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- Chernikova, Dina, 1982, et al.
(författare)
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The neutron-gamma Feynman variance to mean approach: Gamma detection and total neutron-gamma detection (theory and practice)
- 2015
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 782, s. 47-55
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Tidskriftsartikel (refereegranskat)abstract
- Two versions of the neutron gamma variance to mean (Feynman-alpha method or Feynman-Y function) formula for either gamma detection only or total neutron gamma detection, respectively, are derived and compared in this paper. The new formulas have particular importance for detectors of either gamma photons or deleclors sensitive to both neutron and gamma radialion. If applied to a plastic or liquid deleclor, he total neutron-gamma detection Feynman-Y expression corresponds Lo a situation where no discrimination is made between neutrons and gamma parlicles. The gamma variance Lo mean formulas are useful when a detector of only gamma radialion is used or when working with a combined neutron-gamma deleclor at high count rates. The theoretical derivation is based on the Chapman-Kolmogorov equation with the inclusion of general reactions and corresponding intensities for neutrons and gammas, but with the inclusion of prompt reactions only. A one energy group approximation is considered. The comparison of the two different theories is made by using reaction intensities obtained in MCNPX simulations with a simplified geometry for two scintillation detectors and a Cf-252-source. In addition, the variance to mean ratios, neutron, gamma and total neutron-gamma are evaluated experimentally for a weak Cf-252 neutron-gamma source, a Cs-137 random gamma source and a Na-22 correlated gamma source. Due to the focus being on the possibility of using neutron-gamma variance to mean theories for both reactor and safeguards applications, we limited the present study to the general analytical expressions for Feynman-alpha formulas.
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| 4. |
- Polshin, Victor, et al.
(författare)
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Attaining control by design over the hydrolytic stability of Fe-TAML oxidation catalysts
- 2008
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 130:13, s. 4497-4506
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Tidskriftsartikel (refereegranskat)abstract
- The iron(III) complexes of tetra amidato macrocyclic ligands (TAMLs) ([Fe{1-X-1-2-X2C6H2-4,5-(NCOCMe2NCO)(2)CR2}(OH2)](-), 1: X-1 = X-2 = H, R-2 = Me-2 (a), R-2 = (CH2)(2) (b); X-1 = X-2 = Cl, R-2 = F-2, (c), etc.), which the proton is known to demetalate at pH < 3, are also subject to catalyzed demetalation by Bronsted acid buffer components at pH 4-9 such as H2PO4-, HSO3-, and CH3- CO2H, HO2CCH2CO2-. Buffers based on pyridine (py) and tris(hydroxymethyl)aminomethane (TRIS) are catalytically inactive. Where reactions proceed, the products are demetalated TAMLs and iron species of variable composition. Pseudo-first-order rate constants for the demetalation (k(obs)) are linear functions of the acid concentrations, and the effective second-order rate constants k(1),(eff) have a hyperbolic dependence on [H+] (k(1),eff = a(1)[H+]/(b(1)+[H+]). The rate of demetalation of 1a in H2PO4-/HPO42- buffer is appreciable, but the k(obs) values for 1b and 1c are immeasurably low, showing that the rates are strongly affected by the CR2 or "tail" fragments, which are known to potently affect the TAML basicity. The reactivities of 1 depend insignificantly on the aromatic ring or "head" group of 1. The proposed mechanism involves precoordination of the acidic buffer species followed by hydrolysis. The demetalating abilities of buffer species depend on their structures and acidities. Thus, although pyridine-2-carboxylic (picolinic) acid catalyzes the demetalation, its 3- and 4-isomers (nicotinic and isonicotininc acids) are inactive. The difference is rationalized to result from the ability that only coordinated picolinic acid has to deliver a proton to an amidato nitrogen in an intramolecular manner. The reaction order in picolinic acid equals one for la and two for 1a. For 1b, "inactive" pyridine and nicotinic acid speed up the demetalation in the presence of picolinic acid, suggesting that the second order arises from the axial binding of two pyridine molecules, one of which must be picolinic acid. The binding of pyridine- and imidazole-type ligands was confirmed by UV/vis equilibrium measurements and X-ray crystallography. The implications of these mechanistic findings for designing superior Fe-TAML oxidation catalysts and catalyst formulations are discussed using the results of DFT calculations.
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| 5. |
- Rommel, Jens
(författare)
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Can economic experiments contribute to a more effective CAP?
- 2021
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Ingår i: EuroChoices. - 1478-0917. ; 20, s. 42-49
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Tidskriftsartikel (refereegranskat)abstract
- In order to keep pace with the evolution of the objectives and means of the EU's Common Agricultural Policy, evaluation tools also need to adapt. A set of tools that have proved highly effective in other policy fields is economic experiments. These allow the testing of a new policy before its implementation, provide evidence of its specific effects, and identify behavioural dimensions that can influence policy outcomes. We argue that agricultural policy should be subject to economic experiments, providing examples to illustrate how they can inform CAP design. We identify the additional efforts needed to establish further proof-of-concept, by running more – and more robust – experiments related to the CAP. This can happen only by integrating experimental evaluation results within the policy cycle and addressing ethical and practical challenges seriously. To do so, researchers would benefit from a concerted European effort to promote the methodology across the EU; organise the replication in time and across Europe of experiments relevant for the CAP; and build a multi-national panel of farmers willing to participate in experiments. Steps are being taken in this direction by the Research Network of Economics Experiments for CAP evaluation (REECAP).
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