Scientific Russia: St Petersburg University physicists gaining better understanding of how the vacuum breaks down
On 30 June 2021, the Joint Institute for Nuclear Research in Dubna held the International Workshop ‘Superheavy Elements’. Vladimir Shabaev, Professor in the Department of Quantum Mechanics at St Petersburg University, presented the results of the large-scale long-running project that brought together both well-renowned scientists and early-career researchers, including students and postgraduate students. They developed the methods and techniques to assess the role of the effects that were little considered before. Today, Professor Shabaev and his colleagues are studying more refine details of the quantum dynamics processes.
The early 1930s saw the origin of the quantum field theory. Even then the theory could predict a spontaneous electron–positron pair production in strong homogeneous electric fields, intensity of which must be above a threshold value, said Professor Shabaev. Yet scientists were far from being able to prove this hypothesis.
50 years ago, the Soviet physicists Semyon Gerstein, Yakov Zeldovich, Vladimir Popov showed that the field of bare nucleus with a charge over the threshold of 173 caused vacuum instability. The same results were independently obtained by the German scientists headed by Walter Greiner. This can also cause the positron production. The initially neutral vacuum decays into charged vacuum and two positrons.
There are no nucleuses with such large charges in nature. The atomic number of the known heaviest element, i.e. oganesson, is 118. Attempting to create a supercritical field, scientists collide nucleuses with the total charge exceeding the critical value. Yet all their attempts to experimentally see this process have failed so far.
The German scientists headed by Walter Greiner concluded that the vacuum decay could only be experimentally observed if colliding nucleuses adhered for some time due to nuclear force. ‘I had little, if any, hope that nucleuses could adhere when colliding’, said Vladimir Shabaev.
The Russian scientists could show that in certain experiments that focused on measuring the number of positrons produced through the low-energy collision of two bare nucleuses or a bare nucleus and a neutral atom they could see how the spontaneous production of positrons could contribute to the process. This indicates the decay of the vacuum in the supercritical Coulomb field, with no adhesion of nucleuses.