Towards the selenides of the Superheavy Elements copernicium and flerovium: Unexpected Cn-Se bond observation

N.M. Chiera1,2, N. V. Aksenov3, Y. V. Albin3, G. A. Bozhikov3, V. I. Chepigin3, S. N. Dmitriev3, R. Dressler1, R. Eichler1,2, V. Ya. Lebedev3, A. Madumarov3, O. N. Malyshev3 , D. Piguet1, Y.A. Popov3, A. V. Sabel’nikov3, P. Steinegger3, A. I. Svirikhin3, A. Türler1,2, G. K. Vostokin3, A. Vögele1, A. V. Yeremin3 1Paul Scherrer Institute, Villigen, Switzerland, 2University of Bern, Bern, Switzerland, 3Flerov Laboratory of Nuclear Reactions, JINR, Dubna, Russian Federation

1) Studying the chemistry of Superheavy Elements 2) Why copernicium and flerovium? 3) Why selenium?

40 20 group 12 The possibility of a simultaneous production of Cn (Z=112) CnSe group 14 With increasing nuclear charges, and Fl (Z=114) in 48Ca induced nuclear fusion reactions with 0 -20 superheavy elements (SHEs) show 242Pu - 244Pu [2] allows for performing comparative studies. Benchmark for -40 HgSe the CnSe and FlSe GeSe deviations from the periodicity of -60 formation

chemical properties due to relativistic (MSe) -80

298 f PbSe

effects [1]. H -100

∆ SnSe -120 -140 Hence, how the SHEs chemically FlSe CdSe behave? Is their chemical behavior -160 ZnSe -180 similar to their respective -200 homologues? 0 50 100 150 200 250 300 350 400 ∆ 298 Hsubl.(M) Gas chromatography is a fast, Stability trends for selenides of group 12 (in blue) and 14 (in red) [3]. Cn and Fl selective, and efficient method to homologues. study single atoms per time, having The differences in these trends make selenium a good very short half-lives [1]. Sequences of correlated decays identified in the 242,244Pu + 48Ca surface candidate for a comparative study of the chemical reaction. behaviours of copernicium and flerovium.

4) Red amorphous Se and trigonal Se 5) Se surfaces for gas adsorption studies 6) Off-line model experiments results:

100 Among all the selenium allotropes, red amorphous selenium 90 197Hg dep. on a 70% trigonal Se surface Monte-Carlo sim.: 80 ∆ Hg (red a-Se) is the most reactive one [4]. Hads(t-Se) > -60 kJ/mol 70 197Hg dep. on a 95% red a-Se surface 60 Monte-Carlo sim.: Instead, trigonal selenium (t-Se) is thermodynamically the Hg ∆H (a-Se) < -85 kJ/mol most stable selenium allotrope. 50 ads 40

red a-Se coated column trigonal Se coated column Hg adsorption, % Red amorphous Se, being a metastable phase, undergoes a 197 30 20 spontaneous transformation to trigonal Se [4]. Selenium coated columns [5] for off-line model experiments 10 197 with Hg. (γ-emitter 77.35 keV line, t1/2 = 64 h). 0 1 2 3 4 5 6 7 8 9 10 11 column, cm

197Hg was produced at PSI (SINQ) and its deposition was studied in the prepared Se columns at ambient conditions at a gas flow of 25 ml/min He [7]. red a-Se covered PIN diode trigonal Se covered PIN diode A severe kinetic hindrance of the Hg / trigonal Se Selenium coated PIN diodes [6] for on-line experiments interaction is observed, taking into account the Grey trigonal Se Entangled chain structure in red 185 with Hg (α-emitter 5.78 MeV line, t1/2 = 49.1 s). thermodynamic stability of HgSe [7]. amorphous Se

7) ON-LINE experiments preliminary results: Outlook and conclusions:

A 48Ca18+ beam was delivered from the U-400 cyclotron, FLNR Two events detected on Se-covered detectors were attributed The Se surface crystallization at a microscopic level can be institute, Russia, with an energy of 276 MeV into the target to 283Cn (no other SF observed) [9]: monitored by Hg deposition. material producing 185Hg and 283Cn in the nuclear fusion reactions 142Nd(48Ca,5n) and 242Pu(48Ca,3n), respectively. Event 1 Event 2 Ref. [2] The more favorable adsorption of copernicium on trigonal Se, if compared to the interaction of mercury with the same The COLD gas chromatography loop setup used is described in allotropic surface can be the result of: [8]. 1) A lower kinetic hindrance in the Cn/t-Se adsorption process (see Poster P2-20, presented by A. Madumarov) 2) A thermodynamic effect, with −Δ (Cn) Δ (Hg) 3) A kinetic effect due to steric hindrances𝑡𝑡−𝑆𝑆𝑆𝑆 (lattice size𝑡𝑡−𝑆𝑆𝑆𝑆effect) 𝐻𝐻𝑎𝑎𝑎𝑎𝑎𝑎 ≥ − 𝐻𝐻𝑎𝑎𝑎𝑎𝑎𝑎 NR: 6E-4 Further on-line adsorption studies with Hg, Cn, Fl Monte-Carlo simulations of the probability to observe the two on selenium surfaces (trigonal and amorphous) are envisaged 283Cn events on the Se-covered detectors (surface composition in Fall 2016. 93% trigonal Se, 2% red amorphous Se, and 5% quartz) were performed. The ranges in the legend express a probability density, which is maximum for 103 (dark green pattern) and [1] Schädel M., and Shaughnessy D., eds. The chemistry of superheavy elements. minimum for 1 (dark brown pattern). Dordrecht: Kluwer Academic Publishers, 2003. [2] Oganessian Y.,"Heaviest nuclei from 48Ca-induced reactions." Journal of Physics G: Nuclear and Particle Physics 34, no. 4 (2007): R165. 1.00E+03 [3] Chiera N. M. et al., “Towards selenides of the superheavy elements Cn and Fl.” PSI 7.08E+02 -40 5.01E+02 LCH Annual Report (2013): 7. 3.55E+02 2.51E+02 [3] Minaev V. S., "Structural and phase transformations in condensed selenium.“ 1.78E+02 Journal of Optoelectronics and Advanced Materials 7, no. 4 (2005): 1717. 1.26E+02 -50 8.91E+01 [5] Chiera, N. M. et al., "Vapor deposition coating of fused silica tubes with 6.31E+01 amorphous selenium." Thin Solid Films 592 (2015): 8-13. 4.47E+01 3.16E+01 [6] Chiera N. M. et al. “Towards selenides of the superheavy elements Cn and Fl.” PSI -60 2.24E+01 LCH Annual Report (2014): 5. 1.58E+01 (red a-Se), kJ/mol (red 1.12E+01 [7] Chiera N. M. et al., "Interaction of elemental mercury with selenium surfaces:

ads 7.94E+00

The different reactivity of Hg towards the two allotropes H 5.62E+00 Model experiments for investigations of superheavy elements copernicium and ∆ -70 3.98E+00 flerovium” accepted for pubblication (August 2016) in the Journal of Radioanalytical allowed for monitoring the spontaneous transformation of 2.82E+00 2.00E+00 and Nuclear Chemistry red amorphous Se to the trigonal allotrope (i.e., 1.41E+00 [8] Eichler R. et al., "Chemical characterization of element 112." Nature 447, no. 7140 1.00E+00 -80 (2007): 72-75. crystallization), at a microscopic level [7]. -80 -70 -60 -50 -40 [9] Chiera N. M. et al., “Unexpected Cn-Se bond observation.” PSI LCH Annual Report ∆H (trig.-Se), kJ/mol ads (2015), in press.

The 185Hg deposition pattern (grey bars) reveals an advanced CnSe formation is expected to be thermodynamically less >98% crystallization of the red amorphous Se covered favored, but it seems to have a lower kinetic formation detectors after 3 weeks of storage [7]. hindrance than the interaction Hg / trigonal Se [9].