Zeptosecond contact times for element Z=120 synthesis

H M David ,J Khuyagbaatar,E Williams,C Mokry,K Vo-Phuoc,Kazuyuki Sekizawa ,J Walshe ,K J Cook ,P Thörle-Pospiech ,Sunil Kalkal ,C Simenel ,J Runke ,E Prasad ,Ch E Düllmann ,D Y Jeung ,B Lommel ,M Dasgupta ,Κ Eberhardt ,I.p Carter ,C Sengupta ,Ν Trautmann ,J F Smith ,E C Simpson ,D C Rafferty ,David Hinde ,Nikolai R Lobanov ,B Kindler ,A Yakushev

doi:10.1016/j.physletb.2020.135626

Abstract

The synthesis of new superheavy elements beyond oganesson (Z=118) requires fusion reactions with projectile nuclei with proton numbers larger than that of 48Ca (Z=20), which has been successfully employed for the synthesis of elements with Z=112-118. In such reactions, fusion is drastically hindered by fast non-equilibrated dynamical processes. Attempts to produce nuclei with Z=120 using the 64Ni+238U, 58Fe+244Pu, 54Cr+248Cm, and 50Ti+249Cf reactions have been made, which all result in larger Coulomb forces than for 48Ca-induced reactions, but no discovery has been confirmed to date. In this work, mass and angle distributions of fission fragments from these reactions have been measured with large angular coverage to aid in selection of the most promising projectile-target combination that would favor fusion. The results yield information on reaction contact times, with the longest exhibited by 50Ti+249Cf.

Highlights

The search for new elements represents one of the main focus points of physics research
We present QF mass and angular distributions for four Z=120-formation reactions measured with large angular coverage, where significant differences in reaction dynamics are observed through the QF outcomes
An analysis using two-body kinematics was carried out for events measured in coincidence between the forward-angle multi-wire proportional counters (MWPCs) and one of the two backward-angle MWPCs, allowing fission fragment mass ratios, defined as M R = m1/(m1 + m2), and scattering angles to be determined

Summary

Introduction

The search for new elements represents one of the main focus points of physics research. New beam and target combinations must be explored to reach beyond Z=118 as doubly-magic 48Ca projectile ions, successfully used in fusion-evaporation reactions for the production of elements with Z=112-118 [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24], cannot presently be used due to insufficient amounts of target material with Z>98 [25]. Element Z=120 remains undiscovered, suggesting that production cross sections are lower than those for 48Ca-induced reactions. The important question of how much lower the production cross sections are remains unanswered, which is a critical issue for the planning of successful future SHN experiments

Methods

Results

Conclusion