D. Ackermann

Grand Accélérateur National d'Ions Lourds | GANIL · Groupe Physique

Isomeric states in atomic nuclei are a well-known phenomenon all over the complete chart of nuclei. Their properties deliver valuable information on the structure of the nuclei. A region of specific interest are the very heavy and superheavy nuclei, where the occurrence and properties of isomeric states will have an impact on the prediction of loca...

Neutron dark decays have been suggested as a solution to the discrepancy between bottle and beam experiments, providing a dark matter candidate that can be searched for in halo nuclei. The free neutron in the final state following the decay of He6 into He4+n+χ provides an exceptionally clean detection signature when combined with a high efficiency...

The excited states of unstable O20 were investigated via γ-ray spectroscopy following the O19(d,p)O20 reaction at 8 AMeV. By exploiting the Doppler shift attenuation method, the lifetimes of the 22+ and 31+ states were firmly established. From the γ-ray branching and E2/M1 mixing ratios for transitions deexciting the 22+ and 31+ states, the B(E2) a...

Over the past decade, inverse kinematics has been increasingly employed in experimental studies of fission. This approach has yielded a wealth of new observables that can be obtained in single measurements, enabling their analysis and correlations. One ongoing application of this technique involves a series of experiments performed at GANIL using t...

Motivated by the four standard deviations discrepancy between the mean values for the neutron lifetime obtained from beam and bottle experiments, we have searched for a hypothetical neutron dark decay in $^6$He nuclei through the channel $^6{\rm He} \rightarrow ^4{\rm He}+n+\chi$. The experiment used a 25~keV high intensity $^6$He$^+$ beam with a h...

During the last decade, the use of inverse kinematics in the experimental study of fission is bringing a wealth of new observables obtained in single measurements, allowing their analysis and their correlations. An ongoing application of this technique is the basis of a series of experiments performed with the variable-mode, large-acceptance VAMOS+...

Several experiments around the world are looking for a new particle, named Dark Boson, which may do the link between the Ordinary Matter (which forms basically stars, planets, interstellar gas...) and the Hidden Sectors of the Universe. This particle, if it exists, would act as the messenger of a new fundamental interaction of nature. In this paper...

Systematic examination of fusion for 39,41,45,47K+Si28 and Ar36,44+Si28 provides insight into the impact of neutron and proton exchange on fusion for nuclei at and near the N=20 and N=28 shells. Comparison of the reduced excitation functions reveals a marked difference between the behavior of open-shell and closed-shell systems. While coupled chann...

The decay of excited states in 255No was investigated by applying the evaporation-residue–conversion-electron correlation technique. Two new isomeric states were observed in 255No together with the previously known one. Excitation energies of the isomeric states were estimated based on the energies of conversion electrons and γ rays from correlatio...

Systematic examination of fusion for $^{39,41,45,47}$K + $^{28}$Si and $^{36,44}$Ar + $^{28}$Si provides insight into the impact of neutron and proton exchange on fusion for nuclei at and near the N=20 and N=28 shells. Comparison of the reduced excitation functions reveals a marked difference between the behavior of open-shell and closed-shell syst...

The structure of the unbound F15 nucleus is investigated using the inverse kinematics resonant scattering of a radioactive O14 beam impinging on a CH2 target. The analysis of H1(O14,p)O14 and H1(O14,2p)N13 reactions allowed the confirmation of the previously observed narrow 1/2− resonance, near the two-proton decay threshold, and the identification...

Alpha decay and spontaneous fission of the ground-state and the isomeric state of \(^{247}\)Md were investigated with specific emphasis to identify the ground-state of the daughter nucleus \(^{243}\)Es. The decay studies were accompanied by measuring \(\alpha \)-\(\gamma \) coincidences. On the basis of the measured data an improved decay scheme of...

The decay properties of states in \(^{257}\)Rf have been investigated with the detector array GABRIELA at the FLNR, Dubna. The electromagnetic decay of a new excited state in \(^{253}\)No has been observed. The state lies 750 keV above the ground state and is favourably populated in the alpha decay from a low-lying isomeric state in \(^{257}\)Rf. I...

The structure of the unbound $^{15}$F nucleus is investigated using the inverse kinematics resonant scattering of a radioactive $^{14}$O beam impinging on a CH$_2$ target. The analysis of $^{1}$H($^{14}$O,p)$^{14}$O and $^{1}$H($^{14}$O,2p)$^{13}$N reactions allowed the confirmation of the previously observed narrow $1/2^{-}$ resonance, near the tw...

The influence of shell effects on fusion of mid-mass nuclei is explored using isotopic chains of K and Ar ions on an oxygen target. Comparison of the reduced excitation functions reveals that the fusion cross section for the open neutron-shell projectile nuclei K41 and K45 is systematically larger than for the closed neutron-shell projectiles K39 a...

The decay properties of the ground state and excited states of $^{257}$Rf have been investigated with the detector array GABRIELA at the FLNR, Dubna. The electromagnetic decay of a new excited state in $^{253}$No has been observed. The state lies 750 keV above the ground state and is favourably populated in the alpha decay of the low-lying spin iso...

The unbound proton-rich nuclei \(^{16}\)F and \(^{15}\)F are investigated experimentally and theoretically. Several experiments using the resonant elastic scattering method were performed at GANIL with radioactive beams to determine the properties of the low lying states of these nuclei. Strong asymmetry between \(^{16}\)F–\(^{16}\)N and \(^{15}\)F...

The unbound proton-rich nuclei $^{16}$F and $^{15}$F are investigated experimentally and theoretically. Several experiments using the resonant elastic scattering method were performed at GANIL with radioactive beams to determine the properties of the low lying states of these nuclei. Strong asymmetry between $^{16}$F-$^{16}$N and $^{15}$F-$^{15}$C...

Nuclear structure of Fm243, Fm245, and their daughter nuclei were investigated via detection of their radioactive decays, α, γ, and spontaneous fission. Measured α-decay energies, half-lives, and branching ratios improve the literature data significantly. A signature for detection of the hitherto unknown Cm235 was found in the α-decay chains from F...

We present new results on multi-nucleon transfer reactions in low-energy collisions of 48 Ca+ 238 U measured at the velocity filter SHIP of GSI Helmholtz Centre, where we observed around 90 different nuclides from Tl to Am (Z = 81-95). We followed the idea to use uranium targets for the synthesis of neutron-rich MNT products, particularly in the re...

The simultaneous measurement of the isotopic fission-fragment yields and fission-fragment velocities of $^{239}$U has been performed for the first time. The $^{239}$U fissioning system was produced in one-neutron transfer reactions between a $^{238}$U beam at 5.88 MeV/nucleon and a $^{9}$Be target. The combination of inverse kinematics at low energ...

Spontaneous fission properties of the isotopes Rf255, Rf256, and Rf258 produced in the reactions Ti50+Pb207, Ti50+Pb208, and Ti50+Bi209 were studied. The method of time and position correlations was used to identify spontaneous fission events. The correction to the energy deficit in measured total kinetic energy (TKE) determined on the basis of a s...

The simultaneous measurement of the isotopic fission-fragment yields and fission-fragment velocities of U239 has been performed for the first time. The U239 fissioning system was produced in one-neutron transfer reactions between a U238 beam at 5.88 MeV/nucleon and a Be9 target. The combination of inverse kinematics at low energy and the use of the...

The neutron-deficient isotopes 254,255Rf were produced in the fusion-evaporation reaction ⁵⁰Ti + ²⁰⁶Pb at the gas-filled recoil separator TASCA. Decay properties of these nuclei were investigated by applying fast digital electronics. A search for isomeric states in both isotopes was performed by using the accompanying conversion electron emissions....

A direct and complete measurement of isotopic fission-fragment yields of $^{239}$U has been performed for the first time. The $^{239}$U fissioning system was produced with an average excitation energy of 8.3 MeV in one-neutron transfer reactions between a $^{238}$U beam and a $^{9}$Be target at Coulomb barrier energies. The fission fragments were d...

A direct and complete measurement of isotopic fission-fragment yields of U239 has been performed for the first time. The U239 fissioning system was produced with an average excitation energy of 8.3 MeV in one-neutron transfer reactions between a U238 beam and a Be9 target at Coulomb barrier energies. The fission fragments were detected and isotopic...

The analysis of fission events following the implantation of evaporation residues produced in the fusion reaction of 50Ti and 209Bi at different bombarding energies has revealed 5 millisecond decays, which are attributed to the spontaneous fission of proton-evaporation channels. The average cross sections for proton evaporation are found to be ∼100...

The heaviest currently known nuclei, which have up to 118 protons, have been produced in Ca48 induced reactions with actinide targets. Among them, the element tennessine (Ts), which has 117 protons, has been synthesized by fusing Ca48 with the radioactive target Bk249, which has a half-life of 327 d. The experiment was performed at the gas-filled r...

Fusion-evaporation reactions with the doubly magic projectile ⁴⁸ Ca were used to access neutron-deficient nuclei around neptunium at the velocity filter SHIP, and investigated using the COMPASS decay spectroscopy station. With the use of digital electronics, several isotopes produced via neutron, proton, and α evaporation channels were identified b...

After publication of the paper, the authors noticed some errors in the affiliations. Their correct version is given in this erratum.

Transactinide nuclei around neutron number N=162 display axially deformed equilibrium shapes. In the present study we are particularly interested in the occurrence of high-K isomers in the axially deformed isotopes of Rf (Z=104), Sg (Z=106), Hs (Z=108), and Ds (Z=110), with neutron number N=160-166 and the effect of the N=162 closure on the structu...

The superheavy isotope ²⁵⁸Db was produced in the ²⁰⁹Bi(⁵⁰Ti, 1n)²⁵⁸Db reaction at GSI, Germany. A detailed \( \alpha\)-spectroscopy study of this isotope and its \( \alpha\)-decay daughter products was performed. Two long-lived \( \alpha\)-decaying states in ²⁵⁸Db are observed. A spin-parity of \( 0^{-}\) is tentatively assigned to the ground state...

The results for nuclei above curium, produced in multi-nucleon transfer reactions of ⁴⁸Ca + ²⁴⁸Cm at the velocity filter SHIP of GSI Darmstadt, are presented. Spontaneous fission and \( \alpha\)-activities have been used to study the population of nuclei with lifetimes ranging from few milliseconds to several days. We observed several, relatively n...

Fission at low excitation energy, is a process in which both macroscopic and microscopic aspects are involved. Some features in the total kinetic energy and in the N/Z distributions of the fragments, commonly associated with shell effects, came out in a series of recent experiments with high excitation energy fusionfission reactions in inverse kine...

The isotopes 255,256,258 Rf were produced in the fusion-evaporation reactions ⁵⁰ Ti + 207,208 Pb and ⁵⁰ Ti + ²⁰⁹ Bi at GSI Darmstadt, using the velocity filter SHIP. Total kinetic energies of fragments from spontaneous fission for these isotopes were evaluated with a correction to pulse-height defect.

After more than half a century of research addressing the synthesis and nuclear structure of superheavy nuclei (SHN) a boost for its progress is expected from the advent of new instrumentation. An order of magnitude in beam intensity increase is envisaged to be provided by new powerful accelerators like the new DC280 cyclotron at the SHE factory of...

Short-lived α-decaying nuclei “northeast” of Pb208 in the chart of nuclides were studied using the reaction Ca48+Am243 with the decay station TASISpec at TASCA, GSI Darmstadt. Decay energies and times from pile-up events were extracted with a tailor-made pulse-shape analysis routine and specific α-decay chains were identified in a correlation analy...

The isotopic distribution of nuclei produced in the ⁵⁰Ti + ²⁴⁹Cf reaction has been studied at the gas-filled recoil separator TASCA at GSI Darmstadt, which separates ions according to differences in magnetic rigidity. The bombardment was performed at an energy around the Bass barrier and with the TASCA magnetic fields set for collecting fusion-evap...

One of the most important atomic properties governing an element’s chemical behavior is the energy required to remove its least-bound electron, referred to as the first ionization potential. For the heaviest elements, this fundamental quantity is strongly influenced by relativistic effects which lead to unique chemical properties. Laser spectroscop...

Until recently, ground-state nuclear moments of the heaviest nuclei could only be inferred from nuclear spectroscopy, where model assumptions are required. Laser spectroscopy in combination with modern atomic structure calculations is now able to probe these moments directly, in a comprehensive and nuclear-model-independent way. Here we report on u...

We studied multinucleon transfer reactions in the Au197+Te130 system at Elab=1.07 GeV by employing the PRISMA magnetic spectrometer coupled to a coincident detector. For each light fragment we constructed, in coincidence, the distribution in mass of the heavy partner of the reaction. With a Monte Carlo method, starting from the binary character of...

We report the first measurement of the fusion excitation functions for K39,47+Si28 at near-barrier energies. Evaporation residues resulting from the fusion process were identified by direct measurement of their energy and time of flight with high geometric efficiency. At the lowest incident energy, the cross section measured for the neutron-rich K4...

Cross sections and corresponding momentum distributions have been measured for the first time at zero degrees for the exotic nuclei obtained from a beam of ¹⁸O at 8.5 MeV/A impinging on a 1 mg/cm²²³⁸U target. Sizable cross sections were found for the production of exotic species arising from the neutron transfer and proton removal from the projecti...

A compact silicon detector array with high spatial granularity and fast, fully digital data recording has been developed and commissioned for the investigation of heavy and superheavy nuclear species. The detector array can be combined in close geometry with large volume germanium detectors. It offers comprehensive particle and photon coincidence a...

Decay spectroscopy is a powerful tool to study the low lying nuclear structure of heavy and superheavy nuclei (SHN). Single particle levels and other structure features like K isomerism, being important in the fermium-nobelium region as well as for the spherical shell stabilized SHN, can be investigated. The new separator-spectrometer combination S...

The EXOTIC facility was developed to produce light radioactive beams and it is installed at Laboratori Nazionali di Legnaro (LNL) of INFN. We have explored the capabilities of EXOTIC as a beam separator for studies of heavy ion fusion-evaporation reactions. For this purpose, the facility has been slightly modi ed so to allow the detection and ident...

Dieter Ackermann explains why element 110 occupies a significant place in the superheavy corner of the periodic table.

An experimental scheme combining the mass resolving power of a Penning trap with contemporary decay spectroscopy has been established at GSI Darmstadt. The Universal Linear Accelerator (UNILAC) at GSI Darmstadt provided a Ca48 beam impinging on a thin Er170 target foil. Subsequent to velocity filtering of reaction products in the Separator for Heav...

We report the first measurement of the fusion excitation functions for $^{39,47}$K + $^{28}$Si at near-barrier energies. Evaporation residues resulting from the fusion process were identified by direct measurement of their energy and time-of-flight with high geometric efficiency. At the lowest incident energy, the cross-section measured for the neu...

The quantum-mechanic nature of nuclear matter is at the origin of the vision of a region of enhanced stability at the upper right end of the chart of nuclei, the so-called 'island of stability'. Since the 1960s in the early second half of the last century, various models predict closed shells for proton numbers 114–126 and neutron numbers such as 1...

Using the sensitive Radiation Detected Resonance Ionization Spectroscopy (RADRIS) technique an optical transition in neutral nobelium (No, Z = 102) was identified. A remnant signal when delaying the ionizing laser indicated the influence of a strong buffer gas induced de-excitation of the optically populated level. A subsequent investigation of the...

A sequence of three events observed in an irradiation of ²⁴⁸Cm with ⁵⁴Cr at the velocity filter SHIP of the GSI - Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany, had been interpreted as a decay chain consisting of three α particles. On the basis of measured energies, a possible assignment to the decay of an isotope of elem...

An experiment was performed at LNL to obtain information concerning the yield distributions in both the 132Sn (N = 82) and the 208Pb (N = 126) regions of the nuclide chart. The experimental set-up was composed of the large-acceptance magnetic spectrometer PRISMA to detect the light partner of the reaction, in conjunction with a recently installed a...

Multineutron and multiproton transfer channels, populated in the inverse kinematics reaction 197Au+130Te at Elab=1.07 GeV, were measured at Laboratori Nazionali di Legnaro using the presently heaviest ion beam delivered by the PIAVE-ALPI accelerator complex and detecting both projectile-like and targetlike ions. To this end the large solid angle ma...

The spectrum of physics, discussed in the 7th edition of the “Fusion” conference series, included a number of topics, ranging from reaction dynamics to structure studies, from the lightest to the heaviest nuclei, from inelastic reactions to fusion and fission, with applications of astrophysical interest and the newest developments and findings in t...

Electron capture decay of 258 Db was measured directly via delayed coincidences between K X-rays and/or conversion electrons (from the electron capture decay), and spontaneous fission or \(\alpha\) decay of the daughter nuclide 258Rf. Delayed K X-rays were also measured in prompt coincidence with conversion electrons, showing that electron capture...

Optical spectroscopy of a primordial isotope has traditionally formed the basis for understanding the atomic structure of an element. Such studies have been conducted for most elements and theoretical modelling can be performed to high precision, taking into account relativistic effects that scale approximately as the square of the atomic number. H...

The experimental determination of atomic levels and the first ionization potential of the heaviest elements ( ) is key to challenge theoretical predictions and to reveal changes in the atomic shell structure. These elements are only artificially produced in complete-fusion evaporation reactions at on-line facilities such as the GSI in Darmstadt at...

Recently, we reported the observation of several new isotopes with proton numbers \(Z \geq 92\) in low-energy collisions of ⁴⁸Ca + ²⁴⁸Cm . The peculiarity is that the nuclei were produced in multinucleon transfer reactions, a method which is presently discussed as a possible new way to enter so far unknown regions in the upper part of the Chart of...

Alpha- and Electron capture (EC) decay properties of 257 Rf were investigated by measuring \( \alpha\) - \( \gamma\) coincidences and correlations between conversion electrons (CE) emitted during the process of EC decay of 257Rf and \( \alpha\) decays of the daughter isotope 257Lr. So far, previously unobserved \( \alpha\) (8296 keV)- \( \gamma\) (...

Isomeric states in Po194 and Po192 were studied at the velocity filter SHIP. The isotopes were produced in the fusion-evaporation reactions Pr141(Fe56, p2n)Po194 and Sm144(V51, p2n)Po192. Several new γ-ray transitions were attributed to the isomers and γ−γ coincidences for both isomers were studied for the first time. The 459-keV transition earlier...

Isomeric states in Po194 and Po192 were studied at the velocity filter SHIP. The isotopes were produced in the fusion-evaporation reactions Pr141(Fe56, p2n)Po194 and Sm144(V51, p2n)Po192. Several new γ-ray transitions were attributed to the isomers and γ−γ coincidences for both isomers were studied for the first time. The 459-keV transition earlier...

The unexplored area of heavy neutron rich nuclei is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleogenesis. For the production of heavy neutron rich nuclei located along the neutron closed shell N=126 (probably the last "waiting point" in the r-process of...

Products of the fusion-evaporation reaction 48Ca + 243Am were studied with the TASISpec set-up at the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. Amongst the detected thirty correlated α-decay chains associated with the production of element Z=115, two recoil-α-fission and five recoil-α-α-fis...

The Super Separator Spectrometer (S3S3) facility is developed in the framework of the SPIRAL2 project [1]. S3S3 has been designed to extend the capability of the facility to perform experiments with extremely low cross sections, taking advantage of the very high intensity stable beams of the superconducting linear accelerator of SPIRAL2. It will ma...

In the last period, two classes of experiments have been carried out with the large acceptance magnetic spectrometer PRISMA. In particular, the one- and two-neutron transfer processes at energies ranging from the Coulomb barrier to deep below it and the population of exotic neutron rich nuclei in the A~130 and A~200 mass regions have been studied....

The fission process still remains a main factor that determines the stability of the atomic nucleus of heaviest elements. Fission half-lives vary over a wide range, 10−19−1024 s. Present experimental techniques for the synthesis of the superheavy elements that usually measure α-decay chains are sensitive only in a limited range of half-lives, often...

Two short-lived isotopes U221 and U222 were produced as evaporation residues in the fusion reaction Ti50+Yb176 at the gas-filled recoil separator TASCA. An α decay with an energy of Eα=9.31(5) MeV and half-life T1/2=4.7(7) μs was attributed to U222. The new isotope U221 was identified in α-decay chains starting with Eα=9.71(5) MeV and T1/2=0.66(14)...

We investigated the formation of nuclear molecules and the occurrence of time delays in reactions of the superheavy systems 64Ni + 207Pb ($ Z_{1}+Z_{2}=110$), 132Xe + 208Pb ($ Z_{1}+Z_{2}=136$) and 238U + 238U ($ Z_{1}+Z_{2}=184$. In deep inelastic binary reactions of Ni + Pb and Xe + Pb we observed clear signatures for the formation of long-living...

New decay data for the isotopes 259Sg and 255Rf were obtained at the velocity filter SHIP using an α-decay spectroscopy measurement. Both isotopes were produced and studied via a one neutron evaporation channel in the compound fusion reaction 54Cr+208 Pb. New isomeric states were observed and the single-particle level systematics for isotones with...