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The excitation spectra in the deformed nucleus 228Th have been studied by means of the (p, t) reaction, using the Q3D spectrograph facility at the Munich Tandem accelerator. The angular distributions of tritons were measured for about 110 excitations seen in the triton spectra up to 2.5 MeV. Firm 0+ assignments are made for 17 excited states by comparison of experimental angular distributions with the calculated ones using the CHUCK3 code. Assignments up to spin 6+ are made for other states. [ABSTRACT FROM AUTHOR]

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The isomeric first excited state of 229Th exhibits the lowest nuclear excitation energy in the whole landscape of known nuclei. Due to its extremely low energy of 7.6(5) eV and its long lifetime of ca. 104 s, it exhibits an extremely sharp relative linewidth of ΔE/E≈1020, thus rendering 229mTh an ideal candidate for a nuclear optical clock with very high accuracy. An experimental approach is introduced, based on a spatially decoupled population and de-excitation of the isomeric state, aiming at a first direct identification of the 163(11) nm UV fluorescence and targeting to improve on the accuracy of the transition wavelength, thus enabling an all-optical control via laser excitation. [ABSTRACT FROM AUTHOR]

The photofission cross-section of 238U was measured in the sub-barrier energy region as a function of the γ energy using, for the first time, a monochromatic, high-brilliance, Compton backscattered beam. This prototype experiment was performed at the HIγS gamma beam facility of the Duke University at Durham (North Carolina, US) using the 238U(γ, f) reaction at a beam energy varied between Eγ = 4.7-6.0 MeV and with an energy resolution of ΔE = 150-200 keV (ΔE=E ≈ 3%). The photofission cross-section was determined down to E* = 4.7 MeV. Indications of transmission resonances have been observed at excitation energies of E" = 5.1 and 5.6 MeV with moderate amplitudes. [ABSTRACT FROM AUTHOR]

Presently two new research facilities are either already under construction ('MEGa-Ray' at Lawrence Livermore National Laboratory/US) or soon ready to start construction (ELI-Nuclear Physics in Bucharest/ Romania), both aiming to provide highly brilliant γ beams with so far unprecedented properties (ca. 1013 photons/s, energy resolution ≤10-13 via Compton-backscattering of laser photons from a high-quality relativistic electron beam. With these intense, monochromatic γ beams, a new era of photonuclear physics will be enabled. It is envisaged to exploit the novel beams for highly-selective studies of extremely deformed nuclei in the multiple-humped potential energy landscape of the actinides via photofission. We will be able to populate gateway states in the first potential minimum of nuclei, predominantly originating from collective states in the (superdeformed) second or (hyperdeformed) third potential minimum, tunnelling back into the first well. The γ beam energy resolution of 10-13 allow to resolve individual resonances due to the lower level density in the higher potential minima. Excited states in these minima can be rather selectively populated with much larger intensities than achieved with former methods based on light-ion induced reactions. Also the large background from prompt fission with σisomer/σprompt ≈10-5 is avoided. Hence a detailed γ spectroscopy in the second and third minimum will be enabled. [ABSTRACT FROM AUTHOR]

The fission probability of 232Pa was measured as a function of the excitation energy in order to search for hyperdeformed (HD) transmission resonances using the (d,pf) transfer reaction on a radioactive 231Pa target. The experiment was performed at the Tandem accelerator of the Maier-Leibnitz Laboratory (MLL) at Garching using the 231Pa (d,pf) reaction at a bombarding energy of Ed = 12MeV and with an energy resolution of ΔE = 5:5 keV. Two groups of transmission resonances have been observed at excitation energies of E* = 5:7 and 5.9MeV. The fine structure of the resonance group at E* = 5:7MeV could be interpreted as overlapping rotational bands with a rotational parameter characteristic to a HD nuclear shape (ħ²/2Θ = 2:05 keV). The fission barrier parameters of 232Pa have been determined by fitting TALYS nuclear reaction code calculations to the overall structure of the fission probability. [ABSTRACT FROM AUTHOR]

Presently, large efforts are conducted toward the development of highly brilliant γ beams via Compton back scattering of photons from a high-brilliance electron beam, either on the basis of a normal-conducting electron linac or a (super-conducting) Energy Recovery Linac (ERL). Particularly, ERLs provide an extremely brilliant electron beam, thus enabling the generation of highest-quality γ beams. A 2.5 MeV γ beam with an envisaged intensity of 10 photons s, as ultimately envisaged for an ERL-based γ-beam facility, narrow band width (10), and extremely low emittance (10 mm mrad) offers the possibility to produce a high-intensity bright polarized positron beam. Pair production in a face-on irradiated W converter foil (200 μm thick, 10 mm long) would lead to the emission of 2×10 (fast) positrons per second, which is four orders of magnitude higher compared to strong radioactive Na sources conventionally used in the laboratory. Using a stack of converter foils and subsequent positron moderation, a high-intensity low-energy beam of moderated positrons can be produced. Two different source setups are presented: a high-brightness positron beam with a diameter as low as 0.2 mm, and a high-intensity beam of 3×10 moderated positrons per second. Hence, profiting from an improved moderation efficiency, the envisaged positron intensity would exceed that of present high-intensity positron sources by a factor of 100. [ABSTRACT FROM AUTHOR]

We propose to produce neutron-rich nuclei in the range of the astrophysical r-process (the rapid neutron-capture process) around the waiting point N=126 (Kratz et al. in Prog. Part. Nucl. Phys. 59:147, ; Arnould et al. in Phys. Rep. 450:97, ; Panov and Janka in Astron. Astrophys. 494:829, ) by fissioning a dense laser-accelerated thorium ion bunch in a thorium target (covered by a polyethylene layer, CH), where the light fission fragments of the beam fuse with the light fission fragments of the target. Using the 'hole-boring' (HB) mode of laser radiation pressure acceleration (RPA) (Robinson et al. in Plasma Phys. Control. Fusion 51:024004, ; Henig et al. in Phys. Rev. Lett. 103:245003, ; Tajima et al. in Rev. Accel. Sci. Technol. 2:221, ) using a high-intensity, short pulse laser, bunches of Th with solid-state density can be generated very efficiently from a Th layer (ca. 560 nm thick), placed beneath a deuterated polyethylene foil (CD with ca. 520 nm), both forming the production target. Th ions laser-accelerated to about 7 MeV/u will pass through a thin CH layer placed in front of a thicker second Th foil (both forming the reaction target) closely behind the production target and disintegrate into light and heavy fission fragments. In addition, light ions (d,C) from the CD production target will be accelerated as well to about 7 MeV/u, also inducing the fission process of Th in the second Th layer. The laser-accelerated ion bunches with solid-state density, which are about 10 times more dense than classically accelerated ion bunches, allow for a high probability that generated fission products can fuse again when the fragments from the thorium beam strike the Th layer of the reaction target. In contrast to classical radioactive beam facilities, where intense but low-density radioactive beams of one ion species are merged with stable targets, the novel fission-fusion process draws on the fusion between neutron-rich, short-lived, light fission fragments from both beam and target. Moreover, the high ion beam density may lead to a strong collective modification of the stopping power in the target by 'snowplough-like' removal of target electrons, leading to significant range enhancement, thus allowing us to use rather thick targets. Using a high-intensity laser with two beams with a total energy of 300 J, 32 fs pulse length and 3 μm focal diameter, as, e.g. envisaged for the ELI-Nuclear Physics project in Bucharest (ELI-NP) (, ), order-of-magnitude estimates promise a fusion yield of about 10 ions per laser pulse in the mass range of A=180-190, thus enabling us to approach the r-process waiting point at N=126. First studies on ion acceleration, collective modifications of the stopping behaviour and the production of neutron-rich nuclei can also be performed at the upcoming new laser facility CALA (Center for Advanced Laser Applications) in Garching. [ABSTRACT FROM AUTHOR]

We propose to search for neutron halo isomers populated via γ-capture in stable nuclei with mass numbers of about A=140-180 or A=40-60, where the 4 s or 3 s neutron shell model state reaches zero binding energy. These halo nuclei can be produced for the first time with new γ-beams of high intensity and small band width (≤0.1%) achievable via Compton back-scattering off brilliant electron beams, thus offering a promising perspective to selectively populate these isomers with small separation energies of 1 eV to a few keV. Similar to single-neutron halo states for very light, extremely neutron-rich, radioactive nuclei (Hansen et al. in Annu. Rev. Nucl. Part. Sci. 45:591-634, ; Tanihata in J. Phys. G., Nucl. Part. Phys. 22:158-198, ; Aumann et al. in Phys. Rev. Lett. 84:35, ), the low neutron separation energy and short-range nuclear force allow the neutron to tunnel far out into free space much beyond the nuclear core radius. This results in prolonged half-lives of the isomers for the γ-decay back to the ground state in the 100 ps-μs range. Similar to the treatment of photodisintegration of the deuteron, the neutron release from the neutron halo isomer via a second, low-energy, intense photon beam has a known much larger cross section with a typical energy threshold behavior. In the second step, the neutrons can be released as a low-energy, pulsed, polarized neutron beam of high intensity and high brilliance, possibly being much superior to presently existing beams from reactors or spallation neutron sources. [ABSTRACT FROM AUTHOR]

High power short-pulse lasers with peak powers presently reaching Terawatts and even Petawatt levels routinely reach focal intensities of 1018 - 1021 W/cm². These lasers are able to produce a variety of secondary radiation, from relativistic electrons and multi-MeV/nucleon ions to highenergetic X-rays and γ-rays. In many laboratories world-wide large resources are presently devoted to a rapid development of this novel tool of particle acceleration, targeting nuclear, fundamental and high-field physics studies as well as various applications e.g. in medical technology for diagnostics and tumor therapy. Within the next 5 years a new EU-funded large-scale research infrastructure (ELI: Extreme Light Infrastructure) will be constructed, with one of its four pillars exclusively devoted to nuclear physics based on high intensity lasers (ELI-Nuclear Physics, to be built in Magurele/Bucharest). There the limits of laser intensity will be pushed by three orders of magnitude to yet unprecedented 1024 W/cm². [ABSTRACT FROM AUTHOR]