An Erratum to this paper has been published: https://doi.org/10.1134/S1547477125020025

In experiments involving the synthesis of super-heavy elements through heavy ion reactions, it was crucial to precisely adjust the mean energy of the heavy ion beam to identify the narrow peaks of the excitation functions. A motorized manipulator was developed to degrade the heavy ion beam, enabling the adjustment of the mean energy in finer increments and faster than was achievable by the cyclotron alone. Thin metal foils used as ion beam energy degraders were positioned on an aluminum mount with windows. The ion beam traverses these degraders, leading to energy loss, and the final energy can be adjusted to the desired value by varying the effective thickness of the foils. This study includes a calculation of the ion beam energy after energy loss, along with an experimental evaluation of energy loss straggling and a calculation of energy distribution inside the target. The tests carried out revealed that simulations may underestimate beam energy loss straggling, highlighting the importance of experimental measurements of the beam energy distribution for real material dimensions.

Mass measurement allows to determine the full binding energy of the nucleus—the integral characteristic of all atomic and nuclear forces which is the key for solving the fundamental physics problems, which includes nuclear physics, astrophysics, physics of fundamental interactions and symmetries, neutrino physics. High precision mass spectrometry could solve the problems of proton and neutron shells location in the nucleus (precision ΔM/M 10–6), the study the nuclei deformation phenomena, searching of so-called “halo-nuclei”, the correct description of the heaviest elements formation during astrophysical r- and rp-processes of fast neutron and proton captures respectively (precision ΔM/M 10–7). For this reason, a new facility for the high precision mass-spectrometry of heaviest nuclei is being built at the Flerov Laboratory of Nuclear Reactions, JINR, Dubna. It will include new target block, gas-filled separator for the reaction products, cryogenic gas-filled ion stopping cell (“Cryocell”), radio-frequency quadrupole transport system and the multi-reflection time-of-flight mass-spectrometer (MR-TOF-MS). This setup could provide mass measurements with the precision of about ΔM/M 10–7. “Cryocell” is one of the most crucial component of it. This is a powerful instrument for the fundamental research due to its high conversion coefficient of the fluxes of reaction products with heavy ions at energies 5–10 MeV/nucleon into low energy secondary beam and low extraction time. It could open the possibility to perform mass analysis of short-lived isotopes with the lifetime of 100 ms and more.

The separation efficiency and extraction time of mass separator MASHA, which is a combination of solid ISOL method and classic mass spectroscopy, were obtained for mercury and radon isotopes produced in complete fusion reactions 40 Ar + 144 Sm = 184– xn Hg and 40 Ar + 166 Er = 206– xn Rn. The extraction time and separation efficiency at the MASHA setup for both reactions are determined by the ratio of cross sections measured with mass separator to absolute cross sections obtained in our previous experiments [1].

The complete-fusion excitation functions of xn-evaporation channels for the reactions Sm-144(Ar-40, xn)Hg184-x, Sm-148(Ar-36, xn)Hg184-x, Nd-144(Ca-40, xn)Hg184-x, Nd-142(Ca-48, xn)Hg190-x, and Er-166(Ar-40, xn)Rn206-x have been measured by using the catcher foil technique. Its modified version as well as a corresponding software of data processing, including a deconvolution procedure to take into account effects caused by spreading the energy of the beam at its passing through absorbing foils, have been described. The measured excitation functions have been compared with ones theoretically calculated with the coupled-channel model.

A modified catcher foil technique is used to measure the absolute cross sections of xn -evaporation channels in complete fusion reactions 144 Sm( 40 Ar, xn ) 184− x Hg, 148 Sm( 36 Ar, xn ) 184− x Hg, 144 Nd( 40 Ca, xn ) 184− x Hg, 142 Nd( 48 Ca, xn ) 190− x Hg, and 166 Er( 40 Ar, xn ) 206− x Rn. The effect the spread of the beam’s energy has on the excitation functions as it moves through absorbing foils and the target is addressed by means of deconvolution. The measured excitation functions are compared to ones calculated theoretically using the coupled-channel model.

The MASHA facility [1-3] was developed as a high precision mass-spectrometer for heavy and super heavy elements with masses up to 450 a.m.u. It uses ISOL (Isotope Separation On-Line) method. Its unique properties opens great prospective for the investigation of neutron-rich nuclei produced in multinucleon transfer reactions. Mainly nuclei near the neutron N = 126 and N = 152 shell closures are of great interest. This region of nuclei is not so far thoroughly enough investigated while its research has direct relation to the synthesis of super heavy elements. As is known the island of stability close to super heavy elements (Z = 112-118) exists due to the shell effects in nuclei. More detailed investigation of these shell effects can greatly help in the synthesis of next super heavy elements. Heavy neutron rich radon isotopes were produced in the multinucleon transfer reaction Ar-40 + Th-232 at Flerov Laboratory of Nuclear Reactions, Dubna. Radon isotopes with given masses were detected using two types of detectors: a multi-strip well-type detector (made in Canberra) and a position-sensitive quantum counting hybrid pixel detector of the Timepix type [4]. The latter detector has an array of 256x256 square pixels each with a pitch size of 55 mu m for the full sensitive area 14x14mm(2). Radon isotopes implanted into the detector emit then alpha and beta particles until they reach the stable or long-lived isotopes at the end of their decay chains. The positions of radon isotopes, the tracks, times and energies of the beta particles were measured and analyzed. New software for the particle recognition and data analysis of the results obtained from the experiment was developed and used. It has been proven that MASHA + Timepix setup is a powerful instrument for investigation of neutron-rich isotopes far from stability limits.

Experiments on measuring the separation efficiency of evaporation residues produced in complete fusion reactions with heavy ions have been performed on the MASHA mass separator. A new design has been developed for a hot catcher based on the use of thin paper from graphite nanotubes and graphene. The catcher is to be used for the synthesis of nuclei at a high intensity of the primary beam to increase the efficiency of separation. A 16-strip silicon detector was used for continuous monitoring during an experiment to measure the mass spectrometer’s efficiency of separation in the intermediate focal plane.

The MASHA setup designed as the mass-separator with the resolving power of about 1700, which allows mass identification of superheavy nuclides is described. The setup uses solid ISOL (Isotope Separation On-Line) method. In the present article the upgrade of some parts of MASHA are described: target box (rotating target + hot catcher), ion source based on electron cyclotron resonance, data acquisition, beam diagnostics and control systems. The upgrade is undertaken in order to increase the total separation efficiency, reduce the separation time, of the installation and working stability and make possible continuous measurements at high beam currents. Ion source efficiency was measured in autonomous regime with using calibrated gas leaks of Kr and Xe injected directly to ion source. Some results of the first experiments for production of radon isotopes using the multi-nucleon transfer reaction 48Ca+242Pu are described in the present article. The using of TIMEPIX detector with MASHA setup for neutron-rich Rn isotopes identification is also described.

A new beam diagnostic system based on the PXI standard was developed, tested, and used in the MASHA setup experiment. The beam energy and beam current measurements were carried out using several methods. The online time-of-flight energy measurements were carried out using three pick-up detectors. We used two electronic systems to measure the time between the pick-ups. The first system was based on fast Agilent digitizers (2-channel, 4-GHz sampling rate), and the second one was based on a constant fraction discriminator (CFD) connected to a time-to-digital converter (TDC, 5-ps resolution). A new graphical interface to monitor the electronic devices and to perform the online calculations of energy was developed using MFC C++. The second system based on microchannel plate (time-of-flight) and silicon detectors for the determination of beam energy and the type of accelerated particles was also used. The beam current measurements were carried out with two different sensors. The first sensor is a rotating Faraday cup placed in front of the target, and the second one is an emission detector installed at the rear of the target. This system is now used in experiments for the synthesis of super-heavy elements at the U400M cyclotron of the Flerov Laboratory of Nuclear Reactions (FLNR).

The results of the development and the general information about the data acquisition system which was recently created at the MASHA setup (Flerov laboratory of nuclear reactions at Joint institute for nuclear research) are presented. The main difference from the previous system is that we use a new modern platform, National Instruments PXI with XIA multichannel high-speed digitizers (250 MHz 12 bit 16 channels). At this moment system has 448 spectrometric channels. The software and its features for the data acquisition and analysis are also described. The new DAQ system expands precision measuring capabilities of alpha decays and spontaneous fission at the focal plane position-sensitive silicon strip detector which, in turn, increases the capabilities of the setup in such a field as low-yield registration of elements.