Joakim Cederkall

This work presents a systematic study of the properties (Light Output Non-Uniformity (LONU) and energy resolution) of two CsI (Tl) scintillation units over a span of almost three years, under adverse conditions of humidity and temperature. These two crystals are part of the CALIFA detector, a highly segmented calorimeter and spectrometer for γ rays and light-charged particles, that is placed surrounding the reaction target at Cave C, the experimental cave of the R 3 B (Reactions with Radioactive Relativistic Beams) collaboration at the GSI-FAIR facilities in Darmstadt, Germany. The findings obtained after the experiment indicate that there was no significant impact on the performance in terms of resolution and LONU. This suggests that the employed wrapping for light collection effectively serves as an excellent barrier against humidity. As a result, the crystal is preserved in a far better condition than initially anticipated.

It is a rare occasion when your research can change the course of a field. This happened when Arne Johnson, as a Ph. D. student, observed irregularities in the energy spectrum of 160Dy. Remarkably, Arne was not even assigned to study this nucleus. He was specifically instructed by his supervisors to work on odd-even nuclei and not the even-even ones. Characteristic of his curiosity and love for accuracy, he wanted to understand the cause of that irregularity and pin down its origin. Further analysis eventually showed that a remarkable feature emerged from the data, showing that nuclei, when spinning faster and faster, undergo a structural change called “the backbending.” His extraordinary contribution to the discovery of the backbending phenomenon is further evidenced by an invitation, still being a Ph. D. student, to write a review paper in Physics Reports,“Nuclear Rotation at High Angular Velocities,” jointly …

For the first time a measurement of 8B+ 64Zn reaction has been performed at HIE-ISOLDE at CERN at energies around the Coulomb barrier, to understand how the debated halo structure of the light nucleus can affect reaction dynamics.

The simulation of 100 eV positrons transmitted in conical capillary was performed with inserted beam intensity from 0.04 fA/mm2 to 10 fA/mm2. At lower injected intensity of sub-fA, the transmission profile is geometrical and dominated by direct transmission. As the tilt angle increases, the intensity of the transmitted positron decreases rapidly, which is consistent with the experimental data. After increasing injected current intensities to several fA/mm2, charge deposited in the capillary significantly enhances the transmission rate, and the positrons can transmit the capillary with larger tilt angles. The transmitted current density is shown to increase up to a factor of 4.8 with respect to the injected one. These results provide evidence that the low-energy positrons can be guided and significantly focused by insulating conical capillary.

Proton- coincidences from reactions between a beam and a deuterated polyethylene target have been analyzed with the inverse Oslo method to find the nuclear level density (NLD) and -ray strength function (SF) of . The capture cross section has been calculated using the Hauser-Feshbach model in TALYS using the measured NLD and SF as constraints. We confirm that acts as a bottleneck when relying on one-zone nucleosynthesis calculations. However, we find that the impact of this reaction is strongly damped in multi-zone low-metallicity AGB stellar models experiencing i-process nucleosynthesis.

Presently under construction in Lund, Sweden, the European Spallation Source (ESS) will be the world’s brightest neutron source. As such, it has the potential for a particle physics program with a unique reach and which is complementary to that available at other facilities. This paper describes proposed particle physics activities for the ESS. These encompass the exploitation of both the neutrons and neutrinos produced at the ESS for high precision (sensitivity) measurements (searches).

The NNBAR experiment for the European Spallation Source will search for free neutrons converting to antineutrons with an expected sensitivity improvement of three orders of magnitude compared to the last such search. This paper describes both the simulations of a key component for the experiment, the neutron optical reflector and the expected gains in sensitivity.

The first experiment using radioactive beams post-accelerated by the HIE-ISOLDE facility has enabled to obtain a precise set of B (E 2) transition probabilities in neutron-rich Zn 74, 76 isotopes. The resulting B (E 2; 2 1+→ 0 1+) values are consistent with those determined in earlier REX-ISOLDE measurements. While the B (E 2; 4 1+→ 2 1+) transition probability in Zn 76 is also in agreement with earlier Coulomb-excitation results, the value obtained for Zn 74 is considerably lower. For the first time, a spectroscopic quadrupole moment of the 2 1+ state was measured for an exotic nucleus in this mass region. A detailed comparison is presented with large-scale shell-model and Monte Carlo shell-model calculations.

The first low-energy Coulomb-excitation measurement of the radioactive, semi-magic, two proton-hole nucleus 206 Hg, was performed at CERN's recently-commissioned HIE-ISOLDE facility. Two γ rays depopulating low-lying states in 206 Hg were observed. From the data, a reduced transition strength B (E 2; 2 1+→ 0 1+)= 4.4 (6) Wu was determined, the first such value for an N= 126 nucleus south of 208 Pb, which is found to be slightly lower than that predicted by shell-model calculations. In addition, a collective octupole state was identified at an excitation energy of 2705 keV, for which a reduced B (E 3) transition probability of 30− 13+ 10 Wu was extracted. These results are crucial for understanding both quadrupole and octupole collectivity in the vicinity of the heaviest doubly-magic nucleus 208 Pb, and for benchmarking a number of theoretical approaches in this key region. This is of particular importance given …

The 8 B+ 64 Zn reaction at 38.5 MeV has been studied at HIE-ISOLDE CERN to investigate proton halo effect on the reaction dynamics. For the first time it was used the only existing post-accelerated 8 B beam. The measured elastic scattering angular distribution showed a small suppression of the Coulomb-nuclear interference peak, opposite to what observed for the one-neutron halo nucleus 11 Be on the same target where a large suppression was observed instead. Inclusive angular and energy distributions of breakup fragments were also measured showing that, both, elastic and non-elastic breakup contribute. The presence of the additional Coulomb interactions halo-core and halo-target in 8 B makes the reaction dynamics in this proton-halo nucleus different than the neutron-halo case.

The first experiment using radioactive beams post-accelerated by the HIE-ISOLDE facility has enabled to obtain a precise set of B (E2) transition probabilities in neutron-rich Zn74, 76 isotopes. The resulting B (E2; 21+→ 01+) values are consistent with those determined in earlier REX-ISOLDE measurements. While the B (E2; 41+→ 21+) transition probability in Zn76 is also in agreement with earlier Coulomb-excitation results, the value obtained for Zn74 is considerably lower. For the first time, a spectroscopic quadrupole moment of the 21+ state was measured for an exotic nucleus in this mass region. A detailed comparison is presented with large-scale shell-model and Monte Carlo shell-model calculations.

The ISOLDE Scientific Infrastructure at CERN offers a unique range of post-accelerated radioactive beams. The scientific program can be improved with the “Isolde Superconducting Recoil Separator” (ISRS), an innovative spectrometer able to deliver unprecedented (A, Z) resolution. In this paper we present an overview of the physics and ongoing technical developments.

The anomaly in lithium abundance is a well-known unresolved problem in nuclear astrophysics. A recent revisit to the problem tried the avenue of resonance enhancement to account for the primordial Li 7 abundance in standard big-bang nucleosynthesis. Prior measurements of the Be 7 (d, p) Be* 8 reaction could not account for the individual contributions of the different excited states involved, particularly at higher energies close to the Q value of the reaction. We carried out an experiment at HIE-ISOLDE, CERN to study this reaction at E c. m.= 7.8 MeV, populating excitations up to 22 MeV in Be 8 for the first time. The angular distributions of the several excited states have been measured and the contributions of the higher excited states in the total cross section at the relevant big-bang energies were obtained by extrapolation to the Gamow window using the talys code. The results show that by including the …

We measured 135 cross sections of residual nuclei produced in fragmentation reactions of C 12, N 14, and O 13− 16, 20, 22 projectiles impinging on a carbon target at kinetic energies of near 400 A MeV, most of them for the first time, with the R B 3/LAND setup at the GSI facility in Darmstadt (Germany). The use of this state-of-the-art experimental setup in combination with the inverse kinematics technique gave the full identification in atomic and mass numbers of fragmentation residues with a high precision. The cross sections of these residues were determined with uncertainties below 20% for most of the cases. These data are compared to other previous measurements with stable isotopes and are also used to benchmark different model calculations.

We present the design, prototype developments and test results of the new time-of-flight detector (ToFD) which is part of the RB 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 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.

A design study, named for European Spallation Source neutrino Super Beam, has been carried out during the years 2018–2022 of how the 5 MW proton linear accelerator of the European Spallation Source under construction in Lund, Sweden, can be used to produce the world’s most intense long-baseline neutrino beam. The high beam intensity will allow for measuring the neutrino oscillations near the second oscillation maximum at which the CP violation signal is close to three times higher than at the first maximum, where other experiments measure. This will enable CP violation discovery in the leptonic sector for a wider range of values of the CP violating phase and, in particular, a higher precision measurement of. The present Conceptual Design Report describes the results of the design study of the required upgrade of the ESS linac, of the accumulator ring used to compress the linac pulses from 2.86 ms to 1.2 μs, and …

The nature of quadrupole and octupole collectivity in 222Rn was investigated by determining the electric-quadrupole (E2) and octupole (E3) matrix elements using subbarrier, multistep Coulomb excitation. The radioactive 222Rn beam, accelerated to 4.23 MeV/u, was provided by the HIE-ISOLDE facility at CERN. Data were collected in the Miniball γ-ray spectrometer following the bombardment of two targets, 120Sn and 60Ni. Transition E2 matrix elements within the ground-state and octupole bands were measured up to 10ℏ and the results were consistent with a constant intrinsic electric-quadrupole moment, 518(11)efm2. The values of the intrinsic electric-octupole moment for the 0+→3− and 2+→5− transitions were found to be respectively 2360+300−210efm3 and 2300+300−500efm3 while a smaller value, 1200+500−900efm3, was found for the 2+→1− transition. In addition, four excited non-yrast states were identified in this work via γ−γ coincidences.

The NNBAR experiment for the European Spallation Source will search for free neutrons converting to antineutrons with a sensitivity improvement of three orders of magnitude compared to the last such search. This paper describes progress towards a conceptual design report for NNBAR. The design of a moderator, neutron reflector, beamline, shielding and annihilation detector is reported. The simulations used form part of a model which will be used for optimisation of the experiment design and quantification of its sensitivity.

The elastic and inelastic scattering of 7 Be from 12 C have been measured at an incident energy of 35 MeV. The inelastic scattering leading to the 4.439 MeV excited state of 12 C has been measured for the first time. The experimental data cover an angular range of θ c m= 15∘-120∘. Optical model analyses were carried out with Woods-Saxon and double-folding potential using the density dependent M3Y (DDM3Y) effective interaction. The microscopic analysis of the elastic data indicates breakup channel coupling effect. A coupled-channel analysis of the inelastic scattering, based on collective form factors, shows that mutual excitation of both 7 Be and 12 C is significantly smaller than the single excitation of 12 C. The larger deformation length obtained from the DWBA analysis could be explained by including the excitation of 7 Be in a coupled-channel analysis. The breakup cross section of 7 Be is estimated to be …

The cosmological lithium problem [1] is a widely studied and yet unsolved problem in nuclear astrophysics. The problem delineates a serious discrepancy between the observed abundance of 7Li and that predicted by the Big Bang Nucleosynthesis (BBN) theory [2]. The BBN calculations rely on nuclear physics inputs. So it is natural to study in details the nuclear reactions pertinent to the abundance anomaly of 7Li. Sensitivity studies [3] involving the 7Be (d, p) 8Be (2α)(Qgs= 16.67 MeV) reaction has shown that the primordial lithium problem can be resolved if the reaction rate is a factor of 100 larger at the relevant Gamow energies. Recent experiments studying the destruction of 7Be with deuterons could not find any significant enhancement in the reaction rate to resolve the anomaly [4]. However, these experiments did not measure the contributions of high lying excitations above 11.35 MeV in 8Be, in particular the 16.6 MeV state.