0000000000555744
AUTHOR
M. Dahlinger
Resonance ionization spectroscopy in a buffer gas cell with radioactive decay detection, demonstrated usingTl208
An ultrasensitive laser spectroscopic method has been developed to perform hyperfine spectroscopy of heavy-ion-induced reaction products. It is based on resonance ionization in a buffer gas cell combined with radioactive decay detection. The feasibility has been demonstrated using the \ensuremath{\beta}-active ${\mathrm{isotope}}^{208}$ Tl. A sensitivity of 1.3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ of the two-step resonance-ionization process via the n=17 Rydberg level has been determined, utilizing a pulsed excimer-dye-laser combination. The previously unknown nuclear magnetic moment \ensuremath{\mu}${(}^{208}$Tl) = 0.292(13)${\mathrm{\ensuremath{\mu}}}_{\mathi…
Evidence for molecular-cluster states in222Th
The groundstate and a negative parity band of222Th have been observed in the208Pb (180, 4n)222Th reaction by conversion electron and γ-ray spectroscopy identifying the evaporation residues in a recoil separator. The de-excitation pattern is characterized by strong El transitions interconnecting the levels of alternating parity. The yrast levels may be interpreted as a molecularcluster band.
Excited states in neutron deficient even-even thorium isotopes (218?A?222)
The nuclei218, 220, 222Th were investigated by conversion electron andγ-ray spectroscopy after compound nucleus reactions of14N with209Bi and16, 18O with208Pb. The intenseγ-background from fission was suppressed by spectroscopy of conversion electrons andγ-rays in coincidence with the evaporation residues or theirα-decay. Level schemes were determined for218Th up toIπ=10+ and for220Th and222Th up toIπ=15−. The observed structure of218Th may be explained in the spherical shell model with residual interaction by two neutron excitation. ForN≧130 completely different level schemes are observed showing very intense, collective electric dipole transitions (B(E1)−10−2 W.u.) with energies of typica…
In-beam spectroscopy of224Th
A rotational band with states of alternating parity has been populated in224Th via the208Pb(18O, 2n) reaction. Spins up to Iπ=10>+ (11−) are identified. Stretched El and E2 transitions compete in the deexcitation, the average ratio of the reduced transition probabilities being B(E1)/B(E2)=(1.5±0.4)×10−6 fm−2. This ratio implies that224Th has one of the largest intrinsic electric dipole moments observed so far.
First observation of a resonance ionization signal on242mAm fission isomers
The feasibility of a hyperfine spectroscopy on242mAm fission isomers has been demonstrated at the low target production rate of 10/s. The experimental method employed is based on resonance ionization spectroscopy in a buffer gas cell with detection of the ionization process by means of the fission decay of the isomers. The resonance ionization has been performed in two steps, utilizing an excimer dye laser combination with a repetition rate of 300 Hz. The first resonant step proceeds through theJ=7/2 term at 21440.35 cm−1, which has been excited with the tuncable dye laser beam of a wavelength of 466.28 nm, the second non-resonant step is achieved with the 351 nm radiation of the excimer la…