Magicity versus Superfluidity around ^{28}O viewed from the Study of ^{30}F.

The neutron-rich unbound fluorine isotope ^{30}F_{21} has been observed for the first time by measuring its neutron decay at the SAMURAI spectrometer (RIBF, RIKEN) in the quasifree proton knockout reaction of ^{31}Ne nuclei at 235  MeV/nucleon. The mass and thus one-neutron-separation energy of ^{30}F has been determined to be S_{n}=-472±58(stat)±33(sys)  keV from the measurement of its invariant-mass spectrum. The absence of a sharp drop in S_{n}(^{30}F) shows that the "magic" N=20 shell gap is not restored close to ^{28}O, which is in agreement with our shell-model calculations that predict a near degeneracy between the neutron d and fp orbitals, with the 1p_{3/2} and 1p_{1/2} orbitals becoming more bound than the 0f_{7/2} one.

Elucidating the nature of the proton radioactivity and branching ratio on the first proton emitter discovered Co.

The observation of a weak proton-emission branch in the decay of the 3174-keV Co isomeric state marked the discovery of proton radioactivity in atomic nuclei in 1970. Here we show, based on the partial half-lives and the decay energies of the possible proton-emission branches, that the exceptionally high angular momentum barriers, [Formula: see text] and [Formula: see text], play a key role in hindering the proton radioactivity from Co, making them very challenging to observe and calculate. Indeed, experiments had to wait decades for significant advances in accelerator facilities and multi-faceted state-of-the-art decay stations to gain full access to all observables.

N=16 Magicity Revealed at the Proton Drip Line through the Study of ^{35}Ca.

The last proton bound calcium isotope ^{35}Ca has been studied for the first time, using the ^{37}Ca(p,t)^{35}Ca two neutron transfer reaction. The radioactive ^{37}Ca nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid hydrogen target CRYPTA, to produce tritons t that were detected in the MUST2 detector array, in coincidence with the heavy residues Ca or Ar. The atomic mass of ^{35}Ca and the energy of its first 3/2^{+} state are reported.

First observation of O.

Subjecting a physical system to extreme conditions is one of the means often used to obtain a better understanding and deeper insight into its organization and structure. In the case of the atomic nucleus, one such approach is to investigate isotopes that have very different neutron-to-proton (N/Z) ratios than in stable nuclei. Light, neutron-rich isotopes exhibit the most asymmetric N/Z ratios and those lying beyond the limits of binding, which undergo spontaneous neutron emission and exist only as very short-lived resonances (about 10 s), provide the most stringent tests of modern nuclear-structure theories.

Structure of ^{36}Ca under the Coulomb Magnifying Glass.

Detailed spectroscopy of the neutron-deficient nucleus ^{36}Ca was obtained up to 9 MeV using the ^{37}Ca(p,d)^{36}Ca and the ^{38}Ca(p,t)^{36}Ca transfer reactions. The radioactive nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid hydrogen target CRYPTA, to produce light ejectiles (the deuteron d or triton t) that were detected in the MUST2 detector array, in coincidence with the heavy residues identified by a zero-degree detection system. Our main findings are (i) a similar shift in energy for the 1_{1}^{+} and 2_{1}^{+} states by about -250  keV, as compared with the mirror nucleus ^{36}S; (ii) the discovery of an intruder 0_{2}^{+} state at 2.

4D-imaging of drip-line radioactivity by detecting proton emission from Ni pictured with ACTAR TPC.

Proton radioactivity was discovered exactly 50 years ago. First, this nuclear decay mode sets the limit of existence on the nuclear landscape on the neutron-deficient side. Second, it comprises fundamental aspects of both quantum tunnelling as well as the coupling of (quasi)bound quantum states with the continuum in mesoscopic systems such as the atomic nucleus.

Extending the Southern Shore of the Island of Inversion to ^{28}F.

Detailed spectroscopy of the neutron-unbound nucleus ^{28}F has been performed for the first time following proton/neutron removal from ^{29}Ne/^{29}F beams at energies around 230  MeV/nucleon. The invariant-mass spectra were reconstructed for both the ^{27}F^{(*)}+n and ^{26}F^{(*)}+2n coincidences and revealed a series of well-defined resonances. A near-threshold state was observed in both reactions and is identified as the ^{28}F ground state, with S_{n}(^{28}F)=-199(6)  keV, while analysis of the 2n decay channel allowed a considerably improved S_{n}(^{27}F)=1620(60)  keV to be deduced.

Strong Neutron Pairing in core+4n Nuclei.

The emission of neutron pairs from the neutron-rich N=12 isotones ^{18}C and ^{20}O has been studied by high-energy nucleon knockout from ^{19}N and ^{21}O secondary beams, populating unbound states of the two isotones up to 15 MeV above their two-neutron emission thresholds. The analysis of triple fragment-n-n correlations shows that the decay ^{19}N(-1p)^{18}C^{*}→^{16}C+n+n is clearly dominated by direct pair emission. The two-neutron correlation strength, the largest ever observed, suggests the predominance of a ^{14}C core surrounded by four valence neutrons arranged in strongly correlated pairs.

Quasifree (p, 2p) Reactions on Oxygen Isotopes: Observation of Isospin Independence of the Reduced Single-Particle Strength.

Quasifree one-proton knockout reactions have been employed in inverse kinematics for a systematic study of the structure of stable and exotic oxygen isotopes at the R^{3}B/LAND setup with incident beam energies in the range of 300-450  MeV/u. The oxygen isotopic chain offers a large variation of separation energies that allows for a quantitative understanding of single-particle strength with changing isospin asymmetry. Quasifree knockout reactions provide a complementary approach to intermediate-energy one-nucleon removal reactions.

Measurement of the isoscalar monopole response in the neutron-rich nucleus 68Ni.

The isoscalar monopole response has been measured in the unstable nucleus (68)Ni using inelastic alpha scattering at 50A  MeV in inverse kinematics with the active target MAYA at GANIL. The isoscalar giant monopole resonance (ISGMR) centroid was determined to be 21.1 ± 1.

Experimental study of the two-body spin-orbit force in nuclei.

Energies and spectroscopic factors of the first 7/2-, 3/2-, 1/2-, and 5/2- states in the (35)Si21 nucleus were determined by means of the (d, p) transfer reaction in inverse kinematics at GANIL using the MUST2 and EXOGAM detectors. By comparing the spectroscopic information on the Si35 and S37 isotones, a reduction of the p3/2-p1/2 spin-orbit splitting by about 25% is proposed, while the f7/2-f5/2 spin-orbit splitting seems to remain constant. These features, derived after having unfolded nuclear correlations using shell model calculations, have been attributed to the properties of the two-body spin-orbit interaction, the amplitude of which is derived for the first time in an atomic nucleus.

Spectroscopy of 26F to probe proton-neutron forces close to the drip line.

A long-lived J(π) = 4(1)(+) isomer, T(1/2) = 2.2(1) ms, has been discovered at 643.4(1) keV in the weakly bound (9)(26)F nucleus.

Search for superscreening effects in a superconductor.

The decay of (19)O(β(-)) and (19)Ne(β(+)) implanted in niobium in its superconducting and metallic phases was measured using purified radioactive beams produced by the SPIRAL GANIL facility. Half-lives and branching ratios measured in the two phases are consistent within a 1σ error bar. This measurement casts strong doubts on the predicted strong electron screening in a superconductor, the so-called superscreening.

Unveiling the intruder deformed 02(+) state in 34Si.

The 02(+) state in 34Si has been populated at the GANIL-LISE3 facility through the β decay of a newly discovered 1(+) isomer in 34Al of 26(1) ms half-life. The simultaneous detection of e(+)e(-) pairs allowed the determination of the excitation energy E(02(+))=2719(3)  keV and the half-life T(1/2)=19.4(7) ns, from which an electric monopole strength of ρ(2)(E0)=13.

Prolate-spherical shape coexistence at N=28 in 44S.

The structure of 44S has been studied by using delayed γ and electron spectroscopy. The decay rates of the 02+ isomeric state to the 2(1)+ and 0(1)+ states, measured for the first time, lead to a reduced transition probability B(E2: 2(1)+→0(2)+)=8.4(26) e(2) fm4 and a monopole strength ρ2(E0: 0(2)+→0(1)+)=8.

Migration of nuclear shell gaps studied in the d(24Ne,pγ)25Ne reaction.

The transfer of neutrons onto 24Ne has been measured using a reaccelerated radioactive beam of 24Ne to study the (d,p) reaction in inverse kinematics. The unusual raising of the first 3/2+ level in 25Ne and its significance in terms of the migration of the neutron magic number from N=20 to N=16 is put on a firm footing by confirmation of this state's identity. The raised 3/2+ level is observed simultaneously with the intruder negative parity 7/2- and 3/2- levels, providing evidence for the reduction in the N=20 gap.

Breakdown of the Z=8 shell closure in unbound 12O and its mirror symmetry.

An excited state in the proton-rich unbound nucleus 12O was identified at 1.8(4) MeV via missing-mass spectroscopy with the 14O(p,t) reaction at 51 AMeV. The spin-parity of the state was determined to be 0+ or 2+ by comparing the measured differential cross sections with distorted-wave calculations.

Discovery of a new broad resonance in 19Ne: implications for the destruction of the cosmic gamma-ray emitter 18F.

Six proton-emitting states in 19Ne were studied through the inelastic scattering reaction H(19Ne,p);{19}Ne; (p)18F. Their energies and widths were derived from the protons detected at zero degree, while proton-proton angular correlations between the detector at zero degree and a segmented annular detector were used to determine their spin value. In addition to the known states, a new broad J=1/2 resonance has been evidenced at E_{x} approximately 7.

Collapse of the N=28 shell closure in (42)Si.

The energies of the excited states in very neutron-rich (42)Si and (41,43)P have been measured using in-beam gamma-ray spectroscopy from the fragmentation of secondary beams of (42,44)S at 39A MeV. The low 2(+) energy of (42)Si, 770(19) keV, together with the level schemes of (41,43)P, provides evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that (42)Si is best described as a well-deformed oblate rotor.

Reduction of the spin-orbit splittings at the n = 28 shell closure.

The N = 28 shell closure has been investigated via the 46Ar(d,p)47Ar transfer reaction in inverse kinematics. Energies and spectroscopic factors of the neutron p(3/2), p(1/2), and f(5/2) states in 47Ar were determined and compared to those of the 49Ca isotone. We deduced a reduction of the N = 28 gap by 330(90) keV and spin-orbit weakenings of approximately 10(2) and 45(10)% for the f and p states, respectively.

Enhanced core polarization in (70)Ni and (74)Zn.

The reduced transition probabilities B(E2;0(+) --> 2(+)(1)) of the neutron-rich (74)Zn and (70)Ni nuclei have been measured by Coulomb excitation in a (208)Pb target at intermediate energy. These nuclei have been produced at Grand Accélérateur National d'Ions Lourds via interactions of a 60A MeV (76)Ge beam with a Be target. The B(E2) value for (70)Ni(42) is unexpectedly large, which indicates that neutrons added above N=40 strongly polarize the Z=28 proton core.

(68)(28)Ni(40): Magicity versus superfluidity.

The neutron-rich (66,68)Ni have been produced at GANIL via interactions of a 65.9A MeV 70Zn beam with a 58Ni target. Their reduced transition probability B(E2;0(+)(1)-->2+) has been measured for the first time by Coulomb excitation in a (208)Pb target at intermediate energy.