M. Carlen

Nuclear structure of 166Tm from (α,3n) γ-ray and conversion electron measurements

Abstract Excited levels of the strongly-deformed odd-odd nucleus 166 Tm, populated by the 165 Ho(α,3nγ) reaction, were investigated using standard in-beam γ-ray spectroscopy, including measurements of a few conversion electron lines, and by high-resolution curved-crystal spectroscopy. A level scheme consisting of 178 transitions among 6 well-developed and 4 partial rotational bands is proposed. Level spins and parities were determined and the results were interpreted in the framework of the Nilsson model by comparison with predictions. The Gallagher-Moszkowski splitting for the { π 1 2 + [411] ± ν 5 2 + [642] } configuration was determined to be 245(20) keV. An anomalous signature splitting was observed for the {π 7 2 + [404] + ν 5 2 + [642]}K π = 6 + configuration.

Signature inversion and electromagnetic properties of aligned bands in 166Tm

Abstract Excited states of 166 Tm were investigated by means of the 165 Ho(α, 3n) reaction. Two rotational bands were identified up to tentative spins of 20 − and 18 + . Their electromagnetic.properties were studied and interpreted in the framework of the cranking shell model (CSM) and of the particle-rotor model (PRM). Both the revised Donau and Frauendorf formula (CSM) and the PRM calculations reproduce the experimental results rather well for spins between 10 and 14, whereas they fail at low and high angular momenta. The two models predict different I -dependences for the B (M1) values in the angular momentum region of I j p + j n . The existence and interpretation of the signature inversion of the yrast band is discussed using three different models. The results show that the occurrence of signature inversion does not necessarily mean the presence of trixial nuclear shape.

Distribution of KαLn satellite yields for medium Z elements bombarded with 16O ions

Kα X-ray spectra were measured with a Du Mond type curves crystal spectrometer for42Mo and46Pd targets bombarded with oxygen ions at 5.5 MeV/u energy (i.e. at velocity closely matching those of the targetL-shell electrons). The distribution ofL-shell vacancies produced in collisions with simultaneousK-shell ionization is deduced from the measured yield distribution of theKα X-ray satellites. The distribution shows deviations from the binomial ones. The deviations can be accounted for by assuming that theL-shell vacancy production is due to two uncorrelated processes: the direct ionization by impact and the electron capture from theL-shell of the target atom into theK-shell of the projectile, both occurring at nearly central collisions. The corresponding probability values are deduced using simple statistical considerations.

In-beam bent-crystal spectrometer for studies of multiple inner shell ionization

Abstract A diffraction spectrometer with a quartz crystal bent to the radius of 4.64 m has been installed at the beam line of KVI variable energy cyclotron. The instrument is intended for a detailed study of KX-rays from multiply ionized atoms with Z > 56. The KX-ray spectra of Tb bombarded with 15 MeV/amu 4He and 20Ne ions are presented along with the calibration 84.257 keV gamma line of 170Yb. The L-shell ionization probabilities in near central collisions are deduced from the measured L-satellite yield distribution.

X-ray Kβ satellites induced in molybdenum by 4He ions

The Kβ X-ray spectrum of molybdenum bombarded by 28 MeV 4He ions was measured with a transmission curved crystal spectrometer. L and even M satellite lines were observed and resolved. Experimental energies are compared with those calculated with a MCDF program. Satisfactory agreement is found. Measuring the Kβ X-ray spectra with high resolution is a novel technique to also determine the M-shell ionization probability in central collisions. Comparison of the value obtained for Mo with theoretical (SCA) predictions demonstrates the importance of the recoil term.

Inner-shell ionization in near-central collisions of 6.7 MeV/amu4He ions with mid-Z atoms

TheKβ spectra of molybdenum, palladium and lanthanum bombarded by 6.7 MeV/amu4He ions were measured with a transmission curved crystal spectrometer.L andM satellite lines were observed and resolved. Experimental energies are compared with those calculated with a MCDF program.M -shell ionization probabilities are deduced from the measured satellite intensity ratios and compared with theoretical (SCA) predictions. The experimental values are found to be higher than the calculated ones (by a factor of 2 for La and a factor of about 4 for Mo and Pd). The influence of coupling effects, electron wave functions, electron capture, electron correlation and target activation is discussed.

Non-binomial distribution of palladium KαLn X-ray satellites emitted after excitation by 16O ions

The experimental distribution of Kα X-ray satellite yield from 46Pd atoms bombarded with oxygen ions at 5.4 MeV/u energy (i.e. closely matching the target L-shell electron velocity) shows significant deviations from the binomial distribution. The deviations can be accounted for by assuming that the L-shell ionization is due to two uncorrelated processes: the direct ionization by impact and the electron capture from the L-shell of the target atom to the K-shell of the projectile, both occurring at nearly central collissions. The corresponding probability values are obtained using simple statistical considerations.