Alpha-emitting Nuclides Research Articles

Comparison of Nuclear Medicine Therapeutics Targeting PSMA among Alpha-Emitting Nuclides.

Currently, targeted alpha therapy (TAT) is a new therapy involving the administration of a therapeutic drug that combines a substance of α-emitting nuclides that kill cancer cells and a drug that selectively accumulates in cancer cells. It is known to be effective against cancers that are difficult to treat with existing methods, such as cancer cells that are widely spread throughout the whole body, and there are high expectations for its early clinical implementation. The nuclides for TAT, including 149Tb, 211At, 212/213Bi, 212Pb (for 212Bi), 223Ra, 225Ac, 226/227Th, and 230U, are known. However, some nuclides encounter problems with labeling methods and lack sufficient preclinical and clinical data. We labeled the compounds targeting prostate specific membrane antigen (PSMA) with 211At and 225Ac. PSMA is a molecule that has attracted attention as a theranostic target for prostate cancer, and several targeted radioligands have already shown therapeutic effects in patients. The results showed that 211At, which has a much shorter half-life, is no less cytotoxic than 225Ac. In 211At labeling, our group has also developed an original method (Shirakami Reaction). We have succeeded in obtaining a highly purified labeled product in a short timeframe using this method.

A review of radiation doses and associated parameters in Western Australian mining operations (2018–20)

In the 2019–20 reporting period, 19 mining operations in Western Australia were identified as having workers who were likely to be exposed to ionising radiation stemming from naturally occurring radioactive materials, 17 of which, known hereinafter as reporting entities (REs), were required to submit an annual report of the dose estimates of their workforce to the mining regulatory authority. In 2018 the International Commission for Radiological Protection published the revision of the dose coefficients (DCs) for occupational intakes of radionuclides of the uranium-238 and thorium-232 decay series, in ICRP-137 and ICRP-141. The 2019–20 annual reports are the first to apply the revised DCs to estimate worker doses. The mean effective dose (ED) reported by the 17 REs increased by 32.4% to 0.94 mSv in 2019–20 from 0.71 mSv reported in 2018–19, indicating that the mean ED is approaching the 1 mSv annual dose estimate at which regulatory intervention should be considered. The mean committed effective dose (CED) from inhalation of dusts containing long-lived alpha-emitting (LLα) nuclides has increased by 35% from 0.40 mSv in 2018–19 to 0.54 mSv in 2019–20. The maximum CED from LLα increased by 16.3% from 3.20 mSv in 2018–19 to 3.72 mSv in 2019–20. The authors consider that, in the absence of other explanations provided by the REs, the increase is largely attributable to the revised DC’s published in ICRP-137 and ICRP-141, but highlight that there are significant variations between REs that make a generalised conclusion problematic. The maximum reported ED in 2019–20 was 6.0 mSv, an increase of 36.4% from 2018 to 2019 (4.4 mSv). The 2019–20 reporting period is the first time in a decade in which mine worker EDs have been elevated to the point that EDs have exceeded 5 mSv, a level at which personal monitoring and additional institutional controls are required.

Actinide in Air (Rn-Progeny Rejected) Alpha Spectroscopy With Tensioned Metastable Fluid Detectors

Abstract This article discusses outcome of research for deriving a methodology and apparatus for ascertaining for the presence of ultratrace-level actinides in air from their alpha emission signatures, while remaining blind to the relatively large (1000× higher activity) alpha emissions from Rn-progeny. Apparatus and techniques were developed to collect and characterize alpha-emitting nuclides of Rn-progeny and actinides in air on a polycarbonate 3 μm pore size continuous air monitor (CAM) filter. A wet-chemistry approach was developed and validated for successfully separating the Rn-progeny alpha emitting isotopes of Po-214 and Po-218, while extracting the actinides (U, Pu, Am) in a fluid mixture that is suitable for conduct of alpha spectroscopy with a centrifugally tensioned metastable fluid detector (CTMFD). The resulting α-TMFD technology was compared against the state-of-art “Alpha-Sentry™” Continuous Air Monitor (CAM) system commonly utilized world-wide. Results indicate that the α-TMFD technology can potentially offer complementary and superior performance in multiple performance categories, and ∼18× improvement in the time to detect (e.g., at 0.02 derived air concentration (DAC) within ∼3 h, versus ∼70 h for Alpha-Sentry) for actinides of interest while also remaining ∼100% blind to ∼103× higher Rn-progeny background—with the added potential for offering few keV scale energy resolution without resorting to peak shape fitting, versus ∼300–400 keV for existing CAM systems.

Assessment of radiation hazard of uranium enterprises for the environment

The purpose of the article is to describe monitoring studies on the radiation state of air in populated and working areas near the uranium processing enterprise in the Republic of Uzbekistan. Ac-cording to the analytical measurement, the exposure dose of gamma radiation is equivalent to the equilibrium volume activity of radon, specific activity of long-lived alpha-emitting nuclides in the zone of influence of the enterprise, the working area, premises for storing uranium materials and manufacturing dumps, tailings dams and areas of underground uranium leaching. It was shown that the measurement results do not exceed the regional background and regulatory levels of radioactive radiation by all indicators. The dependence of the volume activity of radon at production facilities on the density of the radon flux from the soil was studied. The most intensive radioactive objects – uranium dumps – were identified. It was found out that there is no excess radioactive impact of the uranium enterprise on the environmental objects.

Plutonium and americium in the deep Black Sea bottom sediments

The new data on 239+240Pu, 238Pu, 241Pu, 241Am vertical distribution in the deep western Black Sea sediments was analyzed. The sediment dating, obtained by means of 238Pu/239+240Pu activity ratio vertical distribution, suggested the upper 3 cm layer of sediments to be formed during 27 years after the Chernobyl accident and the deeper layers to be formed earlier in pre-Chernobyl time (before 1986). The whole data set on profiles of radionuclides studied was shown to reflect the history of their input into the basin and elimination of these radionuclides from the water column. Analysis of inventories of plutonium alpha-emitting nuclides ensured a more significant contribution of Chernobyl fallout into the present total 238Pu inventory than into 239+240Pu one. The 241Am inventory after-deposition enhancement due to 241Pu decay was estimated at 74% in pre-Chernobyl sediment layer and the general contribution of 241Pu support in the total 241Am inventory in situ enhancement was estimated at 49%.

Защита персонала от аэрозольных выбросов при проведении дезактивационных работ при выводе из эксплуатации радиационно опасных объектов

This article discusses the experience of using low-pressure fog generation systems to ensure the safety of work in contaminated and emergency rooms for fixing suspended particles of dust fractions containing alpha-emitting nuclides mobilized by convective air flows, and provides data on the required size of droplets and the method of their further deposition.

Radon and Progeny Detection Using Tensioned Metastable Fluid Detectors.

Radon and other alpha-emitting nuclides in air can be a significant risk for health hazards in the workplace and in dwellings. Radon gas in US homes causes over 21,000 deaths from lung cancer annually, according to the US Environmental Protection Agency (US EPA). Alpha-emitting radionuclides from airborne contamination in the nuclear industry also constitute a known safety and security-safeguards related issue. Purdue University, along with Sagamore Adams Laboratories LLC, have developed the tensioned metastable fluid detector (TMFD) sensor technology for general-purpose alpha-neutron-fission. For radon detection, radon gas in air is sparged through the TMFD detection fluid, after which this radon-bearing fluid is placed into a tensioned metastable state. In this metastable state, an audible-visible cavitation (alpha radiation) detection event is created and electronically recorded. Tailoring the level of tension enables spectroscopic information through energy discrimination of radon and its progeny; This is also applicable to other alpha emitting isotopes (Pu, Cm, U…). TMFDs boast high intrinsic detection efficiencies (>95%) for alpha spectroscopy while remaining blind to background beta and gamma radiation even in ~10 R h fields. The immunity to beta and gammas allows for reusability of the detection fluid through immunity to beta buildup from thoron and radon progeny. TMFD technology was used to measure the concentration of radon and radon progeny in air for concentrations from 74 Bq m to 740 Bq m. The system measures radon concentration between these levels within 24 h with an intrinsic relative error (IRE) of ± 15% according to the standards set forth by the American Association of Radon Scientists and Technicians-National Radon Proficiency Program (AARST-NRPP) Device Evaluation Program (DEP). Precision evaluation defined using the relative standard deviation set by the AARST-NRPP measured a deviation of <5%, which exceeds the requirement of <25%. Temperature effects from 10°C and 27°C were assessed and corrected for dynamically. A radon decay correction method was introduced to correct for the radon activity decrease in the detection fluid over the counting period due to the ~3.8 d half-life. Blind testing was also successfully performed* with standards from the ; within 6 h, the TMFD-based technology accurately measured the concentration of radon to within 20% of the reference standards. Non-condensing relative humidity levels up to 95% per AARST-NRPP were assessed for and were found to have no impact on radon detection. This work improves upon the previous work by splitting the calibration curve into two distinct regions and adds additional information pertaining to the effects of relative humidity on the system.

Progress in Targeted Alpha-Particle Therapy. What We Learned about Recoils Release from In Vivo Generators.

This review summarizes recent progress and developments as well as the most important pitfalls in targeted alpha-particle therapy, covering single alpha-particle emitters as well as in vivo alpha-particle generators. It discusses the production of radionuclides like 211At, 223Ra, 225Ac/213Bi, labelling and delivery employing various targeting vectors (small molecules, chelators for alpha-emitting nuclides and their biomolecular targets as well as nanocarriers), general radiopharmaceutical issues, preclinical studies, and clinical trials including the possibilities of therapy prognosis and follow-up imaging. Special attention is given to the nuclear recoil effect and its impacts on the possible use of alpha emitters for cancer treatment, proper dose estimation, and labelling chemistry. The most recent and important achievements in the development of alpha emitters carrying vectors for preclinical and clinical use are highlighted along with an outlook for future developments.

Automated astatination of biomolecules--a stepping stone towards multicenter clinical trials.

To facilitate multicentre clinical studies on targeted alpha therapy, it is necessary to develop an automated, on-site procedure for conjugating rare, short-lived, alpha-emitting radionuclides to biomolecules. Astatine-211 is one of the few alpha-emitting nuclides with appropriate chemical and physical properties for use in targeted therapies for cancer. Due to the very short range of the emitted α-particles, this therapy is particularly suited to treating occult, disseminated cancers. Astatine is not intrinsically tumour-specific; therefore, it requires an appropriate tumour-specific targeting vector, which can guide the radiation to the cancer cells. Consequently, an appropriate method is required for coupling the nuclide to the vector. To increase the availability of astatine-211 radiopharmaceuticals for targeted alpha therapy, their production should be automated. Here, we present a method that combines dry distillation of astatine-211 and a synthesis module for producing radiopharmaceuticals into a process platform. This platform will standardize production of astatinated radiopharmaceuticals, and hence, it will facilitate large clinical studies focused on this promising, but chemically challenging, alpha-emitting radionuclide. In this work, we describe the process platform, and we demonstrate the production of both astaine-211, for preclinical use, and astatine-211 labelled antibodies.

Typical uncertainties in alpha-particle spectrometry

Alpha-particle spectrometry is routinely performed with the aim of measuring absolute activities, activity ratios between different alpha-emitting nuclides or decay data such as branching factors, alpha emission probabilities and relative half-lives. It is most commonly performed with ion-implanted silicon detectors. Strong features of the technique are the low background levels that can be achieved due to low sensitivity to other types of radiation, the intrinsic efficiency close to 1 which reduces the efficiency calculations to a geometrical problem and the uniqueness of the energy spectra for each α-decaying nuclide. The main challenge is the limitation to the attainable energy resolution, even with thin and homogenous sources, which causes alpha energy peaks to be partially unresolved due to their width and low-energy tailing. The spectral deconvolution often requires fitting of analytical functions to each peak in the alpha spectrum. True coincidence effects between alpha particles and subsequently emitted conversion electrons cause distortions of the alpha spectra which lead to significant changes in the apparent peak area ratios. Optimum energy resolution can only be achieved on very thin sources, which puts constraints on the source preparation techniques. Radiochemical separations may be needed to extract the alpha emitters from voluminous matrices and efficiency tracing is performed by adding in another isotope by known amounts. Typical uncertainty components are discussed by means of some hypothetical examples.

Application of a Monte Carlo lung dosimetry code to the inhalation of thoron progeny.

To determine radiation doses incurred by inhaled thoron progeny, the Monte Carlo radon progeny lung dosimetry code IDEAL-DOSE was adapted to the inhalation of thoron progenies, comprising the alpha-emitting nuclides 216Po, 212Bi and 212Po. Dose calculations for defined exposure conditions yielded a dose conversion coefficient (DCC) of 4.6 mSv WLM(-1) or 94.2 nSv (Bq h m(-3))(-1) when compared with a DCC of 3.8 mSv WLM(-1) if based on the International Commission on Radiological Protection Human Respiratory Tract Model. Bronchial doses were computed for different thoron progenies exposure conditions measured in a Bavarian half-timbered house and in a thoron experimental house at the Helmholtz Zentrum München. DCCs ranged from 4.9 to 12.9 mSv WLM(-1), depending on particle size, unattached fraction and fractional activity concentrations. For exposure-specific indoor aerosol parameters, the thoron progeny DCC is smaller than the radon progeny DCC by about a factor of 2.

A review of electrodeposition methods for the preparation of alpha-radiation sources

This paper addresses an approach to the theory and practice of electrodeposition processes of alpha-emitting nuclides. Some of the main contributions made to this field are reviewed, including the rotating disk electrode technique. Also, several interpretations concerning the electrodeposition process as well as a number of practical recommendations are included in the study.

Characteristics of formvar films used to prevent alpha-detector contamination

Alpha spectrometry is an extremely useful and sensitive for detection of alpha-emitting nuclides. Contamination of the silicon detectors for low-level alpha spectrometry by recoil nuclides is a serious problem in the measurement of alpha emitters decaying to daughter nuclides with short half-lives. This unwanted contamination leads to decreased measurement sensitivity causing a degradation of the limit of detection. The simplest method to prevent this radioactive contamination of detector is to use a catcher film between the alpha source and the detector. In this work we describe the obtaining of the thin formvar films as stopper foils for recoil nuclei and we investigated the influence of these films on alpha spectrometry parameters, as energy shift (~30 keV) and resolution (~7%). No significant deterioration of the alpha spectrometry parameters was observed when using thin formvar films. Using the ASTAR web databases, which calculate stopping powers for alpha particles, the thickness of formvar films was estimated to be about 5.355 × 10−5 g/cm2. The measurements were performed with an ORTEC SOLOIST alpha spectrometer with PIPS detector.

Lead–gold eutectic: An alternative liquid target material candidate for high power spallation neutron sources

One of the main technical concerns of Megawatt-class spallation neutron sources is the removal of the heat deposited in the target station. A way to overcome it is to use targets consisting of flowing liquid metals, but the already tested materials – mercury and lead–bismuth eutectic (LBE) – are not unproblematic. We show here that another eutectic alloy containing lead and gold (LGE) could be a suitable alternative. Besides a chemical toxicity lower than mercury, this low melting-point alloy has the advantage of being solid at RT. Moreover, it combines a neutron production similar to mercury and LBE with smaller amounts of alpha-emitting nuclides, relieving safety and environmental requirements. Further advantages are a reduced decay heat a few weeks after stopping operation and density variations in the solid state significantly smaller than LBE. Steel corrosion appears to be more important than expected but if it remains manageable, the current research suggests that LGE could be a valuable alternative to LBE and mercury.

Nanoscopic study of chemical species during uranium electrodeposition for alpha spectrometry sources

High resolution alpha spectrometry (AS) is commonly applied for the determination of actinides and other alpha-emitting nuclides in many applications. Electrodeposition is the standard procedure for preparing α-particle sources usually made of a thin and uniform radioactive deposit onto a metallic substrate. Natural U sources prepared by the Hallstadius method are known to contain co-deposited Pt from the anode. In this sense, the main aim of this work is to conclusively review the behaviour of Pt and U in the electrodeposition process and their distribution in the resulting deposit, factors that are responsible for the thickness and uniformity of the sources. In addition to new scanning electron microscopy/energy dispersive spectroscopy (SEM–EDX) and X-ray absorption fine structure (XAFS) data, the electrodeposited surface has been analyzed using both atomic force microscopy (AFM) and synchrotron radiation Grazing Incidence X-ray diffraction (GI-XRD). The results concerning morphology of the deposit, surface roughness, topography and surface structure obtained from sources prepared at different electrodeposition times agree with the AS results concerning electrodeposition yield and spectral resolution.

Effect of Calcium Silicate Hydrate Precipitates at Cementitious and Bentonite Material Interface on Long-Term Engineered Barrier System Performance in TRU Waste Disposal Facilities

AbstractChemical conditions and mass transport properties of engineered barrier systems in TRU waste facilities would change with time due to the interaction of cement/bentonite materials. (‘TRU waste’ is one of categories of the radioactive wastes and contains a significant amount of alpha-emitting transuranic nuclides. In some countries, these wastes are classified into the Intermediate Level Waste (ILW).) Previous numerical model analyses to assess the long-term performance of engineered barrier systems in TRU waste repositories predicted to form Calcium Silicate Hydrate (C-S-H) species at the interface between the cementitious and bentonite materials. If C-S-H precipitates in the bentonite side of the boundary, mass transport in the bentonite buffer decreases and mineralogical alterations are expected to be restricted for a long period. The evidence of C-S-H precipitation in the bentonite side, however, still has not been identified in the former experimental studies. To improve the reliability of numerical analyses, immersion experiments were performed using contact samples of cementitious and bentonite materials, and X-ray absorption fine structure (XAFS) analysis was carried out to detect C-S-H precipitation at the contacting interface. Precipitation of C-S-H was confirmed from the obtained XAFS spectra. This result is one of the evidences to show the validity of the current numerical model analyses, which suggests that the bentonite buffer performance as an engineered barrier would be kept over a long period.

Alpha emitters from uranium mining in the environment

Uranium mining and milling activities usually generate an enhancement of radionuclide concentrations in the environment that may cause increased radiological exposure to mankind. For risk assessment and radiological protection of man and environment in these areas, usually, it is needed to implement radiological surveillance of water, soils, agricultural products, aerosols, and mining waste discharges as well. Radionuclides to be monitored in priority are alpha-emitting nuclides of the uranium natural series. Radioactivity analysis of materials from uranium mining areas of Portugal shows departure from secular radioactive equilibrium amongst uranium series radionuclides, thus rendering invalid the assumption of equilibrium and requiring the actual determination of each radionuclide. Radionuclide measurements performed with high resolution alphaspectrometry, as reported herein, produce accurate results on specific radionuclides that are essential in computing radiation doses to critical groups of the population.

Ratio of nose blow results to intakes during the decommissioning of a facility at Dounreay

During the decommissioning of a large glove box facility at Dounreay, in addition to engineering and administration controls, workers wore pressurised suits to minimise their intake of radionuclides. The workers provided nose blows after each suited operation to provide an indication of the effectiveness of protective measures. The nose blows were also used as indicators of radiological significant intakes. This paper examines the distribution of ratios of nose blow to assessed intake. A geometric mean and variance of the ratio of nose blows to intakes have been derived. The nose blows were provided over a period of 2 y and the alpha-emitting nuclides present are 239Pu, 241Am and 238Pu. Twenty-two nose blow results each with follow-up urine and faecal results are included in the study. The effectiveness of nose blows as an indicator of radiological conditions and as a trigger for the investigation of significant doses is considered. The ratio between assessed intake and nose blow result was shown to be very large.

Effect of inhomogeneous activity distributions and airway geometry on cellular doses in radon lung dosimetry

The human tracheobronchial system has a very complex structure including cylindrical airway ducts connected by airway bifurcation units. The deposition of the inhaled aerosols within the airways exhibits a very inhomogeneous pattern. The formation of deposition hot spots near the carinal ridge has been confirmed by experimental and computational fluid and particle dynamics (CFPD) methods. In spite of these observations, current radon lung dosimetry models apply infinitely long cylinders as models of the airway system and assume uniform deposition of the inhaled radon progenies along the airway walls. The aim of this study is to investigate the effect of airway geometry and non-uniform activity distributions within bronchial bifurcations on cellular dose distributions. In order to answer these questions, the nuclear doses of the bronchial epithelium were calculated in three different irradiation situations. (1) First, CFPD methods were applied to calculate the distribution of the deposited alpha-emitting nuclides in a numerically constructed idealised airway bifurcation. (2) Second, the deposited radionuclides were randomly distributed along the surface of the above-mentioned geometry. (3) Finally, calculations were made in cylindrical geometries corresponding to the parent and daughter branches of the bifurcation geometry assuming random nuclide activity distribution. In all three models, the same 218Po and 214Po surface activities per tissue volumes were assumed. Two conclusions can be drawn from this analysis: (i) average nuclear doses are very similar in all three cases (minor differences can be attributed to differences in the linear energy transfer (LET) spectra) and (ii) dose distributions are significantly different in all three cases, with the highest doses at the carinal ridge in case 3.

Electrodeposition and determination of nano-scale uranium and plutonium using alpha-spectroscopy

A simple method was used to design and set up an electrodeposition device for the alpha-emitting nuclides. The designed electroplating facility is leak proof and simple in operation and dismantled. The effect of current, pH of electrolyte, and the plating time on the electrodeposition efficiency have been investigated in a sodium bisulphate, sulphuric acid electrolyte in order to determine the optimum conditions. It was shown that a current of 900-1000 mA, plating time of 80-90 minutes and pH range of 2-2.3 are the best conditions for deposition of nano-scale uranium and plutonium. In these circumstances, it was possible to deposit 0.004 ng . g-1 Pu and 60 ng . g-1 U in an electroplating planchette. The device and modified procedures were successfully applied for soil samples. Prior to electrodeposition of the elements, a column extraction chromatography has been used to separate the Pu and U and eliminate most matrix and interferences in environmental samples.