ACCULINNA scientific group home page

About ACCULINNA scientific group

at FLNR JINR, Dubna

Progress in the production of very short lived nuclei and the development of radioactive ion beams (RIBs) provide access to the study of the most exotic nuclei. Since 1996, when the fragment separator ACCULINNA was built, RIBs became a powerful tool used in the Flerov Laboratory of Nuclear Reactions (FLNR) in the studies of exotic nuclei.

Within the recent years the ACCULINNA group not only used recognized techniques to RIB research. It proposed, developed, and practically applied a novel approach, to the investigation of resonant states or nuclei in proximity and beyond the neutron drip-line. This work was not restricted solely to the derivation of invariant/missing mass spectra. It succeeded to show that, in the experiments performed with certain kinematical settings, correlations inherent to the reaction products become an extremely rich source of information about the structure of the studied exotic nuclei. A unique technical feature of the ACCULINNA separator is the availability of intense tritium beams accelerated at the U-400M cyclotron and possibility to work with cryogenic tritium targets. At the moment it is the only place in the world where the availability of the tritium target and the beam is combined with the RIB research.

There are several factors which favor to achieve interesting physics results at the ACCULINNA facility. Primary heavy ion beams ( e.g. ⁷Li, ¹¹ B, ¹⁸0, ²⁰Ne, ³²S, ⁴⁸Ca) provided by the U-400M cyclotron fall into quite a low energy domain restricted to 35-55 MeV /amu. However, the record intensities of these beams partly compensate the deficiency in the RIB production rate inevitable in this case. The higher cross sections inherent to some important nuclear reactions at low RIB energies accessible at ACCULINNA counterbalance their relatively low intensities. Further, energy range of the exotic beams provided by ACCULINNA is optimal for the nuclear structure studies done by means of transfer reactions. Due to their transparent mechanism the transfer reactions are well understood and clear explanation becomes available for the data obtained low (compared to the other in-flight separators) RIB energy provides prerequisite for better energy resolution in the measurements done in different experimental conditions. Complete kinematical measurements performed for the reactions induced by these beams result in the observation of very clean, background-free spectra. Essential consequence of such correlation measurements is the possibility of unambiguous spinparity identification for the observed resonance states. The choice of kinematical conditions selecting specific reaction mechanisms (i.e., direct transfers, quasi-free scattering, and spin alignment in zero geometry transfers) simplifies data interpretation.

Setups and projects

ACCULINNA fragment-separator

The separator ACCULINNA is in operation since 1996. High intensity primary beams of ⁷Li, ¹¹B, ¹³C, ¹⁵N and ¹⁸O with energy values ranging between 32 and 50 AMeV are delivered by the U-400M cyclotron to the production target of the separator. The secondary beams of ⁶He and 8He nuclei with energies of about 25 AMeV allowed us to gain new insights into the structure of neutron halo nuclei through the study of one- and two- neutron transfer reactions made with hydrogen and helium targets.

ACCULINNA-2 fragment-separator

The new fragment separator ACCULINNA-2 in the Flerov Laboratory of Nuclear reactions, JINR Dubna is in the commissioning phase since 2016. It is 36 meters long achromatic separator consisting of two 45-degree dipole magnets, 14 quadrupoles, 8 multipoles (3 octupoles and 5 sextupoles) and 4 steering magnets. The high intensity primary beams are delivered by the U-400M cyclotron to the rotating production target module installed in the first intermediate focal plane F1 to produce radioactive ion beams in fragmentation reactions via in-flight method.

DERICA: Dubna Electron–Radioactive Ion Collider fAcility

In this section, consideration is given to the concept and the research agenda of the promising accelerator–storage ring complex for RIB research, which is a proposed international megaproject on the basis of the FLNR JINR. The motivation of the new project is described and the RIB production characteristics of the complex are briefly presented, which are comparable in some aspects with the characteristics of advanced world centers known as RIB factories. In this project, emphasis is placed on investigating short-lived RIBs in storage rings. One unique feature of the project is the possibility of studying the interaction between electrons and radioactive isotopes in a collider experiment for determining fundamental properties of nuclear matter such as electromagnetic form factors of exotic nuclei.

EXPERT - EXotic Particle Emission and Radioactivity by Tracking

The joint proposal EXPERT is aimed at studies of the nuclear landscape beyond the proton and neutron drip-lines and intends to push researches up to limits of nuclear existence. By combining the EXPERT instrumentation in different scenarios, phenomena of radioactivity, resonance decays, β-delayed decays and exotic excitation modes can be studied via observations of particle emissions, including the 2p, 4p, n, 2n, 4n channels.

RIBs diagnostic instruments

RIBs diagnostic system of ACCULINNA-2 complex consists of time-of-flight (ToF) and tracking detectors. For precise particle identification, two ToF scintillation detectors are installed in F3 and F5 focal planes of ACCULINNA-2 at a distance of 12.3 meters. Depending on the experimental program these detectors can be equipped by organic scintillator (e.g. BC404) with a thickness down to 25 μm with an active area of 60 mm in diameter. Each scintillator is coupled with four Hamamatsu R7600-200 photomultiplier tubes (PMT). In the case of scintillator thickness of 125 μm, the time resolution of 100 ps (sigma) can be obtained.

Cryogenic targets

The studies of exotic nuclei at both Dubna fragment separators are mainly carried out with cryogenic targets (all stable helium and hydrogen isotopes including even tritium). The available cryogenic target cells 25 or 30 mm in diameter with nominal thicknesses from 0.4 to 6 mm have modular construction and can have a thickness up to 10²² at/cm². The cells have stainless steel windows with thickness from 6 to 9 μm.
In collaboration with FSUE RFNC - VNIIEF in Sarov started development of new tritium target complex. The maximum volume of liquid or solid T₂ will be about 1 cm³, which corresponds to activity about 2.7 kCi.

Particle detectors

The ACCULINNA-2 team has a full set of charged particle detector telescopes. We have annular and square shaped single sided and double sided silicon strip detectors with thickness from 20 μm to 1.5 mm. The CsI(Tl) segmented arrays with square and annular shape are complementing well with corresponding Si telescopes. In addition, 40 neutron detection modules, based on stilbene crystals with corresponding PMTs assembled into the “neutron wall” can by effectively used for broad variety of experiments.

DAQ

All particle detectors and RIBs diagnostic system of ACCULINNA-2 with appropriate electronics are implemented to one distributed multi-processor data acquisition (DAQ) system based on Multi Branch System (MBS). Main DAQ combines VME crates with installed CES RIO4 or RIO3 VME controllers, distributed along the beam line. One VME crate have CVC-GTBV4 VME-CAMAC brunch to read out old school electronics. Each controller operates under LynxOS real-time operation system. Via TRIVA modules all crates connected to the common trigger bus for event synchronization. An additional Linux based MBS event builder PC allows to merge all data flows from each VME controller into single data stream of the reconstructed events. Flexible user readout interface of MBS allows to implement almost any configuration of the detectors spaced from each other by more than the length of existing fragment separator. The online monitoring and visualization of experimental data proceed by the Go4 analysis Framework. For further offline data analysis ROOT or any ROOT-based frameworks can be easily applied.

Zero angle magnet spectrometer

The ACCULINNA-2 experimental complex devoted to studies of exotic nuclear systems and its decay products. To distinguish between different charged particles, to measure their energies and angles, in 2017 at ACCULINNA-2 facility dipole magnet for zero-angle spectrometer was installed. It is 20 tones open-frame magnet with 180 mm gap. The reaction products enter the front aperture and bent by the well mapped magnetic field providing that their magnetic rigidities (and hence the momentum values) can be defined if their individual trajectories are measured accurately. The tracking detectors of ACCULINNA-2 provide 1.25-mm accuracy in the hit positions of RIB nuclei on the physics target. It means that, to use this dipole as zero-angle spectrometer, it should be equipped by specially designed position-sensitive detectors, which will provide similar precision in measuring coordinates of particles at the entrance and exit of the magnetic field. It is also important to use a ToF detector installed at the exit border of the magnet. This will give access to the velocity measurement and, taking into account the measured momentum values, to the determination of particle mass. Development of these detectors and appropriate electronics are in progress.

RF-kicker

The purification level of ACCULINNA-2 separator is typically enough for preparation of quite pure beams in final focal plane F5 in the case of neutron-reach fragmentation products. The neutron-deficit radioactive beams suffer from large number of contaminations. To deal with it, in 2019 the vertically deflecting radio-frequency (RF) kicker take place in a distance of 25 meters from production target just after the achromatic focal plane F3. It has 70 mm gap between electrodes and operates at the maximum field of 15 kV/cm with a frequency from 15 to 22 MHz.

ACCULINNA theory group

ACCULINA group employs several people who work mainly in the field of theory and on the theoretical support of experimental activities of the group. The origins of the group can be tracked to the so called "Kurchatov few-body school" which in the Soviet times was one of the strongest scientific schools in this field. The theoretical "subsystem" of ACCULINNA group possess a unique expertise in the studies of three-body phenomena in discrete spectrum and continuum.

ExpertROOT software

ExpertROOT is a FAIRroot based framework for simulation of the detectrors’ responce, event reconstruction and data analysis in the EXPERT project at Super-FRS@FAIR and ACCULINNA-2 fragment-separator in JINR. It includes core services for detector simulation and offline analysis of particle physics data.