APS : Alternative approach to populate and study the $^{229}$Th nuclear clock isomer

Verlinde, M.; Vantomme, A.; Laatiaoui, M.; Lima, T.A.L.; Moens, J.; Geldhof, S.; Marsh, B.A.; Fedosseev, V.N.; Moore, I.; Raeder, S.; Manea, V.; Wilkins, S.G.; Kraemer, S.; Van den Bergh, P.; De Witte, H.; Ferrer, R.; Chrysalidis, K.; Van Duppen, P.; Cottenier, S.; Granados, C.A.; Correia, J.G.; Lin, P.C.; Fraile, L.M.; Wahl, U.; Verstraelen, E.; Fedorov, D.V.; Pereira, L.M.C.

doi:10.1103/PhysRevC.100.024315

Article
Report number	arXiv:1904.10245
Title	Alternative approach to populate and study the $^{229}$Th nuclear clock isomer
Author(s)	Verlinde, M. (Leuven U.) ; Kraemer, S. (Leuven U.) ; Moens, J. (Leuven U.) ; Chrysalidis, K. (CERN) ; Correia, J.G. (Lisbon, IST) ; Cottenier, S. (U. Gent (main) ; Unlisted, BE) ; De Witte, H. (Leuven U.) ; Fedorov, D.V. (Kurchatov Inst., Moscow) ; Fedosseev, V.N. (CERN) ; Ferrer, R. (Leuven U.) ; Fraile, L.M. (UCM, Madrid, Dept. Phys.) ; Geldhof, S. (Jyvaskyla U.) ; Granados, C.A. (CERN) ; Laatiaoui, M. (Helmholtz Inst., Mainz ; Mainz U., Inst. Kernchem.) ; Lima, T.A.L. (Leuven U.) ; Lin, P.C. (Leuven U.) ; Manea, V. (Leuven U.) ; Marsh, B.A. (CERN) ; Moore, I. (Jyvaskyla U.) ; Pereira, L.M.C. (Leuven U.) ; Raeder, S. (Helmholtz Inst., Mainz ; Darmstadt, GSI) ; Van den Bergh, P. (Leuven U.) ; Van Duppen, P. (Leuven U.) ; Vantomme, A. (Leuven U.) ; Verstraelen, E. (Leuven U.) ; Wahl, U. (Leuven U. ; IST, Lisbon (main)) ; Wilkins, S.G. (CERN)
Publication	2019-08-12
Imprint	2019-04-23
Number of pages	10
Note	11 pages, 5 figures, 2 tables
In:	Phys. Rev. C 100 (2019) 024315
DOI	10.1103/PhysRevC.100.024315
Subject category	nucl-ex ; Nuclear Physics - Experiment
Abstract	A new approach to observe the radiative decay of the $^{229}$Th nuclear isomer, and to determine its energy and radiative lifetime, is presented. Situated at a uniquely low excitation energy, this nuclear state might be a key ingredient for the development of a nuclear clock, a nuclear laser and the search for time variations of the fundamental constants. The isomer's $\gamma$ decay towards the ground state will be studied with a high-resolution VUV spectrometer after its production by the $\beta$ decay of $^{229}$Ac. The novel production method presents a number of advantages asserting its competitive nature with respect to the commonly used $^{233}$U $\alpha$-decay recoil source. In this paper, a feasibility analysis of this new concept, and an experimental investigation of its key ingredients, using a pure $^{229}$Ac ion beam produced at the ISOLDE radioactive beam facility, is reported.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) Publication: © 2019-2025 authors

$Simulation of the escape probability of the electron from the host metal: The conversion electron DOS is shown in (a) for Th:Nb and Th:Au, obtained form DFT calculations. E$_{\textrm{F}}=0$, therefore, the shaded area corresponds to occupied states. The Light shaded areas represent electrons that are energetically not allowed to leave the bulk while the dark shaded areas represent electrons that - if not scattered - will cross the surface. The work functions for gold and niobium are 5.5 and 4.9 eV, repectively. (b) depicts the implantation depth distribution in niobium for different implantation energies, calculated via SRIM software. (c) shows the probability of an electron to reach the bulk surface as a function of its implantation depth and its energy with respect to the Fermi surface. The estimated escape probability given by \cref{escape} as a function of implantation energy is given in (d) for niobium and gold hosts. For details see text.$ $The known experimental data on the isomer, $^{229\textrm{m}}$Th, mentioned in section \ref{sec:intro}, are shown alongside the most important parameters concerning the $\beta$ decay of $^{229}$Ac, mentioned in section \ref{sec:229Ac}. The total feeding probabilities of the $^{229}$Ac $\beta^-$ decay to both isomer and ground state are shown. The value for the radiative half-life of the isomer, T$_{1/2,\textrm{radiative}}$, is a theoretical prediction. The $\mu_{\textrm{exp}}$ and Q$_{\textrm{exp}}$ are the experimental magnetic- and quadrupole moments, respectively \cite{Thielking2018,Campbell2011,Seiferle2017a,NNDC,Minkov2017a,Tkalya2015}.$ $Experimental 2D emission channeling patterns of $^{229}$Ac implanted at room temperature into CaF$_2$, measured in the vicinity ($\pm$ $2$ deg) of four major crystallographic directions ($\left\langle 211\right\rangle $, $\left\langle 111\right\rangle $,$\left\langle 100\right\rangle $ and $\left\langle 110\right\rangle $). The color scale represents the relative amount of electrons hitting the detector, where blue zones indicate that more electrons are emitted. The green lines represent crystallographic planes along which the electrons channel.$ Show more plots

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