Two-proton radioactivity of exotic nuclei beyond proton drip-line

To search for new candidates of the true and simultaneous two-proton (2p) radioactivity, the 2p decay energies (Q_2p) are extracted by the Weizsäcker–Skyrme-4 (WS4) model, the finite-range droplet model (FRDM), the Koura–Tachibana–Uno–Yamada (KTUY) model and the Hartree–Fock–Bogoliubov mean-field model with the BSk29 Skyrme interaction (HFB29). Then, the 2p radioactivity half-lives are calculated within the generalized liquid drop model by inputting the four types of Q_2p values. By the energy and half-life constraints, it is found that the probable 2p decay candidates are the nuclei beyond the proton-drip line in the region of Z≤50 based on the WS4 and KTUY mass models. For the FRDM mass model, the probable 2p decay candidates are found in the region of Z≤44. However, the 2p-decaying candidates are predicted in the region of Z≤58 by the HFB29 mass model. It means that the probable 2p decay candidates of Z>50 are only predicted by the HFB29 mass model. Finally, the competition between the true 2p radioactivity and α-decay for the nuclei above the N=Z=50 shell closures is discussed. It is shown that ¹⁰¹Te, ¹¹¹Ba and ¹¹⁴Ce prefer to 2p radioactivity and the dominant decay mode of ¹⁰⁷Xe and ¹¹⁶Ce is α-decay.