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Results for “IRON 61”

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DOE OSTI2010

Large-scale shell-model calculations for even-odd {sup 61-65}Fe isotopes

Large-scale shell-model calculations have been performed to calculate the negative-parity states of even-odd {sup 61-65}Fe isotopes. The results are compared with the recent experimental data reported at Legnaro National Laboratories and also with earlier calculations with fpg interaction in a truncated configuration space. It is observed that negative parity states of {sup 61}Fe can be well reproduced with GXPF1A interaction in full fp space without truncation. For {sup 63}Fe the correct ordering of levels is not reproduced. The structure of the wave function for the ground state and first excited state suggests that the ordering of the single-particle energy levels gets modified due to monopole correction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2015

Nuclear Data Sheets for A = 61

The evaluated spectroscopic data are presented for known nuclides of mass 61 (Sc,Ti,V,Cr,Mn,Fe,Co,Ni, Cu,Zn,Ga,Ge). Excited-state data are nonexistent for {sup 61}Sc, {sup 61}Ti, {sup 61}V, and {sup 61}Ge. Significant amounts of new data have been added since the previous NDS evaluation of A=61 nuclides (1999Bh04). {sup 61}Sc nuclide is now experimentally known, but without any knowledge of its half-life. The ground state half-lives of {sup 61}Ti and {sup 61}V are now determined. Excited-state data have become available for {sup 61}Cr, {sup 61}Mn and {sup 61}Ga, while for {sup 61}Ge, five excited states were erroneously assigned in the previous evaluation, these have been omitted here. Improved and extensive high-spin excitations are available for {sup 61}Fe, {sup 61}Cu and {sup 61}Zn, including several new superdeformed structures in {sup 61}Cu and {sup 61}Zn. Thermal neutron capture γ-ray data are available in detail from 2004Ra23. The radioactive decay schemes of {sup 61}Sc and {sup 61}Ti are not known, while those for {sup 61}V, {sup 61}Fe and {sup 61}Ge are poorly known. This work benefited from the earlier full evaluations of A=61 published by 1999Bh04, 1983Ek01 and 1975Au05 and the one published in an ‘update’ mode by 1992Zh31. The data and conclusions presented in the current work supersede those in all the previous evaluations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2018

Influence of pH on the balance between methanogenesis and iron reduction

Methanogenesis and iron reduction play major roles in determining global fluxes of greenhouse gases. Despite their importance, environmental factors that influence their interactions are poorly known. Here, we present evidence that pH significantly influences the balance between each reaction in anoxic environments that contain ferric (oxyhydr)oxide minerals. In sediment bioreactors that contained goethite as a source of ferric iron, both iron reduction and methanogenesis occurred but the balance between them varied significantly with pH. Compared to bioreactors receiving acidic media (pH 6), electron donor oxidation was 85% lower for iron reduction and 61% higher for methanogenesis in bioreactors receiving alkaline media (pH 7.5). Thus, methanogenesis displaced iron reduction considerably at alkaline pH. Geochemistry data collected from U.S. aquifers demonstrate that a similar pattern also exists on a broad spatial scale in natural settings. In contrast, in bioreactors that were not augmented with goethite, clay minerals served as the source of ferric iron and the balance between each reaction did not vary significantly with pH. We therefore conclude that pH can regulate the relative contributions of microbial iron reduction and methanogenesis to carbon fluxes from terrestrial environments. We further propose that the availability of ferric (oxyhydr)oxide minerals influences the extent to which the balance between each reaction is sensitive to pH. Here, the results of this study advance our understanding of environmental controls on microbial methane generation and provide a basis for using pH and the occurrence of ferric minerals to refine predictions of greenhouse gas fluxes.

58 GEOSCIENCES↗

DOE OSTI2017

Adsorptive recovery of neodymium and dysprosium in phosphorous functionalized nanoporous carbon

Here, phosphorus functionalized nanoporous carbon was synthesized from lignin by periodical reactions with potassium hydroxide and triphenylphosphine. It has the BET surface area of 837 m 2 /g and total pore volume 0.41 cm 3 /g along with 0.9 atom% phosphorus. The adsorption of neodymium (Nd (III)) and dysprosium (Dy(III)) were in the range of 335–344 mg/g upto their initial concentration of 500 ppm in water and such adsorption amount is higher than that of majority of the adsorbents reported in literature. The adsorption capacity showed negligible dependency on the solution pH. The distribution coefficients for Nd(III) and Dy(III) were within 1000 to 10,000 mL/g. The adsorption capacity of iron (Fe(III)) under the similar conditions was one order of magnitude lower and it suggests a possible separation of these rare earth elements from iron. The maximum selectivity of separation of Nd(III) and Dy(III) from iron was ca. 32 to 61. Kinetic study revealed that the adsorption of Dy was faster than that of Nd(III). The results of kinetic study were better fit with pseudosecond order kinetics. XPS studies on both Nd(III) and Dy(III)-adsorbed carbons revealed a small shift in the P 2p 3/2 energy level of phosphorus towards higher energy level hereby suggesting a possible formation of metallic phosphates. Additionally, Similar studies on Nd(III) and Dy(III)-adsorbed carbon indicated small amounts carbonates and oxides of rare earth elements that might have also been formed. In conculsion, the overall results suggest that this carbon can be used as a potential sorbent for enrichment and separation of Nd(III) and Dy(III).

36 MATERIALS SCIENCE↗

DOE OSTI2013

Insights into the Structure and Metabolic Function of Microbes That Shape Pelagic Iron-Rich Aggregates ( Iron Snow )

Metaproteomics combined with total nucleic acid-based methods aided in deciphering the roles of microorganisms in the formation and transformation of iron-rich macroscopic aggregates (iron snow) formed in the redoxcline of an acidic lignite mine lake. Iron snow had high total bacterial 16S rRNA gene copies, with 2 x 109 copies g (dry wt)-1 in the acidic (pH 3.5) central lake basin and 4 x 1010 copies g (dry wt)-1 in the less acidic (pH 5.5) northern lake basin. Active microbial communities in the central basin were dominated by Alphaproteobacteria (36.6%) and Actinobacteria (21.4%), and by Betaproteobacteria (36.2%) in the northern basin. Microbial Fe-cycling appeared to be the dominant metabolism in the schwertmannite-rich iron snow, because cloning and qPCR assigned up to 61% of active bacteria as Fe-cycling bacteria (FeB). Metaproteomics revealed 70 unique proteins from central basin iron snow and 283 unique proteins from 43 genera from northern basin. Protein identification provided a glimpse into in situ processes, such as primary production, motility, metabolism of acidophilic FeB, and survival strategies of neutrophilic FeB. Expression of carboxysome shell proteins and RubisCO indicated active CO2 fixation by Fe(II) oxidizers. Flagellar proteins from heterotrophs indicated their activity to reach and attach surfaces. Gas vesicle proteins related to CO2-fixing Chlorobium suggested that microbes could influence iron snow sinking. We suggest that iron snow formed by autotrophs in the redoxcline acts as a microbial parachute, since it is colonized by motile heterotrophs during sinking which start to dissolve schwertmannite.

acidic/ iron cycling / iron snow / metaproteomics/↗

DOE OSTI2018

Uncertainties in secondary angular distributions and their impact on shielding, criticality and kinetics analysis - 25556

The availability of the covariance data improved over the last decades. Use of covariance matrices of different origin (such as JEFF, JENDL, ENDF, TENDL, SCALE, etc.) and types (files MF31, MF33, MF34, MF35) in sensitivity and uncertainty analysis of vast list of cases ranging from fission to fusion and from criticality, kinetics and shielding to adjustment applications was already studied in the past. The present work focuses on the status and the availability of the covariance of the angular distributions of scattered neutrons (secondary angular distributions - SAD covariances). SAD uncertainties are usually neglected in classical uncertainty propagation codes, even though the methods and codes for calculating the sensitivities are available for decades and excellent agreement was demonstrated between different deterministic and Monte Carlo codes. Of particular concern is still the availability, quality and completeness of covariance matrices. Indeed, in most evaluations the SAD covariances are limited to P1 term, if available at all. Furthermore, some differences were observed between different evaluations, e.g. in the case of iron. (author)

61 RADIATION PROTECTION AND DOSIMETRY↗

DOE OSTI2016

A new insight into neutrino energy loss by electron capture of iron group nuclei in magnetar surfaces

Based on the relativistic mean-field effective interactions theory, and the Lai dong model, we discuss the influences of superstrong magnetic fields (SMFs) on electron Fermi energy, nuclear blinding energy, and single-particle level structure in magnetar surfaces. Using the Shell-Model Monte Carlo method and the Random Phase Approximation theory, we analyze the neutrino energy loss rates (NELRs) by electron capture for iron group nuclei in SMFs. First, when B {sub 12} < 100, we find that the SMFs have a slight influence on the NELRs for most nuclides at relativistic low temperatures (e.g., T {sub 9} = 0.233); nevertheless, the NELRs increase by more than four orders of magnitude at relativistic high temperatures (e.g., T {sub 9} = 15.53). When B {sub 12} > 100, the NELRs decrease by more than three orders of magnitude (e.g., at T {sub 9} = 15.53 for {sup 52–61}Fe, {sup 55–60}Co, and {sup 56–63}Ni). Second, for a certain value of magnetic field and temperature, the NELRs increase by more than four orders of magnitude when ρ{sub 7}⩽10{sup 3}, but as the density increases (i.e., when ρ{sub 7}>10{sup 3}), there is almost no influence on the density of NELRs. For the density around ρ{sub 7}=10{sup 2}, there is an abrupt increase in NELRs when B {sub 12} ≥ 10{sup 3.5}. Such jumps are an indication that the underlying shell structure has changed due to single-particle behavior by SMFs. Finally, we compare our NELRs with those of Fuller et al. (FFN) and Nabi and Klapdor-Kleingrothaus (NKK). For the case without SMFs, one finds that our rates for certain nuclei are close to about five orders of magnitude lower than FFN and NKK at relativistic low temperatures (e.g., T {sub 9} = 1). However, at a relativistic high temperature (e.g., T {sub 9} = 3), our results are in good agreement with NKK, but about one order of magnitude lower than FFN. For the case with SMFs, our NELRs for some iron group nuclei can be about five orders of magnitude higher than those of FFN and NKK. (Note that B {sub 12}, T {sub 9}, and ρ {sub 7} are in units of 10{sup 12} G, 10{sup 9} K, and 10{sup 7} g cm{sup −3}, respectively.)

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

THE ELUSIVE {sup 60}Fe IN THE SOLAR NEBULA

No {sup 60}Ni or {sup 61}Ni anomalies have been detected in troilite inclusions from Muonionalusta, a 4565.3 {+-} 0.1 Ma old IVA iron meteorite, to the level of the analytical precision of 10 ppm. Because Muonionalusta troilite is very old, has a high Fe/Ni ratio, and is free of {sup 61}Ni anomalies, it is the ideal material in which to search for potential excesses of {sup 60}Ni produced by the decay of {sup 60}Fe (t{sub 1/2} = 2.62 Ma). The {sup 60}Ni/{sup 58}Ni and Fe/Ni ratios (up to 1680) measured here imply an upper limit for the initial {sup 60}Fe/{sup 56}Fe for the Muonionalusta troilite of 3 Multiplication-Sign 10{sup -9}. Assuming that {sup 60}Fe was homogeneously distributed across the nebula, this result suggests that the solar system initial {sup 60}Fe/{sup 56}Fe ratio was less than 5 Multiplication-Sign 10{sup -9}, which is lower than previously measured by at least a factor of 50.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2010

Influence of the vg{sub 9/2} orbital on level structures of neutron-rich {sup 61,62} Mn{sub 36,37}.

Level structures in {sup 61,62}Mn{sub 36,37} were studied with Gammasphere in the reaction of a 430-MeV {sup 64}Ni beam and a thick {sup 238}U target. The newly identified levels decrease in excitation energy compared to the analogous structures in the lighter Mn isotopes and behave similarly to states in the corresponding Fe isotones that involve g{sub 9/2} neutron excitations. This behavior illustrates the importance of the inclusion of the ?g{sub 9/2} orbital in any realistic shell-model calculations in this region.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Annotation of DOM metabolomes with an ultrahigh resolution mass spectrometry molecular formula library

Current approaches to analyzing metabolomic data often rely on matching MS/MS fragmentation data to sparse libraries or databases. This approach results in limited identification of features, often with less than 10% of the dataset being annotated. A complementary approach is to assign molecular formula to features based on accurate mass measurements, but the platforms commonly used for metabolomics do not have the needed accuracy or resolving power to do this robustly, particularly for larger molecules. Using our newly modified analysis tool, CoreMS, we generated a library of molecular formula from pooled samples analyzed with LC-21T FT-ICR MS. This library successfully annotated approximately 53.2% of features identified from the exometabolome of marine diatom Phaeodactylum tricornutum – a nearly ten-fold increase over the 5.9% annotation rate achieved using a conventional MS/MS library matching approach. Using this FT-ICR MS library approach, we were able to differentiate differences in the exometabolome of P. tricornutum in iron replete and iron limited conditions, with 668 metabolites being differentially expressed (p < 0.05, 2 x intensity difference) under these conditions. The traditional MS/MS fragmentation-based annotation approach only annotated 61 of these metabolites, while our novel pipeline annotated 450 metabolites and revealed 12 metabolites that were significantly more abundant under low iron conditions. Our results demonstrate the utility of ultrahigh resolution mass spectrometry for generating more comprehensive and confident molecular annotations.

21T-FTICR-MS, CoreMS↗

DOE OSTI2016

TH-CD-BRA-08: Novel Iron-Based Radiation Reporting Systems as 4D Dosimeters for MR-Guided Radiation Therapy

Purpose: To compare novel radiation reporting systems utilizing ferric ion (Fe{sup 3+}) reduction versus ferrous ion (Fe{sup 2+}) oxidation in gelatin matrixes for 3D and 4D (3D+time) MR-guided radiation therapy dosimetry. Methods: Dosimeters were irradiated using an integrated 1.5T MRI and 7MV linear accelerator (MR-Linac). Dosimeters were read-out with both a spectrophotometer and the MRI component of the MR-Linac immediately after irradiation. Changes in optical density (OD) were measured using a spectrophotometer; changes in MR signal intensity due to the paramagnetic differences in the iron ions were measured using the MR-Linac in real-time during irradiation (balanced-FFE sequences) and immediately after irradiation (T{sub 1}-weighted and inversion recovery sequences). Results: Irradiation of Fe{sup 3+} reduction dosimeters resulted in a stable red color with an absorbance peak at 512 nm. The change in OD relative to dose exhibited a linear response up to 100 Gy (R{sup 2}=1.00). T{sub 1}-weighted-MR signal intensity (SI) changed minimally after irradiation with increases of 8.0% for 17 Gy and 9.7% after escalation to 35 Gy compared to the un-irradiated region. Irradiation of Fe{sup 2+} oxidation dosimeters resulted in a stable purple color with absorbance peaks at 440 and 585 nm. The changes in OD, T{sub 1}-weighted-MR SI, and R{sub 1} relative to dose exhibited a linear response up to at least 8 Gy (R{sup 2}=1.00, 0.98, and 0.99) with OD saturation above 40 Gy. The T{sub 1}-weighted-MR SI increased 50.3% for 17 Gy compared to the un-irradiated region. The change in SI was observed in both 2D+time and 4D (3D+time) acquisitions post-irradiation and in real-time during irradiation with a linear increase with respect to dose (R{sup 2}>0.93). Conclusion: The Fe{sup 2+} oxidation-based system was superior as 4D dosimeters for MR-guided radiation therapy due to its higher sensitivity in both optical and MR signal readout and feasibility for real-time 4D dose readout. The Fe{sup 3+} reduction system is recommended for high dose applications. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. LH-102SPS.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2016

SU-F-T-671: Effects of Collimator Material On Proton Minibeams

Purpose: To investigate the dosimetric effects of collimator material on spatially modulated proton minibeams (pMBRT). Methods: pMBRT holds promise to exhibit shallow depth normal-tissue sparing effects similar to synchrotron based microbeams while also retaining potential for uniform dose distributions for tumor targets. TOPAS Monte Carlo simulations were performed for a 5cm thick multislit collimator with 0.3mm slits and 1mm center-to-center spacing for a 50.5MeV proton minibeam while varying collimator material between brass, tungsten, and iron. The collimator was placed both “flush” at the water phantom surface and at 5cm distance to investigate the effects on surface dose, peak-to-valley-dose-ratio (PVDR) and neutron contribution. Results: For flush placement, the neutron dose at the phantom surface for the tungsten collimator was approximately 20% higher than for brass and iron. This was not reflected in the overall surface dose, which was comparable for all materials due to the relatively low neutron contribution of <0.1%. When the collimator was retracted, the overall neutron contribution was essentially identical for all three collimators. Surface dose dropped by ∼40% for all collimator materials with air gap compared to being flush with the phantom surface. This surface dose reduction was at the cost of increase in valley dose for all collimator materials due to increased angular divergence of the mini-beams at the surface and their consequent geometric penumbra at depth. When the collimator was placed at distance from the phantom surface the PVDR decreased. The peak-to-entrance-dose ratio was highest for the iron collimator with 5cm air gap. Conclusion: The dosimetric difference between the collimator materials is minimal despite the relatively higher neutron contribution at the phantom surface for the tungsten collimator when placed flush. The air gap between the collimator and phantom surface strongly influences all dosimetry parameters due to the influence of scatter on the narrow spatial modulation.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2017

Iron and nickel isotope compositions of presolar silicon carbide grains from supernovae

Here we report the carbon, silicon, iron, and nickel isotope compositions of twenty-five presolar SiC grains of mostly supernova (SN) origin. The iron and nickel isotope compositions were measured with the new Chicago Instrument for Laser Ionization, CHILI, which allows the analysis of all iron and nickel isotopes without the isobaric interferences that plagued previous measurements with the NanoSIMS. Despite terrestrial iron and nickel contamination, significant isotopic anomalies in 54 Fe/ 56 Fe, 57 Fe/ 56 Fe, 60 Ni/ 58 Ni, 61 Ni/ 58 Ni, 62 Ni/ 58 Ni, and 64 Ni/ 58 Ni were detected in nine SN grains (of type X). Combined multi-isotope data of three grains with the largest nickel isotope anomalies (>100% or <-100% in at least one isotope ratio, when expressed as deviation from the solar value) are compared with the predictions of two SN models, one with and one without hydrogen ingestion in the He shell prior to SN explosion. One grain's carbon-silicon-iron-nickel isotope composition is consistent with the prediction of the model without hydrogen ingestion, whereas the other two grains' isotope anomalies could not be reproduced using either SN models. The discrepancies between the measured isotope compositions and model predictions may indicate element fractionation in the SN ejecta prior to or during grain condensation, and reiterate the need for three-dimensional SN models.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Feasibility study for detection of fuel assemblies state inside sealed dry storage casks using external gamma flux measurements - 25445

The license for the storage of spent nuclear fuel assemblies in dry casks is limited to 40 years. In Germany, a site for a final repository of spent fuel is not yet available. Therefore, this license has to be renewed for prolonged storage period. Currently, there is no experience with dry cask storage worldwide that goes beyond a period of 40 years. Beside regulatory and security aspects, there are questions concerning the long-term integrity of the spent fuel assemblies as this is of relevance for final transportation and reloading to final waste repository casks. Once the cask is filled and sealed, the knowledge about the state of the fuel assemblies is limited. This study investigates the feasibility of using external gamma flux measurements to detect the state of the spent fuel assemblies inside the cask. Monte-Carlo simulations were performed to evaluate the gamma flux distribution outside the sidewall of a cask with all intact fuel assemblies and a cask with one damaged fuel assembly, mimicking a fuel assembly with expanded rods and fuel relocation. The evaluation was performed for different location of the damaged fuel assembly and different storage times. The results of the investigation showed that the intensity and the shape of the gamma flux outside the sidewall of the cask are sufficient to identify the damaged fuel assembly, in case it is located near the inner wall of the cask. The detection of the inner damaged fuel assemblies, however, is less feasible. Due to the self-shielding of the fuel assemblies, the gamma photons which come from the inner fuel assemblies stopped within the fuel basket and assemblies materials. The gamma photons which do survive the fuel assemblies self-shielding reach the inner cask wall with not enough energy to escape the shielding of the thick cast iron wall. In general, it can be concluded that the more the damaged fuel assembly is close to the cask inner walls and that the damage is in a large scale (i.e., significant fuel relocation), the more it can be detected by external gamma flux measurements. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2018

Activation in injection area of J-PARC 3-GeV rapid cycling synchrotron and its countermeasures - 25344

The 3-GeV rapid cycling synchrotron in Japan Proton Accelerator Research Complex aims to deliver a 1-MW proton beam to the neutron target and the main ring synchrotron. The existing beam power of the Rapid Cycling Synchrotron is up to 500 kW, and higher radiation doses are concentrated in the injection area. These activations are caused by the interaction between the foil and the beam. To reduce dose exposure to workers near the injection point, we study a new design of the injection scheme to secure sufficient space for radiation shielding and bellows. Experience has shown that eddy currents are generated in the metal flange near the magnet owing to the effect of the pulsed magnetic field used for injection, and the temperature exceeds 100 deg. C. The shield installed in the new injection system needs to have a layer structure, in which an insulator is inserted between iron shields to reduce the eddy current. From the results of the shielding calculation, even if 1 mm of polyethylene was inserted between two 9-mm-thick SUS 316 plates, which serve as shielding material, the shielding performance was reduced only about 5%, and we confirmed that it would function well. (authors)

43 PARTICLE ACCELERATORS↗

DOE OSTI2014

Measurement and Analysis of Dose Rate Distribution in the Seismic Base-Isolation pit of the Electron Linac Oncology Facility - Paper 87

Recently electric linac oncology facilities incorporating seismic base-isolation structure have become very popular in Japan to prevent strong impact to the equipment by the earthquakes. When the boundary of the controlled area is set below the base-isolated foundations, additional shielding of iron plate is needed and the cost for shielding sometimes increases up to $1 M Since no one usually accesses underneath the treatment room, except short maintenance period for base-isolation structure, it is reasonable to set the boundary around the downstairs room (pit) by fence. However, it is very difficult to estimate the dose rate of new boundary by using the simple shielding calculation method, because of rotating gantry head and effect of scattering radiation in the base-isolation floor. In this study detail calculations by using Monte-Carlo calculation code MCNP5 have been performed to find out the practical shielding design. To be more specific, investigation for the complicated behavior of photons in the 'pit' have been performed by the analysis, i.e. (1) How much can we reduce the thickness of additional iron plate?, (2) Which angle of the beam direction will influence the most to the dose rate at the new boundary?, (3) Which component of the radiation is dominant at the new boundary? We also verified the calculated results by the measurement. We have performed the analysis of the behavior of photons in the pit and found out no additional iron shielding was necessary, which carried out an extreme reduction of costs. The main contribution to the dose rate at the boundary was scattered photons in the case of 0- degree beam direction. Good agreement between calculated and measured results were obtained, and passed the examination by the authority. It is concluded that the Monte-Carlo calculation code MCNP5 is very effective for the optimistic design of the electron linac oncology facilities incorporating seismic base-isolation structure. (authors)

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

SU-F-T-361: Dose Enhancement Due to Nanoparticle Addition in Skin Radiotherapy: A Monte Carlo Study Using Kilovoltage Photon Beams

Purpose: This study investigated the dose enhancement due to addition of nanoparticles with different types and concentrations in skin radiotherapy using kilovoltage photon beams. Methods: An inhomogeneous water phantom (15×15×10 cm{sup 3}) having the skin target layer (0.5–5 mm), added with different concentrations (3–40 mg/ml) of nanoparticles (Au, Pt, I, Ag and Fe{sub 2}O{sub 3}), was irradiated by the 105 and 220 kVp photon beams produced by a Gulmay D3225 Orthovoltage unit. The circular cone of 5-cm diameter and source-to-surface distance of 20 cm were used. Doses in the skin target layer with and without adding the nanoparticles were calculated using Monte Carlo simulation (the EGSnrc code) through the macroscopic approach. Dose enhancement ratio (DER), defined as the ratio of dose at the target with nanoparticle addition to the dose without addition, was calculated for each type and concentration of nanoparticle in different target thickness. Results: For Au nanoparticle, DER dependence on target thickness for the 220 kVp photon beams was not significant. However, DER for Au nanoparticle was found decreasing with an increase of target thickness when the nanoparticle concentration was increased from 18 to 40 mg/ml using the 105 kVp photon beams. For nanoparticle concentration of 40 mg/ml, DER variation with target thickness was not significant for the 220 kVp photon beams, but DEF was found decreasing with the target thickness when lower energy of photon beam (105 kVp) was used. DEF was found increasing with an increase of nanoparticle concentration. The higher the DEF increasing rate, the higher the atomic number of the nanoparticle except I and Ag for the same target thickness. Conclusion: It is concluded that nanoparticle addition can result in dose enhancement in kilovoltage skin radiotherapy. Moreover, the DER is related to the photon beam energy, target thickness, atomic number and concentration of nanoparticles.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2011

POSSIBLE SIGNS OF WATER AND DIFFERENTIATION IN A ROCKY EXOPLANETARY BODY

Spitzer observations reveal the presence of warm debris from a tidally destroyed rocky and possibly icy planetary body orbiting the white dwarf GD 61. Ultraviolet and optical spectroscopy of the metal-contaminated stellar photosphere reveal traces of hydrogen, oxygen, magnesium, silicon, iron, and calcium. The nominal ratios of these elements indicate an excess of oxygen relative to that expected from rock-forming metal oxides, and thus it is possible that water was accreted together with the terrestrial-like debris. Iron is found to be deficient relative to magnesium and silicon, suggesting the material may have originated as the outer layers of a differentiated parent body, as is widely accepted for the Moon.

79 ASTRONOMY AND ASTROPHYSICS↗