L. O. Norlin

The effect of pressure on the positive muon spin precession in iron and nickel

Abstract We have determined the pressure dependence of the local magnetic fields at μ + sites to be: ( ∂ In B / ∂p ) 298K = -1.05 (2) × 10 -3 /kbar for Fe, +0.43 (6) × 10 -3 /kbar for Ni. The dependence on temperature (also measured here) is discussed on the basis of these results.

Muon diffusion in copper bolow 2K

Transverse field μSR experiments were performed on several different samples of copper in the temperature range below 2K, including isotope separated copper, Fe and Si doped polycrystalline copper and monocrystalline copper. No strong isotope dependent effect was observed. A63Cu and a natural copper sample of identical purity both yield 0.16 μs−1 for the low-temperature plateau, while an increased linewidth inthe65Cu case may be related to the strong effects of Fe impurities. Careful transverse field measurements on large single crystals at 0.08K reveal non-Gaussian lineshapes in accordance with the picture of diffusing muons at this temperature. This allows us to reject several of the existing models for muon behaviour in copper below 2K.

A technique for lifetime measurements of long-lived atomic states utilising laser excitation of stored ion beams

Abstract A laser probing technique for atomic lifetime measurements of metastable states using an ion storage ring is presented. The method benefits from the high spectral resolution of conventional fast ion beam laser spectroscopy, and is applicable to metastable systems in lowly charged ions with lifetimes in the 10 ms–1 s regime. Due to strong probing mechanisms, the technique can be applied to ion beams with low metastable fractions. A comprehensive description of the laser probing technique is given, with examples from recent experiments on singly charged calcium, strontium and xenon, and future prospects are discussed.

IN-BEAM SPECTROSCOPY AT THE PROTON-DRIP LINE - FIRST OBSERVATION OF EXCITED-STATES IN SB-106 AND SB-107

Neutron deficient nuclei close to Sn-100 have been investigated in-beam using the NORDBALL detector array. A target of Fe-54 was bombarded with a beam of Ni-58 at 270 MeV. Evaporation residues were identified by detecting protons and alpha particles in a 4 pi charged particle multi-detector set-up and neutrons in a 1 pi neutron detector wall in coincidence with gamma rays. Excited states of the proton drip line nucleus Sb-106 and of Sb-107 were identified for the first time. The yrast level schemes constructed from gamma-gamma-particle coincidence and gamma-gamma angular correlation analysis are presented and discussed within the framework of the nuclear shell model.

Temperature and Magnetic Field Dependence of Muonic Knight Shifts in Semimetals

The muon spin precession frequencies in the semimetals As, Sb and Bi have been studied as function of temperature and applied magnetic field. In Sb an anomalously large, temperature dependent and anisotropic Knight shift was found (at T = 2 K, Kiso = 0.9%, Kax = 0.3%). The shift is small above 100 K. The results are qualitatively discussed in terms of two models: (i) a shallow donor state and (ii) as partly bound electron states at an impurity charge in a metal. This large Knight shift is not found in As and Bi.

High-spin studies near 100Sn with NORDBALL: New results on 102In, 104In and 108Sb

The NORDBALL detector array has been used in a gamma-ray spectroscopic study of neutron deficient nuclei close to 100Sn. A beam of 270 MeV 58Ni ions was used to bombard a target of Fe-54. Reaction channel separation was achieved with a 4pi charged particle Si-ball together with a 1pi neutron detector wall. Altogether 29 final nuclei were identified and excited states were observed for the first time in 8 of them. The weakest identified channel was 100Cd which represented 4.10(-3) % of the observed total yield. Level schemes Of 102In, 104In and 108Sb constructed from gamma-gamma-particle-coincidence and gamma-gamma-angular correlation analyses are presented. The observed structures are discussed in the framework of the nuclear shell-model. In 108Sb also a deformed, strongly coupled, level sequence is observed. This deformed structure is interpreted as built on a pig9/2(-1)xnuh11/2 configuration in agreement with TRS calculations.

Perturbed alpha-gamma angular correlation studies of radon recoils into aluminium

Abstract The quadrupole interaction of 222 Rn and 220 Rn implanted by α-particle-decay in Al metal and Al-oxide has been investigated. The experimental results indicate an electrical interaction in cubic Al metal not in agreement with earlier measurements using isotope implanted sources.

The FERRUM Project: Experimental Transition Probabilities of [Fe II] and Astrophysical Applications

We report on experimental transition probabilities for thirteen forbidden (Fe II) lines originating from three dierent metastable Feii levels. Radiative lifetimes have been measured of two metastable states by applying a laser probing technique on a stored ion beam. Branching ratios for the radiative decay channels, i.e. M1 and E2 transitions, are derived from observed intensity ratios of forbidden lines in astrophysical spectra and compared with theoretical data. The lifetimes and branching ratios are combined to derive absolute transition probabilities, A-values. We present the first experimental lifetime values for the two Fe II levels a 4 G9=2 and b 2 H11=2 and A-values for 13 forbidden transitions from a 6 S5=2, a 4 G9=2 and b 4 D7=2 in the optical region. A discrepancy between the measured and calculated values of the lifetime for the b 2 H11=2 level is discussed in terms of level mixing. We have used the code CIV3 to calculate transition probabilities of the a 6 D-a 6 S transitions. We have also studied observational branching ratios for lines from 5 other metastable Fe II levels and compared them to calculated values. A consistency in the deviation between calibrated observational intensity ratios and theoretical branching ratios for lines in a wider wavelength region supports the use of (Fe II) lines for determination of reddening.

Gyromagnetic ratios of first 2+ states in126, 128, 130, 132Xe

Gyromagnetic ratios of first 2+ states in126, 128, 130, 132Xe were determined by implantation perturbed angular correlations (IMPAC). The effective hyperfine magnetic field together with the transient magnetic field at xenon nuclei in iron was utilized to obtain the precession of the angular correlation. The precession due to the transient field was taken from systematics to be φ/g=−36±6 mrad. The effective hyperfine magnetic field was determined in an experiment on126Xe in iron to be 900±200 kG. The results for theg-factors areg(128)=0.41±0.07,g(130)=0.38±0.07 andg(132)=0.37±0.05. Theg-factor of the 2+ state in126Xe was determined in a separate experiment using a radioactive source of126I to beg(126)=0.37±0.07, and was used as calibration for the IMPAC-data.

Nuclear magnetic moments of the first and the second excited states in 127I

Abstract By means of the method of perturbed angular correlations, the nuclear magnetic moments of the 58 keV and the 203 keV states in 127 I are investigated. The first moment is found to be μ 58 = 2.02±0.15 n.m. and for the latter moment 1.07 n.m. is the lower limit. The lifetimes of the levels are measured to be τ 58 = 2.79±0.10 ns and τ 203 = 0.47±0.03 ns. The results are compared to the predictions by Kisslinger and Sorensen.