T. Tuurnala

The Isomeric 9/2+ and the Lowest 7/2- State in the Weakly Deformed N = 89 Nuclei

The decays of the isomeric 9/2+ states which have been produced by (d, pγ) and (3He, xnγ) reactions, have been investigated in three N = 89 nuclei. The half-lives have been determined to be 5.1 ± 0.3 ns in 149Nd and 3.5 ± 0.4 μs in 153Gd. In 155Dy a 5.5 ns half-life was found, but we were unable to assign it to the 9/2+ state. The calculated E1 transition probability from the 9/2+ state has been used as a probe in suggesting the following main components for the lowest-lying 7/2- state: 7/2 5/2-[523] in 149Nd, 7/2 3/2-[521] in 153Gd and 7/2 3/2-[521] in 155Dy. The corresponding 7/2- state in 151Sm is proposed to be 7/2{1}3/2-[532] + 5/2-[523]{1}. All calculations have been performed using a particle-rotor model with a nonspheroidal Woods-Saxon potential.

The decay of 1.4 min173Er

A 1.4 ± 0.1 min activity which is assigned to β−-decay of68173Er has been produced with 14–15 MeV neutrons through the reaction176Yb(n, α)173Er. Its decay has been studied with Ge(Li) detectors and several (γ)(γ) as well as (γ)(β) coincidence arrangements. Eight gamma rays with energies 94.2, 116.14, 118.6, 122.40, 192.8, 199.2, 800.8 and 895.2 keV were assigned to the decay of173Er. The proposed level scheme of the daughter nuclide69173Tm contains levels at 0, 2.5, 118.6, 124.9, 317.7, 411.9 and 1212.8 keV. The 317.7 keV level is an isomeric state with a measured half-life of 10±3 μs. This 10 μs isomer and the 411.9 keV level are thought to be the band head and 9/2− rotational member of 7/2− [523] Nilsson state, respectively. The levels at 0, 2.5, 118.6 and 124.9 keV are interpreted as 1/2+, 3/2+, 5/2+ and 7/2+ members of the 1/2+ [411] band and the level at 1212.8 keV as the 9/2− [514] Nilsson state. Some systematic considerations and theoretical transition probability calculations are also included.

Cross Sections of Er Isotopes for Neutron Induced Reactions at 14.8 MeV

Cross sections of the reactions 170Er(n, α)167Dy, 170Er(n, t)168Ho, 170Er(n, np/d)169Ho, 170Er(n, p)170Ho and 168Er(n, α)165mDy as well as the (n, p) reaction cross sections of 166-168Er isotopes and the (n, 2n) reaction cross sections of 162-166Er isotopes have been measured at neutron energy 14.8 ± 0.7 MeV by using the activation method with Ge(Li) γ-ray detection. The experimental (n, 2n), (n, p) and (n, α) cross sections have been compared with the evaporation model or pre-equilibrium model predictions.

Low-spin states in151Gd

The level structure of the 87-neutron nucleus151Gd has been investigated by studying the EC- andβ+-decay of151Tb. Gamma-ray and conversion electron spectra as well as gamma-gamma coincidence spectra were measured by using semiconductor spectrometers and a high-capacity two-parameter recording system. The proposed decay scheme contains several new energy levels in151Gd, among them a 5−/2 state at 427 keV. To explain the low-energy level structure, a small stable deformation is assumed for151Gd. Using a single-particle-plus-rotor model based on a generalized Woods-Saxon potential, complete mixing of the shells 1h9/2, 2f7/2 and separately 1i13/2 is observed. By these mixings the correct level order and approximately correct excitation energies up to 1 MeV are reproduced.

Low-spin states of153Gd observed in the decay of153Tb

Level structure of the 89-neutron nucleus153Gd has been investigated by studying theEC-decay of isotope-separated153Tb sources with several semiconductor detectors. In addition to singles gamma and electron spectra,γ-γ ande−-γ coincidences were investigated by using Ge(Li) and Si(Li) spectrometers and a high-capacity two-parameter recording system. In all, 191γ-rays are assigned to the decay of the 2.4d153Tb. The proposed level scheme of153Gd containing most of the observed transitions shows a very high density of low-spin states (45 states below 1.5MeV). Spin and/or parity assignments based mainly on coincidence data and measured transition multipolarities are proposed for a majority of these states. Nilsson model classifications of some levels are discussed. On the basis of logf t values the spin and parity of the ground state of153Tb are suggested to be 3/2+ or 5/2+.

Examination of oil paintings by using a PIXE/PIGME combination

Abstract The applicability of the simultaneous use of particle induced X-ray and gamma-ray emission (PIXE/PIGME) for nondestructive analysis of art paintings has been investigated. By proper choice of detection geometry and proton energy the PIXE/PIGME combination yields almost covering elemental analysis of inorganic pigments even through the surface varnish of the painting. Accordingly the method is very suitable for example for a rapid detection of pallette errrors.

An external helium flushed milli-beam for combined PIXE and PIGE analysis

A helium flushed external beam PIXE/PIGE facility for nondestructive multielemental analysis has been developed and tested. By using proton energies Ep≈4.1 MeV and simultaneous detection of X- and gamma-rays, nearly complete analysis of all elements is achieved with nondestructively low ion current of Ip≈1 nA (except H, He, C, O and Ne are detected in a single measurement with sensitivities from the ppm level to about one percent). For most of the elements there are at least two channels of identification, which is a special advantage in analyzing unfavourable matrices, where the radiations of certain elements may interfere with each other.

Nanosecond lifetimes of the low-spin states in the nucleus 147Nd: A particle-rotor model interpretation of the results

Abstract Nanosecond lifetimes of several states in 147 Nd have been studied using the reaction 146 Nd(d, pγ) 147 Nd with 10 MeV deuterons. The following lifetimes were observed: the 7 2 − level at 49.9 keV, 2.5±0.5 ns; the 5 2 − level at 127.9 keV, ≦ 0.8 ns; the 9 2 − level at 190.3 keV, 1.1±0.3 ns and the 1 2 − level at 214.6 keV, 5.8±0.8 ns. The wave functions of the states were constructed using an axial particle-plus-rotor model. The free parameters used are compared to the systematics observed in the neighbouring heavier N = 87 isotones as well as in the N = 89 and 91 isotones. Transition rates within the f 7 2 and h 9 2 based excitations, separately, are reasonably well reproduced, but the connecting transitions indicate too strong a mixing of the shells in the calculation.

Level structure of170Er observed in the decay of the 2.76 min170Ho

TheΒ−-decay of the longer-lived170Ho isomer produced through the170Er(n, p)170Ho reaction has been investigated by using a versastile detector and coincidence equipment. The half-life andΒ−-decay energy were determined to beT1/2=2.76±0.05 min andQβ =3.85±0.15 MeV, respectively. In addition to the ground state band and some higher energy levels, the proposed level scheme of170Er contains 11 states between 1.0 and 1.6 MeV (6 new ones), which are connected mutually by previously unknown low-energy transitions. Spin and/or parity assignments based mainly on coincidence data and multipolarity determinations are suggested for most of these states. By using systematic considerations and the nuclear projection model calculations several bands withK≧2 can be assigned tentatively. As a side result the half-life of169Ho was determined to be 4.7 ±0.2 min.

Energies and Intrinsic Structures of the 43 s and 2.76 min States of 170Ho

The β--decay energies of the 43 s and 2.76 min states of 170Ho have been determined simultaneously in a two parametric β-γ coincidence experiment. According to the results the 2.76 min state is the ground state and the 43 s state a 120 ± 70 keV excitation. Intrinsic structures of these states are discussed in terms of the Nilsson model.