Ackermann, D.

Andel, B.

Antalic, S.

Droese, C.

Even, J.

Hessberger, F.

Kalaninova, Z.

Laatiaoui, M.

Piot, J.

Vostinar, M.

GSI Repository

Direct proof of electron capture decay of 258Db∗F.P. Heßberger†1,2, D. Ackermann1, B. Andel3, S. Antalic3, C. Droese2,4, J. Even2, Z. Kalaninova´3, M.Laatiaoui2, J. Piot5, and M. Vostinar51GSI, Darmstadt, Germany; 2HIM, Mainz, Germany; 3Comenius University, Bratislava, Slovakia; 4Ernst-Moritz-ArndtUniversita¨t, Greifswald, Germany; 5GANIL, Caen, FranceBesides spontaneous fission (sf) and α emission, elec-tron capture (EC) decay is the third essential decay modeof transuranium nuclei, providing valuable information ontheir nuclear structure. Experimental data are, however,quite scarce in the region of Z> 100. The heaviest nucleusfor which so far nuclear structure information was obtainedis 253Md, produced by EC decay of 253No [1].Study of EC decay is also of interest from an other pointof view: for a couple of odd-odd nuclei sf branches are re-ported, among them the members terminating the α - decaychains assigned to start from odd-odd nuclei of elementswith Z = 113, 115 and 117, produced in actinide based ’hotfusion’ reactions. Because of the strong hindrance of sfof odd-odd nuclei due to two unpaired nucleons, it can beassumed that the terminating sf activities stem from even-even nuclei produced by EC decay. As the latter is a securesource for emission of K X-rays, the proof of EC decaywould go along with an unambiguous Z - identification -which is still missing for all elements Z> 112 - of the de-caying nucleus and its precursors up to the head of the de-cay chain. If, further, EC decay populates excited states inthe daughter nucleus it also will be a tool for nuclear struc-ture investigations complementary to α emission.A candidate suited to test the technical feasibility is 258Db,which can be produced in the reaction 209Bi(50Ti,n)258Dbwith a relatively large cross-section of σ≈ 4 nb. For thatnucleus an EC branch of ≈ 33% was assumed from the ra-tio of α decays and sf events which were ascribed to sf of258Rf, the EC-decay daughter of 258Db [2]. A direct proofof this assumption had already been attempted in 1982 atSHIP by measuring delayed coincidences between γ - raysand sf - events; indeed, some candidates for K X-rays wereobserved as shown in Fig. 1a, but the result was not not re-garded as a completely convincing proof [3].A new experiment was performed in may 2014 at SHIP. Inan experimental run of about 200 h irradiation time roughly1250 sf events were collected. The spectrum of γ - rays(in coincidence with conversion electrons) preceeding ansf event within ∆t ≤ 39 ms is shown in Fig. 1b; clearly theKα1,α2 and Kβ′1 - lines of rutherfordium are visible. Fromthe time distributions (γ-sf) a half-life of 13±11 ms wasextracted for the sf activity, which is in-line with the value14.7+1.2−1.0 ms [4], reported for 258Rf. The observation ofconversion electrons in coincidence with the X-rays further∗Work supported by GSI(UNILAC)/HI Mainz/European CommunityFP7 - Capacities, contract ENSAR contract No. 262010/French-GermanCollaboration agreement INP2 P3-DSM/CEA and GSI/Slovak GrantAgency VEGA, contract No. 1/0576/13† f.p.hessberger@gsi.deproves the population of at least one excited level in 258Rf,their energy distribution suggest an excitation energy rangeof ≈ 400 − 500 keV. Assuming population of the ground-state rotational band this would lead to population of the8+ or a higher-spin state.01234a)counts / keVcounts / keVE  / keVK (Rf)K (Rf)K (Rf)K (Rf)  125 130 135 140 145 150 155 16004812 b)  Figure 1: Energy spectra of γ - events observed in delayedcoincidence with sf - events a) SHIP experiment in 1982[3], ∆t(γ-sf)≤ 30 ms, b) SHIP experiment in 2014, ∆t(γ-sf)≤ 39 ms, electron occuring in prompt coincidence withγ - event required; the full red lines represent the expectedspectra using the theoretical X-ray energies [5] and a de-tector resolution of 2 keV(FWHM).References[1] S. Antalic et al., Eur. Phys. J. A 47:62 (2011)[2] F.P. Heßberger et al., Z. Phys. A 322, 557 (1985)[3] F.P. Heßberger, PHD, TH Darmstadt 1985, GSI Report GSI-85-11[4] J.M. Gates et al., PRC 77, 034603 (2008)[5] T.A. Carlson, C.W. Nestor Jr., ADNDT 19, 153 (1977)GSI SCIENTIFIC REPORT 2014 MU-NUSTAR-SHE-P-09DOI:10.15120/GR-2015-1-MU-NUSTAR-SHE-P-09 177

Direct proof of electron capture decay of $^{258}$Db

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Direct proof of electron capture decay of $^{258}$ Db

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Direct proof of electron capture decay of 258^{258}258Db

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Direct proof of electron capture decay of $^{258}$ Db