NCBJ: isomers of superheavy elements may be much more stable than previously thought
Some isomeric states of superheavy elements can have lifetimes measured in seconds, tens of thousands of times longer than the lifetimes of their highly unstable ground states. If such exotic nuclear states are created experimentally, they will be stable enough to study their chemical properties.
These conclusions are indicated by the results of the team's work, theorist The study was carried out by the National Centre for Nuclear Research (NCBJ) and the University of Zielona G ra rski (UZ).
The Periodic Table currently contains 118 elements in, but only 80 of them have stable isotopes. isotope nuclei in unstable prior or p later they undergo decay. In some nuclei in isomeric states form atoms that have chemical properties similar to those of nuclei in the ground state. All isotopes of the elemental in the heaviest. Life times of kr The current state of technology does not allow to determine the chemical properties of the element, in particular The energies and other quantum parameters of the states of the The NCBJ press release reads.
Atomic nuclei are systems composed of proton and neutron , which elements interact with each other in a way b, kt At present we are able to describe only approximately. In the heaviest nuclei the total number of nucleons – proton in and neutron in – reaches 300. In the macroscopic world, known from everyday experience, complex systems can undergo perturbations, e.g. start to oscillate or rotate, while still remaining bound. In the world of the system in complex nuclei forming atomic nuclei, which is governed by the laws of quantum physics, perturbations may also occur, and system transitions correspond to them into a state in the excited ones. R difference – and essentially the essence of the world on a quantum scale – is that the energies and other parameters of the quantum states in excited states, they cannot change freely as a result of a disorder. Permissible changes are strictly portioned, i.e., quantized – explain NCBJ experts.
According to NCBJ, the nucleus in the excited state has an energy higher than that of the ground state and in the excited state it decays It is expected that such nuclei are the best candidates for long-lived isomers in the basic ones – reads the announcement in gamma. However, in some In all nuclei there are such excited states, which hich last for a significantly longer time – they are called isomers. One of the manifestations of the in their internal excitation can be a change in spin, the quantum equivalent of angular momentum, measuring how „the components of the system are spinning fast”. Nuclei in the isomeric state form atoms with the same chemical properties as those in the ground state.
– In 2001 an isomer of the darmstadt isotope with mass number 270 was discovered in the GSI center in Germany. It turned out that the nucleus decays through the emission of an alpha particle, as do most of the in the superheavy, but its lifetime is approx. 60 times longer than the lifetime of the same isotope in the ground state. Isomers living longer than the ground state were known in the case of lighter nuclei. However, the decay of the darmstadt isomer by emission of an alpha particle meant that a typical electromagnetic (gamma) decay is less likely for this nucleus. There is a natural question if there are other isomers of the element in the superheavy, which hich lifetimes are extended in relation to those of in the life of their state in the fundamental – we read in the announcement.
syndrome Polish physicist In the present state of technology it is not possible to determine the chemical properties of an element I will assess the effect responsible for the decay of the alpha decay. Scientists, carrying out calculations and estimates, looked for such superheavy nuclei, for which The alpha decay of the nucleus would be the most susceptible. Such nuclei can be expected to be the best candidates for long-lived isomers.
– Purely experimental determination of the structure of the excited state is in principle impossible – explains prof. Michał Kowal, head of the NCBJ Department of Theoretical Physics, quoted in the press release. – So far, it was suspected that the observed stability of the darmsztadt-270m isomer is due to the excitation of the neutron pair. From our calculations It follows that stability is determined rather by proton excitations – he adds.
Excited states, with which hich we are dealing with here, can be imagined as systems, in which of which a part of the nucleon – for example two protons, two neutrons or both at the same time – are not in their fundamental position, but circulate around The core of the nucleus in the same direction. In some r these nuclei such excited state can have total spin with value of up to 19 or 20 Planck constants. The dominating decay channel of the nuclei under consideration is alpha decay, i.e. emission of a helium nucleus built of two ch proton in and two ch neutron . The alpha decay of nuclei with a in isomeric can occur to the ground state or to kt state of the in the excited progenitor (final) nucleus.
– No one today knows how to calculate exactly the isomer lifetime because of the alpha decay – adds prof. Kowal. – It is well known, however, that the abatement of alpha decay is connected with at least three reasons: r tructure or spin state in the initial and final and r he energy difference of these states . Alpha decay to the progenitor nucleus in the ground state requires a change in the spin of the nucleus by 20 units of Planck's constant. It is very much! The centrifugal barrier connected with such a change is huge and practically blocks this decay. Moreover, due to a completely different structure of the In the initial and final stages, the decay is additionally strongly excited. These two effects make decay to the ground state of the daughter nucleus extremely unlikely. On the other hand, the decay to a progeny nucleus in an excited state with a similar spin as the original isomeric nucleus, occurs with a high probability only if this state has a sufficiently low excitation energy in por In comparison to the excitation energy of the emitting nucleus. In case of some For some of the nuclei considered by us it is not so and therefore we suspect that for these states there will be a strong suppression of the alpha decay in the initial ones, and consequently the isomeric state will have a long lifetime – explains the scientist.
Work of Polish physicists The paper was published in the journal "Physical Review C" and was presented during this year's summer nuclear physics conferences. – We analyzed exotic states in the heaviest nuclei with even numbers of protons in and neutron – says prof. Janusz Skalski (NCBJ). – We have described the decay mechanism and given a candidate in long-lived nuclear states. Our calculations and estimates indicate that long-lived isomeric states with the structure of simultaneous dw pairs – proton and neutron, should appear in four isotopes of darmstadt. We do not expect such isomeric long-lived configurations to occur in isotopes of the element in atomic numbers Z=106, 108 and 112 – m i.
– Our predicted alpha decay decay temps of the states in biproton nuclei are large for virtually all darmstadt nuclei – complements dr Piotr Jachimowicz from the University of Zielona G ra rski. – The estimated in this paper lifetimes of these isomeric in hundreds or even thousands of milliseconds, that is by three to five orders of magnitude in magnitude more than the lifetimes of their states in the basic ones – he points out.
The presented result is so far only a theoretical prediction. Scientists, however, hope that in the near future their prediction will be verified experimentally. – It is quite probable that similar states were already produced in experiments conducted in the past, but nobody noticed them, because the measurements were aimed at lifetimes of much smaller tsze – explains prof. Kowal. – At the moment there should be no major problems in making appropriate measurements . Several laboratories in the world has the right capabilities. Perhaps in a few years such experiments will be possible also in Warsaw, if the project of purchase of a new cyclotron for the Environmental Heavy Ion at the University of Warsaw. If our predictions about the stability of the isomer If it is confirmed, it will open up completely new possibilities for research on the chemistry of in superheavy – m i.
Source: Source: PAP – Science in Poland, NCBJ, photo. NCBJ. On the picture: Scheme of alpha decay of sister nuclei 270Ds and 270Cn with marked transitions between states of analogous structure (marked in red). The length of the transition line is related to the stability of the state. The longer the line, the kr a shorter lifespan, i.e. faster decay. Different line lengths justify high stability of isomeric state in 270Ds (kr long red line – longer lifetime) and low stability at 270Cn (long red line – kr tki lifespan).