Doped with Tb3+ and Eu3+ for further Applications in Radiology

Rare earth activators are impurities added in the phosphor material to enhance probability of visible photon emission during the luminescence process. The main activators employed are rare earth trivalent ions such as Ce+3, Tb+3, Pr3+ and Eu+3. In this work, four terbium-activated Gd2O2S (GOS) powder screens with different thicknesses (1049 mg/cm2, 425.41 mg/cm2, 313 mg/cm2 and 187.36 mg/cm2) and one europium-activated GOS powder screen (232.18 mg/cm2) were studied to investigate possible applications for general radiology detectors. Results presented relevant differences in crystallinity between the GOS:Tb doped screens and GOS:Eu screens in respect to the dopant agent present. The AE (Absolute efficiency) was found to rise (i) with the increase of the X-ray tube voltage with the highest peaking at 110kVp and (ii) with the decrease of the thickness among the four GOS:Tb. Comparing similar thickness values, the europium-activated powder screen showed lower AE than the corresponding terbium-activated.

Measurement of absolute γ-ray emission probabilities in the decay of 235U

Accurate measurements were performed of the photon emission probabilities following the α decay of 235U to 231Th. Sources of highly enriched 235U were characterised in terms of isotopic composition by mass spectrometry and their activities were standardised by means of alpha-particle counting at a low defined solid angle. The standardised sources were subsequently measured by high-resolution γ-ray spectrometry with calibrated high-purity germanium detectors to determine the photon emission probabilities. Four laboratories participated in this work and reported emission probabilities for 33 γ-ray lines. Most of them agree with previously published evaluated data. In addition, new values are proposed for γ-lines which have been measured only once in the past.

Determination of photon emission probabilities for the main gamma-rays and half-life measurements of 64Cu

The National Institute of Standards and Technology (NIST) performed new standardization measurements for 64Cu. As part of this work the photon emission probabilities for the main gamma-rays and the half-life were determined using several high purity germanium (HPGe) detectors. Half-life determinations were also carried out with a NaI(Tl) well counter and two pressurized ionization chambers.

Determination of photon emission probability for the main gamma ray and half-life measurements of 64Cu

The National Institute of Standards and Technology (NIST) performed new standardization measurements for 64Cu. As part of this work the photon emission probability for the main gamma-ray line and the half-life were determined using several high-purity germanium (HPGe) detectors. Half-life determinations were also carried out with a NaI(Tl) well counter and two pressurized ionization chambers.

Hydrogen-like atom in a superstrong magnetic field: Photon emission and relativistic energy level shift

Following our previous work, additional arguments are presented that in superstrong magnetic fields B ≫ (Zα)2 B 0, B 0 = m 2 c 3/eħ ≈ 4.41 × 1013 G, the Dirac equation and the Schrodinger equation for an electron in the nucleus field following from it become spatially one-dimensional with the only z coordinate along the magnetic field, “Dirac” spinors become two-component, while the 2 × 2 matrices operate in the {0; 3} subspace. Based on the obtained solution of the Dirac equation and the known solution of the “onedimensional” Schrodinger equation by ordinary QED methods extrapolated to the {0; 3} subspace, the probability of photon emission by a “one-dimensional” hydrogen-like atom is calculated, which, for example, for the Lyman-alpha line differs almost twice from the probability in the “three-dimensional” case. Similarly, despite the coincidence of nonrelativistic energy levels, the calculated relativistic corrections of the order of (Zα)4 substantially differ from corrections in the absence of a magnetic field. A conclusion is made that, by analyzing the hydrogen emission spectrum and emission spectra at all, we can judge in principle about the presence or absence of superstrong magnetic fields in the vicinity of magnetars (neutron stars and probably brown dwarfs). Possible prospects of applying the proposed method for calculations of multielectron atoms are pointed out and the possibility of a more reliable determination of the presence of superstrong magnetic fields in magnetars by this method is considered.

Resonantly Enhanced Emission from a Luminescent Nanostructured Waveguide.

Controlling the characteristics of photon emission represents a significant challenge for both fundamental science and device technologies. Research on microcavities, photonic crystals, and plasmonic nanocavities has focused on controlling spontaneous emission by way of designing a resonant structure around the emitter to modify the local density of photonic states. In this work, we demonstrate resonantly enhanced emission using luminescent nanostructured waveguide resonance (LUNAR). Our concept is based on coupling between emitters in the luminescent waveguide and a resonant waveguide mode that interacts with a periodic nanostructure and hence outcouples via diffraction. We show that the enhancement of resonance emission can be controlled by tuning the design parameters. We also demonstrate that the enhanced emission is attributable to the accelerated spontaneous emission rate that increases the probability of photon emission in the resonant mode, accompanied by enhanced the local density of photonic states. This study demonstrates that nanostructured luminescent materials can be designed to exhibit functional and enhanced emission. We anticipate that our concept will be used to improve the performance of a variety of photonic and optical applications ranging from bio/chemical sensors to lighting, displays and projectors.

Annihilation of the scalar pair into a photon in a de Sitter universe

The annihilation of massive scalar particles in one photon in de Sitter expanding universe is studied, using perturbative QED. The amplitude and probability corresponding to this process is computed using the exact solutions of the Klein–Gordon and Maxwell equations on de Sitter geometry. Our results show that the expression of the total probability of photon emission is a function dependent on the ratio mass/expansion factor. We perform a graphical study of the total probability in terms of the parameter mass/expansion factor, showing that this effect is significant only in strong gravitational fields. We also obtain that the total probability for this process vanishes in the Minkowski limit.

Activity standardization, photon emission probabilities and half-life measurements of 177Lu

Activity standardization of 177Lu and measurement of two nuclear parameters were done. Activity standardization of 177Lu was done utilizing the 4πβ–γ coincidence method with a combined standard uncertainty of 0.28%.Emission probability of 112.95keV and 208.37keV was measured by calibrated spectrometer with HPGe detector. The efficiency was computed with MCNP code and validated using experimental points. Half-life was derived from prolonged measurement of peak area by three different spectrometer systems and also from measurement with ionization chamber.

The influence of phonon bath on the control of single photon**Project supported by the Fundamental Research Funds for the Central Universities of Central South University, China (Grant No. 2014zzts145).

The influence of vacuum fluctuation and phonon bath on the probability of single photon emission are both considered in the two-level system model theoretically; by using the master equations and generating function method we get the analytical expression of the second-order fluorescence correlation function, probability of single photon emission, and Mandel’s Q parameter. The results manifest that the coupling between the phonon bath and single photon source destroys the superposition state induced by the square laser pulse, the Rabi oscillation damped rapidly with the increasing of temperature. Theoretically, when the structure parameter of arsenide quantum dots α scaled to 0.1 times of the sample, the critical coherence-temperature will rise up to hundreds of Kelvin, which means a step forward to the realization of coherent control of single photon source at room temperature.

Determination of photon emission probabilities for the main gamma-rays of 223Ra in equilibrium with its progeny

The currently published 223Ra gamma-ray emission probabilities display a wide variation in the values depending on the source of the data. The National Institute of Standards and Technology performed activity measurements on a 223Ra solution that was used to prepare several sources that were used to determine the photon emission probabilities for the main gamma-rays of 223Ra in equilibrium with its progeny. Several high purity germanium (HPGe) detectors were used to perform the gamma-ray spectrometry measurements.

Two-channel scattering and emission of electron in quantum quasi-one-dimensional well

It is shown that electron currents in heterostructures may emit photons in the far infrared band of frequencies. The two-channel scattering of electrons on δ-shaped potential (the point defect) is considered and it is shown that the scattering proceeds mainly via the second channel with the same transmission and reflection amplitudes. It is shown that at the interaction of scattering electrons with an external linearly polarized electromagnetic wave, the transition of an electron from the second to the first channel occurs with emission of photons. The probability of photon emission in unit time was obtained for two special cases of external wave propagation. The range of emission frequencies was assessed and it was shown that during the heterostructure the electron emits a photon at ∼1013 Hz frequency.

Radiation from electrons in graphene in strong electric field

We study the interaction of electrons in graphene with the quantized electromagnetic field in the presence of an applied uniform electric field using the Dirac model of graphene. Electronic states are represented by exact solutions of the Dirac equation in the electric background, and amplitudes of first-order Feynman diagrams describing the interaction with the photon field are calculated for massive Dirac particles in both valleys. Photon emission probabilities from a single electron and from a many-electron system at the charge neutrality point are derived, including the angular and frequency dependence, and several limiting cases are analyzed. The pattern of photon emission at the Dirac point in a strong field is determined by an interplay between the nonperturbative creation of electron–hole pairs and spontaneous emission, allowing for the possibility of observing the Schwinger effect in measurements of the radiation emitted by pristine graphene under DC voltage.

Ultrafast electrical control of a resonantly driven single photon source

We demonstrate generation of a pulsed stream of electrically triggered single photons in resonance fluorescence, by applying high frequency electrical pulses to a single quantum dot in a p-i-n diode under resonant laser excitation. Single photon emission was verified, with the probability of multiple photon emission reduced to 2.8%. We show that despite the presence of charge noise in the emission spectrum of the dot, resonant excitation acts as a “filter” to generate narrow bandwidth photons.

Field-induced orbital distortion in high-order-harmonic generation from aligned and oriented molecules within adiabatic strong-field approximation

We describe high-order-harmonic generation (HHG) within the adiabatic strong-field approximation (ASFA) where the ground state and its energy adiabatically follows the instantaneous external field and within the Stark-shift-corrected SFA (SSFA), where only the energy shift is accounted for. We show that the molecular polarizability reflects the significance of field-induced orbital distortion in the HHG process. We show that for CO${}_{2}$, which possesses a relatively low polarizability, the two-center interference minimum can be clearly seen in both the ASFA and the SSFA. This finding is in agreement with experimental data at large wavelength. Moreover, we introduce a method for analyzing the recombination events. This method relies on averaging the recombination matrix elements weighted with the photon emission probability of each harmonic. In the case of CO${}_{2}$ this method confirms that the interference minimum is determined by recombination to the two O atoms. We use the example of N${}_{2}$O, which has a moderate polarizability, to show that the number of centers taking part in the creation of the interference minimum may change depending on the intensity. Finally, we show that in the short-pulse limit, the minimum in the HHG spectrum from oriented N${}_{2}$O strongly depends on the molecular orientation and carrier-envelope phase.

Phonon-induced effects on exciton dynamics and photon emission from a semiconductor quantum dot microcavity: phonon coherent state representation

A microscopic theory to study the combined dynamics of a quantum dot exciton coupled to a single cavity mode as well as acoustic phonons is presented. By considering the phonon subsystem in the coherent state representation, the phonon’s impact on the emitted photons is investigated. The single photon emission probability and phonon effects on this quantity are studied. On the other hand, we illustrate that while a quantum dot interacts with a single cavity mode, the collapse and revival phenomenon will occur. It is demonstrated that acoustic phonons have a pronounced impact on the collapse and revival of the quantum dot exciton. Our finding reveals that at elevated temperatures the phonon interaction decreases the Rabi frequency. Moreover, the cavity mode possesses non-classical features such as sub-Poissonian statistics.

Photon emission from a single molecule in a solid matrix: Phase-delay control

In this paper, we study the influence of time-dependent phase delay on the emission of few photons from a single molecule in a solid matrix. The results demonstrate that a time-dependent phase of the pulses can be used to control the photon emission and strongly affects the spectrum of single molecules. The spectrum of the photon emission probabilities reflects the fast dynamics of the states of the system when the duration of the driven laser pulses is short. Also, it is shown that the coupling between the system and the rf field strongly affects the spectrum of the photon emission probabilities in space.

Photon emission probabilities of 176Lu

An aqueous solution containing dissolved lutetium nitrate with a natural isotopic composition was measured by means of gamma-ray spectrometry to determine emission probabilities of photons which are emitted as a consequence of the decay of the primordial isotope 176Lu. The geometry and matrix of the sample were taken into account in terms of efficiency transfer factors computed with the aid of the upgraded Monte Carlo simulation software GESPECOR. A combination of these results, with the activity determination via liquid scintillation counting using the CIEMAT/NIST efficiency tracing method, yields absolute values of PX(54.61keV)=0.095(4), PX(55.79keV)=0.168(5), Pγ(88.36keV)=0.149(5), Pγ(201.83keV)=0.777(9) and Pγ(306.84keV)=0.929(9). In addition, the upper limit of the probability for a potential electron-capture decay of 176Lu was improved using additional high resolution gamma-ray spectra taken with a planar HPGe detector.

Activity determination and nuclear decay data of 177Lu

The activity concentration of a 177Lu solution was measured within the scope of the international comparison CCRI(II)-K2.Lu-177, starting in 2009. At PTB, the solution was measured by means of 4πβ–γ coincidence counting using a proportional counter and a NaI detector. In addition, liquid scintillation counting using the CIEMAT/NIST efficiency tracing method as well as the triple-to-double coincidence ratio (TDCR) method was applied. The efficiency computation for the TDCR method was realized by means of the MICELLE2 program, applying a stochastic model for the computation of electron emission spectra.The activity concentrations derived from the three methods were found to be in good agreement and the relative standard uncertainty of the combined result was found to be 0.19%.At PTB, the combined result was used to calibrate a 4π ionization chamber for future calibrations of this isotope which is frequently used in nuclear medicine.In addition, activity standardizations were combined with gamma-ray spectrometry to determine photon emission probabilities. To this end, the comparison solution as well as another 177Lu solution was used. The results are in good agreement with previous measurements at PTB but show a considerable discrepancy to recently published values from Deepa et al. (2011).The decay curve of a third solution was followed by liquid scintillation counting for about 66 days to determine the half-life of 177Lu, which was found to be T1/2=6.639(9)d.

Description of dipole strength in heavy nuclei in conformity with their quadrupole degrees of freedom

In conformity to new findings about the widespread occurrence of triaxiality arguments are given in favor of a description of the giant dipole resonance in heavy nuclei by the sum of three Lorentzians. This TLO parameterization allows a strict use of resonance widths {\Gamma} in accordance to the theoretically founded power law relation to the resonance energy. No additional variation of {\Gamma} with the photon energy and no violation of the sum rule are necessary to obtain a good agreement to nuclear photo-effect, photon scattering and radiative capture data. Photon strength other than E1 has a small effect, but the influence of the level density on photon emission probabilities needs further investigation.

Coherent synchrotron radiation and radiative electron polarization

The process of radiative electron polarization through the mechanism of coherent synchrotron radiation (CSR) has been considered in the semi-classical approach. The CSR process is characterized by increasing photon emission probability from each electron proportional to number of electrons in a bunch if the wavelength of the emitted photon is greater than the bunch length. Estimations for built-up polarization of the electron beam Pcoh and the self-polarization time Tcoh caused by CSR mechanism were obtained and the comparison with ones for incoherent synchrotron radiation was performed. Despite the low probability of spin-flip transitions a significant particle polarization can be achieved for comparatively low values of the Lorentz factor (γ ⩽ 100) due to the huge number of photons emitted by each electron.