Jfw Jansen

SEARCH FOR HIGH-SPIN ISOMERIC STATES IN THE RARE-EARTH REGION

Several new high-spin (I>10) isomeric states in the mass region A=144–164 are located in a systematic search with 12C induced reactions, employing a sixteen NaI (Tl)Ge(Li) detector multiplicity filter. The proximity to the N=82 neutron shell closure strongly suggests that shell effects contribute significantly to this isomerism.

In-beam γ-ray studies of complex band structures and of isomeric states in 152, 153Dy nuclei

Abstract The high-spin level structures of 152 Dy and 153 Dy were studied experimentally with 154, 155 Gd(α xnγ ) in-beam reactions, and for 152 Dy also with 144, 146 Nd ( 12 C, x n γ) reactions. The experiments included measurements of singles γ-ray and conversion-electron spectra, γ-ray angular distributions and E γ - t and E γ - E γ - t coincidences. A multiplicity filter set-up was used to study the feeding and decay of isomeric states in 152 Dy. In 152 Dy about twenty so far unknown levels were found, including two high-spin isomeric states with T 1 2 ≈ 60 and ≈ 13 ns at excitation energies E x ≈ 5.04 and 6.08 MeV, respectively. These states are compared with recent calculations on yrast traps. The level scheme of 153 Dy contains 28 levels up to E x = 4.1 MeV and J π = ( 37 2 + ) . Band structures in both nuclei are discussed in comparison with other N = 86 and N = 87 isotones.

Positive- and negative-parity yrast bands in the transitional nucleide 150Sm and the interacting boson approximation

Abstract The 150Nd(α, 4n) reaction at Eα = 45 MeV has been used to study high spin states in the 15062Sm88 nucleide. The experiments comprised measurements of singles γ-ray and conversion electron spectra, γ-ray angular distributions, three-parameter (Eα−Eα−t) coincidences and a γ-ray anti-Compton spectrum. Predominantly populated were the ground-state band (g.s.b.) extending to Jπ = 12+ and tentatively to 16+ and a negative-parity odd spin band (n.p.b.) extending from Jπ = 5− through 15− and tentatively to 19−. The bands are interpreted in the framework of the interacting boson approximation model with a Hamiltonian appropriate for a transitional nucleus, far away from either the rotational or vibrational limit. It is found that the model gives a very satisfactory description of the energies of the two bands observed as well as of the branching ratios of the intra- and inter-band transitions. The gentle backbending of the 2ℷ h 2 versus (ħω)2 curve for g.s.b. above Jπ = 10+ is reproduced in the calculation without making use of the band-crossing concept. The absolute reaction cross sections have been determined at 45 MeV bombarding energy to be σtot = 1380 ± 170 mb and σ4n = 800 ± 100 mb.

State-of-the-art of NORM nuclide determination in samples from oil and gas production : Validation of potential standardization methods through an interlaboratory test programme

Gas and oil companies frequently encounter build up of Naturally Occurring Radioactive Material (NORM) in their production and processing facilities. In the Netherlands NORM is subject to strict national regulations and, consequently, installations have to be screened on a regular basis. The availability of accurate and reliable NORM sampling and analysis techniques is therefore essential. A number of years ago, the “Nederlandse Aardolie Maatschappij B.V.” (NAM) actively initiated an investigation on analysis techniques for NORM samples from gas and oil companies. Within this framework, Shell Research Amsterdam organized a four-stage interlaboratory test programme in which representative samples of increasing complexity were analyzed by a number of Dutch institutes. Whereas a large spread in results was observed in the first stage, results in the last stage deviated less than ±10% from the values certified by an independent referee institute, even for comple, sludge samples. It was found that in particular the use of different values for the γ-yields and branching ratios amongst the institutes was responsible for the initial spread.

High-spin states in 232U investigated with the 232Th(α, 4nγ) reaction

The ground-state rotational band of 232U is established up to Iπ = 16+ (tentatively 18+) through a study of the 232Th(α, 4nγ) reaction. Conversion electron spectroscopy is found to be especially useful in circumventing the difficulties caused by strong fission competition.

Negative parity bands in 100Ru and 150Sm and the interacting boson approximation

Ground-state band members up to Jπ = 10+ in 100Ru and up to 14+ in 150Sm and odd-spin negative parity states up to 15− in both nuclei have been identified from (α, 4n) in-beam γ-ray and conversion electron spectra. The data are interpreted in terms of interacting quadrupole and octupole bosons.

Search for Short-Lived Axions in a Nuclear Isoscalar Transition

Axions, if existing, can cause a strong signal of positron-electron pairs in isoscalar M1 transitions in competition with gamma-ray emission. We have searched for such a signal in the 3.59 MeV transition in 10B with a fourfold Mini-Orange spectrometer. No axion events were found within one percent of the prediction for the standard axion- to γ-ray branching ratio.

E0 transitions between lowest Kπ=0+ bands in 232U and 234U

Regular patterns of E0 transitions were observed after 232Th(α,xn reactions. They indicate that the moments of inertia of β- and ground-state bands are nearly equal in 234U, in contrast to its even-even neighbours 232Th, 232U and 236U.

Band structures in 98Ru and 99Ru

Abstract The level schemes of 98, 99Ru were studied with the reactions 98Mo(α, 3nγ) and 98Mo(α, 4nγ) at Eα = 35 to 55 MeV, using a large variety of in-beam γ-ray detection techniques and conversion-electron measurements. A search for the 3− state was carried out with the reaction 98Ru(p, p′). The ground-state band of 98Ru was excited up to Jπ = (12)+ and a negative-parity band up to (15)−. New levels in 98Ru were found at Ex = 2285 (Jπ = 4+), 2435 (Jπ = (3−, 4+)), 2671, 3540, 4224, 4847, 4915 (Jπ = (12)+), 4989 (Jπ = (12+)), 5521 (Jπ = (13)−), 5889, 6591 (Jπ = (15)−), and 7621 keV. New unambiguous spin and parity assignments were made for the levels at Ex = 2014 and 3852 keV, as Jπ = 3+ and 9−, respectively. New levels in 99Ru were found at Ex = 1976, 2021 ( J π = ( 15 2 + ) ), 2393, 2401 ( J π = ( 17 2 + ) ), 2875 (π = (+)), 3037, 3201 ( J π = ( 23 2 ) − ), 3460 ( J = ( 17 2 ) ), 3484 ( J π = ( 21 2 + ) ), 3985, 4224 ( J π = ( 27 2 − ) ), and 5359 keV. The 1070 keV, J π = 11 2 − level in 99Ru has a half-life of 2.8 ns. A strongly excited negative-parity band is built on this level. A positive-parity band based on the ground state was excited up to J π = ( 21 2 + ) . The level schemes are well reproduced by the interacting boson model in the vibrational limit.

A DOUBLE MINI-ORANGE SPECTROMETER

Abstract The use of a double Mini-Orange electron spectrometer is discussed and is illustrated with in-beam spectroscopy on the 232 Th(α, 4n) reaction. The arrangement is a first step to such investigations with multiple electron detection.