Internal Conversion Coefficients Research Articles

Internal organ dose rate conversion coefficients of Japanese macaques to 134Cs,137Cs and 131I†.

The purpose of this study was to estimate the internal dose of radiation in Japanese macaques (aka Nihonzaru or snow monkey) due to the Fukushima nuclear power plant accident. Images of a male Japanese macaque weighing ~10kg were acquired using a multi-slice computed tomography (CT) scan with a 64-row segment detector. The CT images were used to create voxel phantoms of the bones, bone marrow, brain, eyes, heart, lungs, stomach, liver, spleen, pancreas, kidneys, intestines, bladder, testes, thyroid and miscellaneous tissue. The Particle and Heavy Ion Transport System (PHITS) Monte Carlo code was used to calculate the internal exposure rate conversion factors for 134Cs, 137Cs and 131I isotopes for the created voxel phantoms with a statistical precision higher than 1%. The PHITS-calculated energy deposits were compared with those for rhesus monkeys. The results showed that the fractions of energy deposits for β-radiation in different organs were almost identical between the two species. For γ-radiation, there was excellent agreement in the self-absorption rate with the approximate curve of the Japanese macaque, with an average deviation of 2%. The maximum deviation of 12% was for the kidney, which has two organs, so the error with the approximate curve is slightly larger due to the energy loss created between organs.

Analysis of a neutron-induced conversion electron spectrum of gadolinium

A 100-nm-thick gadolinium layer deposited on a pixelated silicon sensor was activated in a neutron field to measure the internal conversion electron (ICE) spectrum generated by neutron capture products of 155Gd and 157Gd. The experiment was performed at the ISIS neutron and muon facility, using a bespoke version of the HEXITEC spectroscopic imaging camera. Signals originating from internal conversion electrons, Auger electrons, x rays and gamma rays up to 150 keV were identified. The ICE spectrum has an energy resolution of 1.8–1.9 keV at 72 keV and shows peaks from the K, L, M, N+ ICEs of the 79.51 keV and 88.967 keV 2+-0+ gamma transitions from the first excited states in 158Gd and 156Gd, respectively, as well as the K ICEs of the 4+-2+ transitions at 181.931 keV and 199.213 keV from the respective second excited states. Spectrum analysis was performed using a convolution of a Gaussian with exponential functions at the low and high energy side as the peak shaping function. Relative ICE intensities were derived from the fitted peak areas and compared with internal conversion coefficient (ICC) values calculated from the BrIcc database. Relative to the dominant L shell contribution, the K ICE intensity conforms to BrIcc and the M, N, O+ ICE intensities are somewhat higher than expected.

Precise conversion electron intensities of low energy gamma transitions for efficiency calibration of electron detectors

Precise energies and relative intensities of gamma transitions and conversion electrons in the electron capture decay of 153Gd have been determined independently with our well-tested and optimized gamma and electron spectrometers - a large-volume (60 cc) HPGe detector and a mini-orange electron transporter paired to a Si(Li) detector, respectively. The experimental internal conversion coefficients of the gamma transitions in 153Eu have been determined using Normalized Peak to Gamma method and compared with the theoretical values adopted by Nuclear Data Sheets to assign multipolarities of all the transitions. The precise internal conversion electron intensities of the low energy transitions can be used as standards for calibration purposes of electron detectors and spectrometers.

Dose Rate Assessment Exercises with Stylized Phantom of Neon Flying Squid from Northwest Pacific

Radiation protection for non-human marine organisms still faces many challenges. To establish a more realistic radiation dosimetry model of cephalopods, this study developed a stylized phantom of neon flying squid (Ommastrephesbartramii) containing ten organs and tissues based on magnetic resonance imaging (MRI) technology. The internal and external dose conversion coefficients for eight radionuclides (134Cs, 137Cs, 131I, 110mAg, 60Co, 54Mn, 65Zn, 95Zr) of each organ/tissue were determined with Monte Carlo simulation using the Geant4 toolkit. Furthermore, with the reported coastal seawater radioactivity levels at the coastal area of Fukushima Daiichi Nuclear Power Plant after the accident in 2011 as the source term, the radiological dose rate for O. bartramii was evaluated with the stylized phantom developed in this study and with the conventional whole-organism ellipsoidal model in the ERICA Assessment Tool. Both results showed that the dose rate for O. bartramii derived from the FDNPP accident releases exceeded the generic no-effects screening benchmark level (10 μGy h−1).

Internal Conversion Coefficients for Observed Low-Energy Gamma Transitions

Internal Conversion Coefficients for Observed Low-Energy Gamma Transitions

New Measurements of Internal Conversion Coefficients in $${}^{{111}}$$Cd

New Measurements of Internal Conversion Coefficients in $${}^{{111}}$$Cd

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.

Precision Measurements of Internal Conversion Coefficients of Low Energy Transitions in $${}^{169}$$Tm for Efficiency Calibration of Electron Detectors

The 32.018 d beta decay of $${}^{169}$$ Yb is studied with a high resolution precisely calibrated 8 $$K$$ PC based Multi-Channel Analyzer coupled HPGe gamma spectrometer system and liquid nitrogen cooled Si(Li) detector coupled to a well calibrated Mini-Orange magnetic spectrometer. Precise energies and relative intensities of gamma transitions and conversion electron intensities of gamma transitions have been determined for the first time with better accuracy. The experimental internal conversion coefficients of the gamma transitions in $${}^{169}$$ Tm have been determined using Normalized Peak to Gamma method and compared with the theoretical values adopted by Nuclear Data Sheets to assign multipolarities of all the transitions. The precise internal conversion electron intensities of the low energy transitions can be used as standards for calibration purposes of electron detectors and spectrometers.

K -shell internal conversion coefficient for M4 decay of the 30.8 keV isomer in Nb93

The 30.8 keV ${(1/2)}^{\ensuremath{-}}$ isomeric state in $_{41}^{93}\mathrm{Nb}$ decays by an $M4$ transition to the ${(9/2)}^{+}$ ground state. We have measured the $K$-shell internal conversion coefficient ${\ensuremath{\alpha}}_{K}$ for this transition in order to test the validity of current methods of calculation for a case with relatively low atomic number, low transition energy, and a high value of ${\ensuremath{\alpha}}_{K}$. Taking the fluorescence yield of niobium to be 0.751(4), we obtain ${\ensuremath{\alpha}}_{K}=2.56(9)\ifmmode\times\else\texttimes\fi{}{10}^{4}$, a result that agrees with the Dirac-Fock calculations that take into account the presence of a $K$ vacancy in the final state, and disagrees by 1.7 standard deviations with calculations that ignore the vacancy. We also determine the energy of the isomeric state to be 30.760(5) keV, a fourfold improvement in precision over the currently accepted value.

Internal exposure rate conversion coefficients and absorbed fractions of mouse for 137Cs, 134Cs and 90Sr contamination in body.

The aim of this study was to determine parameters for estimating the internal exposure of all organs in mouse experiments from the radioactivity concentration in organs. The estimation of internal exposure rate conversion coefficients and absorbed fractions for 137Cs, 134Cs and 90Sr by the Particle and Heavy Ion Transport code System (PHITS) with a voxel-based mouse phantom is presented. The geometry of the voxel phantom is constructed from computer tomography images of a mouse 9cm in length weighing 23.9g. The voxel-based mouse phantom has the following organs: brain, skull, heart, lungs, liver, stomach, spleen, kidneys, bladder, testis and tissue (tissue and other organs). Gamma- and beta-rays from 137Cs, 134Cs and 90Sr sources in each source organ are generated and scored for every target organ. The internal exposure rate conversion coefficients and absorbed fractions are calculated from deposition energies in each target organ from each source organ and are used to generate an internal exposure rate conversion coefficient matrix and an absorbed fraction matrix. The absorbed fractions of beta-rays in the source organs are roughly 0.5-0.8 for 137Cs and 134Cs, and the absorbed fractions of gamma-rays are <0.04 for 137Cs and <0.03 for 134Cs. The internal exposure rate conversion coefficient matrix is defined using the absorbed fractions. The calculated internal exposure rate coefficient matrix is tested under a uniform radioactivity concentration of 1Bq/kg for 137Cs, 134Cs and 90Sr. The estimated internal exposure rates in the mouse whole body for 137Cs, 134Cs and 90Sr are 3.28×10-3, 2.55×10-3 and 1.20×10-2 μGy/d, respectively. These values are very similar to those for an ellipsoid frog (31.4g) and an ellipsoid crab egg mass (12.6g) reported in ICRP Publication 108.

Electron spectrometer for electric monopole (E0) transition studies in nuclei

The study of electric monopole (E0) transitions between two 0+ states is important because the monopole strength carries vital information about the nuclear structure due to its direct link with the mean squared charge radius r2 and quadrupole deformation parameter β. Therefore, the measurement of internal conversion electrons (ICE) or internal pair formation (IPF) is crucial for E0 transition studies. Transitions between 0+ states do not change angular momentum. Hence, single-photon emission is forbidden, but can decay by conversion electrons or pair formation and two-photon emission which is mostly negligible. In order to implement E0 studies at iThemba LABS, an electron spectrometer that uses a solenoidal magnetic field acting as a lens and a Si(Li) detector has been refurbished and characterized using calibration sources of ICE. Figures of merit have been extracted and compared with simulations. The spectrometer coupled with an array of LaBr3:Ce detectors and Low Energy Photon Spectrometers (LEPS) was successfully implemented for in-beam experiments. Measurements of internal conversion coefficients (ICC) and monopole strengths extracted from in-beam measurements of 72As, 72Ge, and 72Se are presented.

226Th nuclear decay data evaluation

Following the recent evaluation of the nuclear decay data of 230U, a similar evaluation for its daughter, 226Th, a radionuclide of interest for targeted alpha therapy, was undertaken within the Decay Data Evaluation Project (DDEP) and an IAEA Coordinated Research Project. The nuclear decay data presented are: the half-life, decay energy, alpha-particle emission energies and probabilities, internal conversion coefficients and gamma-ray energies and emission intensities. These new data will be included in the DDEP database NUCLEIDE.

Conversion electron spectroscopy of the 59.54 keV transition in 241Am alpha decay

A windowless Peltier-cooled silicon drift detector (SDD) was used to measure internal conversion electron (ICE) spectra of thin 241Am sources. The ICE peaks associated with the 59.54 keV gamma transition in 237Np were deconvoluted and relative ICE intensities were derived from the fitted peak areas. Corrections were made for energy dependence of the full-energy-peak counting efficiency, based on Monte Carlo simulations. As expected for this anomalous E1 transition, a significant discrepancy was found with the theoretical internal conversion coefficient (ICC) values calculated from the BrIcc database. Penetration effects are known to cause such anomalies in highly retarded transitions. The measured ICE intensities are in good agreement with a specific combination of literature data obtained with magnetic spectrometers.

Confirming band assignments in 167ytterbium with gamma-gamma-electron triple-coincidence spectroscopy

Multipolarity measurements are presented for transitions in the deformed odd-mass nucleus 167 Yb in support of tentative spin assignments and level interpretations based upon the cranked-Nilsson model. Internal-conversion coefficients were measured with the SAGE (Silicon And GErmanium) spectrometer confirming several E2 transition assignments. The array of high-purity germanium detectors enabled the recording of high-multiplicity events from which $\gamma\gamma\gamma$ and $\gamma\gamma e^{-}$ data sets were extracted and the technique of high-fold $\gamma$-ray gating was demonstrated to cleanly isolate transitions of interest.

Precise measurement of αK and αT for the 39.8-keV E3 transition in Rh103 : Test of internal-conversion theory

Neutron-activated sources of $^{103}$Ru and $^{103}$Pd both share the isomeric first-excited state in $^{103}$Rh as a daughter product. From independent measurements of both decays, we have measured the $K$-shell and total internal conversion coefficients, $\alpha_K$ and $\alpha_T$, for the 39.8-keV $E$3 transition, which de-excites that state in $^{103}$Rh, to be 141.1(23) and 1428(13), respectively. When compared with Dirac-Fock calculations, our new results disagree with the version of the theory that ignores the $K$-shell atomic vacancy, which is consistent with our conclusion drawn from a series of measurements on high multipolarity transitions in nuclei with higher $Z$. Calculations that include the atomic vacancy indicate that the transition actually has a small $M$4 component with mixing ratio $\delta$ = 0.023(5).

E0 transition strengths in 110Pd

Internal conversion coefficients have been measured for transitions in 110Pd to allow the determination of electric monopole (E0) transition strengths. Excited states were populated through inelastic alpha scattering and the SPICE+TIGRESS detectors at TRIUMF-ISAC-II were used to detect the emitted gamma rays and internal conversion electrons. The E0 transition strengths are found to be small and are consistent with the expectation for transitions from a K = 2 band to the K = 0 ground-state band in the axial rotor model.

Influence of octupole vibration on the low-lying structure of Fm251 and other heavy N=151 isotones

The structure of low-lying excited states in $^{251}\mathrm{Fm}$, populated by the $\ensuremath{\alpha}$ decay of $^{255}\mathrm{No}$, has been investigated by means of combined $\ensuremath{\gamma}$ and internal conversion electron spectroscopy. The values for the internal conversion coefficients for the $1/{2}^{+}\ensuremath{\rightarrow}5/{2}^{+}$ and $5/{2}^{+}\ensuremath{\rightarrow}9/{2}^{\ensuremath{-}}$ transitions have been measured. The determined $M2/E3$ mixing ratio and lifetime for the $5/{2}^{+}$ decay to the ground state allowed to determine the corresponding reduced transitions strengths of $B(E3)=18(6)$ W.u. and $B(M2)=3.0(6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ W.u. These results, as well as the results of previous studies in $N=151$ isotopes, are compared to theoretical calculations beyond the mean-field approach, including the first QRPA calculations using the Gogny D1M parametrization for such heavy odd-$N$ nuclei. The comparison points to the importance of accounting for the octupole vibrations for a proper understanding of the low-lying nuclear structure of some of the heaviest elements.

New evaluated radioxenon decay data and its implications in nuclear explosion monitoring

This work presents the last updated evaluations of the nuclear and decay data of the four radioxenon isotopes of interest for the Comprehensive Nuclear-Test-Ban Treaty (CTBT): Xe-131 m, Xe-133, Xe-133 m and Xe-135. This includes the most recent measured values on the half-lives, gamma emission probabilities (Pγ) and internal conversion coefficients (ICC). The evaluation procedure has been made within the Decay Data Evaluation Project (DDEP) framework and using the latest available versions of nuclear and atomic data evaluation software tools and compilations. The consistency of the evaluations was confirmed by the very close result between the total available energy calculated with the present evaluated data and the tabulated Q-value. The article also analyzes the implications on the variation of the activity ratio calculations from radioxenon monitoring facilities depending on the nuclear database of reference.

Identification of significant E0 strength in the [formula omitted] transitions of 58,60,62Ni

The E0 transition strength in the 22+→21+ transitions of 58,60,62Ni have been determined for the first time following a series of measurements at the Australian National University (ANU) and the University of Kentucky (UK). The CAESAR Compton-suppressed HPGe array and the Super-e solenoid at ANU were used to measure the δ(E2/M1) mixing ratio and internal conversion coefficient of each transition following inelastic proton scattering. Level half-lives, δ(E2/M1) mixing ratios and γ-ray branching ratios were measured at UK following inelastic neutron scattering. The new spectroscopic information was used to determine the E0 strengths. These are the first 2+→2+E0 transition strengths measured in nuclei with spherical ground states and the E0 component is found to be unexpectedly large; in fact, these are amongst the largest E0 transition strengths in medium and heavy nuclei reported to date.

230U nuclear decay data evaluation

The evaluation of the nuclear decay data of 230U, a radionuclide of interest in nuclear medicine (targeted alpha therapy), was performed within the Decay Data Evaluation Project (DDEP) and an IAEA Coordinated Research Project. The nuclear decay data presented are: the half-life, decay energy, alpha-particle emission energies and probabilities, internal conversion coefficients and gamma-ray energies and emission intensities. These new data, obtained using the DDEP methodology and software tools, will be included in the DDEP database NUCLEIDE.