The joint proposal EXPERT is suggested by the consortium GSI (Darmstadt, Germany) – FLNR JINR (Dubna, Russia) – University of Warsaw (Warsaw, Poland) – PTI (Ioffe Physics-Technical Institute of Russian Academy of Science, St. Petersburg, Russia) – KI (National Research Center “Kurchatov Institute”, Moscow) and the structure is open for other institutes to be involved. It 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, beta-delayed decays and exotic excitation modes can be studied via observations of particle emissions, including the 2p, 4p, n, 2n, 4n channels. Therefore the main objectives of the EXPERT proposal are:
Exotic 2p radioactivity studies and search for novel types of radioactive decays: 4p, 2n, 4n.
- Studies of p, 2p, 4p, n, 2n, 4n resonance decays coupled with spectroscopy of continuum.
- Quest to discover the limits of existence of nuclear structure. Search for systems located far beyond the drip-lines aimed to answer for the basic question: “Where is the borderline between a resonant behavior and continuum response of nuclear matter”?
- Studies of beta-delayed particle (multi-particle) emission from exotic isotopes near and beyond the drip-lines.
For the systems which ground states decay by (multy-) nucleon emission the proposed setup covers two important lifetime ranges of 1 s – 100 ns, and 1 ps – 100 ns by applying the implantation-decay and decay-in-flight techniques, respectively. For the short-lived systems the resonance properties and information about continuum dynamics is extracted on the basis of the angular correlations between the products. The above types of measurements are augmented with information about gamma-deexcitation and betta-delayed particle emission of the decay products.
Schematic layout of the proposed experiments for exploratory studies of nuclei beyond the proton and neutron drip-lines.
The illustrated scenario suggests a population of two-proton (green) or two-neutron (orange) precursor in a secondary reaction of one-nucleon knockout by using radioactive beam.
Theoretical/MC simulation framework is mentioned in this graph as a component of the proposal required in most considered experimental scenarios.
EXPERT components and subsystems
There are three main components for measurements of decays-in-flight of exotic nuclei:
- Radiation-hard silicon strip detectors SSDs. These compact and universal beam detectors of the SuperFRS provide information on time-of-flight, position and energy loss of ions, and they will be used for tracking of the secondary beam impinging the secondary target.
- Micro-strip silicon (Si) tracking detectors. The detectors are essential for applications of tracking technique for studies radioactive decays-in-flight and provide information on trajectories of all charged decay products, which is sufficient for determination of half-life values in the range of 1 ps – 100 ns as well as on decay energies and angular correlations of decay products.
- The NeuRad (Neutron Radioactivity) fine-resolution detector of neutrons. Together with Si detectors, this small-size 40x40x100 cm3 neutron detector can provide precise information on angular correlations of decay neutrons with a charged fragment, which is used to derive the decay energy of exotic radioactive decays (e.g., an unobserved yet phenomenon of neutron radioactivity is suggested to be probed in the decay energy range of 0.1-100 keV).
The EXPERT components augmenting the tracking subsystem are:
- The GADAST (Gamma-ray Detectors Around Secondary Target) array. It measures gamma-rays and light particles emitted instantaneously after secondary reaction. In the context of the proposal it could allow to disentangle the decays channels with a heavy fragment resulted in an excited state (and thus instantaneously de-excited by gamma emission).
- The OTPC (Optical Time Projection Chamber) for radioactivity studies by the implantation-decay
method. The detector measures trajectories of all charged fragments of radioactive precursors with
lifetimes in the range 1 s – 100 ns.
- Theoretical/Simulation framework. In order to obtain physics results, the information provided by
tracking/angular measurements needs the detailed theoretical analysis followed by Monte Carlo
simulations. Moreover, solid theoretical predictions like the first theory of 2p and 2n radioactivity make strong motivation for performing high-risk pioneering studies.