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From experiment to evaluation, the case of n+238U (Vol. 49, No. 1)
Evaluated nuclear data represent the bridge between experimental and theoretical achievements and final user applications. The complex evolution from experimental data towards final data libraries forms the cornerstone of any evaluation process. Since more than 90% of the fuel in most nuclear power reactors consists of 238U, the respective neutron induced cross sections are of primary importance towards accurate neutron transport calculations. Despite this significance, the relevant experimental data for the 238U(n,γ) capture reaction have only recently provided for a consistent description of the resonance region. In this work, the 238U(n,γ) average cross sections were evaluated in the energy region 5-150 keV, based on recommendations by the IAEA Neutron Standards projects and experimental data not included in previous evaluations.
A least squares analysis was applied using exclusively microscopic data. This resulted in average cross sections with uncertainties of less than 1%, fulfilling the requirements on the High Priority Request List maintained by the OECD-NEA. The parameterisation in terms of average resonance parameters maintained consistency with results of optical model and statistical calculations. The final deliverable is an evaluated data file for 238U, which was validated by independent experimental data.
I. Sirakov, R. Capote, O. Gritzay, H.I. Kim, S. Kopecky, B. Kos, C. Paradela, V.G. Pronyaev, P. Schillebeeckx, and A. Trkov, Evaluation of cross sections for neutron interactions with 238U in the energy region between 5 keV and 150 keV, Eur. Phys. J. A 53, 199 (2017)
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Quantum manipulation power for quantum information processing gets a boost (Vol. 49, No. 1)
Improving the efficiency of quantum heat engines involves reducing the number of photons in a cavity, ultimately impacting quantum manipulation power.
Traditionally, heat engines produce heat from the exchange between high-temperature and low-temperature baths. Now, imagine a heat engine that operates at quantum scale, and a system made up of an atom interacting with light (photons) confined in a reflective cavity of sub-atomic dimensions. This setup can either be at a high or low temperature, emulating the two baths found in conventional heat engines. Controlling the parameters influencing how such quantum heat engine models work could dramatically increase our power to manipulate the quantum states of the coupled atom-cavity, and accelerate our ability to process quantum information. In order for this to work, we have to find new ways of improving the efficiency of quantum heat engines. In a study published recently, the authors show methods for controlling the output power and efficiency of a quantum thermal engine based on the two-atom cavity.
K.W. Sun, R. Li and G.-F. Zhang, A quantum heat engine based on the Tavis-Cummings model, Eur. Phys. J. D 71, 230 (2017)
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Temperature gradients influencing the hysteresis of ferromagnetic nanostructures (Vol. 49, No. 1)
For future data storage technology, in which downscaling of magnetic bit unit sizes is crucial, heat-assisted magnetic recording (HAMR) is one key technology to ensure the writability for magnetic bits. It relies on a laser heating pulse to lower the coercive field HC of the magnetic bit unit. Here, we investigated the temperature- and temperature gradient-dependent switching behaviour by HC measurements of individual, single-domain CoNi and FeNi alloy nanowires via measurements of the magneto-optical Kerr effect. While the switching field generally decreased under isothermal conditions at elevated temperatures, temperature gradients (ΔT) along the nanowires led to an increased switching field up to 15 % for ΔT = 300 K in Co39Ni61 nanowires. We attribute this enhancement to a stress-induced contribution of the magneto-elastic anisotropy that counteracts the thermally assisted magnetization reversal process. Our results demonstrate that a careful distinction between locally elevated temperatures and temperature gradients has to be made in future HAMR devices.
A.-K. Michel and 12 co-authors, Temperature gradient-induced magnetization reversal of single ferromagnetic nanowires, J. Phys. D: Appl. Phys. 50, 494007 (2017)
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Droplet explosion by shock waves, relevant to nuclear medicine (Vol. 49, No. 1)
An arrow shooting through an apple, makes for a spectacular explosive sight in slow motion. Similarly, energetic ions passing through liquid droplets induce shock waves, which can fragment the droplets. In a study published recently, the authors have proposed a solution to observe the predicted ion-induced shock waves. They believe these can be identified by observing the way incoming ions fragment liquid droplets into multiple smaller droplets. The discovery of such shock waves would change our understanding of the nature of radiation damage with ions to cancerous tumour. This matters for the optimisation of ion-beam cancer therapy, which requires a thorough understanding of the relation between the physical characteristics of the incoming ion beam and its effects on biological tissues. The predicted shock waves significantly contribute to the thermomechanical damage deliberately inflicted on tumour tissue. Specifically, the collective flow intrinsic to the shock waves helps to propagate biologically harmful reactive species, such as free radicals, stemming from the ions. This mechanism increases the volume of tumour cells exposed to reactive species.
E. Surdutovich, A. Verkhovtsev and A. V. Solov’yov, Ion-impact-induced multifragmentation of liquid droplets, Eur. Phys. J. D 71, 285 (2017)
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