Disk Source Research Articles

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.

Did the Event Horizon Telescope Detect the Base of the Submilliarsecond Tubular Jet in M87?

Abstract A high-sensitivity, 7 mm Very Long Baseline Array image of M 87 was previously analyzed in order to estimate the bulk flow jet velocity between 0.4 and 0.65 mas from the point of origin using the asymmetry between the well-characterized double-ridged counter-jet (unique to this image) and the double-ridged jet. We use this same image to estimate the cross-sectional area of this tubular stream. The velocity, acceleration, cross-sectional area, and flux density along this stream determine a unique, perfect magnetohydrodynamic jet solution that satisfies conservation of energy, angular momentum, and mass (a monotonic conversion of Poynting flux to kinetic energy flux along the jet). The solution is protonic and magnetically dominated. The bilateral jet transports ≈1.2 × 10−4 M ⊙ yr−1 and ≈1.1 × 1042 erg s−1, placing strong constraints on the central engine. A Keplerian disk source that also produces the Event Horizon Telescope (EHT) annulus of emission can supply the energy and mass if the vertical magnetic field at the equator is ∼1–3.5 G (depending on location). A Parker spiral magnetic field, characteristic of a wind or jet, is consistent with the observed EHT polarization pattern. Even though there is no image of the jet connecting with the annulus, it is argued that these circumstances are not coincidental and the polarized portion of the EHT emission is mainly jet emission in the top layers of the disk that is diluted by emission from an underlying turbulent disk. This is a contributing factor to the relatively low polarization levels that were detected.

The JCMT Transient Survey: Four-year Summary of Monitoring the Submillimeter Variability of Protostars

Abstract We present the four-year survey results of monthly submillimeter monitoring of eight nearby (<500 pc) star-forming regions by the JCMT Transient Survey. We apply the Lomb–Scargle Periodogram technique to search for and characterize variability on 295 submillimeter peaks brighter than 0.14 Jy beam−1, including 22 disk sources (Class II), 83 protostars (Class 0/I), and 190 starless sources. We uncover 18 secular variables, all of them protostars. No single-epoch burst or drop events and no inherently stochastic sources are observed. We classify the secular variables by their timescales into three groups: Periodic, Curved, and Linear. For the Curved and Periodic cases, the detectable fractional amplitude, with respect to mean peak brightness, is ∼4% for sources brighter than ∼0.5 Jy beam−1. Limiting our sample to only these bright sources, the observed variable fraction is 37% (16 out of 43). Considering source evolution, we find a similar fraction of bright variables for both Class 0 and Class I. Using an empirically motivated conversion from submillimeter variability to variation in mass accretion rate, six sources (7% of our full sample) are predicted to have years-long accretion events during which the excess mass accreted reaches more than 40% above the total quiescently accreted mass: two previously known eruptive Class I sources, V1647 Ori and EC 53 (V371 Ser), and four Class 0 sources, HOPS 356, HOPS 373, HOPS 383, and West 40. Considering the full protostellar ensemble, the importance of episodic accretion on few years timescale is negligible—only a few percent of the assembled mass. However, given that this accretion is dominated by events on the order of the observing time window, it remains uncertain as to whether the importance of episodic events will continue to rise with decades-long monitoring.

Laser welding of current collector foil stacks in battery production\u2013mechanical properties of joints welded with a green high-power disk laser

The qualification of production systems that enable reliable and stable production processes is a major challenge in manufacturing large-format lithium-ion batteries. During cell assembly, the electrode sheets of the anode and the cathode are stacked, and are electrically contacted by a welding process. It was shown that laser beam welding employing a beam source in the green wavelength range is a promising joining approach in terms of high productivity. Therefore, the influence of the process parameters, such as the laser power, the welding speed, the pulse frequency, and the pulse duration, on the weld seam quality was investigated. Particular emphasis was placed on the mechanical strength of the weld seam. Statistically planned experiments were used to determine feasible parameter sets for welding the most common current collectors of lithium-ion battery electrodes, copper (Cu), and aluminum (Al). The influence of the individual process parameters on the tensile shear force was evaluated. Stacks of 40 metal foils were welded with a thin metal sheet in lap joint configuration. Based on an analysis of the requirements for minimum mechanical seam strengths, this study confirms that laser beam welding using a green high-power disk source is an auspicious process for the internal contacting of lithium-ion batteries.

Evaluation of BenzoDODA grafted polymeric resin for rapid and reliable assaying of plutonium in sediment samples

The paper reports a new rapid radioanalytical procedure for the determination of plutonium (Pu) in sediments by solid phase extraction chromatography (SPEC) using Bis-(2-ethylhexyl) carbamoyl methoxy phenoxy-bis-(2-ethylhexyl) grafted resin, abbreviated as Benzodioxodiamide (BenzoDODA) grafted resin. The resin was synthesized and evaluated for its sorption behaviour towards Pu in batch and column mode to determine its efficacy for selective recovery of Pu from sediment samples. The analytical procedure was based on the radiochemical separation of samples by acid digestion, followed by preconcentration of actinides by co-precipitation with Fe(OH)3 and finally selective recovery of Pu by SPEC using a column filled with BenzoDODA grafted resin. Pu was then radiometrically assayed by preparing alpha disc sources with electro-deposition followed by alpha spectrometry. The method was further validated with IAEA reference materials. This method gives reliable and reproducible results for the activity concentration of Pu in sediment samples within 24 h.

3DGShield: A new 3D gamma ray shielding code for arbitrary source and shield geometry based on point kernel technique

3DGShield, A new 3D gamma ray shielding code, based on the method of point kernel technique, has been developed for arbitrary regular & irregular shaped source and shield geometries. The 3D geometry modeling and its mesh generation are performed using Gmsh, a free open source finite element mesh generation software. The output of the Gmsh software is in Gmsh MSH (.msh) file format which will be used as an input of geometry description of our code. The salient features of 3DGShield are (i) ability to handle any type of complex source geometries including regular source shapes like point, line, disc, box, cylinder, sphere, hexagonal cylinder, cone etc. and irregular source shapes like pieces of broken glass, piece of brick etc., (ii) handling discrete as well as distributed photon energy sources, (iii) modeling any kind of regular and irregular complex multilayered shield geometries, (iv) having provision to export the output results into ParaView, an open source data analysis and visualization software, for quick visualization and analyzing of the results. Buildup factor is the correction factor which takes account the contribution of scattered photon. Various appropriate multilayer build-up factor formulas have been incorporated in our code. Out of these, the most popular methods are Blizard's method, Goldstein method of an effective atomic number and Broders's method. Verification and validation of the code have been done by a number of benchmark problems available in literature. The results are presented in this paper which demonstrate the accuracy and efficiency of the code in complex geometries. This code is written in Python-2.7 language and compatible both in Windows and Linux operating system.

Application of a hybrid method for efficiency calibration of a NaI detector

A previously proposed hybrid analytical–numerical method for efficiency calibration of a NaI detector for a point γ-source is extended and applied for other shapes of sources. The shapes include line, disk, and cylindrical sources of various dimensions and locations with respect to the right circular cylindrical NaI detector. The results obtained by this method have been evaluated through comparison with Monte Carlo (MC) calculations. A relative maximum difference of 3.5% is found between the two methods.

Infiltration models and soil characterisation for hemispherical and disc sources based on Green-Ampt assumptions

In the present paper a set of physically based expressions for estimating the infiltrated volume and the flow rate from hemispherical and disc sources are presented. The proposed formula depends on four parameters: the initial and the saturated soil water contents, the saturated hydraulic conductivity and the wetting front suction head. The developed models allow the accurate estimation of the infiltrated flow when compared with the same phenomena simulated with Richardś equation. Dimensionless expressions were also deduced which help draw general conclusions on the infiltration processes. Taking advantage of the small number of parameters included in the developed expressions, it was proposed a simple procedure for soils characterization. The method requires measuring both the initial and saturated soil water content and the infiltrated volume over time from a disc source and, aided with the developed expressions, allows deducing both the saturated hydraulic conductivity and the wetting front suction head.

NEUTRON DEPTH PROFILE CALCULATIONS USING ARTIFICIAL NEURAL NETWORKS

Neutron depth profiling (NDP) is a non-destructive technique used for identifying the concentration of impurity isotopes below the sample surface. NDP is carried out by detection of the emitted charged particles resulting from bombarding the sample with neutrons. NDP specifies the isotopic concentration versus the sample depth for a few micrometers below the surface. The sample is bombarded inside a research reactor using a thermal neutron beam. Charged particles like alpha particles or protons are produced from the neutron induced reactions in the sample. Each neutron isotopic interaction produces a certain Q, indicating a specific kinetic energy for the emitted charged particle. As the charged particle travels through the sample to eject the surface, it loses energy to atoms (electrons) on its path. The charged particle energy loss holds information regarding the number of atoms by which the emitted particle passed, thus indicating its original depth. The purpose of this work is to check the capability of Artificial Neural Networks (ANNs) in predicting the boron concentration profile across a boro-silicate sample of thickness 3.5 μm divided into 10 layers. Each layer included different boron concentration than the other. Also, the boron concentration had the values {0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1}. Training, validation, and test data were generated synthetically using MCNP6 in which the boron concentrations varied in the layer number from one sample to another. MCNP6 model consisted of a silicon barrier detector, boro-silicate sample, chamber body and an idealized thermal neutron source. The detector, sample, and the source were located in a voided chamber. The samples were irradiated with a 0.025 eV monoenergetic thermal neutron beam from a monodirectional disk source. To cover the whole area of the samples, the thermal neutron beam had a radius of 3 cm. The silicon detector active volume was modelled as a 100 μm thick and 3 cm radius facing the sample directly. The sample, beam, and the detector were placed on the same axis. Ten ANN regression models were developed, one for each layer boron concentration prediction where the input for each model was the alpha spectrum read by the detector, while the output was the boron concentration for each layer. Results showed regression values higher than 0.94 for all of the developed models. ANNs proved its capability of predicting the boron profile form the alpha spectrum read by the detector regarding neutron depth profiling in a boro-silicate samples.

On the origin & thermal stability of Arrokoth's and Pluto's ices

In this paper we discuss in a thermodynamic, geologically empirical way the long-term nature of the stable majority ices that could be present in Kuiper Belt object (KBO) 2014 MU69 (also called Arrokoth; hereafter “MU69”) after its 4.6 Gyr residence in the Edgeworth-Kuiper belt (EKB) as a cold classical object. We compare the upper bounds for the gas production rate (~1024 molecules/s) measured by the New Horizons (NH) spacecraft flyby on 01 Jan 2019 to estimates for the outgassing flux rates from a suite of common cometary and KBO ices at the average ~ 40 K sunlit surface temperature of MU69, but do not find the upper limit very constraining except for the most volatile of species (e.g. CO, N2, CH4). More constraining is the stability versus sublimation into vacuum requirement over Myr to Gyr, and from this we find only 3 common ices that are truly refractory: HCN, CH3OH, and H2O (in order of increasing stability), while NH3 and H2CO ices are marginally stable and may be removed by any positive temperature excursions in the EKB, as produced every 108–109 years by nearby supernovae and passing O/B stars. To date the NH team has reported the presence of abundant CH3OH and H2O on MU69's surface (Stern et al., 2019; Grundy et al., 2020). NH3 has been searched for, but not found. We predict that future absorption feature detections, if any are ever derived from higher signal-to-noise ratio spectra, will be due to an HCN or poly-H2CO based species. Consideration of the conditions present in the EKB region during the formation era of MU69 lead us to state that it is highly likely that it “formed in the dark”, in an optically thick mid-plane, unable to see the nascent, variable, highly luminous Young Stellar Object (YSO)/TTauri Sun, and that KBOs contain HCN and CH3OH ice phases in addition to the H2O ice phases found in their short period (SP) comet descendants. Finally, when we apply our ice thermal stability analysis to bodies/populations related to MU69, we find that methanol ice is likely ubiquitous in the outer solar system; that if Pluto isn't a fully differentiated body, then it must have gained its hypervolatile ices from proto-planetary disk (PPD) sources in the first few Myr of the solar system's existence; and that hypervolatile rich, highly primordial comet C/2016 R2 was placed onto an Oort Cloud orbit on a similar few Myr timescale.

A Detailed View of the Circumstellar Environment and Disk of the Forming O-star AFGL 4176

Abstract We present a detailed analysis of the disk and circumstellar environment of the forming O-type star AFGL 4176 mm1, placing results from the Atacama Large Millimeter/submillimeter Array (ALMA) into context with multiwavelength data. With ALMA, we detect seventeen 1.2 mm continuum sources within 5″ (21,000 au) of AFGL 4176 mm1. We find that mm1 has a spectral index of 3.4 ± 0.2 across the ALMA band, with >87% of its 1.2 mm continuum emission from dust. The source mm2, projected 4200 au from mm1, may be a companion or a blueshifted knot in a jet. We also explore the morphological differences between the molecular lines detected with ALMA, finding 203 lines from 25 molecules, which we categorize into several morphological types. Our results show that AFGL 4176 mm1 provides an example of a forming O-star with a large and chemically complex disk, which is mainly traced by nitrogen-bearing molecules. Lines that show strong emission on the blueshifted side of the disk are predominantly oxygen-bearing, which we suggest are tracing a disk accretion shock. The molecules C34S, H2CS, and CH3CCN trace a slow wide-angle wind or dense structures in the outflow cavity walls. With the Australia Telescope Compact Array (ATCA), we detect a compact continuum source (<2000 × 760 au) at 1.2 cm, associated with mm1, of which >96% is from ionized gas. The ATCA NH3(1, 1) and (2, 2) emission traces a large-scale (r ∼ 0.5 pc) rotating toroid with the disk source mm1 in the blueshifted part of this structure offset to the northwest.

Action spectroscopy of spin forbidden states in the gas phase: A powerful probe for large non-luminescent molecules.

Triplet action spectra of two similar copper porphyrins, copper tetraphenylporphyrin (CuTPP) and copper octaethylporphyrin (CuOEP), have been studied in the gas phase at low temperatures in the absence of external perturbations by using a resonant pump and a 193 nm probe, ionizing the 3ππ* orbital localized on the porphyrin cycle. The molecules were prepared by laser desorption in a disk source, then cooled in a helium supersonic expansion, and finally excited in the Q band system (S1 ← S0). This type of experiment allows the spectroscopic characterization of large non-luminescent molecules in the absence of solvent perturbations. The two copper porphyrins exhibit a broad electronic origin Q00 absorption spectrum, partly caused by the short lifetime of the excited (S1) state. The two porphyrins differ strongly with a strong Q00 band for CuOEP and a weak one for CuTPP, in agreement with the Gouterman four-orbital model. The two molecules exhibit different solvent shifts: CuOEP is blue shifted in non-polar solvents owing to its alkyl substituents, while CuTPP is red shifted as for regular transitions to ππ* orbitals. The decay dynamics of the triplet state exhibit a collision-free lifetime of 70 ± 7 ns for CuTPP atop a microsecond decay. This non-exponential decay can be viewed as evidence of time evolution of two states combining the state with spin 1 borne by the porphyrin ring and that by the Cu atom 12. Therefore, this method allows solvent-free spectrodynamics of large molecules in a short microsecond time range.

Preliminary study on the detection efficiency and estimation of minimum detectable activity for a NaI(Tl)-based seawater monitoring system

To monitor radioactivity levels in seawater Korea Institute of Nuclear Safety has installed and been operating 18 NaI(Tl)-based gamma detectors around the Korean peninsula. This study was conducted to estimate the detector efficiency and MDA of 137Cs in seawater for measurement situations. For this purpose, experiments in the air and a water tank, and Monte Carlo simulations were performed using a seawater radioactivity monitor system with 3 in. × 3 in. NaI(Tl) scintillation detector.In the geometry reliability assessment using certified reference materials in a disc source, the validity of simulations was obtained by comparing measurement and Monte Carlo simulation results. The FWHM of the seawater radioactivity monitor were obtained from the results of the water tank measurement for applying a Gaussian Energy Broadening (GEB) option to Monte Carlo N-Particle (MCNP) radiation transport code. In addition, the detection efficiency of 40K in the water tank was measured and compared with the Monte Carlo simulation results in order to estimate the MDA and the detection efficiency of the seawater radioactivity monitoring system. For the based condition of water tank, 40K concentration in water tank was controlled to 10.13±0.18 Bq/L, similar to that of real marine.In laboratory water tank experiments, the detection efficiency of the radioactivity monitor for 40K was measured at 0.184±0.005 cps/(Bq/L), the Monte Carlo simulations showed the similar result of 0.182±0.002 cps/(Bq/L), and the detection efficiency of 137Cs was estimated to be 0.224±0.009 cps/(Bq/L) from the simulations. For 3h measurement in the water tank based condition, the MDA of 137Cs was estimated to be 0.077±0.003 Bq/L. Future research will include detailed studies for detector sizes and seawater salinities.

Methanol and water maser observations separate disc and outflow sources in IRAS 19410+2336

ABSTRACT We investigate the kinematics of high-mass protostellar objects within the high-mass star-forming region IRAS 19410+2336. We performed high angular resolution observations of 6.7-GHz methanol and 22 GHz water masers using the Multi-Element Radio Linked Interferometer Network (MERLIN) and e-MERLIN interferometers. The 6.7-GHz methanol maser emission line was detected within the ∼16–27 km s−1 velocity range with a peak flux density ∼50 Jy. The maser spots are spread over ∼1.3 arcsec on the sky, corresponding to ∼2800 au at a distance of 2.16 kpc. These are the first astrometric measurements at 6.7 GHz in IRAS 19410+2336. The 22-GHz water maser line was imaged in 2005 and 2019 (the latter with good astrometry). Its velocities range from 13 to ∼29 km s−1. The peak flux density was found to be 18.7 and 13.487 Jy in 2005 and 2019, respectively. The distribution of the water maser components is up to 165 mas, ∼350 au at 2.16 kpc. We find that the Eastern methanol masers most probably trace outflows from the region of millimetre source mm1. The water masers to the West lie in a disc (flared or interacting with outflow/infall) around another more evolved millimetre source (13-s). The maser distribution suggests that the disc lies at an angle of 60° or more to the plane of the sky and the observed line-of-sight velocities then suggest an enclosed mass between 44 M⊙ and as little as 11 M⊙ if the disc is edge-on. The Western methanol masers may be infalling.

New mathematical approach to calculate the geometrical efficiency using different radioactive sources with gamma-ray cylindrical shape detectors

The geometrical efficiency of a source-to-detector configuration is considered to be necessary in the calculation of the full energy peak efficiency, especially for NaI(Tl) and HPGe gamma-ray spectroscopy detectors. The geometrical efficiency depends on the solid angle subtended by the radioactive sources and the detector surfaces. The present work is basically concerned to establish a new mathematical approach for calculating the solid angle and geometrical efficiency, based on conversion of the geometrical solid angle of a non-axial radioactive point source with respect to a circular surface of the detector to a new equivalent geometry. The equivalent geometry consists of an axial radioactive point source with respect to an arbitrary elliptical surface that lies between the radioactive point source and the circular surface of the detector. This expression was extended to include coaxial radioactive circular disk source. The results were compared with a number of published data to explain how significant this work is in the efficiency calibration procedure for the γ-ray detection systems, especially in case of using isotropic radiating γ-ray sources in the form of point and disk shapes.

Diagnostic accuracy of midkine on hepatocellular carcinoma: A meta-analysis.

To evaluate the dependability and accuracy of midkine (MK) in the diagnosis of hepatocellular carcinoma (HCC). PubMed, EMBASE, Web of Science, China Biology Medicine disc and grey literature sources were searched from the date of database inception to January 2019. Two authors (B-H.Z. and B.L.) independently extracted the data and evaluated the study quality using the Quality Assessment of Diagnostic Accuracy Studies-2 tool. The sensitivity, specificity, positive likelihood ratio (LR+) and negative likelihood ratio (LR-) were estimated using a bivariate model. Moreover, hierarchical summary receiver operating characteristic curves were generated. The diagnostic odds ratio (DOR) and area under the curve (AUC) were pooled using a univariate model. Nine articles (11 studies) were included (1941 participants). The bivariate analysis revealed that the sensitivity and specificity of MK for HCC diagnosis were 0.85 (95% CI 0.78-0.91) and 0.83 (95% CI 0.76-0.88), respectively. We also found a LR+ of 5.05 (95% CI 3.33-7.40), a LR- of 0.18 (95% CI 0.11-0.28), a DOR of 31.74 (95% CI 13.98-72.09) and an AUC of 0.91 (95% CI 0.84-0.99). Subgroup analyses showed that MK provided the best efficiency for HCC diagnosis when the cutoff value was greater than 0.5 ng/mL. MK has an excellent diagnostic value for hepatocellular carcinoma.

Coherence of radiation from incoherent sources: II. Ball and disk sources and coherence of sunlight.

Following the development of the companion paper [J. Opt. Soc. Am.36, 1433 (2019)JOAOD60740-323210.1364/JOSAA.36.00XXXX], additional models for the coherence of quasi-monochromatic light are constructed by placing incoherent monopole and dipole sources inside a spherical ball and on a circular plane disk. The paraxial approximation, which is valid for sunlight, reduces the number of different models from eight to three. Based on the solar images corresponding to these three models, the ball model is considered the most appropriate. The ball model can be modified to match the limb-darkening observations.

Identification of activation products and radiation dose estimates in Havar® foils for a GE PETtrace800 medical cyclotron via high resolution gamma ray spectroscopy and MCNPX simulation

During production of F-18 in a medical cyclotron, high energy protons and secondary neutrons hit the highly reactive components of the target assembly resulting to activation products. In determining the presence of activation products and quantifying their respective activities, high resolution gamma spectroscopy using high purity germanium (HPGe) was used. From the results of the spectroscopy analysis, the doses were estimated using two methods: calculation method and MCNPX simulations. For the gamma spectroscopy analysis, the sample was prepared using aqua regia and was sent to PNRI. The analysis was done using GEM Series HPGe Coaxial Detector System. The results of the gamma spectroscopy showed the presence of 56Co, 57Co, 58Co, and 54Mn after a cooling period of eighty (80) days. For the MCNP simulations, the Havar® window foil was simulated as an isotropic disc source and a soft - tissue mimicking box detector was used and positioned at 100 cm from the center of the simulated window foil. *F8 tally was used to estimate the effective dose arising from a single activation product homogeneously distributed in the window foil and was done under the assumption that no other radiation sources were present in the simulation. Using calculation method, the effective dose estimates of 56Co, 57Co, 58Co, and 54Mn were found to be of minimal values during replacement of 18O vial at one meter. Moreover, it was found out that the highest contributors of dose during replacement of an 18O vial and maintenance of cyclotron are 56Co and 58Co. After a period of one year, the guiding activation products become 57Co and 54Mn due to their long half - lives. Furthermore, the annual dose estimates of these activation products were found to not exceed the annual dose limits for the whole body and for the extremities. As for disposal and storage, a period of four years will allow the Havar® window foil to reach the exemption levels set by PNRI.

Disk sources of the Kerr and Tomimatsu-Sato spacetimes: Construction and physical properties

We construct the disk sources matched to the exact vacuum Kerr and to the two classes of Tomimatsu-Sato spacetimes. We analyze two models of the matter forming these disks. At each radius we consider either a rotating massive ring with pressure or two counter-rotating streams of particles in circular geodesic motion. Dragging effects present in such spacetimes lead either to rotation of rings or asymmetry of both streams. We demonstrate that the model of rotating rings is general enough to describe all axisymmetric stationary disk sources with vanishing radial pressure which satisfy weak energy condition, and that centrifugal effects present in the disk sources of spacetimes with large angular momentum prevent the construction of highly compact sources made of counter-rotating streams of geodesic particles. We illustrate the radial distribution of the mass inside the disks and the angular velocities of both geodesic streams.

Star Formation Rates of Massive Molecular Clouds in the Central Molecular Zone

Abstract We investigate star formation at very early evolutionary phases in five massive clouds in the inner 500 pc of the Galaxy, the Central Molecular Zone (CMZ). Using interferometer observations of H2O masers and ultra-compact H ii regions, we find evidence of ongoing star formation embedded in cores of 0.2 pc scales and ≳105 cm−3 densities. Among the five clouds, Sgr C possesses a high (9%) fraction of gas mass in gravitationally bound and/or protostellar cores, and follows the dense (≳104 cm−3) gas star formation relation that is extrapolated from nearby clouds. The other four clouds have less than 1% of their cloud masses in gravitationally bound and/or protostellar cores, and star formation rates 10 times lower than predicted by the dense gas star formation relation. At the spatial scale of these cores, the star formation efficiency is comparable to that in Galactic disk sources. We suggest that the overall inactive star formation in these CMZ clouds could be because there is much less gas confined in gravitationally bound cores, which may be a result of the strong turbulence in this region and/or the very early evolutionary stage of the clouds when collapse has only recently started.