The cyclotron trap for antiprotons

The cyclotron trap is a device to increase the stop density of negatively charged particles. Its working principle is to wind up the range of a stopping particle in a weak focusing magnetic field. Its main application in the past was the spectroscopy of exotic atoms. A modern application is the production of low energy muon or antiproton beams.     

Damage to model DNA fragments from very low-energy (<1 eV) electrons

Although electrons having enough energy to ionize or electronically excite DNA have long been known to cause strand breaks (i.e., bond cleavages), only recently has it been suggested that even lower-energy electrons (most recently 1 eV and below) can also damage DNA. The findings of the present work suggest that, while DNA bases can attach electrons having kinetic energies in the 1 eV range and subsequently undergo phosphate-sugar O-C sigma bond cleavage, it is highly unlikely (in contrast to recent suggestions) that electrons having kinetic energies near 0 eV can attach to the phosphate unit's P=O bonds. Electron kinetic energies in the 2-3 eV range are required to attach directly to DNA's phosphate group's P=O pi orbital and induce phosphate-sugar O-C sigma bond cleavages if the phosphate groups are rendered neutral (e.g., by nearby counterions). Moreover, significant activation barriers to C-O bond breakage render the rates of both such damage mechanisms (i.e., P=O-attached and base-attached) slow as compared to electron autodetachment and to other damage processes.     

Melanin content of cultured human melanocytes and UV-induced cytotoxicity

Cultured melanocytes originating from persons with different skin phototypes were utilized for measurement of endonuclease sensitive sites induced by UVB and the determination of cell survival after UVA or UVB irradiation. During culture, the melanocytes largely maintained their phenotypic characteristics according to their original skin phototype. Total melanin concentrations were 4.9 times higher in the darker skin phototype (IV-VI) melanocytes when compared to the cells from lighter skin phototypes (I-III). Also phaeomelanin contents were higher (2.5 times) in the skin phototype (IV-VI) melanocytes which implies that the cells from light skin types contain less melanin, but a relatively high proportion of phaeomelanin. After UVB irradiation a stronger induction of endonuclease sensitive sites was found for melanocytes with a lower level of total melanin and a high content of pheomelanin. By measuring the clone forming ability in different melanocyte cultures after UVB irradiation, significant better survival was found in case of the cells with the higher melanin content. Despite the large variations in melanin content, no significant difference in survival after UVA irradiation could be demonstrated in this way. Our results suggest a protective effect of melanin for UVB and indicate the importance of the measurements of melanin content and composition when different parameters of UV-induced damage are studied in melanin producing cells.     

Measurement of balmer and lyman X-rays in antiprotonic hydrogen isotopes at pressures below 300 hPa

X-Rays of Balmer and Lyman transitions in antiprotonic hydrogen and of Balmer transitions in antiprotonic deuterium were observed at pressures below 300 hPa using Si(Li) semiconductor detectors. The measurement was performed at the LEAR-facility at a beam momentum of 202 MeV/c. In order to stop antiprotons in a low pressure gaseous target with high efficiency, a novel technique, the cyclotron trap has been used. Absolute yields were determined and compared with cascade calculations. A distinct difference in the cascade of antiprotonic hydrogen and deuterium is found. The parameters of strong interaction in antiprotonic hydrogen are determined to be? _1s=?(620±100) eV,Γ _1s=(1130±170) eV andΓ _2p=(32±10) meV.     

Determination of the spectroscopic quadrupole moments of 33 75 As and 29 63 Cu

The HFS-splitting of the 2s-2p and 3d-2p transitions of muonic arsenic and 3d-2p transitions of copper have been measured with high resolution Ge-semiconductor detectors to determine the nuclear quadrupole moments. A coincidence measurement was performed to separate the 2s-2p transition from the background. The nuclear spectroscopic quadrupole moments were found to be:Q _spec=0.314(6) b for ₃₃ ⁷⁵ AsQ _spec=0.220(15) b for ₂₉ ⁶³ Cu. In addition, generalized Barrett moments were determined in a model-independent analysis of muonic transition energies.