L. Vanneste

Nuclear orientation of on-line separated isotopes

Abstract On-line techniques have proven to be successful for the study of nuclei far from stability in performing spectroscopy. Further information on these short-lived nuclei can be obtained by measuring anisotopy coefficients of β- and γ-transitions. These measurements permit the clarifying of decay schemes and the study of nuclear moments. We thus propose the combination of on-line mass-separation with low temperature nuclear orientation. A system for this is being set up at the LISOL facility. The main part consists of a 3 He- 4 He dilution cryostat with high cooling power. It features a side-access port to allow direct implantation on the cold finger. A liquid helium cooled transport line with adjustable baffles makes the connection to the isotope separator. Nuclei with a lifetime down to a few minutes can be continuously implanted into a ferromagnetic host and oriented by the hyperfine field at temperatures lower than 30 mK. The limit of the lifetime is set by the spin-lattice relaxation time. In order to study shorter lived nuclei an “on-line” immediate orienting mechanism is installed: the beam line includes a UHV-chamber, where polarization is achieved by scattering at grazing incidence on a magnetized nickel single crystal. For preserving the obtained orientation during measurement the low temperature implantation is still required. Both mentioned orienting mechanisms completement each other for a nuclear study of short-lived isotopes. Sets of deflection plates and a movable part of the beam line allow a quick transition from one mode to another. Furthermore the cooled collecting foils can be changed in a short time without breaking the cooling cycle it removal of the daughter activities is requested.

On-line nuclear orientation of Au isotopes at KOOL

On-line low temperature nuclear orientation measurements were performed on shortlived185Au,186Au,189mAu,191mHg implanted in an iron matrix. As decay products185IrFe and191mAuFe were studied too. Besides magnetic moment determinations spectroscopic information on spin values of excited levels and mixing ratios of transitions in the daughter nuclei Pt and Au are presented. The results are interpreted in a Nilsson + Coriolis + pairing model.

Nicole: New on-line orientation facility at ISOLDE/CERN

This paper presents off-line and on-line orientation results obtained with the new on line nuclear orientation device NICOLE in CERN. Magnetic moments of187,185Ptg and186Irm, electric quadrupole moment ratios between Pt isotopes with mass number 185, 187 and 189, the spin of the 2 h isomer of186Ir and a new decay scheme of184Au involving a metastable state are established. The shape variation versus mass number of the Pt isotopes leads to sign change of the spectroscopic quadrupole moment between A=187 and 185.

Nuclear orientation of neutron deficient isotopes in the Z = 50 region

Abstract The first low temperature nuclear orientation measurements on electromagnetically separated short lived nuclei (5.1 min. ⩽ t 1 2 ⩽ 58 min. ) are presented. A systematic magnetic moment study of the series 105–108 In and of 101–102 Ag has been performed. This investigation permitted to deduce ground state characteristics. The spin values of the high spin isomers of the odd-odd indiums have been fixed.

Nuclear orientation at ISOLDE/CERN

A facility for Nuclear Implantation into Cold On-Line Equipment (NICOLE) is being installed at the new on-line isotope separator ISOLDE 3 at CERN. The first on-line run was in the beginning of July 1988. The low temperature equipment has been successfully tested and first off-line experiments on various isotopes have been performed. NMR/ON has been done on vaious isotopes (Co, Xe, Pt, Au) in iron host. First experience with the top-loading dilution refrigertor (Oxford Instruments Limited) shows that it performs very well. The cooling power is 400 μW at 100 mK and 34 μW at 25 mK. The base temperature can be kept continuously well below 5 mK. NMR/ON can be performed at temperatures below 5.5 mK. The base temperature on-line is expected to be lower then 6 mK. The sample can be cooled down from room temperature to 10 mK within two hours, to 6 mK within 3 hours which is not only important for off-line but also for on-line experiments when samples have to be changed to remove long lived daughter activity. The latest results will be reported.

Nuclear orientation techniques applied to on-line separated isotopes

Abstract Recent advances using the on-line nuclear orientation facility KOOL are described. Examples are given from results on nuclear moments, spins and multipolarities in different regions of the nuclear chart. The first on-line nuclear magnetic resonance results are discussed, as well as the first particle anisotropy measurements. Each one of these technical improvements is shown to lead to substantial increase of accuracy and/or surprises in physics. A short review is given of recent experiments aimed at eliminating the lower limit on nuclear lifetimes which exists in pure low-temperature nuclear orientation.

Shape transition in light Pt isotopes: Magnetic moments and electric quadrupole moment ratios for185,187,189Pt

Nuclear orientation and nuclear magnetic resonance experiments were performed on185, 187, 189Pt isotopes oriented in Fe and single crystal Zn at temperatures down to about 6 mK. The hyperfine splitting frequencies of185Pt and187Pt in iron were determined to be 164.9(2) and 261.1(2) MHz, respectively. With the hyperfine field of −126.1(2.5) T, the g-factors are deduced to be |g(185Pt)|=0.172(3) and |g(187Pt)|=0.272(5).The spectroscopic quadrupole moment of187Pt was found to be negative with magnitude similar to that of189Pt, indicating a predominantly oblate ground state deformation for both isotopes. The spectroscopic quadrupole moment of185Pt was found to be positive, with the ratio Q(185Pt)/Q(189Pt)=−3.6(9), clearly indicating a change to prolate ground state deformation.

Magnetic moments of Po isotopes and the quenching of nuclear magnetism in the 208Pb region

The nuclear magnetic moments of the short-lived isotopes 199mPo, 201mPo, 201Po and 203Po, determined with on-line nuclear orientation, are reported for the first time. Together with other recently measured moments in this region, variations with Z and N can be derived which may offer a clue to an understanding of nuclear magnetism around 208Pb.

The hyperfine field of Francium in iron and the systematics of alkaline fields

Abstract The hyperfine field of Fr in iron is reported for the first time, obtained from on-line nuclear orientation experiments on Fr isotopes. The completed alkaline systematics are compared with recent self-consistent hyperfine field theories.

Nuclear quadrupole alignment in Zn, Lu, and Re and the quadrupole moments of69mZn and177mLu

We report low-temperature nuclear quadrupole alignment of69mZn,177m, gLu and186, 188Re in the corresponding metal single crystal hosts. A comparison with data on these systems from other laboratories is given, and sources of systematic error discussed. In the Lu system, measurements on in situ irradiated and implanted samples are found to be in agreement. From the measured quadrupole frequencies, we derive the following quadrupole moments: Q(69mZn, 13.86 h, 9/2+)=−0.45(7)b,Q(177mLu, 161 d, 23/2−) =4.23(67)b,Q(186Re, 90h, 1−)=0.57(9)b, andQ(188Re, 16.7h, 1−)=0.38(17)b.