Anticoincidence Counting Research Articles

JEPM April 2018–Abstracts

A solution of 124I was standardized for activity by 4πβ(LS)-γ(NaI) live-timed anticoincidence (LTAC) counting, with confirmatory measurements by triple-to-double coincidence ratio (TDCR) and CIEMAT-NIST efficiency tracing (CNET) liquid scintillation counting. The LTAC-based standard was shown to be in agreement (within k = 1 uncertainties) with previous measurements at NIST and elsewhere. Calibration settings for radionuclide calibrators were determined and a discrepancy with literature values, partially due to a calibration methodology dependent upon an erroneous setting for 18F, was identified and explained.

Deconvolution method to split up X-ray peaks emitted by 223Ra

The Radium-223 ( 223 Ra) has being used as a medicine for localized treatment of patients with osteoblastic metastasis originated by prostate cancer resistant of castration or hormone refractory. For a better treatment with this radionuclide, clinical images are one path to turn achievable organ's dosimetry for each patient. The X-rays emitted by 223 Ra demonstrated as the main way to turn the image acquiring feasible. In order to study this X-ray area, deconvolution is necessary to split up the mains X-ray peaks that are measured by a high-purity germanium detector as doublet peaks in a complex region of the spectrum below 100 keV. For this, the Colegram® code was applied using the Low Energy X Voigt fitting curve on raw data source from Maestro® software. Results of activity using the deconvolution data from this work were in agreement with values obtained at absolute standardization live-time anticoincidence counting. The Colegram® code demonstrates a powerful tool to aid Maestro to split up the mains overlapped X-rays emitted by 223 Ra.

134Cs activity standardization by 4πβ(LS)-γ(NaI-Tl) anticoincidence counting and submission to international reference system

From a commercial supplier a solution containing 134Cs has been standardized at National Laboratory for Ionizing Radiation Metrology (LNMRI) for the first time using three Liquid scintillation based measurement. These measurement methods are 4πβ-γ live-timed anticoincidence counting, 4πβ-γ coincidence counting and 3H-standard efficiency tracing with the CNET methods. The results obtained by anticoincidence counting was adopted as reference value and its combined uncertainty was 0.38%. The agreement of this reference value with coincidence counting and CNET methods were 0.39% and 0.34% respectively and were in consistency with each uncertainty method. The weighted mean results coincidence counting and CNET methods are also in close agreement 0.03% with anticoincidence counting method and meets the requirement of primary and national standard.This standardization was made in order to reduce the uncertainty in 134Cs measurement in Brazil and also following a request made by Bureau International des Poids and Mesures for new submission to International Reference System. The LNMRI last submission was made in 1987. Therefore from a 134Cs master solution a NIST ampoules was prepared and LNMRI/IRD submitted it to the International Reference System, Bureau International of Poids and Measures (SIR/BIPM). In this paper will be analyzed the LNMRI measurement and performance each measurement methods and also take into account the reference value of KCDB, we determined also the 134Cs gamma emission probabilities of main energy.

68(Ge+Ga) activity standardization by 4πβ(LS)-γ(NaI(Tl)) anticoincidence counting measurements

In this work, a 68(Ge+Ga) solution has been standardized at the National Institute of Ionizing Radiation Metrology (LNMRI), in Brazil, in the frame of an international key comparison CCRI(II)-K2.Ge-68 piloted by National Institute of Standards and Technology (NIST/USA). The 4πβ(LS)-γ(NaI(Tl)) anticoincidence method with live-time and extended dead-time was used and its result was validated by 4πβ(LS)-γ(NaI(Tl)) coincidence counting and liquid scintillation counting using the Triple to Double Coincidence Ratio (TDCR) method. The deviations of the activity concentration values of coincidence and TDCR measurements from the anticoincidence result were 1.7% and 0.63%, respectively, which were within experimental evaluated uncertainties at ~95% level of confidence (coverage factor k = 2). The combined relative standard uncertainties were 0.65%, 0.70% and 0.53% for anticoincidence, coincidence and TDCR methods, respectively. These values are consistent with the results reported by Cessna at the ICRM2017 conference.

Monte Carlo modelling of live-timed anticoincidence (LTAC) counting for Cu-64

The radionuclide copper-64 is a promising candidate for nuclear medicine, but its complex decay creates challenges in the primary standardization of its activity. Monte Carlo simulations of live-timed anticoincidence (LTAC) counting of 64Cu were used to calculate corrections to extrapolation intercepts, resulting in improved activity determinations. A small correction (−0.33%) to the linear extrapolation of LTAC data acquired with a γ-gate over the 1346keV gamma peak was determined. We discuss the physical origin of the correction. We also use experimental data to demonstrate a Monte Carlo scaling that allows for inclusion of data acquired with a γ-gate set over the annihilation photon peak(s).

Application of modern anticoincidence (AC) system in HPGe γ-spectrometry for the detection limit lowering of the radionuclides in air filters

The use of active and passive shields can substantially reduce the Minimum Detectable Activity (MDA) of the γ-ray counting systems, rejecting events induced by cosmic-rays or by environmental radioactivity. However, the size and geometry of the samples lead to limitations in the background reduction in routine measurements. The Minimum Detectable Activity (MDA) values for low energy of γ-ray emitting radionuclides (<200 keV) deposited in three typical air filter geometries have been compared for anticoincidence and single HPGe detector mode of γ-spectrometry systems. The relative increase in the Figure Of Merit (FOM) values from to 10–37% has been achieved for AC counting mode for radionuclides of 210Pb, 234Th, 235U and 226Ra deposited on the three kinds of air filters.

Standardization of 106Ru/Rh by live-timed anticoincidence counting and gamma emission determination

The absolute activity standardization measurement system of radionuclide by live-timed anticoincidence counting was implemented at LNMRI in 2008 to reduce the effects of some correction factors on the determination of activity with coincidence counting technique used for decades in the laboratory, for example, the corrections of dead time and resolution.With the live-timed anticoincidence system, the variety of radionuclides that can be calibrated by LNMRI was increased in relation to the type of decay. The objective of this study was to standardize the 106Ru activity, determine gamma emission probabilities by spectrometric method for some energies, and estimate measurement uncertainties.

Standardisation and half-life measurements of 111In

The standardisation of 111In by 4π(LS)-γ coincidence and anticoincidence counting is presented. Absolute measurements were performed for samples with different concentrations of carrier solution and for different window settings in the gamma channel. The radioactive concentration of the master solution determined on the same reference date was consistent for all measurements performed. The evaluated typical uncertainty was 0.43%. The half-life of 111In was determined using a time series of measurements performed with an ionisation chamber. A least squares fit of the measured data resulted in a half-life of 2.8067 (34) days consistent with Decay Data Evaluation Project recommended value (0.064% higher than the DDEP value).

Long-term stability of carrier-added 68Ge standardized solutions

Tests for chemical stability were carried out on carrier-added 68Ge solutions prepared and calibrated in 2007 and 2011 to evaluate the suitability of the specific composition as a potential Standard Reference Material. Massic count rates of the stored solutions were measured using a NaI(Tl) well counter before and after gravimetric transfers. The present activity concentration of the 2007 solution was also measured using live-timed anticoincidence counting (LTAC) and compared to the 2007 calibrated value. The well counter data indicated no change in massic count rate to within uncertainties for either solution. The LTAC measurements gave a difference of −0.49% in the activity concentration 2007 solution over 7 years. However, the uncertainty in the decay correction over that time, due to the uncertainty in the 68Ge half-life, accounted for the majority (0.67% out of 0.83%) of the standard uncertainty on the activity concentration. The results indicate that these carrier-added solutions are stable with regard to potential activity losses over several half-lives of 68Ge.

HOW OLD IS IT? - 241PU/241AM NUCLEAR FORENSIC CHRONOLOGY REFERENCE MATERIALS.

One material attribute for nuclear forensics is material age. 241Pu is almost always present in uranium- and plutonium-based nuclear weapons, which pose the greatest threat to our security. The in-growth of 241Am due to the decay of 241Pu provides an excellent chronometer of the material. A well-characterized 241Pu/241Am standard is needed to validate measurement capability, as a basis for between-laboratory comparability, and as material for verifying laboratory performance. This effort verifies the certification of a 38 year old 241Pu Standard Reference Material (SRM4340) through alpha-gamma anticoincidence counting, and also establishes the separation date to two weeks of the documented date.

Anticoincidence counting further improves detection limits of short-lived products by pseudo-cyclic instrumental neutron activation analysis

A systematic investigation was carried out on the merits and limitations of anticoincidence counting for short-lived radionuclides (t 1/2 < 75 s) used in instrumental neutron activation analysis (INAA) and pseudo-cyclic INAA (PC-INAA) methods for single as well as simultaneous multielement determinations in botanical and nutritional reference materials. The list of radionuclides of interest included: 108Ag, 110Ag, 165mDy, 20F, 75mGe, 179mHf, 86mRb, 46mSc, 77mSe, and 177mYb. Precision and accuracy of measurements were good, and detection limits were of the order of µg kg−1.

Standardization of 237Np

The standardization of 237Np was investigated. The certified massic activity for 237Np was obtained by 4παβ liquid scintillation (LS) counting with correction for the 233Pa daughter using the CIEMAT/NIST efficiency tracing method using a 3H standard. Confirmatory measurements were also performed by high-resolution HPGe gamma-ray spectrometry, and by 4παβ(LS)-γ(NaI) anticoincidence counting. All results agree within the respective method's uncertainties. It was confirmed that the 237Np/233Pa radioactive equilibrium is disturbed when making dilutions and/or removing aliquots.

A new NIST primary standardization of 18F

A new primary standardization of 18F by NIST is reported. The standard is based on live-timed beta-gamma anticoincidence counting with confirmatory measurements by three other methods: (i) liquid scintillation (LS) counting using CIEMAT/NIST 3H efficiency tracing; (ii) triple-to-double coincidence ratio (TDCR) counting; and (iii) NaI integral counting and HPGe γ-ray spectrometry. The results are reported as calibration factors for NIST-maintained ionization chambers (including some “dose calibrators”). The LS-based methods reveal evidence for cocktail instability for one LS cocktail. Using an ionization chamber to link this work with previous NIST results, the new value differs from the previous reports by about 4%, but appears to be in good agreement with the key comparison reference value (KCRV) of 2005.

Standardization of Sm-153 solution by absolute methods

Standardization of 153Sm by 4π(LS)-γ coincidence and anticoincidence counting and the CIEMAT/NIST method in three LS-counters is presented. This short half-life radionuclide is applied in tumor therapy and bone pain palliation. A simplified disintegration scheme of 153Sm was applied in the calculation of the counting efficiency. Standard uncertainties of 0.4% for the 153Sm measurements by the 4π(LS)-γ coincidence and anticoincidence techniques and 0.7% by the C/N method were evaluated, respectively. An agreement of the standardization results by both methods within the respective uncertainties was obtained. The half-life of 153Sm of (1.92895±0.00024) days was determined during one month of measurements and correction for europium isotope impurities by the C/N method in the TriCarb 2910 LS-counter.

Evaluation of INAA–anticoincidence counting for measuring nanogram levels of vanadium in relatively high-salt nutritional reference materials

An instrumental neutron activation analysis method in conjunction with anticoincidence counting (INAA–AC) gamma-ray spectrometry was developed for the determination of ppb levels of V in biological, mostly nutritional, reference materials containing varying amounts of salt. The method involved irradiation in the Dalhousie University SLOWPOKE-2 reactor facility at a fission neutron flux of 5 × 1011 cm−2 s−1 for 1 min, decay for 1 min, and counting for 10 min. In order to fully investigate the extent of improvement that can possibly be obtained for V determination by INAA–AC, a theoretical term called the analytical figure of merit was developed and applied to 16 National Institute of Standards and Technology and International Atomic Energy Agency reference materials. The overall background around the 1,434.1-keV photopeak of 52V was reduced by a factor of 5–10 for several materials in the anticoincidence counting mode. The detection limits were lowered by factors of 3–5 in INAA–AC (0.61–9.4 μg kg−1) compared to conventional INAA (1.9–79 μg kg−1) in samples with varying ratios of Na/V (0.24–1,000), Cl/V (0.12–1,827), Al/V (7.45–115) and Mn/V (1.84–66.9) making rapid and reliable V measurements possible at sub-ppb levels without any chemical separation.

Epithermal instrumental neutron activation analysis in conjunction with anti-coincidence gamma-ray spectrometry for investigating iodine levels in Canadian foods

In order to reduce interferences from high activities of 24Na, 56Mn, 82Br, and 38Cl as well as to improve detection limits, precision, and accuracy of measuring iodine levels in biological materials, foods and diets in particular, an epithermal instrumental neutron activation analysis (EINAA) method in conjunction with anti-coincidence (EINAA-AC) gamma-ray spectrometry was employed. The Compton scattering background in the region of the 442.9-keV photopeak of 128I was significantly suppressed by anti-coincidence counting. In order to validate the EINAA-AC method as well as to evaluate its broad applicability to diverse types of biological material, 17 NIST and IAEA reference materials containing very low to high levels of iodine as well as interfering elements were analyzed by the EINAA-AC method. The samples were irradiated in the cadmium-lined pneumatic site at a neutron flux of 2 × 1011 cm−2 s−1 of the Dalhousie University SLOWPOKE-2 Reactor (DUSR) facility for 10 or 20 min followed by 1-min decay and 30-min counting. The detection limit for iodine by EINAA-AC was improved by a factor of 2–5 compared to EINAA depending on the sample matrix and other factors, and a limit of 3–5 μg kg−1 was achieved for low-salt foods. We found the RSD to be about ±5 % above 200, increasing to ±10 % at 20, and then to greater than ±30 % at about 5 μg kg−1 iodine levels.

Standardization of 166mHo and 243Am/239Np by live-timed anti-coincidence counting with extending dead time

The National Laboratory for Metrology of Ionizing Radiation (LNMRI)/Brazil acquired 166mHo and 243Am/239Np solutions from commercial suppliers in order to realize primary standardization and therefore reducing the associated uncertainties. The method used in the standardization was the live-timed 4πβ(LS)-γ(ΝaI(Tl)) anticoincidence counting. The live-timed anticoincidence system is operated since 2006 in LNMRI and is composed of two MTR2 modules donated by Laboratoire National Henri Becquerel (LNE-LNHB)/France. The data acquisition system uses a homemade LabView program and an Excel file for calculus. These systems have been used for primary standardization at LNMRI for many radionuclides and recently took part in the 124Sb and 177Lu International Key Comparisons with good performance.

Coincidence Techniques in Gamma-ray Spectroscopy

Abstract In many different gamma-ray detection systems, the events are registered in coincidence, i.e. within short time interval, by two or more detectors. Depending on purpose of an experiment, these events can be rejected (anticoincidence counting) or acquired (coincidence counting). The construction, setup and application of several coincidence systems in Laboratory for nuclear physics of Department of Physics in Novi sad are presented. The anti-Compton shield for HPGe detector based on big annular NaI(Tl) detector and corresponding measurement which proved existing of 283 keV level in Ba-137 populating by beta decay of Cs-137, is described. The application of this system (in addition with NaI(Tl) plug detector) where HPGe detector is actively shielded by NaI(Tl) detector for investigation of double beta decay of positron emitters (Cr-50, Zn-64,) is also shown. The improving of detection limit of HPGe detector by the active shield consisting of five plastic scintillation detectors is presented, as well as the measurements of cross sections for X-ray production, induced by interaction of cosmic-ray muons with massive lead shield. We found that the prompt and delayed coincidence events between plastic veto detector and Ge detector can be sharply divided in two groups. Also, the bremsstrahlung and annihilation events can be time resolved from (n,n’) events, although all these events belong to the group of delayed events.

K 0-prompt gamma ray activation analysis for estimation of boron and cadmium in aqueous solutions

K 0-PGAA (prompt gamma activation analysis) has been used to estimate boron and cadmium contents in industrial and environmental materials from some different local areas as well as, samples from different locations in Burullus and Qarun Lakes. A high efficiency Compton background suppression gamma-ray spectrometry by anti-coincidence counting with a NaI(Tl) shield around a central HPGe detector for in beam PGAA using a 252Cf neutron source has been calibrated and described in this paper. The facility is principally designed for measurement of the prompt gamma-ray spectra obtained due to thermal neutron capture using 1951.14 keV gamma line of 35Cl as the internal mono-standard comparator. A calibration curves were developed in which a set of boron and cadmium standards were tested and the count rate to boron and cadmium mass curves were determined. This set of boron and cadmium measurements was compared with a method for determining composition using K 0-PGAA. Conventional prompt neutrons capture Gamma-ray results were in a good agreement with the data obtained by K 0-PGAA method. Detection limits and self-shielding study are presented.

A new primary standardization of 229Th

The National Institute of Standards and Technology (NIST) has certified a high-purity (229)Th Standard Reference Material as SRM 4328C, based on live-timed 4pialphabeta-gamma anticoincidence counting (LTAC) of the equilibrium solution. The LTAC system was optimized to minimize the uncertainty in the result due to the two short-lived ground-states present in the decay chain. Confirmatory measurements were carried out by four other methods. Furthermore, the present absolute activity and measured gamma-ray emission rates were combined to obtain gamma-ray emission probabilities.