21 research outputs found
Direct mass measurements above uranium bridge the gap to the island of stability
The mass of an atom incorporates all its constituents and their
interactions. The difference between the mass of an atom and the
sum of its building blocks (the binding energy) is a manifestation
of Einstein\u2019s famous relation E = mc^2. The binding energy determines
the energy available for nuclear reactions and decays (and
thus the creation of elements by stellar nucleosynthesis), and holds
the key to the fundamental question of how heavy the elements can
be. Superheavy elements have been observed in challenging
production experiments, but our present knowledge of the
binding energy of these nuclides is based only on the detection
of their decay products. The reconstruction from extended decay
chains introduces uncertainties that render the interpretation
difficult. Here we report direct mass measurements of transuranium
nuclides. Located at the farthest tip of the actinide species
on the proton number\u2013neutron number diagram, these nuclides
represent the gateway to the predicted island of stability. In
particular, we have determined the mass values of 252-254No
(atomic number 102) with the Penning trap mass spectrometer
SHIPTRAP5. The uncertainties are of the order of 10 keV/c2
(representing a relative precision of 0.05 p.p.m.), despite minute
production rates of less than one atom per second. Our experiments
advance direct mass measurements by ten atomic numbers
with no loss in accuracy, and provide reliable anchor points en
route to the island of stability
Polaron hopping mediated by nuclear tunnelling in semiconducting polymers at high carrier density
<p>The transition rate for a single hop of a charge carrier in a semiconducting polymer is assumed to be thermally activated. As the temperature approaches absolute zero, the predicted conductivity becomes infinitesimal in contrast to the measured finite conductivity. Here we present a uniform description of charge transport in semiconducting polymers, including the existence of absolute-zero ground-state oscillations that allow nuclear tunnelling through classical barriers. The resulting expression for the macroscopic current shows a power-law dependence on both temperature and voltage. To suppress the omnipresent disorder, the predictions are experimentally verified in semiconducting polymers at high carrier density using chemically doped in-plane diodes and ferroelectric field-effect transistors. The renormalized current-voltage characteristics of various polymers and devices at all temperatures collapse on a single universal curve, thereby demonstrating the relevance of nuclear tunnelling for organic electronic devices.</p>