Indian Journal of Pure & Applied Physics Vol. 58, May 2020, pp. 415-417 Competition between alpha and heavy cluster decay in superheavy element 296Og Tinu Ann Jose & K P Santhosh* School of Pure and Applied Physics, Kannur University, Swami Anandatheertha Campus, Payyanur 670 327, India Received 4 May 2020 Systematic study of superheavy nuclei 296Og and its possibilities to emit alpha particle and heavier clusters are studied using Modified Generalized Liquid Drop Model (MGLDM) with Q value dependent preformation factor. Half-lives and branching ratio of all possible cluster emission of 296Og is checked and only those cluster which are within the experimental half-lives limit (less than 1030s) and branching ratio limit (down to 10-19) are considered. Among this, 88Kr is found to be the most probable heavy cluster, leading to doubly magic 208Pb daughter nuclei, with half-lives comparable with alpha decay half-lives. Thus the role of doubly magic daughter nuclei in cluster decay is highlighted here. Again the decay modes of 296Og are also studied by comparing alpha decay half-lives using MGLDM with spontaneous fission half-lives proposed by Bao et al., and from this, it is found that for superheavy element 296Og, decays by 3 alpha chains followed by spontaneous fission. We hope that this study would help when this emission is experimentally detected in near future. Keywords: Alpha decay, Spontaneous fission, Superheavy element 1 Introduction E EV ES EC ER EP . … (1) Studies on Superheavy nuclei (SHN) have become one of the hot and popular research topic in the field Here the terms EV, ES, EC, ER and EP represents the of nuclear physics. Several SHN up to Z = 118 have volume, surface, Coulomb, rotational and proximity been experimentally synthesized so far using both energy terms, respectively. cold fusion reaction1 and hot fusion reaction2. One of For the pre-scission region the volume, surface and the reliable ways to understand the properties of Coulomb energies in MeV are given by, newly produced SHN is to check its decay modes. 2 , … (2) Alpha decay and spontaneous fission are the main EV 15.494(11.8I )A decay modes of SHN. Various theories are proposed 2 2/3 2 ES 17.9439(1 2.6I )A (S / 4R0 ) , … (3) by researchers to explain alpha decay of heavy and 3-8 SHN . In addition to alpha decay, several theoretical E 0.6e2 (Z 2 / R )0.5 (V () /V )(R() / R )3 sin d studies are done to check the possibilities of heavy C 0 0 0 9-12 13-16 … (4) cluster emission from SHN . Royer proposed Generalized Liquid Drop Model (GLDM) by adding Here I is the relative neutron excess and S the quasi-molecular shape and nuclear proximity potential surface of the deformed nucleus,V() is the electrostatic 17 to conventional Liquid Drop Model. Our group potential at the surface andV the surface potential of modified GLDM by including proximity potential 0 18 the sphere. proposed by Blockiet al., and is termed as Modified Generalized Liquid Drop Model (MGLDM) For the post-scission region, 2 2 In our present work, we use MGLDM with Q EV 15.494[(11.8I1 )A1 (11.8I2 )A2 ], ... (5) 19 value dependent preformation to calculate half- 296 2 2/3 2 2/3 , ... (6) lives of all splitting of Og. ES 17.9439[(1 2.6I1 )A1 (1 2.6I2 )A2 ] 2 2 2 2 2 2 Modified Generalized Liquid Drop Model 0.6e Z1 0.6e Z 2 e Z1Z 2 . ... (7) EC (MGLDM) R1 R2 r In MGLDM, for a deformed nucleus, the Here A , Z , R and I are the masses, charges, radii macroscopic energy is defined as: i i i i —————— and relative neutron excess of the fragments,ris the *Corresponding author (E-mail: [email protected]) distance between the centers of the fragments. 416 INDIAN J PURE APPL PHYS, VOL. 58, MAY 2020 -4 The nuclear proximity potential E is given by With a= -0.25736, b=6.37291 x 10 , c=3.35106 P and Q is the Q value or the energy released in a Blockiet al.,18 as: radioactive nuclear reaction. C1C 2 z , ... (8) E p (z) 4b 3 Results and Discussion (C C ) b 296 1 2 Half-lives of all possible splitting of Og is With the nuclear surface tension coefficient: studied using MGLDM with Q value dependent preformation factor. Among all splitting, we 0 .9517 [1 1 .7826 ( N Z ) 2 / A 2 ] considered only those splitting of 296Og which are MeV/fm2, ... (9) below experimental half-life upper limit and within branching ratio limit. Graphical representation of Where N, Z and A represent neutron, proton and logarithm of half-life of all splitting of 296Og versus mass number of parent nucleus respectively, mass number of cluster emitted is plotted and is represents the universal proximity potential20 given shown in Fig. 1. Straight line drawn in the figure as: corresponds to alpha decay half-life of 296Og. From the graph, one can clearly understand the most / 0.7176 4.41e , for ε> 1.9475, ... (10) probable cluster that may be emitted from 296Og with 2 3 half-life comparable with that of alpha decay half-life. 1 .7817 0 .9270 0 .01696 0 .05148 296 Alpha decay half-life of Og is calculated and is for 0 ≤ ε ≤ 1.9475, ... (11) found to be 97.2808 s. Among all splitting within with ε = z/b, where the width (diffuseness) of the experimental limits, 88Kr with 208Pb daughter nuclei 116 180 nuclear surface b ≈ 1 fm and Süsmann central radii Ci and Pd with Hf daughter nuclei are considered as 296 of fragments related to sharp radii Ri as: most probable decay of SHN Og with half-lives comparable with alpha decay half-life. Also, when we b 2 138 C R . ... (12) examine all the splitting, it is evident that Xe with i i 160 Ri Gd daughter nuclei is the most stable heavy cluster reaction possible with minimum half-life among all For Ri we use semi empirical formula in terms of 208 20 decay. Pb daughter nuclei considered above has Z mass number Ai as : 138 =82 and Xe has N= 82. Thus in above considered 1/ 3 1/ 3 Ri 1.28 Ai 0.76 0.8Ai . ... (13) cluster reaction, either cluster emitted or daughter nuclei has neutron number N= 82 or atomic number The barrier penetrability P is calculated with the Z=82, which is a magic number, thereby proving the action integral: role of stability of shell closure in cluster decay. 296 Rout We also calculated the decay modes of Og by 2 exp 2B(r)[E(r) E(sphere)]dr , ... (14) comparing alpha decay half-life with spontaneous Rin fission half-life and are listed in Table 1. Alpha decay 2 Where Rin R1 R2 , B(r) and Rout e Z1Z2 / Q . R1, R2 are the radius of the daughter nuclei and emitted cluster respectively, and the reduced mass and Q the released energy. The partial half-life is related to the decay constant by: ln 2 ln 2 . ... (15) T 1 / 2 P C P The assault frequency has been taken as 1020 s-1 19 and the preformation factor is given as: 2 P 10 aQ bQ C , ... (16) Fig. 1 — Graphical representation of logarithm of half-life versus C mass number of cluster for the splitting of 296Og. JOSE & SANTHOSH: ALPHA AND HEAVY CLUSTER DECAY 417 Table 1 — Decay modes of 296Og by comparing alpha decay half-lives with spontaneous fission half-lives predicted by the framework proposed by Bao et al.,21. Parent Qα TSF Tα Mode of Nuclei (MeV) (s) (s) decay 296Og 9.805 311581.1245 97.2808 α 292Lv 10.775 220330.2358 0.0391 α 288Fl 10.065 898.0416 0.8386 α 284Cn 9.605 0.0051 4.3119 SF half-life are calculated using our method of MGLDM in the form of Research Project under Innovative whereas spontaneous fission half-life are calculated Research Programme. using equation proposed by Bao et al.,21 and is given as: References 2 1 Hofmann S & Munzenberg G, Rev Mod Phys, 72 (2000) Z 2 Z 2 log [T ( yr )] c c c c E h ... (17) 10 1 / 2 1 2 2 3 2 4 sh i 733. (1 kI ) A (1 kI ) A 2 Oganessian Y, J Phys G: Nucl Part Phys, 34 (2007) R165. With c = 1174.35341, c = -47.666855, c = 3 Poenaru D N, Ivaşcu M & Săndulescu A, J Phys G: Nucl 1 2 3 Phys, 5 (1979) L169. 0.471307, c4 = 3.378848, k = 2.6 and hi is blocking 4 Buck B, Merchant A C & Perez S M, Phys Rev C, 45 (1992) 21 effect given in Ref. 2247. From Table 1, when we compare both alpha decay 5 Zhang H F & Royer G, Phys Rev C, 76 (2007) 047304. half-life and spontaneous fission half- life, it is evident 6 Qi C, Xu F R, Liotta R J & Wyss R, Phys Rev Lett,103 (2009) 072501. that the first three sequential alpha decay half-life are 7 Viola J V E & Seaborg G T, J Inorg Nucl Chem, 28 (1966) less in comparison with spontaneous fission half-life. 741. And for the next decay, SF half-life has minimum value. 8 Santhosh K P, Sabina S & Jayesh G J, Nucl Phys A, (2011) Thus we can conclude that SHN 296Og decays by 3 alpha 85034. chain followed by spontaneous fission. 9 Poenaru D N, Gherghescu R A & Greiner W, Phys Rev C, 85 (2012) 034615.