*2.2. High-Energy Fragmentation and ISOL Facilities*

When the beam energy reaches the range suitable for fragmentation reactions, in-flight separation and identification of reaction products can be achieved. The lower beam intensities at high energies and lowered production cross sections are then compensated by the possibility of using thicker targets and higher efficiency of tracking and identification detectors. Unprecedented primary-beam intensities at relativistic energies have become available at the Radioactive Isotope Beam Factory (RIBF) at the RIKEN Nishina Center (Japan).

The reaction products are identified in the BigRIPS fragment separator [48] accompanied by an efficient *γ*-ray array, e.g., EURICA [49] (see Figure 2) consisting of EUROBALL cluster detectors for high-energy resolution or DALI2+ spectrometer [50] for low-resolution spectroscopy. Experiments of this type marked a new chapter in the available data in the 100Sn region including the discovery of new isotopes and proton emitters [51]. An important add-on was the new measurement of the *B(GT)* value for 100Sn *β*-decay measurement made with sufficient accuracy so that the interpretation allowed for distinguishing between different models used [10].

The existing data can be used for *B(GT)* re-determination once the mass measurement of 100Sn is available. Extensive data on lifetimes of *β* decay and *β*-delayed proton

emission, as well as beta-delayed spectroscopy was published in Refs. [52,53]. Large progress on excited states in the region was obtained including gamma-gamma coincidence data for the 100In nucleus [10], identification of excited states in 96Cd [22,54] and others [55,56] based on isomer spectroscopy are mentioned in Section 4.1. The disadvantage of this method is that it does not allow for prompt gamma-ray spectroscopy at the (primary) target.

**Figure 2.** EURICA array consisting of 12 cluster detectors of EUROBALL at RIKEN RIBF in 2012 [49]. See text for details.

Two-step fragmentation is used to study prompt radiation from Coulomb excitation or knockout reactions with the DALI2+ spectrometer. From several experimental campaigns, extensive and spectacular data was collected and, to large extent, published as discussed in Section 4.2. Very recently, in 2020–2021 the HICARI (High-resolution in-beam gamma-ray spectroscopy at RIBF) project [57] used a Ge-detector array to perform several experiments addressing this region.

Efforts continue at NSCL (National Superconducting Cyclotron Laboratory, Michigan, USA) to contribute to the region [58], e.g., with spectroscopy using knock-out reactions [59], or the recent mass measurement of 80Zr [60]. At GSI, revisited isomeric decay in 102Sn and resulting effective neutron and proton charges based on state-of-the-art shell-model calculations were published [61], 13 years after the RISING [62] experiment.

In 2020, the GSI (Society for Heavy Ion Research, Darmstadt, Germany) facility came back into operation again after 6 years with the Fragement Separator (FRS) [63] and DEcay SPECtroscopy (DESPEC) [64] setup including the FATIMA [65] gamma-ray array and a Ge-detector array to address this region of nuclei again with lifetime measurement of intermediate states below isomers or states populated in beta decay.

To determine the excitation energy of long-lived isomeric states, a complementary technique employing the Multi-Reflection Time-of-Flight Mass Spectrometer (MR-TOF-MS) at the FRS Ion Catcher was recently used in this region of nuclei [15].

Alternatively, high-energy and high-intensity protons are used in spallation reaction and the radioactive beam is stored and separated in an ion source. Laser-ionized secondary beams are accelerated to fusion energies to impinge on a secondary target surrounded by a *γ*-ray array. The enormous success of this method was demonstrated at CERN (the European Organization for Nuclear Research) REX-ISOLDE [66] and continued with the HIE-ISOLDE project [67] where secondary beams were used for transfer and Coulombexcitation measurements using the MINIBALL *γ*-ray array [68,69]. Several experiments were devoted to the study of neutron-deficient tin via transfer and Coulomb excitation measurements [70–74].

A similar principle was recently also applied at NSCL in [75] using the JANUS setup [76].
