Short-lived radioactive molecule is first subjected to laser spectroscopy

At CERN performed the first laser spectroscopy of short-lived radioactive molecules. The experiment allows to investigate the unstable system since the life time from hundredths of a second and to look for phenomena beyond the Standard model. Article published in the journal Nature.

Radioactive are called molecules, composed of atoms with unstable nuclei. In some of these systems in comparison with single atoms greatly increase the effects associated with symmetry breaking for the treatment of coordinates and time. This gives the experiments to measure properties of the radioactive molecules of importance from the point of view of fundamental physics. The data of such experiments provide an opportunity to test theoretical models and to go beyond their predictions. On the other hand, in such studies, scientists are faced with a whole set of problems. The interaction between the atoms significantly affect the system of quantum levels and complicate the spectroscopy of molecules, whereas the instability of nuclei limits the life time of the available mass and the speed of production of such systems.

A team of scientists from nine countries, headed by R. F. Garcia Ruiz (R. F. Garcia Ruiz) from the European organization for nuclear research (CERN), conducted the first laser spectroscopy of radioactive molecule radium monofluoride (RaF). Did a physics experiment on the basis of complex ISOLDE (Isotope Separator On-Line Detector) — this setting allows you to make and sort the isotopes in a wide range of masses.

The atoms of radium, which is necessary for formation of RaF molecules, scientists have made more than a month before the spectroscopy. To do this, they for two days were irradiated by accelerated up to an energy of 1.4 GeV beams of protons around the target is uranium carbide. Then the material was placed in a sealed chamber, which is filled with argon, and only 33 days started formation of radioactive molecules. To get the radium isotopes to diffuse to the surface of the target, the experimenters created a temperature of 1300°C and lowered the pressure up to 10-5 mbar (in hundred million times less than typical atmospheric pressure). With the help of special valve they are introduced into the environment gaseous terraformer (CF4), which interacted with the atoms of radium. The product of the reaction into molecular ions RaF+that was removed from the target by an electrostatic field and held high-precision (with a resolution of 1÷2000) sorting in the mass separator. Then, the beam RaF+ for ten milliseconds slowed down in helium at room temperature. Finally, slow molecular ions are passed through a chamber with sodium vapor (which has a similar ionization potential), and taking the last electron, becoming neutral molecules RaF, while the remaining charged ions RaF+ installation rejected to the side.

After that, radioactive molecules were in the area of high vacuum (at a pressure of 10-10 millibar, which is 10 trillion times less than atmospheric), where they alternately shone two laser beams. The wavelength of the first laser, the scientists regulated in the range from 600 to 780 nanometers so that the energy of the photon coincides with the energy of the excited level of the molecule. The second laser had a fixed wavelength of 355 nanometers, the energy of its radiation, the molecule passed from the excited state to the ionized (whereas on the main level of energy for such a transition is not enough). The emerging molecular ions RaF+ recorded the detector. Removing the dependence of number of events in the detector to the wavelength of the first laser, physicists have measured the energy spectrum of excitations (i.e. the set of quantum energy levels) of radioactive molecules.

The authors note that the experience can be used to study not only radium monofluoride, and a number of other volatile compounds with a lifetime from tens of milliseconds that have not previously been explored experimentally (among them RaOH, RaO, RaH, AcF and ThO). In addition, development in this area will help to develop sectors such as quantum chemistry and radiochemistry, and even benefit astrophysicists — the latest in future observations can reliably identify radioactive molecules.

Last month we talked about the results of several advanced experiments, physicists have managed to create entanglement between the atom and the molecule, to detect crystals Pauli and to replace electron in the pion in the helium atom.

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