Superheavy nuclei exist only through quantum shell stabilization, and the predicted 'island of stability' near neutron number N = 184 lies roughly 10–14 neutrons beyond every isotope produced so far, because complete fusion of stable beams with available targets yields only proton-rich products. Multinucleon transfer in low-energy damped heavy-ion collisions — including actinide+actinide damped collisions with the predicted 'inverse quasifission' yield enhancement, and peripheral massive transfer of fission-like fragments detected with active catchers — has been proposed as the one near-term mechanism that could produce neutron-rich superheavy nuclei approaching the island. Whether it can do so with cross sections, excitation-energy distributions, and survival probabilities large enough for practical synthesis remains undetermined: no neutron-rich superheavy nucleus has yet been produced or unambiguously identified via multinucleon transfer; predicted cross sections near N = 184 still span picobarns to sub-femtobarns across model families; the shell-effect and inverse-quasifission mechanism is not experimentally established; and the required beam intensities, targets, separation, and decay-identification technology remain under development. The problem is to settle, by measurement and/or validated theory, the production yields and detectability of neutron-rich superheavy nuclei in such reactions — and thereby how far toward the island of stability this route can actually reach.

Background

Superheavy nuclei (SHN) — nuclei with proton number Z≥104Z ≥ 104 — owe their existence to quantum shell effects: without the extra binding of closed nucleon shells, the liquid-drop model of the nucleus predicts that fission destroys nuclei beyond roughly Z≈104Z ≈ 104. Nuclear-structure calculations since the 1960s predict a region of enhanced stability, the 'island of stability', centered near the closed neutron shell N=184N = 184 and a proton shell closure whose location (Z=114Z = 114, 120, or 126) is model-dependent, where fission barriers and half-lives should be maximal. All SHN synthesized so far — up to oganesson, Z=118Z = 118, made in 'hot fusion' reactions of 48^{48}Ca beams with actinide targets — are proton-rich isotopes that stop about 10–14 neutrons short of N=184N = 184, because no combination of available stable projectiles and targets is neutron-rich enough and the heaviest usable target is californium (Z=98Z = 98). Fusion cross sections also fall steeply with ZZ: from roughly 0.5 picobarn for oganesson to an estimated tens of femtobarns for Z=119Z = 119–120120, while radioactive-ion beams are far too weak to help. Reaching the neutron-rich side of the superheavy region therefore requires a reaction mechanism other than complete fusion.

The leading candidate is multinucleon transfer (MNT) in low-energy damped collisions — deep-inelastic, near-Coulomb-barrier collisions in which two heavy nuclei remain in contact long enough to exchange many nucleons before reseparating. MNT was used in the 1970s–80s to make transfermium isotopes (up to fermium and mendelevium, at cross sections around 0.1 microbarn), and was revived by Zagrebaev and Greiner, whose multidimensional Langevin transport calculations (stochastic simulations of the collective shape evolution of the two touching nuclei) with time-dependent diabatic-to-adiabatic two-center shell-model potentials predict that shell effects drive 'inverse quasifission' — a drift of the colliding system toward larger mass asymmetry, i.e. toward a doubly magic (doubly shell-closed) lead-like fragment plus a very heavy, neutron-rich partner — enhancing heavy trans-target fragment yields by orders of magnitude relative to a smooth exponential falloff in collisions such as 238^{238}U + 248^{248}Cm at energies near the contact threshold, where primary-fragment excitation energies, and hence fission losses during de-excitation, are lowest. The survival probability of an excited primary fragment — the probability that it cools by γ emission and evaporated neutrons instead of fissioning — determines whether the primary yield becomes an observable nucleus. A complementary variant proposed by the Texas A&M / Kraków collaboration uses peripheral massive transfer, in which a fission-like fragment from a fissile target (e.g. 232^{232}Th) is transferred onto a heavy projectile (e.g. 197^{197}Au), with the sought products detected through characteristic high-energy alpha decays in an 'active catcher' — a compact array of fast scintillator implantation units with ΔE–E telescopes (paired detectors measuring a particle's energy loss and residual energy to identify it) built to register nanosecond-scale decays of unseparated products.

Whether any of this delivers neutron-rich SHN near the island in practice is unestablished, as the two source works state explicitly: quantitative yields, achievable neutron richness, excitation-energy distributions, and survival probabilities of the heavy products are unmeasured; the inverse-quasifission mechanism and the role of shell effects in damped collisions have not been cleanly demonstrated experimentally (the one surrogate test, 160^{160}Gd + 186^{186}W, showed enhanced trans-target yields but its interpretation is still debated); and low actinide-beam intensities, scarce neutron-rich targets, and the difficulty of separating and identifying slow, hot, heavy products — whose decay chains may terminate in uninformative spontaneous fission — are severe practical obstacles. Cross-section predictions for the region around N=184N = 184 currently range from picobarns to sub-femtobarns depending on the model family (Langevin-type stochastic transport models, dinuclear-system models that treat capture followed by nucleon exchange between two touching nuclei, quantum-molecular-dynamics simulations, or time-dependent Hartree–Fock mean-field dynamics), so even the order of magnitude of the relevant yields is unsettled.

Problem Statement

Can multinucleon transfer in low-energy damped collisions of heavy ions — actinide + actinide damped collisions with predicted inverse-quasifission enhancement, or peripheral massive transfer of fission-like fragments onto heavy projectiles — produce neutron-rich superheavy nuclei approaching the predicted island of stability (N=184N = 184, Z≈114Z \approx 114–126126) with cross sections, excitation-energy distributions, and survival probabilities large enough for practical synthesis, i.e. at rates that can be produced, separated, and unambiguously identified at present or realistically planned accelerator facilities?

A complete answer would jointly establish, for concrete projectile–target–energy combinations: (i) the production cross sections of surviving (de-excited) neutron-rich superheavy products — how far in ZZ and NN beyond the heaviest known isotopes the yields remain measurable, and at what level; (ii) the excitation-energy distribution of the primary heavy fragments and their survival probability against fission, which together determine whether primary yield becomes observable nuclei; (iii) the reaction mechanism — whether shell effects and inverse quasifission genuinely enhance heavy-fragment yields in damped collisions — established by experiment and/or validated theory rather than only modeled; and (iv) practical detectability — whether in-flight separators, gas catchers (cells that slow and thermalize recoiling products so they can be extracted and identified), or active-catcher α-decay detection can identify the products given beam intensities, product kinematics, and backgrounds. These four aspects jointly answer the single feasibility question posed by the source literature.

The answer may be positive (a demonstrated or reliably predicted feasible route, with quantified yields), negative (an experimentally grounded upper limit, or a validated theoretical demonstration that yields near the island are impractically small), or a sharp delimitation of the reachable region — e.g., up to which ZZ and NN multinucleon transfer is practical and beyond which it is not. No restriction on reaction system, model class, or detection technique is implied; the problem is the general feasibility question in the form the sources pose it.

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