[Show abstract][Hide abstract] ABSTRACT: The recent suggestion that dramatic changes may occur in the lifetime of alpha and beta decay when the activity, in a pure metal host, is cooled to a few Kelvin, is examined in the light of published low temperature nuclear orientation (LTNO) experiments on such sources cooled to as low as 25 mK, with emphasis here on alpha decay. In LTNO observations are made of the anisotropy of radioactive emissions with respect to an axis of orientation. Correction of data for decay of activities in metallic samples held at temperatures at and below 1 Kelvin for periods of several days has been a routine element of LTNO experiments for many years. No evidence for any change of half-life on cooling, with an upper level of order 1%, has been found, in striking contrast to the predicted changes, for alpha decay, of several orders of magnitude. The proposal that such dramatic changes might alleviate problems of disposal of long-lived radioactive waste is shown to be unrealistic.
Nuclear Physics A 11/2006; 793(1-793):1-19. DOI:10.1016/j.nuclphysa.2007.06.003 · 2.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The tilted foil polarization technique has been applied to a beam of radioactive 23Mg (I = 32, T12 = 11.35 s) ions from ISOLDE. To achieve sufficient energy for penetration of the foils a high voltage platform has been constructed and used for acceleration of the initial 120 keV beam of 2+23Mg ions to 480 keV. The resulting asymmetry ϵ of the emitted β-radiation from the 23Mg implanted into a cold Pt stopper has been measured as a function of a holding magnetic field. At B = 0.09 T a value of ϵ = −7.4(1) × 10−3 was found. The asymmetry was reduced to ϵ = −3.3(4) × 10−3 at a field below 0.005 T. It is argued that this hard core asymmetry occurs as a result of the internal interaction between the polarized nuclei and the defects created in the implantation process.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 07/1995; 361(1-2). DOI:10.1016/0168-9002(95)00186-7 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hyperfine interactions at Ce sites of CeNi2Al5 and CeNiSn single crystals were investigated by means of the low-temperature nuclear orientation of the 141Ce isotope. From the temperature dependence of gamma-ray anisotropies the hyperfine fields at Ce nuclei in CeNi2Al5 and CeNiSn were deduced as 92 (+/-6) T and
[Show abstract][Hide abstract] ABSTRACT: Guiding principles in the design of time resolved on-line nuclear orientation experiments are described which, when used in conjunction with time integral on-line nuclear orientation, optimise the simultaneous determination of the oriented state spin andg-factor.
[Show abstract][Hide abstract] ABSTRACT: The technique of NMR on oriented nuclei has been applied to127Sb to measure the magnetic dipole moment of the127Sb ground state. Resonant destruction of gamma-ray anisotropy from127Sbg (I
=7/2+) has been observed at 139.6(2) MHz forB
app=0.30(1) T andat 138.7(1) MHz forB
app=0.25(1) T. The deduced magnetic moment is ||=2.697(6) N.
[Show abstract][Hide abstract] ABSTRACT: The issue of lattice sites of Fr in Fe has been studied with two different techniques, integral low temperature nuclear orientation (LTNO) and emission channelling. Monte Carlo simulations of the system fitted to the channelling spectra reveal a large fraction of Fr in substitutional sites and hint at a possible complex site distribution. Using a two-site model for the LTNO data, a large fraction in high field site, in agreement with the channelling data, is deduced.
[Show abstract][Hide abstract] ABSTRACT: A low temperature nuclear orientation experiment has been performed on the 14.8d225Ra activity. Gamma anistotropy [221Fr (4.8m) and213Bi (45.6m)] and alpha anisotropy [225Ac (10.0d),221Fr,217At (32.3ms) and209Po (4.2μs)] measurements has been carried out and values for the hyperfine field of225Ac and221Fr in iron and the magnetic moment of213Bi are reported.
[Show abstract][Hide abstract] ABSTRACT: The technique of On-line Nuclear Orientation has been applied to light Ir and Re isotopes. Using both (IrFe)-Ir-192 and (MnNi)-Mn-54 thermometers, orientation as a function of temperature was measured over the range 10-100 mK. Pulsed implantation methods were used to obtain spectra with gamma transitions well identified and clear of contaminant activities. Magnetic moment/oriented state spin combinations were obtained for Ir-180, Ir-182, Ir-183 and for Re-180, Re-179. The results are briefly discussed.
[Show abstract][Hide abstract] ABSTRACT: A low temperature nuclear orientation study has been performed on Fr in Fe. Anisotropy measurements of both gamma rays and alpha particles have been done. The best value for the hyperfine field, obtained in the gamma-ray experiment, is 129.7(40) T. The results from the alpha-particle experiment support this value. The value is a factor of 2 larger than measured earlier; at present there is no good explanation for this discrepancy. A lower limit of 37% and an upper limit of 45% of Fr in high field site can be set.
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 02/1992; 64(1-4):227-231. DOI:10.1016/0168-583X(92)95470-C · 1.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The methods of time-resolved and time-integral on-line nuclear orientation have been applied to study short lived nuclei with
the NICOLE facility (Nuclear Implantation into Cold On-Line Equipment) at ISOLDE-3 in CERN using beams of182–186Hg. The half-lives in these decay chains are of the order of seconds and therefore comparable to the spin-lattice relaxation
times of the nuclei in iron. As the relaxation rate depends strongly on the g-factor, g-factors of nuclei in the decay chains
can be deduced from the observation of the time evolution of γ-ray anisotropy. Using this technique the existence of an isomer
in184Au has been found and the g-factors of184Au,184mAu and182Au have been determined. Accurate half-lives have been extracted from the data.
Time-integral nuclear orientation has been observed for short lived as well as longer lived isotopes of the Hg decay chains.
From these measurements, after proper correction for incomplete relaxation, the magnetic moments of183mPt,183Ir and182Ir have been derived.
The applicability of the time-resolved nuclear orientation technique for nuclei far from stability and its possible limitations