Fusion reaction Ca48+Bk249 leading to formation of the element Ts ( Z=117

Abstract

The heaviest currently known nuclei, which have up to 118 protons, have been produced in 48 Ca induced reactions with actinide targets. Among them, the element tennessine (Ts), which has 117 protons, has been synthesized by fusing 48 Ca with the radioactive target 249 Bk, which has a half-life of 327 d. The experiment was performed at the gas-filled recoil separator TASCA. Two long and two short α decay chains were observed. The long chains were attributed to the decay of 294 Ts. The possible origin of the short-decay chains is discussed in comparison with the known experimental data. They are found to fit with the decay chain patterns attributed to 293 Ts. The present experimental results confirm the previous findings at the Dubna Gas-Filled Recoil Separator on the decay chains originating from the nuclei assigned to Ts.

Search for Electron-Capture Delayed Fission in the New Isotope Md244

“…In the present experiment, all signals from the preamplifiers were processed with fast digital electronics, which replaced the previous combined analog and digital electronics [19][20][21][22][23][24]. Signals from the X and Y strips were amplified with different gains to provide two energy branches up to about 20 and 200 MeV.…”

“…An isomeric state is retarded to decay via electromagnetic transitions, thus, it deexcites predominantly through emission of a conversion electron (CE). Recently, it has been shown that CEs from the decay of short-lived isomeric states can be efficiently detected in the digital trace of the preceding signal [23,24,37]. Since in the present experiment the shape of each signal was stored, we inspected the 30 μs-long traces of the seven ER signals followed by α decays of 244 Md, checking for the presence of a low-energy signal associated with the decay of an isomeric state.…”

Search for elements 119 and 120

“…The four target segments were mounted on a wheel, which rotates synchronously to the time structure of the beam. To ensure safe operation, all target segments were continuously monitored using different methods such as online temperature readings during the experiment with a pyrometer [16,30].…”

“…Currently available experimental data on the decay properties of known superheavy nuclei [1,[5][6][7][8][9][10][11][12][13][14][15][16] indicate a stability against fission, thus confirming the concept of the island of stability, but to date the exact location of the center of the island of stability, i.e., proton and neutron shell closures, and its landscape are not yet known. For a long time it was assumed that Z = 114 and neutron number N = 184 would form closed shells [3].…”

“…249 Bk, which decays by β − into 249 Cf with a half-life of only 327.2(3) d [26], is a unique target. Starting with a freshly prepared, pure 249 Bk target, the amount of 249 Bk will continuously decrease over time, and the amount of 249 Cf will increase [16]. This situation provides a unique opportunity to simultaneously search for a direct production of two SHEs in a single longlasting irradiation.…”