Complex Decay Scheme Research Articles

Standardizing by photon-photon coincidence technique to produce electron capture disintegrates radioactive sources

The system using X-gamma coincidence technique for the standardizing radionuclide, which present simple and complex decay scheme with X-rays of energy below 100 keV has deployed by Radionuclide Laboratory (LNMRI), Brazil. The work was carried using a sodium iodide detector, for gamma photons, in combination with a high purity germanium detector for X-rays. Samples of 65Zn and 133Ba were standardized and the results for both radionuclides showed good precision and accuracy when compared with reference values. The standardization differences were 0.72 % for 65Zn and 0.48 % for 133Ba samples.

Systematics of log [formula omitted] values for [formula omitted]−, and EC/[formula omitted]＋ transitions

This work is an update of the 1998 publication by Singh et al. [1] and reviews the logft values for all the known β-decay branches (β−, β＋/EC). Furthermore, an update of all Q-values (from AME2020 [2]), as well as a recalculation of all the logft values (through BetaShape code [3,4]) has been conducted using relevant data in the ENSDF database, as well as in newer literature. Only those cases have been considered in this review, where the beta transitions occur between levels of firm single spin assignments (86% of the transitions), and with probable single spin assignments (14% of the transitions), but with firm parity assignments for all the transitions. Weak β branches of <1% intensity in complex decay schemes have generally been omitted. Out of a total of 26318 β transitions extracted from the ENSDF database and current literature, data for only 4038 β transitions survived the filtering criteria in the present review. The logft values in β decay, spanning about 21 orders of magnitude, have been classified into allowed and forbidden categories according to the classification scheme of Konopinski [5]. All logft values have been deduced using the BetaShape code with new developments presented in this study. A very few number of logft values for very low-energy beta transitions (<5keV) survived the cut criteria and are briefly discussed in terms of atomic overlap corrections. Also tabulated and briefly discussed are seven superallowed cases with ΔT = 0, Tz(parent) = −2, while a known case for 28S to 28P has been omitted as reliable EC/β＋feeding to the analog state in 28P cannot be assigned due to lack of adequate experimental and detailed data for this decay. Centroid, width, minimum and maximum values for each category have been deduced. Uncertainties have been estimated and are also given. For literature coverage in the present review, see discussion in text.

Corrections of HPGe detector efficiency curve due to true coincidence summing by program EFFTRAN and by Monte Carlo simulations

Standard reference sources, used for efficiency curve calibration of detector, often contain radionuclides with complex decay schemes (such as 60Co, 88Y, 152Eu …), introducing a potential problem in gamma-ray spectrometry, due to the appearance of coincidence summing of detected photons, in particular at a low source-detector distance. In this paper, a set of Monte Carlo simulations of an identical experimental setup were performed in order to obtain the efficiency curve of coaxial p-type HPGe detector for energy region (0–2) MeV, with the effect of true coincidence summing and without it. Obtained efficiency curves are compared with the experimental curve after applied EFFTRAN corrections. Fairly well agreement (between simulated and experimental curves with EFFTRAN corrections (with a relative deviation of 10%) proved the reliability of EFFTRAN corrections, as well as the possibility of Monte Carlo simulations for efficiency curve determination.

Standardisation of 133Ba by efficiency extrapolation method and calibration of ionisation chamber

133Ba has been standardised by direct measurements for the first time in the laboratory using two counting systems: (i) the 4πβ (plastic scintillator) -γ coincidence, (ii) the 4πβ (proportional counter) -γ coincidence. Furthermore, this standardisation experiment demonstrates the performance and applicability of the recently developed 4πβ (plastic scintillator)-γ coincidence system for radionuclides decaying with complex decay schemes as well as for e, X-γ emitters. Additionally, 133Ba solution standards were prepared to calibrate the pressurized 4π γ ionisation chamber and determination of the calibration coefficient. The En score is a statistical indicator of the agreement between two independent estimations. Thus, the performance of the PS system was compared to the result obtained with the PC system using the En score as specified in the ISO13528:2015. The results of measurements are acceptable if En ≦ 1.0. An En score of 0.2 was obtained which indicates that, the 133Ba activity concentration obtained by the 4πβ (plastic scintillator) -γ coincidence and 4πβ (proportional counter) -γ coincidence systems are in agreement. This paper presents the standardisation procedure, the results obtained by the measurements and their comparison.

Assessment of operator exposure from shielded and unshielded sources of 18F and 68Ga – Monte Carlo simulations and empirical measurements

Syringe shields originally designed for 18F are now routinely used with 68Ga. However, 68Ga has a more complex decay scheme than the pure positron emitter 18F. Positrons emitted from the decay of 68Ga possess a maximum energy significantly higher than those of 18F, and are also accompanied by a number of gamma emissions. The higher energy positrons of 68Ga will also result in higher energy Bremsstrahlung radiation from the positrons interacting in radiation shields. The purpose of this study was to determine if personal radiation shielding devices and safe radiation work practices, optimised for 18F are appropriate for 68 Ga.

On the photomultiplier-tube asymmetry in TDCR systems

The responses of the three photomultiplier tubes (PMTs) in a triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) system are often not identical. Such asymmetries can have a significant influence on activity determinations. The problem is often solved by means of a minimization algorithm which can easily be applied when analytical methods are used for the efficiency calculation, as is usually done for pure beta emitters. However, for radionuclides with more complex decay schemes, the counting efficiencies are often calculated with stochastic methods and the computation of the required corrections becomes very challenging.This paper presents a new numerical method to overcome the asymmetry problem for such complex decays and a comprehensive study on 55Fe is described in detail. For the measurements, the asymmetry was varied by means of grey filter films which were placed in front of one of the photomultiplier tubes.In the case of the pure electron-capture (EC) radionuclide 55Fe, the asymmetry can also be taken into account with a very simple correction which is derived assuming monoenergetic emissions. This work is also of great importance for the planned extension of the International Reference System (SIR) at the BIPM which will be used for international comparisons in radionuclide metrology.

NEMA NU 2\u20132007 performance characteristics of GE Signa integrated PET/MR for different PET isotopes

BackgroundFully integrated PET/MR systems are being used frequently in clinical research and routine. National Electrical Manufacturers Association (NEMA) characterization of these systems is generally done with 18F which is clinically the most relevant PET isotope. However, other PET isotopes, such as 68Ga and 90Y, are gaining clinical importance as they are of specific interest for oncological applications and for follow-up of 90Y-based radionuclide therapy. These isotopes have a complex decay scheme with a variety of prompt gammas in coincidence. 68Ga and 90Y have higher positron energy and, because of the larger positron range, there may be interference with the magnetic field of the MR compared to 18F. Therefore, it is relevant to determine the performance of PET/MR for these clinically relevant and commercially available isotopes.MethodsNEMA NU 2–2007 performance measurements were performed for characterizing the spatial resolution, sensitivity, image quality, and the accuracy of attenuation and scatter corrections for 18F, 68Ga, and 90Y. Scatter fraction and noise equivalent count rate (NECR) tests were performed using 18F and 68Ga. All phantom data were acquired on the GE Signa integrated PET/MR system, installed in UZ Leuven, Belgium.Results18F, 68Ga, and 90Y NEMA performance tests resulted in substantially different system characteristics. In comparison with 18F, the spatial resolution is about 1 mm larger in the axial direction for 68Ga and no significative effect was found for 90Y. The impact of this lower resolution is also visible in the recovery coefficients of the smallest spheres of 68Ga in image quality measurements, where clearly lower values are obtained. For 90Y, the low number of counts leads to a large variability in the image quality measurements. The primary factor for the sensitivity change is the scale factor related to the positron emission fraction. There is also an impact on the peak NECR, which is lower for 68Ga than for 18F and appears at higher activities.ConclusionsThe system performance of GE Signa integrated PET/MR was substantially different, in terms of NEMA spatial resolution, image quality, and NECR for 68Ga and 90Y compared to 18F. But these differences are compensated by the PET/MR scanner technologies and reconstructions methods.

A realistic solution of overcoming disadvantage of Compton suppression spectrometer

To achieve low detection limits for radionuclide analysis, Compton continuum suppression gamma-ray spectrometer has been used for several decades. The most serious disadvantage arises when radionuclides measured have cascade gamma emissions. This is a major limitation of the technique in environmental sample analysis. The digital list-mode data acquisition techniques in conjunction with time stamped pulse analysis method presented in this paper recovers the undesired full-energy-peak (FEP) coincidence losses for cascade radionuclides while retains suppression of true Compton events to keep the improved detection limit, thus extending the usefulness of the anti-Compton spectroscopy. In this study, software are developed to analyse the radionuclides with a relative simple decay scheme, such as 22Na, 60Co and 88Y, and a complex decay scheme, such as 125Sb, 134Cs, 152Eu and 154Eu. The results indicated that in the reconstruct anticoincidence spectra the FEP restoration efficiency, both for minor and major peaks, is near 100%.

Exposing all the decay paths of 152Eu and their probabilities

Checking the 152Eu 13-year very complex decay scheme, the aim of this paper is the identification, followed by a graphical presentation of all its decay paths and their probabilities, based on the information about particles, emitted energies and probabilities. The decay path followed in the course of the decay process is defined by the cascade transitions from the parent ground state to the daughter ground state. They are 74 paths to the 152Gd ground state and 285 to 152Sm, totalizing 359 cascades. As the decay path is seen as a time-series, the probability to follow this path, calculated here by an excel spreadsheet, can simply be seen as a product of transition probabilities. All such data is necessary for the accurate primary standardization of 152Eu solution through methods as the CIEMAT/NIST for liquid scintillation counting or even the sum peak method, an absolute measurement technique used for activity standardization by gamma-ray spectrometry techniques. The idea is to expose and highlight the difficulties arising from the complexity of such decay, meeting the needs of a didactic presentation to the user community not specifically available in the literature.

Standardization of 64Cu activity

The complex decay scheme that makes 64Cu promising as both an imaging and therapeutic agent in medicine also makes the absolute measurement of its activity challenging. The National Institute of Standards and Technology (NIST) has completed a primary activity standardization of a 64CuCl2 solution using the 4πβ(LS)-γ(NaI) live-timed anticoincidence (LTAC) counting method with a combined standard uncertainty of 0.51 %. Two liquid scintillation (LS) counting methods were employed for confirmatory measurements. Secondary measurements were made by high-purity germanium detectors, pressurized ionization chambers (IC), and a well-type NaI(Tl) counter. Agreement between the LTAC-based standard and standards from other laboratories was established via IC calibration factors. Poor agreement between methods and with theoretical IC responses may indicate a need for improved β+/- branching probabilities and a better treatment of β+/- spectra.

65Zn and 133Ba standardizing by photon-photon coincidence counting

The LNMRI/Brazil has deployed a system using X-gamma coincidence technique for the standardizing radionuclide, which present simple and complex decay scheme with X-rays of energy below 100 keV. The work was carried on radionuclide metrology laboratory using a sodium iodide detector, for gamma photons, in combination with a high purity germanium detector for X-rays. Samples of 65Zn and 133Ba were standardized and the results for both radionuclides showed good precision and accuracy when compared with reference values. The standardization differences were 0.72 % for 65Zn and 0.48 % for 133Ba samples.

Application of the sum-peak method to activity standardizations of 152Eu sources in LNMRI (BR)

The sum-peak method, an absolute measurement technique that uses coincidence counting and γ-ray spectrometry, was applied to activity standardization of 152Eu sources. The decay branch used was that of 152Sm, as it is almost entirely electron capture and exhibits X-rays with a high probability of coincidence with the 121.8keVgamma rays, as evidenced by the matrix technique used for complex decay schemes, a method for deriving counting rate equations describing coincidence summing of gamma and X-rays. The result was compared with the calibration performed by ionization chamber traceable to BIPM. The results presented uncertainty values of 0.50% (k = 1).

Full-Energy peak efficiency of an NaI(Tl) detector with coincidence summing correction showing the effect of the source-to-detector distance

The coincidence summing effect is considered to be one of the most important problems in γ-ray spectrometry. It has played an important role in the detector calibration process, especially at low source-to-detector distances, which are the typical conditions when the environmental samples have to be measured. In this work, the γ–γ coincidence summing correction factors (CSCF) for a 3″× 3″ NaI(Tl) γ-ray detector have been calculated at different distances from the detector end cap. These factors with NaI(Tl) γ-ray detectors have rarely been discussed in the previous literature, due to the lack of the separation process of the close gamma energy lines in the scintillation detector spectrum. The γ–γ CSCF were calculated for 60Co, 133Ba and 152Eu radioactive point sources, which show the simple and the complex decay scheme of several radionuclides. In order to obtain the CSCF, the following parameters must be estimated by the numerical simulation method (NSM): the total efficiency (εT), the full-energy peak efficiency (εP) and the effective solid angle (Ωeff). These parameters were calculated numerically depending on the direct mathematical method and efficiency transfer method. The obtained CSCF was used to correct the measured efficiency curves, which were measured at different distances, then compared to the ETNA and EFFTRAN programs, as well as the CSCF. The results show a good agreement, especially at large source-to-detector distances.

The application of the new matrix method for calculating coincidence summing effects in the case of radionuclide with the more complex decay scheme - 152Eu

In this paper we present the results of applying the new approach for calculating coincidence summing effects. The application of analytical approaches to coincidence summing effects makes it possible to predict all summation peaks that occur in the spectrum. Accordingly, based on the value of the peak area in the spectrum and knowledge of probability transitions between excited states of a nucleus, it is possible to determine the efficiency of detection and activity of radioactive sources. This method is successfully applied to the decay of the radionuclide europium 152Eu. It provides a detailed description of the method of forming the matrix corresponding to the final result – determined activities and the efficiency of detection.The importance of the new method is that it allows us to determine the efficiency of detection and activity of radioactive sources directly without calibration of the detector, which is very important in metrology of radionuclides.

Metrological activity determination of 133Ba by sum-peak absolute method

The National Laboratory for Metrology of Ionizing Radiation provides gamma sources of radionuclide and standardized in activity with reduced uncertainties. Relative methods require standards to determine the sample activity while the absolute methods, as sum-peak, not. The activity is obtained directly with good accuracy and low uncertainties. 133Ba is used in research laboratories and on calibration of detectors for analysis in different work areas. Classical absolute methods don't calibrate 133Ba due to its complex decay scheme. The sum-peak method using gamma spectrometry with germanium detector standardizes 133Ba samples. Uncertainties lower than 1% to activity results were obtained.

Calculation of Coincidence Summing Correction Factors for an HPGe detector using GEANT4

The aim of this paper was to calculate the True Coincidence Summing Correction Factors (TSCFs) for an HPGe coaxial detector in order to correct the summing effect as a result of the presence of 88Y and 60Co in a multigamma source used to obtain a calibration efficiency curve. Results were obtained for three volumetric sources using the Monte Carlo toolkit, GEANT4. The first part of this paper deals with modeling the detector in order to obtain a simulated full energy peak efficiency curve. A quantitative comparison between the measured and simulated values was made across the entire energy range under study. The True Summing Correction Factors were calculated for 88Y and 60Co using the full peak efficiencies obtained with GEANT4. This methodology was subsequently applied to 134Cs, and presented a complex decay scheme.

Performance demonstration of 4πβ(LS)-γ coincidence counting system for standardization of radionuclides with complex decay scheme

A standardization of 134Cs and 131I was carried out in order to demonstrate the performance and applicability of the 4πβ(LS)-γ coincidence counting system for standardization of radionuclides with complex decay scheme. The coincidence analyzer, capable of analyzing coincidence between beta and two gamma windows simultaneously, was developed and used for the standardization. The use of this dual coincidence analyzer has reduced the total experimental time by half. The activity concentrations obtained using the 4πβ(LS)-γ coincidence counting system, a 4πβ(PC)-γ coincidence counting system, and the CIEMAT/NIST method are in excellent agreement with each other within uncertainty limits and hence demonstrates its performance for standardization of radionuclides decaying with complex decay scheme. Hence use of this 4πβ(LS)-γ coincidence counting system can be an alternative method suitable to standardize radionuclides with complex decay scheme with acceptable precision.

Assessment of a fully 3D Monte Carlo reconstruction method for preclinical PET with iodine-124

Iodine-124 is a radionuclide well suited to the labeling of intact monoclonal antibodies. Yet, accurate quantification in preclinical imaging with I-124 is challenging due to the large positron range and a complex decay scheme including high-energy gammas. The aim of this work was to assess the quantitative performance of a fully 3D Monte Carlo (MC) reconstruction for preclinical I-124 PET. The high-resolution small animal PET Inveon (Siemens) was simulated using GATE 6.1. Three system matrices (SM) of different complexity were calculated in addition to a Siddon-based ray tracing approach for comparison purpose. Each system matrix accounted for a more or less complete description of the physics processes both in the scanned object and in the PET scanner. One homogeneous water phantom and three heterogeneous phantoms including water, lungs and bones were simulated, where hot and cold regions were used to assess activity recovery as well as the trade-off between contrast recovery and noise in different regions. The benefit of accounting for scatter, attenuation, positron range and spurious coincidences occurring in the object when calculating the system matrix used to reconstruct I-124 PET images was highlighted. We found that the use of an MC SM including a thorough modelling of the detector response and physical effects in a uniform water-equivalent phantom was efficient to get reasonable quantitative accuracy in homogeneous and heterogeneous phantoms. Modelling the phantom heterogeneities in the SM did not necessarily yield the most accurate estimate of the activity distribution, due to the high variance affecting many SM elements in the most sophisticated SM.

Efficient simulation of voxelized phantom in GATE with embedded SimSET multiple photon history generator

GEANT4 Application for Tomographic Emission (GATE) is a powerful Monte Carlo simulator that combines the advantages of the general-purpose GEANT4 simulation code and the specific software tool implementations dedicated to emission tomography. However, the detailed physical modelling of GEANT4 is highly computationally demanding, especially when tracking particles through voxelized phantoms. To circumvent the relatively slow simulation of voxelized phantoms in GATE, another efficient Monte Carlo code can be used to simulate photon interactions and transport inside a voxelized phantom. The simulation system for emission tomography (SimSET), a dedicated Monte Carlo code for PET/SPECT systems, is well-known for its efficiency in simulation of voxel-based objects. An efficient Monte Carlo workflow integrating GATE and SimSET for simulating pinhole SPECT has been proposed to improve voxelized phantom simulation. Although the workflow achieves a desirable increase in speed, it sacrifices the ability to simulate decaying radioactive sources such as non-pure positron emitters or multiple emission isotopes with complex decay schemes and lacks the modelling of time-dependent processes due to the inherent limitations of the SimSET photon history generator (PHG). Moreover, a large volume of disk storage is needed to store the huge temporal photon history file produced by SimSET that must be transported to GATE. In this work, we developed a multiple photon emission history generator (MPHG) based on SimSET/PHG to support a majority of the medically important positron emitters. We incorporated the new generator codes inside GATE to improve the simulation efficiency of voxelized phantoms in GATE, while eliminating the need for the temporal photon history file. The validation of this new code based on a MicroPET R4 system was conducted for 124I and 18F with mouse-like and rat-like phantoms. Comparison of GATE/MPHG with GATE/GEANT4 indicated there is a slight difference in energy spectra for energy below 50 keV due to the lack of x-ray simulation from 124I decay in the new code. The spatial resolution, scatter fraction and count rate performance are in good agreement between the two codes. For the case studies of 18F-NaF (124I-IAZG) using MOBY phantom with 1 × 1 × 1 mm3 voxel sizes, the results show that GATE/MPHG can achieve acceleration factors of approximately 3.1 × (4.5 ×), 6.5 × (10.7 ×) and 9.5 × (31.0 ×) compared with GATE using the regular navigation method, the compressed voxel method and the parameterized tracking technique, respectively. In conclusion, the implementation of MPHG in GATE allows for improved efficiency of voxelized phantom simulations and is suitable for studying clinical and preclinical imaging.

True coincidence summing correction determination for 214Bi principal gamma lines in NORM samples

The gamma lines 609.3 and 1,120.3 keV are two of the most intensive γ emissions of 214Bi, but they have serious true coincidence summing (TCS) effects due to the complex decay schemes with multi-cascading transitions. TCS effects cause inaccurate count rate and hence erroneous results. A simple and easy experimental method for determination of TCS correction of 214Bi gamma lines was developed in this work using naturally occurring radioactive material samples. Height efficiency and self attenuation corrections were determined as well. The developed method has been formulated theoretically and validated experimentally. The corrections problems were solved simply with neither additional standard source nor simulation skills.