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J Gerl

Publications and source records attributed to J Gerl.

16 recordsLinked to original sources
PubMed2006

Breakdown of K selection in 178Hf.

Coulomb activation of the four quasiparticle Kpi=16+ 178Hf isomer (t1/2=31 y) has led to the measurement of a set of Elamda matrix elements coupling the isomer band to the ground band. The present data combined with earlier 178 Hf Coulomb excitation data have probed the components in the wave functions and revealed the onset and saturation of K mixing in low-K bands, whereas the mixing is negligible in the high-K bands. The implications can be applied to other quadrupole-deformed nuclei.

Journal Article↗
PubMed2006

High energy probe for detecting lymph node metastases with 18F-FDG in patients with head and neck cancer.

AIM: of this study was to validate a newly developed high energy probe (positron emission probe, PEP) optimised for localising PET tracers in vivo. PATIENTS AND METHODS: Physical investigations included determination of full width at half maximum (FWHM) values at a distance of 1 cm and angular resolution using different point sources. Values obtained with the new probe were compared to those of a conventional gamma probe (CGP). Additionally, PET studies were performed in 36 patients (6 women, 30 men) with proven head and neck cancer and suspected lymph node metastases (Axis, Marconi/Philips) after administering 250-320 MBq (18)F-FDG. Subsequent to PET investigations (18)F-FDG uptake in cervical regions was measured using the PEP. PEP investigations were carried out bilaterally in 5 lymph node (LN) levels (Robbins' classification of the neck). Results of probe studies were correlated with visual and semiquantitative PET evaluations, US and histological findings. RESULTS: FWHM of the new probe was 7 mm (CGP 22 mm) at 662 keV ((137)Cs) and angular resolution resulted in 8 degrees (CGP 60 degrees ). In 29 out of 36 patients LN metastases were suspected due to ultrasound investigations. After neck dissection, histology confirmed LN metastases in 21 patients. Sensitivity (sens.) of US amounted to 95% and specificity to 40%. In 18/21 patients LN metastases were detected by PET (sens. 86%). PET scans failed to diagnose the LN status correctly in 6/36 patients (accuracy 83%). Employing the PEP probe in 20/21 patients LN metastases were identified (sens. 95%), and LN status was determined accurately in 29/36 patients (accuracy 81%). Tumour/background ratios of PEP measurement and results of semiquantitative PET analyses were comparable. CONCLUSIONS: PEP measurement is a promising method for preoperative planning of the extent of neck dissection in patients with head and neck cancer and further for radioguided localising PET tracer accumulation during surgery.

Adult↗
PubMed2005

"Safe" Coulomb excitation of 30Mg.

We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient gamma spectrometer MINIBALL. Using 30Mg ions accelerated to an energy of 2.25 MeV/u together with a thin (nat)Ni target, Coulomb excitation of the first excited 2+ states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation gamma-ray yields the B(E2;0(+)gs-->2(+)1) value of 30Mg was determined to be 241(31)e2 fm4. Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope 30Mg resides outside the "island of inversion."

Journal Article↗
PubMed2004

Shell structure of the near-dripline nucleus 23O.

Breakup reactions were used to study the ground-state configuration of the neutron-rich isotope 23O. The 22O fragments produced in one-nucleon removal from 23O at 938 MeV/nucleon in a carbon target were detected in coincidence with deexciting gamma rays. The widths of the longitudinal momentum distributions of the 22O fragments and the one-neutron removal cross sections were interpreted in the framework of a simple theoretical model which favors the assignment of Ipi = 1/2+ to the 23O ground state.

Journal Article↗
PubMed2002

Coulomb excitation paths of high-K isomer bands in 178Hf.

Three distinctly different mechanisms are shown to populate the K(pi)=6(+) (t(1/2)=77 ns), 16(+) (31 yr), and 8(-) (4 s) isomer bands of 178Hf by Coulomb excitation. High spin states of the three isomer bands were populated by Coulomb excitation of a hafnium target with a 650 MeV 136Xe beam. Although direct population of high-K bands is highly K-forbidden, isomer bands in 178Hf were populated up to spins 13(+)(K=6), 20(+)(K=16), and 14(-)(K=8) with in-band gamma yields of approximately 10(-4) of the ground state band. The data are consistent with a rapid increase in K mixing with increasing spin in the isomer bands.

Journal Article↗
PubMed2002

Conversion electron cascades in 254(102)No.

The spectrum of prompt conversion electrons emitted by excited 254No nuclei has been measured, revealing discrete lines arising from transitions within the ground state band. A striking feature is a broad distribution that peaks near 100 keV and comprises high multiplicity electron cascades, probably originating from M1 transitions within rotational bands built on high K states.

Journal Article↗
PubMed2000

A triplet of differently shaped spin-zero states in the atomic nucleus 186Pb

Understanding the fundamental excitations of many-fermion systems is of significant current interest. In atomic nuclei with even numbers of neutrons and protons, the low-lying excitation spectrum is generally formed by nucleon pair breaking and nuclear vibrations or rotations. However, for certain numbers of protons and neutrons, a subtle rearrangement of only a few nucleons among the orbitals at the Fermi surface can result in a different elementary mode: a macroscopic shape change. The first experimental evidence for this phenomenon came from the observation of shape coexistence in 16O (ref. 4). Other unexpected examples came with the discovery of fission isomers and super-deformed nuclei. Here we find experimentally that the lowest three states in the energy spectrum of the neutron deficient nucleus 186Pb are spherical, oblate and prolate. The states are populated by the alpha-decay of a parent nucleus; to identify them, we combine knowledge of the particular features of this decay with sensitive measurement techniques (a highly efficient velocity filters with strong background reduction, and an extremely selective recoil-alpha-electron coincidence tagging methods). The existence of this apparently unique shape triplet is permitted only by the specific conditions that are met around this particular nucleus.

Journal Article↗