Search

A few years ago we observed anomalous electron-positron angular correlations for the 18.15 MeV M1 transition of8Be. This was interpreted as the creation and decay of an intermediate bosonic particle with a mass ofm0c2=16.70±0.35(stat )±0.5(sys) MeV, which is now called X17. The possible relation of the X17 boson to the dark matter problem triggered an enormous interest in the wider physics community. We also observed a similar anomaly in4He, which could be described also by the creation and subsequent decay of the same X17 particle. Very recently, the11B proton capture reaction was used for exciting the 17.2 MeV broad (Γ=1.15 MeV) resonance in12C and studying their internal pair creation decay. Anomalies were observed in the angular correlation of the electron-positron pairs, which together with the8Be and4He data provides kinematic evidence for the X17 particle and supports their vector boson and fifth force explanation.

Recently, we observed anomalous internal pair creation for the M1 transition depopulating the 18.15 MeV isoscalar 1$^+$ state in $^8$Be. We observed a significant (σ = 7.37) peak-like deviation from the predicted angular correlation of the e+ e pairs at θ = 140°. To the best of our knowledge no nuclear physics related description of such deviation can be made. However, the deviation can be described by assuming the creation and subsequent decay of a boson with mass of ≈17 MeV. In order to clarify the interpretation, we re-investigated the $^8$Be anomaly with an improved, and independent setup. We have confirmed the signal of the assumed X(17) particle and constrained its mass (m$_0$c $^2$ = 17.01(16) MeV) and branching ratio compared to the γ-decay (B$_x$ = 6(1) × 10$^{−6}$).

A neutron spectrometer, the European Low-Energy Neutron Spectrometer (ELENS), has been constructed to study exotic nuclei in inverse kinematics experiments. The spectrometer consisting of scintillator bars can be used in the neutron energy range of 100 keV to 10 MeV. To increase the light collection efficiency a special wrapping method was developed for each bars of ELENS. By using the specially heat treated reflector foil 15-20% better light collection is available. The development of wrapping process, the results of the test experiments are also presented.

High resolution experimental data has been obtained for the 40,42,44,48Ca(3He,t)Sc charge exchange reaction at 420 MeV beam energy, which favors the spin-isospin excitations. The measured angular distributions were analyzed for each state separately, and the relative spin dipole strength has been extracted for the first time. The low-lying spin-dipole strength distribution in 40Sc shows some interesting periodic gross feature. It resembles to a soft, dumped multi-phonon vibrational band with $\hbar\omega$= 1.8 MeV, which might be associated to pairing vibrations around $^{40}$Ca.

The fission probability of 232U has been measured using the 231Pa(3He,df) reaction with an energy resolution of 11 keV in the excitation energy region of E* = 4.0 − 6.4 MeV. A number of sub-barrier fission resonances has been observed for the first time in the excitation energy range below E* = 4.8 MeV and interpreted as rotational bands with a rotational parameter characteristic to a hyperdeformed nuclear shape (2/2Θ = 1.96 ± 0.11 keV). Besides, the fine structure of the transition states could also be resolved in the fission probability and proved to have a rotational structure with a rotational parameter characteristic to a superdeformed-like nuclear configuration (2/2Θ = 3.25 ± 0.17 keV).

γ-spectra and integral γ excitation functions of the 98Mo(p, nγ)98Tc reaction were measured with Ge(Li) and hyperpure Ge detectors in the 2.4-4.0 MeV energy interval of the bombarding protons. The conversion electron spectrum of the reaction was measured with a superconducting magnet transporter Si(Li) spectrometer. The level scheme of 98Tc, γ-branching ratios, multipolarity of transitions, level spin and parity values have been deduced. The energies of 98Tc levels were calculated on the basis of the parabolic rule which was derived from the cluster-vibration model. The experimental level scheme of 98Tc has been compared with the available theoretical results.

γ-ray and internal conversion electron spectra of the 82Se(p, nγ)82Br reaction were measured with Ge(Li) and superconducting magnet transporter Si(Li) spectrometers respectively, at 3.5 and 4 MeV bombarding proton energies. The level scheme of 82Br, multipolarities of 11 transitions, γ-branching ratios, level spin and parity values have been deduced. The energies of 82Br levels were calculated on the basis of the parabolic rule derived from the cluster-vibration model. This calculation provided a simple classification of several multiplet states in 82Br.