Value Of Photoionization Cross Section Research Articles

Contribution of near-edge processes to the L X-ray emission lines for various lanthanum (III) compounds

The present measurement illustrates the study of near-edge processes and the intensity ratios [ILl/ILα, ILβ1/ILα and ILl/ILβ1] for Mn Kα1,2 X-rays across the L2 edge of lanthanum in its various chemical forms viz., lanthanum oxide (La2O3), lanthanum oxalate (C6La2O12) and lanthanum acetate (C6H9LaO6) at four different scattering angles i.e. 90°, 105°, 115° and 125° with a lab-scale X-ray fluorescence (XRF) spectrometer. The current observation reveals that the Lβ1 X-ray emission lines exhibit a variance of ∼ (21–40) % between measured and calculated fluorescence cross-sections. Apart from this, the measured values of intensity ratios have been compared with the three data sets of calculated values using L shell emission rates based on the Dirac-Fock (DF) model, total X-ray emission rates and photoionization cross-section values based on the relativistic Hartree-Slater (RHS) model and three sets of Coster-Kronig (CK) and fluorescence yields. The correlation between crystal structure, bond distance and intensity ratio are also discussed in this work.

Study of thermoluminescence (TL) and optically stimulated luminescence (OSL) from α-keratin protein found in human hairs and nails: potential use in radiation dosimetry.

The thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of human nails and hairs containing α-keratin proteins have been investigated. For the present studies, black hairs and finger nails were selectively collected from individuals with ages between 25 and 35 years. The collected hairs/nails were cut to a size of < 1 mm and cleaned with distilled water to remove dirt and other potential physical sources of contamination. All samples were optically beached with 470 nm of LED light at 60 mW/cm(2) intensity and irradiated by a (60)Co γ source. The hair and nail samples showed overlapping multiple TL glow peaks in the temperature range from 70 to 210 ° C. Continuous wave (CW)-OSL measurements of hair samples at a wavelength of 470 nm showed the presence of two distinct OSL components with photoionization cross section (PIC) values of about 1.65 × 10(-18) cm(2) and about 3.48 × 10(-19) cm(2), while measurements of nail samples showed PIC values of about 6.98 × 10(-18) cm(2) and about 8.7 × 10(-19) cm(2), respectively. This difference in PIC values for hair and nail samples from the same individual is attributed to different arrangement of α-keratin protein concentrations in the samples. The OSL sensitivity was found to vary ± 5 times among nail and hair samples from different individuals, with significant fading (60% in 11 h) at room temperature. The remaining signal (after fading) can be useful for dose estimation when a highly sensitive OSL reader is used. In the absorbed dose range of 100 mGy-100 Gy, both the TL and OSL signals of hair and nail samples showed linear dose dependence. The results obtained in the present study suggest that OSL using hair and nail samples may provide a supplementary method of dose estimation in radiological and nuclear emergencies.

Two-step laser excitation and ionization from the 7p 2P3/2 state of potassium

New measurements of photoionization cross-sections from the 7p 2P3/2 excited state of potassium near the first ionization threshold are presented using a two-step laser excitation/ionization technique in conjunction with a time-of-flight (TOF) mass spectrometer. The absolute values of photoionization cross-sections have been determined as (3.52 ± 0.52) Mb, (2.21 ± 0.33) Mb, (1.35 ± 0.22) Mb and (0.54 ± 0.08) Mb at four ionizing laser wavelengths; 1064 nm, 643.61 nm, 532 nm and 355 nm respectively whereas the number density has been determined as (1.6 ± 0.31) × 1010 cm−3. The presently measured experimental values of photoionization cross-sections are in good agreement with the literature experimental and theoretical values.

Characterization of deep energy level defects in α-Al2O3:C using thermally assisted OSL

Abstract Commercially available α-Al2O3:C powder was studied for deep energy level defects by a newly suggested method using thermally assisted optically stimulated luminescence (TA-OSL) phenomenon. The method involves simultaneous application of continuous wave optically stimulated luminescence (CW-OSL) as well as thermal stimulation up to 400 °C, using a linear heating rate of 4 K/s. By using this method, two well-defined peaks at 121 °C and 232 °C were observed. These TA-OSL peaks have been correlated to two different types of deeper defects which can be bleached at 650 °C and 900 °C respectively on thermal treatment. These deeper defects, having larger thermal trap depth and relatively lower photoionization cross-section at room temperature for stimulation with blue LED (470 nm), are stable up to 500 °C, so they can store absorbed dose information even if the sample is inadvertently exposed to light or temperature. As only a fraction of signal is bleached during TA-OSL readout, multiple readouts could be performed on an exposed sample using this technique. The dose vs TA-OSL response from deep traps of α-Al2O3:C was found to be linear up to 10 kGy, thus extending its application for high dose dosimetry. The value of thermally assisted energy (EA) associated with these traps in α-Al2O3:C has been determined to be 0.268 eV and 0.485 eV respectively and the corresponding values of photoionization cross-section at room temperature (25 °C), for optical stimulation with blue light (470 nm), are 5.82 × 10−20 and 3.70 × 10−22 cm2, respectively. The process of thermally assisted OSL has been formulated analytically as well as theoretically for describing the temperature dependence of optical cross-section and evaluation of thermally assisted energy associated with deep traps.

Preliminary non-linear light modulation OSL studies using α-Al2O3: C

Recently, we have given a detailed theoretical description of non-linear optically stimulated luminescence (NL-OSL) phenomenon. The NL-OSL method was suggested to be useful in studying traps having relatively low and closely lying values of photoionization cross-section. The possible advantage of NL-OSL over LM-OSL technique was also discussed. In present studies the experimental values of signal to noise ratio have been compared for NL-OSL and LM-OSL modes of stimulation using α-Al2O3: C phosphor. The experimental results show definite advantage of NL-OSL over LM-OSL and CW-OSL, as NL-OSL technique has been found to be useful in separating fast OSL component more effectively, thus leading to extended dose linearity from the OSL defects having larger photoionization cross-section, particularly in α-Al2O3: C, with added feature of multiple dose assessment for single irradiation.

Photoionization from the 6p2P3/2state of neutral cesium

We report the photoionization studies of cesium from the 6p {sup 2}P{sub 3/2} excited state to measure the photoionization cross section at and above the first ionization threshold, oscillator strength of the highly excited transitions, and extension in the Rydberg series. The photoionization cross section at the first ionization threshold is measured as 25 (4) Mb and at excess energies 0.02, 0.04, 0.07, and 0.09 eV as 21, 19, 17, and 16 Mb, respectively. Oscillator strength of the 6p {sup 2}P{sub 3/2} {yields} nd {sup 2}D{sub 5/2} (23 {<=} n {<=} 60) Rydberg transitions has been extracted utilizing the threshold value of photoionization cross section and the recorded nd {sup 2}D{sub 5/2} photoionization spectra.

Photoionization study of deep centers in GaN∕AlGaN multiple quantum wells

Transient photocapacitance (TPC) measurements were performed to investigate deep centers in GaN∕AlGaN multiple quantum wells. The influence of the persistent photovoltaic effect was successfully separated during the TPC experiments. The resolution obtained by the TPC measurements is much better than that of steady-state photocapacitance. The spectral dependence of photoionization cross section of deep centers in GaN is quantitatively determined in the energy range from 1.68to3.30eV. The absolute values of photoionization cross sections of these centers are found to be of the order of 10−15–10−14cm2.

Non-linear light modulation OSL phenomenon

A theoretical simulation and experimental verification of non-linear light modulation of optically stimulated luminescence (NL-OSL) technique has been demonstrated under first- and general-order kinetics. It is found that the NL-OSL technique gives all the information that can be obtained from the conventional LM-OSL technique with some useful features and flexibilities. It is observed that the NL-OSL curve is more symmetric than the LM-OSL curve. The NL-OSL technique can be useful in analyzing OSL traps having very low and closely lying values of photo-ionization cross-sections of meta-stable traps obeying different order of kinetics.

Calculation of the photoionization cross sections for the ions of the rubidium isoelectronic sequence by the Dirac-Fock method

The photoionization cross sections for the ground and some excited states of 11 ions of the rubidium isoelectronic sequence from Rb through Ag10+ are calculated by the relativistic Dirac-Fock self-consistent field method. The energy dependence of the photoionization cross sections and the changes in the threshold values along the isoelectronic sequence are considered. The influence of the exchange effect and the choice of gauge on the calculated values of photoionization cross sections is examined. For practical use, the calculated cross sections are approximated by an analytical expression. Along with the total photoionization cross sections, the asymmetry parameter in the angular distribution of photoelectrons and the degree of their polarization are also calculated.

Determination of absolute photoionization cross sections of the phenyl radical

Photoionization cross sections of the phenyl radical to form the phenyl cation were measured using tunable vacuum ultraviolet synchrotron radiation coupled with photofragment translational spectroscopy. The phenyl radical was produced via 193- or 248-nm dissociation of chlorobenzene. At 10.0 eV, the photoionization cross sections for the phenyl radical averaged over product channels were found to be 13.4 +/- 2.0 and 13.2 +/- 2.0 Mb, respectively, with very little effect seen from the range of internal excitation produced at the two photolysis wavelengths. Using the photoionization cross section values for each channel, photoionization efficiency curves for the phenyl radical were placed on an absolute scale from 7.8 to 10.8 eV.

Generation of L sub-shell photo-ionization cross-sections for elements 18⩽ Z⩽92 at energies .320–115.606 keV (A computer program ‘LSPICS’)

L sub-shell photo-ionization cross-sections, σ Li, for elements 18⩽ Z⩽92 at energies .320–115.606 keV have been generated from an empirical relation fitted to Scofield's L sub-shell photo-ionization cross-section values. The excitation energy E for an element is constrained by the condition that only L and higher shell vacancies are produced in the elements. The closeness of generated and existing values of Scofield's L sub-shell data recommends the use of generated values in the fields of atomic and molecular physics and for trace elemental analysis. For this purpose computer software ‘LSPICS’ has been developed. On personal computer LSPICS generates L sub-shell photo-ionization cross-section values in barns just by entering the atomic number of element and excitation photon energy in keV.

Determination of L 3 subshell X-ray production cross-sections and fluorescence yields of Pb, Th and U

A study of L 3 subshell X-ray production cross-sections and fluorescence yields by using characteristic K X-rays as the exciting radiation is described. Only the L 3 subshells of Pb, Th and U were excited by the characteristic K X-rays of the elements used as secondary sources. The cross-sections for the production of L l, L α and L β groups of L 3 subshell X-rays of Pb, Th and U have been measured using photoionization by Rb, Nb and Mo K X-rays. The measured L 3 X-ray production cross-section values for Pb, Th and U are in good agreement with the theoretical ones evaluated using L 3 subshell fluorescence yield ω 3, fractions of the radiative width F 3 i and L 3 subshell photoionization cross-section σ 3. The L 3 subshell fluorescence yields ( ω 3) have also been computed using the presently measured cross-section values and the theoretical L 3 subshell photoionization cross-section values. These results are compared with the theoretically predicted values.

Testing the performance of a VUV photoionization source on a double focussing mass spectrometer using alkanes and thiophenes

The performance of a newly developed photoionization source in combination with a high resolution mass spectrometer is tested. The total ion currents for several linear alkanes ( n-pentane to n-decane) and for some thiophenes (2-methylthiophene, 2,5-dimethylthiophene and 2-ethylthiophene) are measured at three fixed wavelengths: the Kr I (10.03 eV and 10.64 eV), Ar I (11.62 eV and 11.83 eV) and Ne I (16.67 eV and 16.85 eV) resonance lines. These total ion currents are compared with the data for the alkanes and thiophenes obtained with low energy (10.6 eV, 11.8 eV and 16.7eV) electron impact ionization on the same mass spectrometer. The loss in ion intensity at several positions throughout this instrument is determined for the photo-ionization source and for the electron impact ionization source. One out of every 1500 ions created in the photoionization source is measured by the detector. For the electron impact ionization source, one out of 180 ions is measured. The introduction of a five-element “Heddle” lens for the transfer of the ions from the photoion source to the mass analyser resulted in an approximately 1.5 fold loss in ion current. From the measured total ion intensities, the photoionization and electron impact ionization cross-sections at energies of 10.6 eV, 11.8 eV and 16.7 eV are calculated. The photoionization cross-section values of the linear alkanes are found to be in the range of 2.5 Mbarn to 355 Mbarn, and the electron impact ionization cross-section values are between 40 Mbarn and 735 Mbarn. The photoionization cross-section values of the thiophenes range from 4 Mbarn to 31 Mbarn, and the electron impact ionization cross-section values from 81 Mbarn to 760 Mbarn.

Atomic data for opacity calculations. XIV. The beryllium sequence

The authors have calculated 1814 energy levels in LS coupling, 33030 oscillator strengths and 859570 photoionization cross section values for the following fifteen members of the beryllium isoelectronic sequence: Be I, B II, C III, N IV, O V, F VI, Ne VII, Na VIII, Mg IX, Al X, Si XI, S XIII, Ar XV, Ca XVII and Fe XXIII. Photoionization is from 1554 bound states lying below the 2s ionization thresholds. The continua are perturbed by resonances converging onto the 2p, 3s, 3p and 3d states of the residual Li-like ions. They delineate the resulting autoionization features by using sufficiently small energy step lengths in regions where the cross sections vary rapidly. Photoexcitation of the core produces large PEC resonances which dominate photoionization of Be I and the less highly ionized ions. They discuss some selected examples drawn from the entire data set and make comparisons with the work of other investigators.

The Absorption Spectrum of B II in the Vacuum Ultraviolet

The spectrum of B II in the range 400-1700 Å has been investigated in absorption using two laser produced plasmas; one producing the B II absorbing medium and the other the background continuum. Series of lines arising from the ground 1S and the 3P0 metastable levels were observed, followed by absorption continua. Values of photoionization cross-section are given for the 2s2 1S-2sεp1 P0 and 2s2p 3P0-2sεd3D channels. Autoionization resonances have been observed in the εp continuum and the profiles fitted with a parametric formula for series of autoionized lines.

Photocapacitance studies of CdS:Cu

Schottky diodes of copper doped CdS have been studied using photocapacitance techniques. Copper doping of CdS gives rise to deep hole states in the lower half of the band gap. The binding energies of the ground state and excited state are 1.1 and 0.34 eV, respectively. Optical emission of both holes and electrons as well as internal transitions followed by thermal emission of holes have been studied and absolute values of photoionization cross sections have been measured. The results are related to previous measurements of luminescence, absorption, photoconductivity, and photo-Hall effect. A model for the electronic structure of the dominant copper related center is discussed.

Branching ratios for the photoionization cross section of atomic oxygen

Branching ratios σ( O 0 3 P → O + 2 D 0) σ( O 0 3 P → O + 4 S 0) and σ( O 0 3 P → O + 2 P 0) σ ( O 0 3 P → 4S 0) are calculated at 584 Å and 304 A employing the close-coupling approximation to compute the photoionization cross section values. The coupled channels include the states dominated by the ground configuration 1 s 22 s 2 p 3 of O +and the next excited configuration ls 22 s2 p 4. It is found that the partial c section σ( 2 D 0) decreases more rapidly than σ( 2 P 0) , and at the lower wavelength 304 Å, the ratio σ( 2 D 0) σ( 4 S 0) < σ( 2 P 0) σ( 4 S 0) . Present results at 304 Å differ considerably from previous work.

Determination of optical ionization cross sections in GaP using charge storage and impurity photovoltaic effect

A simple experimental method is presented for determining absolute values of photoionization cross sections by combining steady state and transient measurements of the extrinsic photovoltaic effect. It is shown that, under certain conditions, the short circuit current caused by a two step excitation process via localized impurity levels, is mainly generated in the transition region of the junction. The equationms for the photovoltaic effect reduce then to a simple form and the photoionization cross sections of the impurity levels involved can be expressed in experimental quantities, where a constant factor is also involved, as a function of energy. To determine this factor, the decay of optically excited stored charge carriers was investigated. The concentration of deep impurity levels in the depletion region of the junction together with capacitance measurements was finally calculated from this constant factor. All experiments were performed with zinc and oxygen doped GaP diodes at room temperature. At 1·78 eV the photo ionization cross sections of an impurity level with binding energy 0·9 eV probably caused by oxygen are found to be 1 × 10 −16 cm 2 and 1·5 × 10 −16 cm 2.

On the autoionization transitions in thallium atoms

A configuration interaction analysis of the absorption cross-section curve of thallium has been carried out on the autoionization transitions 2P1/20-4P3/2 and 2P1/20-2D3/2 and their associated photoionization continua. Intensity stealing from the E(D) continuum amounts to 80% of the oscillator strength for the 2P1/20-4P3/2 transition and 5% for the 2P1/20-2D3/2 transition. Application of the f-sum rule indicates that a considerable contribution to the oscillator strengths must lie to the high wave number side of the above autoionization transitions. Unperturbed photoionization cross-section values of 8.0 Mbn for the E(D) continuum and 1 7 Mbn for the E(S) continuum at the ionization threshold are indicated.