Thick target preparation and isolation of 186Re from high current production via the 186W(d,2n)186Re reaction

Rhenium-186 has a half-life (t1/2 = 3.72 days) and emission of both gamma and beta particles that make it very attractive for use as a theranostic agent in targeted radionuclide therapy. 186Re can be readily prepared by the 185Re(n,γ)186Re reac-tion1. However, that reaction results in low specific activity, severely limiting the use of reactor produced 186Re in radiopharmaceuticals. It has previously been shown that high specific activity 186Re can be produced by cyclotron irradiations of 186W with protons and deuterons2,3. In this investigation we evaluated the 186W(d,2n)186Re reaction using thick target irradiations at higher incident deuteron energies and beam currents than previously reported. We elected not to use copper or aluminum foils in the preparation of our 186W targets due to their activation in the deuteron beam, so part of the investigation was an evaluation of an alternate method for preparing thick targets that withstand μA beam currents. Irradiation of 186W. Initial thick targets (~600-1100 mg) were prepared using 96.86% enriched 186W by hydraulic pressing (6.9 MPa) of tungsten metal powder into an aluminum target support. Those thick targets were irradiated for 10 minu-tes at 10 µA with nominal extracted deuteron energies of 15, 17, 20, 22, and 24 MeV. Isolation of 186Re. Irradiated targets were dissolved with H2O2 and basified with (NH4)2CO3 prior to separation using column(s) of ~100–300 mg Analig Tc-02 resin. Columns were washed with (NH4)2CO3 and the rhenium was eluted with ~80˚C H2O. Gamma-ray spectroscopy was per-formed to assess production yields, extraction yields, and radionuclidic byproducts. Recycling target material. When tested on a natural abundance W target, recovery of the oxidized WO4- target material from the resin was found to proceed rapidly with the addition of 4M HCl in the form of hydrated WO3. The excess water in the WO3 was then removed by calcination at 800 °C for 4 hours. This material was found to undergo reduction to metallic W at elevated temperatures (~1550 °C) in a tube furnace under an inert atmosphere (Ar). Quanti-fication of % reduction and composition analyses were accomplished with SEM, EDS, and XRD and were used to characterize and compare both the WO3 and reduced Wmetal products to a sample of commercially available material. Structural enhancement by surface annealing. In some experiments ~1 g WO3 pellets were prepared from Wmetal that had been chemically treated to simulate the target material recovery process described above. Following calcination, the WO3 was allowed to cool to ambient temperature, pulverized with a mortar and pestle and then uniaxially pressed at 13.8 MPa into 13 mm pellets. Conversion of the WO3 back to Wmetal in pellet form was accomplished in a tube furnace under flowing Ar at 1550 °C for 8 hours. Material characterization and product composition analyses were conducted with SEM, EDS, and XRD spectroscopy. Graphite-encased W targets. Irradiations were conducted at 20 μA with a nominal extracted deuteron energy of 17 MeV using thick targets (~750 mg) of natural abundance tungsten metal powder uniaxially pressed into an aluminum target support between layers of graphite pow-der (100 mg on top, 50 mg on the bottom). Targets were then dissolved as previously described and preliminary radiochemical isola-tion yields obtained by counting in a dose calibrator. Although irradiations of W targets were possible at 10 μA currents, difficulties were encountered in maintaining the structural integrity of the full-thickness pressed target pellets under higher beam currents. This led to further investigation of the target design for irradiations conducted at higher beam currents. Comprehensive target material characterization via analysis by SEM, EDS, XRD, and Raman Spectroscopy allowed for a complete redesign of the target maximizing the structural integrity of the pressed target pellet without impacting production or isolation. At the 10 A current, target mass loss following irradiation of an enriched 186W target was < 1 % and typical separation yields in excess of 70 % were observed. Saturated yields and percent of both 183Re (t½ = 70 days) and 184gRe (t½ = 35 days) relative to 186gRe (decay corrected to EOB) are reported in TABLE 1 below. The reason for the anomalously low yield at 24 MeV is unknown, but might be explained by poor beam alignment and/or rhenium volatility during irradiation. Under these irradiation conditions, recovery yields of the W target material from the recycling process were found to be in excess of 90% with no discernable differences noted when compared to commercially available Wmetal and WO3. Conceptually, increasing the structural integrity of pressed WO3 targets by high temperature heat treatment under an inert atmosphere is intriguing. However, the treated pellets lacked both density and structural stability resulting in disintegration upon manipulation , despite the initially encouraging energy dispersive X-ray spectroscopy (EDS) determination that 94.9% percent of the WO3 material in each pellet had been reduced to metallic W. The use of powdered graphite as a target stabi-lizing agent provided successful irradiation of natural abundance W under conditions where non-stabilized targets failed (20 µA at 17 MeV for 10 minutes). Target mass loss following irradiation of a natW target was < 1 % and a separation yield in excess of 97 % was obtained. In conclusion, the theranostic radionuclide 186Re was produced in thick targets via the 186W(d,2n) reaction. It was found that pressed W metal could be used for beam currents of 10 μA or less. For deuteron irradiations at higher beam currents, a method involving pressing W metal between two layers of graphite provides increased target stability. Both target configurations allow high recovery of radioactivity from the W target material, and a solid phase extraction method allows good recovery of 186Re. An effective approach to the recycling of enriched W has been developed using elevated temperature under an inert atmosphere. Further studies are underway with 186W targets sandwiched by graphite to assess 186Re production yields, levels of contaminant radiorhenium, power deposition, and enriched 186W material requirements under escalated irradiation conditions (20 µA and 17 MeV for up to 2 hours)

Signaling in Secret: Pay-for-Performance and the Incentive and Sorting Effects of Pay Secrecy

Key Findings: Pay secrecy adversely impacts individual task performance because it weakens the perception that an increase in performance will be accompanied by increase in pay; Pay secrecy is associated with a decrease in employee performance and retention in pay-for-performance systems, which measure performance using relative (i.e., peer-ranked) criteria rather than an absolute scale (see Figure 2 on page 5); High performing employees tend to be most sensitive to negative pay-for- performance perceptions; There are many signals embedded within HR policies and practices, which can influence employees’ perception of workplace uncertainty/inequity and impact their performance and turnover intentions; and When pay transparency is impractical, organizations may benefit from introducing partial pay openness to mitigate these effects on employee performance and retention

Targetry investigations of 186Re production via proton induced reactions on natural Osmium disulfide and Tungsten disulfide targets

Introduction Radioisotopes play an important role in nuclear medicine and represent powerful tools for imaging and therapy. With the extensive use of 99mTc-based imaging agents, therapeutic rhenium analogues are highly desirable. Rhenium-186 emits therapeutic − particles with an endpoint-energy of 1.07 MeV, allowing for a small, targeted tissue range of 3.6 mm. Additionally, its low abundance γ-ray emission of 137.2 keV (9.42 %) allows for in vivo tracking of a radiolabeled compounds and dosimetry calculations. With a longer half-life of 3.718 days, synthesis and shipment of Re-186 based radiopharmaceuticals is not limited. Rhenium-186 can be produced either in a reactor or in an accelerator. Currently, Re-186 is produced in a reactor via the 185Re(n,γ) reaction resulting in low specific activity which makes its therapeutic application limited.[1] Production in an accelerator, such as the PETtrace at the University of Missouri Research Reactor (MURR), can theoretically provide a specific activity of 34,600 Ci.mmol−1 Re[2], which represents a 62 fold increase over reactor produced 186Re. The studies reported herein focused on the evaluation of accelerator-based reaction pathways to produce high specific activity (HSA) 186Re. Those pathways include proton and deuteron bombardment of tungsten and osmium targets by the following reactions: 186W(p,n)186Re, 186W(d,2n) 186Re, 189Os(p,α)186Re, and 192Os(p,α3n)186Re. Additional information on target design related to the determination and optimization of production rates, radionuclidic purity, and yield are presented. Material and Methods Osmium and tungsten metals are very hard and thus very brittle. Attempts at pressing the pure metal into aluminum backings resulted in chalky targets, which easily crumbled during handling. Osmium disulfide (OsS2) and tungsten disulfide (WS2) were identified to provide a softer, less brittle chemical form for targets. OsS2 and WS2 targets were prepared using a unilateral press with a 13 mm diameter die to form pressed powder discs. A simple target holder design (FIG. 1) was implemented to provide a stabilizing platform for the pressed discs. The target material was sealed in place with epoxy using a thin aluminum foil pressed over the target face. Initial irradiations of OsS2 were performed using the 16 MeV GE PETtrace cyclotron at MURR. Irradiations were performed for 30–60 minutes with proton beam currents of 10–20 µA. Following irradiation, the OsS2 targets were dissolved in NaOCl and the pH adjusted using NaOH. The resultant aqueous solution was mixed with methyl ethyl ketone (MEK), with the lipophilic perrhenate being extracted into the MEK layer and the osmium and iridium remaining in the aqueous layer. The MEK extracts were then passed through an acidic alumina column to remove any remaining osmium and iridium. Determination of rhenium and iridium activities was done by gamma spectroscopy on an HPGe detector. Preliminary irradiations on WS2 targets were performed at MURR with the beam degraded to 14 MeV with a proton beam current of 10 µA for 60 minutes. After irradiation, WS2 was dissolved using 30% H2O2 with gentle heating and counted on an HPGe detector to determine the radio-nuclides produced. Results and Conclusion Thin natOsS2 targets were produced, irradiated at 16 MeV for 10 µAh, and analyzed for radiorhenium. Under these irradiation conditions, rhenium isotopes were produced in nanocurie quantities while iridium isotopes were produced in microcurie quantities. Future studies with higher proton energies are planned to increase the production of rhenium and decrease the production of iridium. After optimizing irradiation conditions, enriched 189Os will be used for irradiations to reduce the production of unwanted radionuclides. A liquid-liquid extraction method separated the bulk of the rhenium from the iridium. The majority of the rhenium produced was recovered in the first organic aliquot with little iridium observed while the majority of the iridium and osmium was retained in the first aqueous aliquot. Target production with WS2 was successful. A thin target of natWS2 was produced and irradiated at 14 MeV for 10 µAh. Under these irradiation conditions, several rhenium isotopes were produced in microcurie quantities. Target parameters to maximize 186Re production remain to be determined before enriched 186W targets are used for irradiations to reduce the production of unwanted radionuclides. In conclusion, the potential production routes for accelerator-produced high specific activity 186Re are being evaluated. Cyclotron-based irradiations of natOsS2 targets established the feasibility of producing rhenium via the natOs(p,αxn)Re reaction. Current results indicate higher proton energies are necessary to reduce the production of unwanted iridium isotopes while increasing the production of rhenium isotopes. Preliminary irradiations were performed using the 50.5 MeV Scanditronix MC50 clinical cyclotron at the University of Washington to determine irradiation parameters for future higher energy irradiations (20–30 MeV). A rapid liquid-liquid extraction method isolated rhenium from the bulk of the iridium and osmium following irradiation. Preliminary studies indicate WS2 may also provide a suitable target material to produce 186Re via the (p,n) reaction pathway

Wrong Turn in Cyberspace: Using ICANN to Route Around the APA and the Constitution

The Internet relies on an underlying centralized hierarchy built into the domain name system (DNS) to control the routing for the vast majority of Internet traffic. At its heart is a single data file, known as the root. Control of the root provides singular power in cyberspace. This Article first describes how the United States government found itself in control of the root. It then describes how, in an attempt to meet concerns that the United States could so dominate an Internet chokepoint, the U. S. Department of Commerce (DoC) summoned into being the Internet Corporation for Assigned Names and Numbers (ICANN), a formally private nonprofit California corporation. DoC then signed contracts with ICANN in order to clothe it with most of the U. S. government\u27s power over the DNS, and convinced other parties to recognize ICANN\u27s authority. ICANN then took regulatory actions that the U. S. Department of Commerce was unable or unwilling to make itself, including the imposition on all registrants of Internet addresses of an idiosyncratic set of arbitration rules and procedures that benefit third-party trademark holders. Professor Froomkin then argues that the use of ICANN to regulate in the stead of an executive agency violates fundamental values and policies designed to ensure democratic control over the use of government power, and sets a precedent that risks being expanded into other regulatory activities. He argues that DoC\u27s use of ICANN to make rules either violates the APA\u27s requirement for notice and comment in rulemaking and judicial review, or it violates the Constitution\u27s nondelegation doctrine. Professor Froomkin reviews possible alternatives to ICANN, and ultimately proposes a decentralized structure in which the namespace of the DNS is spread out over a transnational group of policy partners with DoC

Assessing managerial power theory: A meta-analytic approach to understanding the determinants of CEO compensation

Although studies about the determinants of CEO compensation are ubiquitous, the balance of evidence for one of the more controversial theoretical approaches, managerial power theory, remains inconclusive. The authors provide a meta-analysis of 219 U.S.-based studies, focusing on the relationships between indicators of managerial power and levels of CEO compensation and CEO pay-performance sensitivities. The results indicate that managerial power theory is well equipped for predicting core compensation variables such as total cash and total compensation but less so for predicting the sensitivity of pay to performance. In most situations where CEOs are expected to have power over the pay setting process, they receive significantly higher levels of total cash and total compensation. In contrast, where boards are expected to have more power, CEOs receive lower total cash and total compensation. In addition, powerful directors also appear to be able to establish tighter links between CEO compensation and firm performance and can accomplish this even in the face of powerful CEOs. The authors discuss the implications for theory and research regarding the determinants of executive compensation

Whatever happened to curriculum theory? Critical realism and curriculum change

In the face of what has been characterised as a ‘crisis’ in curriculum – an apparent decline of some aspects of curriculum studies combined with the emergence of new types of national curriculum which downgrade knowledge – some writers have been arguing for the use of realist theory to address these issues. This paper offers a contribution to this debate, drawing upon critical realism, and especially upon the social theory of Margaret Archer. The paper first outlines the supposed crisis in curriculum, before providing an overview of some of the key tenets of critical realism. The paper concludes by speculating on how critical realism may offer new ways of thinking to inform policy and practice in a key curricular problematic. This is the issue of curriculum change

Reexamining the Pay Differentials-Organizational Outcomes Relationship in Korea : The Role of Organizational Identification

This research examines the effects of pay differentials on financial performance and employee turnover in Korea by considering a critical employee-based factor: organizational identification. Incorporating tournament theory and social identity theory, authors theorize that pay differentials increase financial performance and employee turnover without considering employees organizational identification. If considered, however, whereas the positive effects of pay differentials on financial performance will be weaker, the effects on turnover will be stronger. Using a sample of Korean cross-industry firms, results show pay differentials have a positive influence on only financial performance. Also, as predicted, while the positive relationship between pay differentials and financial performance became weaker, the relationship with turnover became stronger when employees organizational identification is high. Theoretical and practical implications for strategic pay structures are discussed