Disk Source Research Articles

Twins in diversity: understanding circumstellar disc evolution in the twin clusters of W5 complex

ABSTRACT Young star-forming regions in massive environments are ideal test beds to study the influence of surroundings on the evolution of discs around low-mass stars. We explore two distant young clusters, IC 1848-East and West located in the massive W5 complex. These clusters are unique due to their similar (distance, age and extinction) yet distinct (stellar density and far-ultraviolet radiation fields) physical properties. We use deep multiband photometry in optical, near-infrared and mid-infrared wavelengths complete down to the substellar limit in at least five bands. We trace the spectral energy distribution of the sources to identify the young pre-main sequence members in the region and derive their physical parameters. The disc fraction for the East and West clusters down to 0.1 M$_\odot$ was found to be $\sim 27\,\pm$ 2 per cent (N$_\mathrm{disc}$ = 184, N$_\mathrm{discless}$ = 492) and $\sim 17\,\pm$ 1 per cent (N$_\mathrm{disc}$ = 173, N$_\mathrm{discless}$ = 814), respectively. While no spatial variation in the disc fraction is observed, these values are lower than those in other nearby young clusters. Investigating the cause of this decrease, we find a correlation with the intense feedback from massive stars throughout the cluster area. We also identified the disc sources undergoing accretion and observed the mass accretion rates to exhibit a positive linear relationship with the stellar host mass and an inverse relationship with stellar age. Our findings suggest that the environment significantly influences the dissipation of discs in both clusters. These distant clusters, characterized by their unique attributes, can serve as templates for future studies in outer galaxy regions, offering insights into the influence of feedback mechanisms on star and planetary formation.

Resolving Twin Jets and Twin Disks with JWST and ALMA: The Young WL 20 Multiple System

We report the discovery of jets emanating from pre-main-sequence objects exclusively at mid-infrared wavelengths, enabled by the superb sensitivity of JWST’s Mid-Infrared Instrument Medium-Resolution Spectrometer. These jets are observed only in lines of [Ni ii], [Fe ii], [Ar ii], and [Ne ii]. The H2 emission, imaged in eight distinct transitions, has a completely different morphology, exhibiting a wide-angled, biconical shape, symmetrically distributed about the jet axes. Synergistic high-resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations resolve a pair of side-by-side edge-on accretion disks lying at the origin of the twin mid-infrared jets. Assuming coevality of the components of the young multiple system under investigation, the system age is at least (2–2.5) × 106 yr, despite the discrepantly younger age inferred from the spectral energy distribution of the combined edge-on disk sources. The later system evolutionary stage is corroborated by ALMA observations of CO(2−1), 13CO(2−1), and C18O(2−1), which show no traces of molecular outflows or remnant cavity walls. Consequently, the observed H2 structures must have their origins in wide-angled disk winds, in the absence of any ambient, swept-up gas. In the context of recent studies of protostars, we propose an outflow evolutionary scenario in which the molecular gas component dominates in the youngest sources, whereas the fast, ionized jets dominate in the oldest sources, as is the case for the twin jets discovered in the WL 20 system.

Gaia22dkvLb: A Microlensing Planet Potentially Accessible to Radial-velocity Characterization

We report discovering an exoplanet from following up a microlensing event alerted by Gaia. The event Gaia22dkv is toward a disk source rather than the traditional bulge microlensing fields. Our primary analysis yields a Jovian planet with Mp=0.59−0.05+0.15MJ at a projected orbital separation r⊥=1.4−0.3+0.8 au, and the host is a ∼1.1 M ⊙ turnoff star at ∼1.3 kpc. At r′≈14 , the host is far brighter than any previously discovered microlensing planet host, opening up the opportunity to test the microlensing model with radial velocity (RV) observations. RV data can be used to measure the planet’s orbital period and eccentricity, and they also enable searching for inner planets of the microlensing cold Jupiter, as expected from the “inner–outer correlation” inferred from Kepler and RV discoveries. Furthermore, we show that Gaia astrometric microlensing will not only allow precise measurements of its angular Einstein radius θ E but also directly measure the microlens parallax vector and unambiguously break a geometric light-curve degeneracy, leading to the definitive characterization of the lens system.

Monte Carlo dosimetry of Y-90 and Ru-106 /Rh-106 disk sources for ocular melanoma treatment: beta dose falloff study

Monte Carlo dosimetry of Y-90 and Ru-106 /Rh-106 disk sources for ocular melanoma treatment: beta dose falloff study

Characterisation of sealed radioactive source for nuclear forensic purposes

Characterisation of sealed radioactive source for nuclear forensic purposes

Evaluation of full-energy-peak efficiencies for a LaBr3:Ce scintillator through a Virtual Point Detector approach

The aim of this work is to investigate, in a wide range of gamma-ray energies, the validity of the “Virtual Point Detector” (VPD) approach to evaluate Full-Energy-Peak Efficiency (FEPE) values for a Cerium-doped Lanthanum Bromide scintillator (LaBr3:Ce). With VPD approximation, the detector is assumed equivalent to a virtual point inside the crystal where all the interactions can be considered to occur. The distance of VPD from detector cap is evaluated through experimental point source measurements. The knowledge of the trend of VPD depth as a function of gamma radiation energy allows the evaluation of FEPE values starting from an experimental reference value.The validation of the procedure has been performed by applying the VPD approach to measurement geometries already characterized such as a disk source, an Havar foil irradiated inside a target of a medical cyclotron, and a parallelepided sample geometry, an atmospheric particulate paper filter reduced to 6 cm × 6 cm × 0.7 cm dimensions. FEPE values determined by VPD approach lead to radionuclide activities very close to the ones already obtained with measurements carried out with other detectors.

603. Determining Effect of Media and Disk Source on Reproducibility and Relationship between Broth Microdilution and Disk Diffusion Testing of Cefiderocol

Abstract Background Cefiderocol (CFDC) is a siderophore cephalosporin with broad activity against Gram-negative bacteria. Discrepancies in susceptibility testing for CFDC have been reported. In this study susceptibility testing was performed using broth and agar medium and disks from various manufacturers to evaluate the reproducibility across the different sources and determine the relationship between MIC and inhibition zone. Methods 12 Enterobacterales, 12 P. aeruginosa, 12 A. baumannii with in vivo efficacy results in the murine thigh infection model under humanized PK of CFDC were evaluated. MICs were determined (10 replicates per media per isolate per day) using broth microdilution with iron-depleted cation-adjusted Mueller-Hinton broth (ID-CAMHB) prepared from BD BBL, BD Difco, Oxoid and Merck. The disk zone was determined (3 replicates per media/disk per isolate per day) with CFDC disks from Hardy and Liofilchem and Mueller Hinton Agar from BBL and bioMerieux. Testing was conducted for 3 days using the same inoculum for MIC and disk diffusion studies on each day. Susceptibility was interpreted according to 2023 CLSI breakpoints. Results Good reproducibility of MIC was observed for the ID-CAMHB from each manufacturer for all isolates, except for 2 A. baumannii due to heavy trailing and skip. MIC variation was observed between ID-CAMHB from each manufacturer. Best categorical agreement with in vivo efficacy was observed for the MIC obtained with ID-CAMHB from BD BBL. Good reproducibility of disk inhibition zones were obtained for Enterobacterales and P. aeruginosa irrespective of the manufacturer of disks and agar medium. A. baumannii isolates with elevated MIC values frequently showed colonies in the inhibition zones, with more colonies appearing on BBL agar. This phenomenon was not reproducible, so larger variation of inner inhibition zones were observed with these isolates. Conclusion MIC determinations were reproducible with each ID-CAMHB medium, but variability was observed across the different ID-CAHMB; MICs obtained with BD BBL ID-CAMHB showed best correlation with in vivo data. Good categorical agreement was observed for MIC in BD BBL and BD Difco medium and disk zone, despite variable inhibition zones observed for A. baumannii. Disclosures Miki Takemura, n/a, Shionogi & Co., Ltd.: Stocks/Bonds Mizue Saiki, Ph.D., Shionogi & Co., Ltd.: employee Hidenori Yamashiro, Shionogi & Co., Ltd.: employee Naomi Anan, MSc, Shionogi & Co., Ltd.: employee Boudewijn L. DeJonge, PhD, Shionogi Inc.: Employee Christine M. Slover, PharmD, Shionogi,INC: Employee Christopher M. Longshaw, PhD, Shionogi BV: Employee Anne Henriksen, PhD, Shionogi: Employee Yoshinori Yamano, PhD, Shionogi HQ: Employee

Effect of a low sound speed sediment layer on seismo-acoustic propagation in the New England Mud Patch

The New England Mud Patch (NEMP), located off the coast of Massachusetts, comprises at least four distinguishable sediment layers. The upper-most is a relatively thin, fluid-like layer (1) of mud. Below that lies more rigid mud (2) that has varying physical properties with depth. Below the mud is a sand layer (3) with a thickness of approximately 10 m. Finally, there lies a half-space layer (4) with a significantly higher density and faster compressional and shear speeds. In this paper, we explore the effect of the varying rigidity within the mud layer (2) and the sharp transition at the mud–sand interface, on forward-scattering. In the 2022 Seabed Characterization Experiment (SBCEX22), two different types of broadband sources (SUS and Rupture Disk sources) were deployed. The received signals show evidence of acoustic scattering and the generation of interface waves, along the interface between (1) and (2) and the mud-sand interface between (2) and (3). Results from normal mode modeling using Kraken and seismo-acoustic modeling using OASES suggest that the scattering can be attributed to inhomogeneities in the sediment layers. [Work supported by the Office of Naval Research Code 322OA.]

Monte Carlo dosimetry of a novel Yttrium-90 disc source for episcleral brachytherapy.

To calculate the dose distribution using Monte Carlo simulations for a novel high-dose-rate Yttrium-90 (Y-90) disc source recently developed for episcleral brachytherapy and provide a lookup table for treatment planning. Monte Carlo simulations were performed to calculate the in-water dose distribution of the Y-90 disc source using the "GATE", a software based on the "Geant4" Monte Carlo simulation toolkit developed by the international OpenGATE collaboration. The geometry of this novel beta source, its capsule, and the surrounding water medium were accurately modeled in the simulation input files. The standard Y-90 element beta spectrum from ICRU 72 was used, and the physics processes for beta and photon interactions with matters were all included. The dose distribution of this Y-90 disc source was measured in a separate study using Gafchromic EBT-3 films and the results were reported elsewhere. To match the setup of the experiment, a Gafchromic EBT-3 film was also included in the simulation geometry. The simulated dose profiles were exported from the 3D dose distribution results and compared with the measured dose profiles. Transverse dose profiles at different distances from the seed surface were also obtained to study the lateral coverage of the source. The measured percent depth dose (PDD) curves along the central axis perpendicular to the surface of the Y-90 disc were constructed from the experimental and simulated data, and normalized to the reference point at 1mm from the source capsule. Both PDD curves agreed well up to 4mm from the source surface (maximum difference±10%) but deviated from each other beyond 4mm. The deviation might be caused by the increased measurement uncertainty in the low-dose region. The dose rate at the reference point calculated from the Monte Carlo simulation was 1.09cGy/mCi-s and agreed very well with the measured dose rate of 1.05cGy/mCi-s. If the 80% isodose line is selected as the lateral coverage, the lateral dose coverage is maximal (∼4.5mm) at the plane next to the source surface, and gradually decreases with the increasing distance, approaching 3.5mm when the plane is 5mm from the 6-mm diameter source surface. Monte Carlo simulations were successfully performed to confirm the measured PDD curve of the novel Y-90 disc source. This simulation work laid a solid foundation for characterizing the full dosimetry parameters of this source for episcleral brachytherapy applications.

Substructures in Compact Disks of the Taurus Star-forming Region

Observations of substructure in protoplanetary disks have largely been limited to the brightest and largest disks, excluding the abundant population of compact disks, which are likely sites of planet formation. Here, we reanalyze ∼0.″1, 1.33 mm Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations of 12 compact protoplanetary disks in the Taurus star-forming region. By fitting visibilities directly, we identify substructures in six of the 12 compact disks. We then compare the substructures identified in the full Taurus sample of 24 disks in single-star systems and the ALMA DSHARP survey, differentiating between compact (R eff,90% < 50 au) and extended (R eff,90% ≥50 au) disk sources. We find that substructures are detected at nearly all radii in both small and large disks. Tentatively, we find fewer wide gaps in intermediate-sized disks with R eff,90% between 30 and 90 au. We perform a series of planet–disk interaction simulations to constrain the sensitivity of our visibility-fitting approach. Under the assumption of planet–disk interaction, we use the gap widths and common disk parameters to calculate potential planet masses within the Taurus sample. We find that the young planet occurrence rate peaks near Neptune masses, similar to the DSHARP sample. For 0.01 M J/M ⊙ ≲M p/M * ≲0.1 M J/M ⊙, the rate is 17.4% ± 8.3%; for 0.1 M J/M ⊙ ≲M p/M * ≲1 M J/M ⊙, it is 27.8% ± 8.3%. Both of them are consistent with microlensing surveys. For gas giants more massive than 5 M J, the occurrence rate is 4.2% ± 4.2%, consistent with direct imaging surveys.

Using EBT3 Films and Monte Carlo Simulations to Determine the Percent Depth Dose of a New Y-90 Disc Source for Episcleral Brachytherapy

<h3>Purpose/Objective(s)</h3> A novel Y-90-disc beta source was recently developed for episcleral eye plaque brachytherapy. The purpose of this study was to determine the percent depth dose (PDD) of this new source using the EBT3 film measurements and Monte Carlo simulations. <h3>Materials/Methods</h3> Radiographic films of the same batch were calibrated using the 6MV beam of a linear accelerator, and used to measure the dose distribution of this Y-90-disc source in water. Monte Carlo simulations were performed to calculate the in-water dose distribution using the "GATE," a software based on a Monte Carlo simulation toolkit developed by the international OpenGATE collaboration. The simulation codes were first validated with the TG43, ICRU56, and ICRU72 results, and then used to simulate the radiation transport in the Y-90-disc source, its capsule and the surrounding water medium. The standard Y-90 beta spectrum from ICRU 72 was used, and the physics processes for beta and photon interactions with matters were all included. Three-dimensional dose distribution was simulated, from which the PDD curve along the central axis perpendicular to the disk surface was extracted and compared with that obtained from the film measurements. <h3>Results</h3> The measured PDD curve, normalized to the point at 1 mm above the source capsule, agreed well with the simulated PDD curve with an average difference of -0.27±1.5%. Since the eye plaque brachytherapy might be prescribed to a point with a low PDD (e.g., 5%-10%), we further analyzed the agreement in this area. The difference between the measured and simulated PDDs gradually increases for depths larger than 3.5 mm (measured 16.7% vs. simulated 16.6 %). At 5 millimeters (5.9% vs. 4.3%), the simulated PDD is 26.2% lower than the measured, which we believe is still a clinically acceptable agreement. For larger depths, the difference increased quickly to a level that we could not confidently conclude that the measured PDD is accurate. <h3>Conclusion</h3> PDD of this new Y-90 source was successfully measured with the EBT3 films and confirmed by Monte Carlo simulations for depth up to 5 mm from the surface of the plaque. Large discrepancies were observed for depths beyond 5 mm. More studies are needed to confirm the PDD if the treatment needs to be prescribed to a depth larger than 5 mm.

Assessment of the detection efficiency calibration of high-resolution gamma-ray spectrometers by EGSnrc and MCNP6.2 Monte Carlo codes

Determination of the activity content of radionuclides with high accuracy and precision with gamma-ray spectrometry is strongly based on the detection efficiency calibration of the detector. The detector efficiency calibration is determined with standard reference sources and/or Monte Carlo codes. The current study provides methodology that can be used to generate efficiency curve with simulations instead of experiments. As a result, the need for additional experiments can be reduced. The implementation of a specific script written on EGSnrc Monte Carlo code was investigated to calculate the detection efficiency with high-level accuracy for high-purity germanium (HPGe) spectrometry. For this purpose, two HPGe detectors (ORTEC and PGT) used routinely in the activity measurement of gamma emitting radionuclides were modelled with EGSnrc code to obtain detection efficiencies for 40–2000 keV energy range. The detector models were benchmarked against MCNP6.2 Monte Carlo code with a hypothetical source geometry. The code-to-code comparison between EGSnrc and MCNP6.2 codes indicted that the codes can be used to generate a reliable detection efficiency curve. The benchmark results showed that median arithmetic deviations of the efficiencies of ORTEC and PGT detectors are found as 0.88% and 1.69%, respectively. The experimental studies were performed with 22Na, 57Co, 60Co, 137Cs, and 241Am standard disc sources for the ORTEC detector and with in-house prepared 152Eu sandwich-type source for the PGT detector. The sources were counted in the energy range of 59.5–1408 keV. The efficiency values from simulations were used in the calculation of the activities of the aforementioned gamma sources with a mathematical formula and resulting measured activity values were compared with reference activity values given in the certificates. In addition, the applicability of spreadsheet approach that is usually used to determine the combined standard uncertainty for alpha-particle spectrometry was investigated for gamma-ray spectrometry. The performance of the recommended procedure was scored in terms of relative bias, z-score, u-test, trueness, and precision. The activity results obtained with simulated efficiencies showed good agreement with certified values.

Deep near-infrared survey towards the W40 and Serpens South region in the Aquila Rift: A comprehensive catalogue of young stellar objects

ABSTRACT Active star-forming regions are excellent laboratories for studying the origins and evolution of young stellar object (YSO) clustering. The W40–Serpens South region is such a region, and we compile a large near- and mid-infrared catalogue of point sources in it, based on deep near-infrared observations of Canada-France-Hawaii Telescope (CFHT) in combination with Two Micron All Sky Survey (2MASS), UKIRT Infrared Deep Sky Survey (UKIDSS), and Spitzer catalogues. From this catalogue, we identify 832 YSOs, and classify 15, 135, 647, and 35 of them to be deeply embedded sources, Class I YSOs, Class II YSOs, and transition disc sources, respectively. In general, these YSOs are well correlated with the filamentary structures of molecular clouds, especially the deeply embedded sources and the Class I YSOs. The W40 central region is dominated by Class II YSOs, but in the Serpens South region, half of the YSOs are Class I. We further generate a minimum spanning tree (MST) for all the YSOs. Around the W40 cluster, there are eight prominent MST branches that may trace the vestigial molecular gas filaments that once fed gas to the central natal gas clump. Of the eight, only two now include detectable filamentary gas in Herschel data and corresponding Class I YSOs, while the other six are populated exclusively with Class II YSOs. Four MST branches overlap with the Serpens South main filament, and where they intersect, molecular gas ‘hubs’ and more Class I YSOs are found. Our results imply a mixture of YSO distributions composed of both primordial and somewhat evolved YSOs in this star-forming region.

Comparison of Theoretical Disc and Point Source Profiles with Actual-Melt Source Profile in Conduction Welding

Prediction of fusion zone in numerical modelling of welds using a modified heat transfer model requires experimental results for validation. Primarily, the modified heat transfer models are developed from the point and disc source heat models which can be assumed to be a semi-circle or spherical shape. In this study, a simple relationship between melt areas, the depth of penetration and weld width was proposed for point and disc source profiles to represent the actual weld profile. The results obtained for focused and defocused laser beams indicate that the actual weld profile is closer to a point source than the disc source. The transition between the conduction and keyhole regimes was achieved when the actual weld depth of penetration is below that of the point source.

Water-maser survey towards off-plane O-rich AGBs around the orbital plane of the Sagittarius stellar stream

ABSTRACT A 22 GHz water-maser survey was conducted towards 178 O-rich asymptotic giant branch (AGB) stars with the aim of identifying maser emission associated with the Sagittarius stellar stream. In this survey, maser emissions were detected in 21 targets, 20 of which were new detections. We studied the Galactic distributions of H2O- and SiO-maser-traced AGBs towards the Sgr orbital plane, and found an elongated structure towards the (l, b) ∼ (340°, 40°) direction. In order to verify its association with the Sagittarius tidal stream, we further studied the 3D motion of these sources, but found that, kinematically, these maser-traced AGBs are still Galactic disc sources rather than stream debris. In addition, we found a remarkable outward motion, ∼50 km s−1 away from the Galactic Centre of these maser-traced AGBs, but with no systermatic lag of rotational speed as reported in 2000 for solar-neighbourhood Miras.

Beyond the Local Volume. II. Population Scaleheights and Ages of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields

Ultracool dwarfs (UCDs) represent a significant proportion of stars in the Milky Way, and deep samples of these sources have the potential to constrain the formation history and evolution of low-mass objects in the Galaxy. Until recently, spectral samples have been limited to the local volume (d < 100 pc). Here, we analyze a sample of 164 spectroscopically characterized UCDs identified by Aganze et al. in the Hubble Space Telescope (HST) WFC3 Infrared Spectroscopic Parallel Survey (WISPS) and 3D-HST. We model the observed luminosity function using population simulations to place constraints on scaleheights, vertical velocity dispersions, and population ages as a function of spectral type. Our star counts are consistent with a power-law mass function and constant star formation history for UCDs, with vertical scaleheights of 249 pc for late-M dwarfs, 153 pc for L dwarfs, and 175 pc for T dwarfs. Using spatial and velocity dispersion relations, these scaleheights correspond to disk population ages of 3.6 Gyr for late-M dwarfs, 2.1 Gyr for L dwarfs, and 2.4 Gyr for T dwarfs, which are consistent with prior simulations that predict that L-type dwarfs are on average a younger and less dispersed population. There is an additional 1–2 Gyr systematic uncertainty on these ages due to variances in age-velocity relations. We use our population simulations to predict the UCD yield in the James Webb Space Telescope PASSAGES survey, a similar and deeper survey to WISPS and 3D-HST, and find that it will produce a comparably sized UCD sample, albeit dominated by thick disk and halo sources.

Detection efficiency evaluation for low energy of a NaI(Tl) scintillation detector

To improve the characterization of the detection efficiency of a NaI(Tl) scintillation detector in the low energy range, measurements and Monte Carlo simulations were performed with a certified reference material (CRM) and disk sources. The detection efficiency as modeled. In the MCNP simulation, the detection efficiency dropped as expected at 33.17 keV. The X-ray escape correction factors of a 204Tl disk source and MCNP simulations were compared, a factor of the 204Tl was similar. Moreover, Correcting the X-ray escape and using fewer sources than the CRM resulted in better detection efficiency for the NaI(Tl) detector in the low energy range.

On the scattering of a disk source by a rigid sphere for directivity broadening.

The purpose of this study is to model a circular planar loudspeaker placed near a spherical reflector to broaden its directivity pattern, which would otherwise become increasingly narrow at high frequencies. Through ray tracing, it seems intuitively feasible to thus create a virtual point source at very high frequencies, but we provide a more rigorous analysis to determine what will happen at intermediate frequencies where the wavelength is of a similar magnitude to the diameter of the disk or sphere. We show that a smoother off-axis response is obtained with a dipole pressure source, which does not obstruct the scattered sound, rather than a monopole velocity source. Hence, an electrostatic loudspeaker, for example, would be more suitable than a dynamic one. The sphere may also serve as a spherical approximation of a human head, in which case the loudspeaker would become an open headphone that is not sealed to the ear.

Prediction of Fan Tone Radiation Scattered By A Cylindrical Fuselage

A theoretical prediction method of the scattering of fan tone radiation from a turbofan inlet duct by the airframe fuselage is presented. The fan tone noise is modelled by an acoustic disc source that represents the sound field at the inlet duct termination. Adjacent to the source is a cylindrical fuselage that scatters the fan tone radiation. The prediction method is valid for upstream sound radiation. The acoustic pressure on the cylindrical fuselage is affected by refraction of the sound as it propagates through the fuselage boundary layer. This effect known as boundary layer shielding is more prominent forward of the turbofan, since the fan tone noise radiated from the inlet duct is propagating upstream. An asymptotic approach is used to model sound propagation through a boundary layer which is modelled by a thin linear shear velocity profile. Consequently the scattered pressure field can be computed very quickly, thus providing a fast and efficient prediction method. Although a realistic fuselage turbulent boundary layer does not resemble a linear shear layer, it is shown that the effect of acoustic shielding by a turbulent boundary layer can be modelled by taking a liner shear profile with a shape factor that matches the shape factor for a realistic turbulent profile.

Radiation Safety Considerations and Clinical Advantages of α-Emitting Therapy Radionuclides.

CE credit: For CE credit, you can access the test for this article, as well as additional JNMT CE tests, online at https://www.snmmilearningcenter.org Complete the test online no later than March 2025. Your online test will be scored immediately. You may make 3 attempts to pass the test and must answer 75% of the questions correctly to receive Continuing Education Hour (CEH) credit. Credit amounts can be found in the SNMMI Learning Center Activity. SNMMI members will have their CEH credit added to their VOICE transcript automatically; nonmembers will be able to print out a CE certificate upon successfully completing the test. The online test is free to SNMMI members; nonmembers must pay $15.00 by credit card when logging onto the website to take the test.α-emitting radionuclides provide an effective means of delivering large radiation doses to targeted treatment locations. 223RaCl2 is Food and Drug Administration-approved for treatment of metastatic castration-resistant prostate cancer, and 225Ac (225Ac-lintuzumab) radiolabeled antibodies have been shown to be beneficial for patients with acute myeloid leukemia. In recent years, there has been increasing use of α-emitters in theranostic agents with both small- and large-molecule constructs. The proper precautionary means for their use and surveying documentation of these isotopes in a clinical setting are an essential accompaniment to these treatments. Methods: Patient treatment data collected over a 3-y period, as well as regulatory requirements and safety practices, are described. Commonly used radiation instruments were evaluated for their ability to identify potential radioactive material spills and contamination events during a clinical administration of 225Ac. These instruments were placed at 0.32 cm from a 1.0-cm 225Ac disk source for measurement purposes. Radiation background values, efficiencies, and minimal detectable activities were measured and calculated for each type of detector. Results: The median external measured dose rate from 223RaCl2 patients (n = 611) was 2.5 μSv h-1 on contact and 0.2 μSv h-1 at 1 m immediately after administration. Similarly, 225Ac-lintuzumab (n = 19) patients had median external dose rates of 2.0 μSv h-1 on contact and 0.3 μSv h-1 at 1 m. For the measurement of 225Ac samples, a liquid scintillation counter was found to have the highest overall efficiency (97%), whereas a ZnS α-probe offered the lowest minimal detectable activity at 3 counts per minute. Conclusion: In this article, we report data from 630 patients who were undergoing treatment with the α-emitting isotopes 223Ra and 225Ac. Although α-emitters have the ability to deliver a higher internal radiation dose to the exposed tissues than can other unsealed radionuclides, they typically present minimal concerns about external dose rate. Additionally, α-radiation can be efficiently detected with appropriate radiation instrumentation, such as a liquid scintillation counter or ZnS probe, which should be prioritized when surveying for spills of α-emitters.