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Electron screening: can metals simulate plasmas?

Electron screening: can metals simulate plasmas?. Marialuisa Aliotta School of Physics - University of Edinburgh. electron screening d(d,p)t reaction in deuterated materials experimental results and interpretation testing the model overview of final results.

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Electron screening: can metals simulate plasmas?

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  1. Electron screening: can metals simulate plasmas? Marialuisa Aliotta School of Physics - University of Edinburgh • electron screening • d(d,p)t reaction in deuterated materials • experimental results and interpretation • testing the model • overview of final results International Workshop XXXIV on Gross Properties of Nuclei and Nuclear Excitations Hirschegg, Kleinwalsertal, Austria, January 15 - 21, 2006

  2. (E) = exp(-2) S(E) Electron screening assumption: bare nuclei 2 ~ Z1Z2(m/E)½ Ec bare Coulomb potential E + Ue screened E Ratomic 0 Rn Rt inthe laband instellar plasmasinteraction is affected by presence of electrons Energy gain = SCREENING POTENTIAL Uetypically tiny amount (~ 10-100 eV)  corrections typically negligible  except for ultra-low energies

  3. Sscreen(E) ~ exp(Ue/E) flab(E) = Sbare(E) S(E) screened S(E) fit to measured low-energy data  Ue high-energy data extrapolation bare S(E) 0 E Screening potential: experimental approach typically, experimental investigations Ue in excessof theoretical limit ! ideally one would use a plasma to investigate screening effects in plasmas can we use metals instead?

  4. Ni foil LN2-cooled Si Cu pipe -200 V D+ ion beam MxD target x/y wobbling units Si turbo pump aperture 8 mm f  = 130° P = 2x10-8 mbar 100 kV accelerator – Ruhr-Universität Bochum

  5. d(d,p)t t p • thin-target yield  differential thick-target yields • determine cross section • determine solubility y = 1/x • weighted average cross section  S-factor • fit low-energy data to determine Ue thick-target yield curve Experimental procedure target preparation • Kr sputtering at E = 35 keV(remove ~ 200 mono-layers) • D implantation(at Ed ~ 5-30 keV until saturation) • stoichiometry MxD attained experimental run and data analysis

  6. Cu Ue = 470 eV factor ~ 20 higher Nd Ue < 30 eV comparable to gas target case Hf Ue < 30 eV comparable to gas target case Pt Ue = 670 eV factor ~ 25 higher Anomalous behaviour of Ue in deuterated metals compared to D2 gas target (Ue 30 eV) anomalous enhancements observed for some materials but not for others WHY? F. Raiola et al.: Phys. Lett. B547 (2002) 193 F. Raiola et al.: Eur. Phys. J A19 (2004) 283

  7. Results overview 55 samples in total F. Raiola et al.: Eur. Phys. J A19 (2004) 283 • FEATURES: • elements in same group show similar Ue values • exceptions: group 13 (B = insulator) and group 14 (C, Si, Ge = semiconductors) • large effect ~ 300 eV metals with low “H solubility”(1/x) metallic character retained during implantation with D • small effect ~ 30 eVmetals with large “H solubility” metallic character lost during implantation with D

  8. Temperature dependence of H solubility at room temperature metals of group 3 and 4 and lanthanides all have HIGH hydrogen solubility y=1/x solubility decreases with temperature  repeat measurements at T = 200 oC group 4 Ti – group 4 solubility ydrops to a few percent increase in screening potential Ue similarly for all elements of groups 3 & 4 and Lanthanides

  9. overview of final results enhancement clearly linked to properties of the metallic environment

  10. A possible classical explanation? A SIMPLE MODEL: following Debye’s plasma theory: “free” electrons in metals cluster around deuterons in lattice at radius neff = number of quasi-free electrons/atom (typically 1) a = atomic density (typically 6x1028 m-3) for T ~ 300 K  RD ~ 1/10 Ra Ue,D Z1Z2e2/RD Ue,D ~ 300 eV CRITICAL TESTS: TEMPERATURE DEPENDENCE CHARGE DEPENDENCE

  11. Temperature dependence of Ue need elements with almost constant solubility at all T examples: Pt and Co range of T = 20 – 200 oC group 10

  12. Target-charge dependence of Ue Debye radius scales inversely with nuclear charge Ztof target atoms expect increased effect in screening potential with Zt example 7Li(p,a)4He in H2 gastarget:  UA = 300±160 eV in Li metal: neff(Li) = 0.8±0.2  UD = 820±100 eV expect: Ue = UA + UD = 1120±260 eV in PdLix alloy: neff(Pd) = 6.3±1.2  UD = 2800±280 eV (for x < few percent) expect: Ue = UA + UD = 3100±440 eV in insulators: neff = 0  UD = 0 expect: Ue = UA + UD = 300±160 eV

  13. Ue = 3790±330 eV Ue = 1280±60 eV Ue,A = 185±150 eV Results J. Cruz et al. Phys Lett B 624 (2005) 181 similar results observed for 6Li(p,a) (Zt = 3) J. Cruz et al. Phys Lett B 624 (2005) 181 D. Zahnow et al. Z. Phys. A359 (1997)211 9Be(p,a)6Li and 9Be(p,d)8Be (Zt = 4) C. Rolfs, (2005) private communication 50V(p,n)50Cr (Zt = 23) 176Lu(p,n)176Hf (Zt=71) C. Rolfs, (2005) private communication

  14. Summary • enhanced electron screening in metals explained using Debye model • temperature dependence of Ue verified • target-charge dependence of Ue verified • need for improved theory another crucial prediction of Debye model: a metallic environment should alter the half-lives of radioactive decay? measurements currently in progress at Bochum…

  15. the collaboration F.Raiola1, J.Cruz2, G.Gyürky3, Z.Fülöp3, S.Zeng4, M.Aliotta5, H.W.Becker1, B.Burchard1, C.Broggini6, A.Di Leva1, A.D’Onofrio7, M.Fonseca2, L.Gang4, L.Gialanella8, G.Imbriani8, A.P.Jesus2, M.Junker9, K.U.Kettner10, B.Limata8, H.Luis2, J.P. Ribeiro2, V.Roca8, C. Rolfs1, M.Romano8, D. Schürmann1, E.Somorijai3, F.Strieder1, F. Terrasi7 1 Institut für Physik mit Ionenstrhalen, Ruhr-Universität Bochum, Germany 2 Centro de Fisica Nuclear, Universidade de Lisboa, Portugal 3 Atomki, Debrecen, Hungary 4 China Institute of Atomic Energy, Beijing, P.R.China 5 School of Physics, University of Edinburgh, UK 6 INFN, Sezione di Padova, Padova, Italy 7 Dipartimento di Scienze Ambientali, Seconda Università di Napoli, Caserta, Italy 8 Dipartimento di Scienze Fisiche, Università Federico II and INFN, Napoli, Italy 9 Laboratori Nazionali del Gran Sasso dell’INFN, Assergi, Italy 10 Fachhochschule Bielefeld, Germany My special thanks to Francesco RaiolaandJoão Cruzfor much of the material presented

  16. investigate6,7Li(p,a) reactions in different materials to test Ztdependence of UD

  17. target MACOR diamond Cu plate MACOR graphite MACOR diamond heater thermosensor Temperature dependence of H solubility at room temperature metals of group 3 and 4 and lanthanides all have HIGH hydrogen solubility y=1/x in general, hydrogen solubility decreases with temperature modified setup to investigate effects of temperature dependence

  18. Additional remarks previous studies of 9Be(p,a)6Li and 9Be(p,d)8Be reactions [D. Zahnow et al. Z. Phys. A359 (1997)211] on metallic Be targets led to Ue = 900±50 eV, not understood at that time with neff(Be) = 0.21±0.04 T = 293 K Zt = 4 UD = 870±80 eV UA = 240 eV Ue= UA + UD = 1110±80 eV consistent with observation and further supporting Ztscaling of Debye model Zt scaling recently verified also for Zt=23 [50V(p,n)50Cr] and Zt=71 [176Lu(p,n)176Hf] (Rolfs, private communication)

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