A free nucleus recoils upon emission of a y-ray and the energy of the y-ray is reduced by one. If not, lattice vibrations will be induced and the shape of the emission spectrum will depend on the shape of the phonon spectrum of the host solid. If both levels are degenerate and the width of the energy spectrum is due to the finite lifetime, 'I', of the upper state, then the emission spectrum will be given by the Breit-Wigner formula (Lorentzian line shape), .
He then records the number of y-rays passing through the absorber for various velocities of the source, both towards (v > 0) and receding from (v < 0) the absorber. Four mechanisms affecting the shape of the observed velocity spectra were ... important to the present work. Instabilities in the drive or the mechanical mounting of the source and the absorber.. can sometimes also cause line broadening.
A special . effect, which we had to take into account in the experiment at the 47-keV level in w183, is a broadening that occurs when the absorber is a powder and the size of the grains is _::: ~ tm. Each of the (21 + 1) x lines in the magnetic hyperfine spectrum has a corresponding relative intensity that can be determined based on the theory of adative transitions. With these definitions and the conventional definition of the nuclear electric quadrupole moment eQ, the.
The relative intensities of the transitions resulting from these two cases are also presented in the table.
EXPERIMENT
Adequate compensation could be provided and almost the same resolution as in the absence of stray field was achieved. The tubular end of the holder fits firmly on the rod extending from the drive (as in Fig. II. 3). Since the nuclear moments of the 99 keV state were obtained as ratios to the moments of the 100 keV state, the absorbers for w182.
Most of the alloy absorbers were prepared similarly to W alloy absorbers by high-frequency melting, rolling, and tempering. These reflective plates and filler tubes are mounted on the plate covering the top of the cryostat. A central hole in this assembly allows the elongated part of the drive system, containing the source and absorber, to be easily inserted into the cryostat.
A small carbon resistor mounted on the extension is used to monitor the source and absorber temperatures. A C-shaped permanent magnet mounted on the outside of the source tube is used to magnetize the absorber in the direction transverse to the y-ray.
RESULTS
A parameter in the function assigned to fit any one of the spectra can also be used in the functions for other spectra. Since the polarization of the absorber was known, the peak intensities were not allowed to differ from the values listed in the table. a) (2+ - o+) 100-keV transition in w182• The best solution of the spectra obtained in this work is that of Figure m. The internal field at the tungsten core was determined by assuming the value g for the g-factor of the ·2+ state, an average of several recent measurements, S) and in accordance with the.
2, we see that the width of the component peaks in the magnetic hyperfine spectra agrees well with that measured for a pure tungsten absorber, after correction for absorber thickness. The relative intensities of the peaks in the fits were taken to be those appropriate for a pure M1 transition. lO), ll) Fits to the individual spectra revealed a strong. From figure ill. 6 it is seen that the isomeric shift for the alloys decreases linearly with decreasing electronegativity13) of the host element.
Therefore, the analysis of this spectrum is not very sensitive to the relative intensities of the peaks. Since the compound was prepared using the same technique as for the w182 measurement, the relative intensities of the lines were. derived from this measurement and were fixed in a least-squares fitting procedure. The resulting ratio of quadrupole moments is in good agreement with that found from experiments with tungsten disulfide.
For each transition examined, the widths of component peaks of the composite spectra were not significantly different from the width obtained for the unsplit absorber when the broadening effects due to the thickness of the absorber were taken into account. Because these widths matched the width of the unspliced absorber, our confidence in the accuracy of the fits was increased. Factors contributing to the width of the peaks are discussed in Section I. 2a. a) w182, 100 keV. The widths obtained from the.
One can estimate the lifetime of the 5/2 mode if one corrects for the source broadening by assuming that it is caused by distributed electric field gradients. The dependence of the absorption spectrum on the thickness of tungsten metal and tungsten-iron alloy absorbers was investigated. The correction to the extrapolated width is approximately proportional to the grain size measured in units of the recoilless resonant absorption length (t in Eq. I. 6).
The spectra correspond to various magnetic alignments of the absorber relative to the y-ray beam. Plot of the isomeric shift of platinum alloys versus the electronegativity of the host element.
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DISCUSSION
There is better agreement between the results of the present measurements of the internal fields for tungsten incobalt(360± lOkG) and nickel (90 ± 25 kG) and the fields .. obtained in Coulomb excitation experiments23. The difference between the values of the internal field in W-Fe obtained by Mtlssbauer and NMR experiments and the value obtained by the Coulomb excitation technique is not understood at all. The difference may be due to a dependence of the field on the concentration, since many different concentrations were used in the.
Finally, there may be a temperature dependence of the internal field since both the MC1ssbauer and NMR experiments took place. were performed at the temperature of liquid helium, while the Coulomb excitation was performed at room temperature. Heff for different elements in dilute solid solution in Fe, Co and Ni as a function of the magnetic moment µeff (µhost) on the guest atom. In this section a comparison will be made of the experimental results with calculations in terms of the RPC model.
The results of the work of Brockmeier et al., namely the mixing parameters and magnetic matrix elements, and their notation will be used. The mixing of states from the higher bands with the low levels is very small. In this derivation we assumed the correctness of the rotation model for w182. But recent Ml5ssbauer experiments35.
The measured magnetic moments, µ (3/2-) and µ (5/2-), and the measured half-life of the 3/2 state can be compared with values derived from the magnetic parameters by Brockmeier et al. To calculate the magnetic moments, the g-factor of the core rotation, gR, must be assumed and taken here equal to the g-factor of the ground-state spin band of w182. The data used are the results of the current measurements, the value of the ground state magnetic.
The fit is found to be insensitive to the . constraints on these parameters were investigated to determine the reliability of the values obtained for the parameters gR, G112 112 and G112 l/2. One consequence of neglecting the mixing of the K = 1/2 bands with the ground state is that no correction is obtained for the quantity (gK - gR)b0. In Table IV. 2 the results of two calculations of the effective g-factors gz and g+ are given, one accounting for Coriolis mixing with the. . s s
Experimental information is available for the 2+ states in Pt, so that a comparison of the predicted and measured values of the g-factor can be made. The matrix elements of the spin operators have been calculated based on recent Nilsson wave functions (Ref.
