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C60H56Cl2N12Ni3O6, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 12.684(5) Å, b = 12.827(5) Å, c = 19.100(7) Å, α = 84.641(4)°, β = 81.178(4)°, γ = 85.471(4)°, V = 3050.7(19) Å3, Z = 2, R gt (F) = 0.0267, wR ref (F 2) = 0.0735, T = 298 K.

19 pags., 16 figs., 8 tabs., We present the design, prototype developments and test results of the new time-of-flight detector (ToFD) which is part of the R3B experimental setup at GSI and FAIR, Darmstadt, Germany. The ToFD detector is able to detect heavy-ion residues of all charges at relativistic energies with a relative energy precision σΔE/ ΔE of up to 1% and a time precision of up to 14 ps (sigma). Together with an elaborate particle-tracking system, the full identification of relativistic ions from hydrogen up to uranium in mass and nuclear charge is possible., This work received support from BMBF (05P19RFFN1, 05P15RDFN1, 05P19RDFN1) and HIC for FAIR. J.P. has been supported by the Institute for Basic Science (IBS-R031-D1). E.C. has been supported by the Ministry of Science and Innovation in Spain (PGC2018-099746-B-C22). J.L.R.S. thanks the support from the Regional Government of Galicia under the program of postdoctoral fellowships ED481B-2017-002 and ED481D-2021-018. O.T. has been supported by AEI/FEDER, UE project No. PID2019-104390GB-I00. G.B., A.H., H.T.J., B.J. and T.N. have been supported by the Swedish Research Council under contract 2017-03839. This work was supported by the Royal Society and UK STFC awards ST/L005727/1, ST/P003885/1.

This article aims to describe the key scientific problems, historical developments and prospects of the radioactive ion beam (RIB) physics. There exist only less than 300 stable nuclides in the universe, whereas the the number of unstable nuclei can be as high as 10000. The production and study of such radioactive nuclides (RIB physics) are an exploration of an undiscoveredarea, which necessities new experimental tools and theoretical models. Numerous new findings have been reported at the initial stage ofRIB physics research based on new observations. Typical examples include the halo and cluster structures, new magic numbers, shellevolution and soft dipole resonances. The study of unstable nuclei is also closely related to that of nuclear astrophysics processes as well as the synthesis of superheavy nuclei, which are belonging to the most important interdisciplinary problems worldwide. Investigations on unstable nucleus provide experimental data for nuclear energy systems; thus, they have strategic application value. The advantages of HIAF are associated with high beam intensity. When combined with advanced technologies for RIB separation and experimental detection, HIAF would play certain leading roles in the international community.

Radioactive-ion beam (RIB) experiments open up new exciting fields and frontiers in nuclear physics and nuclear astrophysics. The experiments can provide unprecedented opportunities to explore new phenomena such as new magic numbers and probe the isospin mechanisms occurring in shell evolution. Other experiments probe the limits of nuclear stability on the neutron-rich side, provide insights into the synthesis of superheavy elements and nuclear giant halo structures, and offer the possibility to investigate new nuclear decay modes as well as the nucleosynthesis of nuclides beyond Iron. To achieve this goal, many nuclear physics laboratories all over the world are building large-scale powerful new RIB facilities. The “Beijing Isotope-Separation-On-Line Neutron-Rich Beam Facility (BISOL)” is a joint project proposed by the China Institute of Atomic Energy (CIAE) and Peking University. This facility will combine two techniques: Projectile fragmentation (PF) and isotope separation on line (ISOL). The BISOL facility will operate based on a dual driver system, including reactor driving and intense deuteron-beam driving modes. The existing high flux research reactor, the China Advanced Research Reactor at CIAE provides reactor driving. At the BISOL facility ISOL separation of fission fragments, post acceleration, and fragmentation of neutron-rich fission fragment beams will be available. By combining ISOL and PF techniques in one facility the technical advantages of both can be merged. The BISOL will deliver intensive rare ion beams of very neutron-rich isotopes; the intensity of these beams will be of the order of at least 1-2 magnitudes higher than currently available ones. Intense deuteron-beam driving is an established technology, which provides an intense neutron beam source and can be operated independently in the facility. Characterizing material performance and performing lifetime experiments are the challenges facing researchers working on the current and next-generation nuclear energy systems. Intense radiation sources, especially neutron sources, are indispensable for these experiments. The intense deuteron accelerator proposed in this project will be able to generate intense neutron beam. These beams will be able to probe nuclear materials and will provide vital results to push forward the boundaries of nuclear physics.

The experimental data of the isotopic distribution for projectile-like fragments are presented for the 17,18N + 197Au reaction at 33 MeV/u. The width of the isotopic distributions for 18N projectile is significantly broader than that for 17N projectile, and the average N/Z ratio of the former shifts to higher neutron number side. As long as the realistic nucleon density distribution is used, the isotopic distribution for fragments is reproduced by the simple abrasion-ablation model calculation, which thus provides an independent way to determine the surface distribution of the nuclear matter density for neutron-rich nuclei.

A neutron detector array was used in a breakup reaction experiment at RIKEN with an 82.5 MeV/u 8He beam impinging on the CH2 and C targets. The array was calibrated using the cosmic ray, the γ ray from the 6He+Pb reaction and the mono-energetic neutrons from the 7Li(p, n)7Be(g.s.+0.43 MeV) reaction. The position resolution, timing resolution and neutron detection efficiency were obtained accordingly. Cross-talk rejection conditions were developed based on analysis of the data taken from the 7Li(p, n)7Be(g.s.+0.43 MeV) test experiment, and finally a preliminary two-neutron correlation function for the 8He breakup reaction was investigated.

An experiment for knockout reaction induced by 8He beam at 82.5 MeV/nucleon on CH2 and C targets was carried out. The 6He and 4He core fragments at forward angles and the recoiled protons at large angles were detected coincidently. From this exclusive measurement the valence nucleon knockout mechanism and the core knockout mechanism are separated, which can be applied to the exclusive spectroscopic study on the structure of exotic nuclei.

Efficient calibration methods have been applied to a complex neutron detector array by using the cosmic-ray muons. Through a differential operation on the time difference spectrum, the two edges of this spectrum can be precisely determined, corresponding to the geometrical two ends of the bar, and therefore the relationship between the position and time difference spectrum can be deduced for each bar. The alignment between different bars is realized by choosing cosmic-rays which are perpendicular to the bars. The position resolutions are extracted through a track fitting procedure which uses all tracks detected coincidently by the whole system, together with a simulation analysis. A method is also developed to calibrate the deposited energy by using cosmic-rays at different incident angles.

A knockout reaction experiment was carried out by using the 6He beam at 82.5 MeV/nucleon impinging on CH2 and C targets. The α core fragments at forward angles were detected in coincidence with the recoiled protons at larger angles. From this exclusive measurement the valence nucleon knockout mechanism and the core knockout mechanism are separated. This study provides a basis for the exclusive spectroscopic investigation of the exotic nuclei.

The latest progress made in the field of radioactive ion beam physics is outlined and the key problems still under investigation are indicated. The focal points are the limit of nuclear existence, shell evolution and new magic numbers, halo and cluster structures, new excitation modes, and strong coupling between reaction channels. This field is still at a starting phase and much more new outcomes are foreseen.

The Halo and cluster structure at the ground state of unstable nuclei are among the most exciting phenomena of current nuclear physics. Probing these structures requires a careful selection of reaction tools. In the past twenty years, knockout reactions have been used intensively to investigate spectroscopically the structure of unstable nuclei. In this report we have illustrated the latest development of the knockout reaction tool and have emphasized the recoiled proton tagging method. A quantitative criteria is developed to evaluate the quasi-free feature of the knockout process. The newly discovered "towing mode" reaction tool is also outlined and its applicability at transit energies is discussed.

To perform a kinematically complete measurement of the dissociation reaction for neutron-rich nuclei, a multi-neutron correlation spectrometer is proposed at Peking University. A Monte Carlo simulation code based on GEANT4 is developed for a single scintillation bar which processes not only the energy deposition but also the light propagation in the scintillator and the light collection and conversion to signal at the end of the bar in a realistic way. The simulating method is described in detail in this paper, and the timing and position resolutions and detector efficiency are studied based on the simulation and compared with the experimental results. A new method of crosstalk rejection has been demonstrated to be important for the design of the whole spectrometer.

The design principle for a multi-wire proportional chamber with a cathode strip and delay-line readout is described. A prototype chamber of a size of 10 cm ×10 cm was made together with the readout electronics circuit. A very clean signal with very low background noise was obtained by applying a transformer between the delay-line and the pre-amplifier in order to match the resistance. Along the anode wire direction a position resolution of less than 0.5 mm was achieved with a 55Fe-5.9 keV X ray source. The simple structure, large effective area and high position resolution allow the application of a gas chamber of this kind to many purposes.

Four high-purity germanium 4-fold segmented Clover detectors have been applied in the experiment of neutron-rich nucleus 21N. The performance of those four Clovers have been tested with radioactive sources and in-beam experiments, and the main results including energy resolution, peak-to-total ratios, the variation of the hit pattern distribution in different crystals of one Clover detector with the energy of γ ray, and absolute full energy peak detection efficiency curve, were presented.

We have tested and analyzed the properties of two-dimensional Position-Sensitive-silicon-Detector (PSD) with new integrated preamplifiers. The test demonstrates that the best position resolution for 5.5 MeV α particles is 1.7 mm (FWHM), and the best energy resolution is 2.1%, which are notably better than the previously reported results. A scaling formula is introduced to make the absolute position calibration.

The β-delayed neutron and γ energy spectra taken from the decay of neutron-rich nucleus 21N were measured by using the β–γ and β – n coincidence detection method. Thirteen new neutron groups ranging from 0.28MeV to 4.98MeV and with a total branching ratio of 88.7 ± 4.2% were observed and presented. One γ transition with an energy of 1222keV emitted from the excited state of 21O, and four γ transitions with energies of 1674, 2397, 2780, and 3175keV emitted from the excited states of 20O were identified in the β decay chain of 21N. The β decay half-life for 21N is determined to be 82.9 ± 1.9 ms. The uncertainty of half-life is much smaller than the previous result.