B. Perny

Dumond curved crystal spectrometer for in-beam X- and gamma-ray spectroscopy☆

An in-beam curved crystal spectrometer facility has been installed at the SIN variable energy cyclotron. The radius of curvature is 3.15 m. Using the (110) planes of different bent quartz laminas, diffraction peaks down to Δθ = 5 arcsec FWHM are obtained. The energy resolution is thus ΔE ⋍ 0.01 E2/n, where n is the diffraction order, ΔE being expressed in eV and E in keV. The spectrometer has been constructed to cover an angular range of ±10°. Transitions in the range 17 to about 350 keV have so far been observed. Measurements have been performed in conventional line source DuMond geometry and in slit geometry. The instrument is being used for the high-resolution observation of X- and gamma-rays induced by proton, helium- and oxygen-ion bombardment.

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.

Anomalous g-factors in odd-odd 174Lu

Abstract The branching ratios for the γ-decay of the lowest states in the {π 7 2 + (404)±ν 5 2 − (512)}K π =1 ground-state band and Kπ=6−142 d isomeric rotational band have been measured following 176Yb(p, 3nγ)174 Lu excitation. These results are combined with known magnetic moments to deduce gyromagnetic factors. Anomalous values are evinced for the higher K-configuration.

Study of the levels in 174Lu by (p, 3nγ) spectroscopy

Abstract The nuclear levels in 174 Lu were investigated by means of 176 Yb(p, 3nγ) reaction spectroscopy. Standard germanium detector techniques as well as an on-line curved crystal spectrometer were used. Six well-developed rotational bands are observed. These results confirm and extend the scheme previously obtained by direct reactions. The presented data document a study on the anomalous g -factors of the 142 d isomeric band.

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.

High resolution in‐beam γ‐ray spectroscopy

An in‐beam curved crystal facility has been installed at the SIN variable energy cyclotron. Using the (110) planes of a 3.0 mm thick quartz lamina bent at 3.15 m, diffraction peaks typically 6 arcsec wide (FWHM) are obtained. The energy resolution is thus, for instance, 110 eV at 170 keV in 3rd order. Due to a sophisticated detector system and heavy shielding, the sensitivity of the instrument is quite good. The facility proves quite useful in (p,xnγ) reaction studies whenever the γ‐ray spectrum is very complex, e.g. in the study of odd‐odd deformed nuclei. Complicated multiplets appearing in the 176Yb(p,3nγ)174Lu spectrum could be successfully resolved. From the results we derive that the g‐factors of the 142 d, Jπ=6− isomer, take anomalous values.

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.