High-Z electron screening: the cases ⁵⁰V(p,n)⁵⁰Cr and ¹⁷⁶Lu(p,n)¹⁷⁶Hf

Abstract

The electron screening in 50 V(p,n) 50 Cr has been studied at E p = 0.75 to 1.55 MeV for different environments: VO 2 insulator, V metal and PdV 10% alloy. Relative to the insulator we find for the metal and alloy a large screening energy U D = 27 ± 9 and 34 ± 11 keV, respectively. We also studied 176 Lu(p,n) 176 Hf at similar proton energies for a Lu 2 O 3 insulator, a Lu metal and a PdLu 10% alloy; here we observed a narrow resonance at E pr = 0.81 MeV exhibiting a prominent Lewis peak and a shift in proton resonance energy of U D = 32 ± 2 and 33 ± 2 keV for the metal and alloy, respectively, relative to the insulator. The data demonstrate that the electron screening occurs across the periodic table and is not restricted to reactions among light nuclides studied so far. The two reactions with neutrons in the exit channel demonstrate furthermore that the electron screening is an effect in the entrance channel of the reaction and is not influenced by the ejectiles of the exit channel, i.e. by the charged particles of the exit channel studied so far. The U D values can be explained by the plasma model of Debye applied to the quasi-free electrons in the metallic samples. The data together with previous studies of the fusion reactions d+d, Li+p and Be+p in metals verify the Debye model prediction, i.e. a scaling of U D with the nuclear charge of the target atoms. Finally, we discuss the possibility for an enhanced α-decay rate of transuranic waste in metals.

On the absence of appreciable half-life changes in alpha emitters cooled in metals to 1 Kelvin and below

“…However the results throw direct light upon the suggestions made by Kettner et al in Ref. [1]. Brief mention of evidence from experiments involving beta decay is made in the discussion.…”

“…In a recent paper ideas were presented which led to the suggestion that the half-lives of alpha emitters, particularly those of lower decay energy, would be strikingly reduced if the activity was in a metallic environment and cooled to temperatures of a few Kelvin as compared to 'normal' decay in insulating materials at room temperature [1]. The authors surmised that, through the influence of the conduction, 'valence' or 'free', electron potential near the nucleus, the alpha decay barrier would be effectively lowered and thus cooling of long-lived radioactive waste might lead to their much more rapid decay and safe disposal.…”

Catalysis of Nuclear Reactions by Electrons

“…This means that our results represent only lower limits on ωγ s . First of all one notices that the resonance energy shifts have no connection to the measured electron screening potentials, meaning that the two phenomena have a different origin, despite the fact that they have been previously treated together [17]. Secondly, all resonance shifts are towards lower beam energies compared to the normal kinematics reaction.…”

The influence of electron screening on half-lifes

“…As a result, a 10% increase as proposed by [3] can be clearly excluded. Furthermore, a 1/ √ T temperature dependence of U e as it was proposed by [3,5] when the Debye-Hückel model is applied is unlikely. …”

“…As a consequence, a change of lifetimes of low-energy β and α emitters may also be considered if they are situated in a metal. In addition, a temperature dependence of the screening effect has been proposed [2], dramatically changing some half-lifes if the metal is cooled [3,5]. We checked these claims experimentally by measuring the decay rate of 22 Na in a piece of aluminum activated by a 70 MeV proton beam.…”