Magnetic Foil Research Articles

Magnetic moments in the backbending region of 158Dy

Yrast levels in the backbending region of 158Dy were Coulomb excited with a 4.7 MeV/u 208Pb beam. Employing the transient field technique with a thin magnetized iron foil, the precessions of the angular correlations of decay γ-rays from levels up to spin I π = 16 + were measured. The results show a clear reduction of the g-factor for states in the backbending region relative to that of the low-spin levels, thus demonstrating that the backbending in 158Dy is mainly caused by the alignment of i 13 2 neutrons. In a similar experiment, precession measurements on Coulomb excited low-spin levels of 164Dy served to determine the static hyperfine field of Dy in Fe and the g-factor of the 6 + state in 164Dy.

Magnetic moments of the21+levels inZr92andZr94

The g factors of the 2/sup +//sub 1/ levels of /sup 92/Zr and /sup 94/Zr have been measured using the dynamic magnetic field which acts on fast ions traversing a thin magnetized iron foil. The results obtained are g(/sup 92/Zr,2/sup +//sub 1/)=-0.03 +- 0.05 and g(/sup 94/Zr,2/sup +//sub 1/)=-0.26 +- 0.06. The present results indicate sizable admixture of components other than d/sub 5/2/ neutrons in the wave functions of these levels.

Design and calibration of a source and a polarimeter for polarized 14.4 keV Mössbauer gamma rays

A source of polarized 14.4 keV Mössbauer γ rays, using a magnetized foil, and a polarizer using a single crystal of siderite, are described. The procedures for determining the polarization of the γ rays, and for calibrating and using the polarimeter, are described in detail.

Magnetic moments of the2+first excited states of even iron isotopes

The large magnetic fields that act on fast-moving ions traversing thin magnetized Fe foils were utilized to remeasure the magnetic moments of the first excited ${2}^{+}$ states of $^{54}\mathrm{Fe}$ and $^{58}\mathrm{Fe}$. The technique reported here does not require an accurate knowledge of the nuclear lifetime and does not depend on the static magnetic field of Fe in Fe. Assuming $g(^{56}\mathrm{Fe},{2}^{+})=0.61\ifmmode\pm\else\textpm\fi{}0.08$, we obtain $g=1.68\ifmmode\pm\else\textpm\fi{}0.38$ and $g=0.46\ifmmode\pm\else\textpm\fi{}0.10$ for the first ${2}^{+}$ states of $^{54}\mathrm{Fe}$ and $^{58}\mathrm{Fe}$, respectively. The present results agree well with previous measurements and support the existing models for the structure of these states.NUCLEAR REACTIONS $^{54,\phantom{\rule{0ex}{0ex}}56,\phantom{\rule{0ex}{0ex}}58}\mathrm{Fe}$ ($^{32}\mathrm{S}$, $^{32}\mathrm{S}\ensuremath{'}$) $^{54,\phantom{\rule{0ex}{0ex}}56,\phantom{\rule{0ex}{0ex}}58}\mathrm{Fe}^{*}$ (${2}_{1}^{*}$) $E=72$ MeV, enriched targets; measured $W(\ensuremath{\theta},H,\ensuremath{\infty})$ in polarized iron. Deduced $g(^{54}\mathrm{Fe},{2}_{1}^{+})=1.68\ifmmode\pm\else\textpm\fi{}0.38$, $g(^{58}\mathrm{Fe},{2}_{1}^{+})=0.43\ifmmode\pm\else\textpm\fi{}0.10$.

Direct evidence for enhanced transient fields on fastFe56ions recoiling through thin iron

Results of ion-implantation perturbed-angular-correlation measurements on /sup 56/Fe ions recoiling through magnetized Fe at high recoil energy (E/sub R/ approx. = 56 MeV) are reported. Angular shifts were measured using targets of various thicknesses for which the excited nuclei either stopped in or recoiled out of the iron. The results clearly establish the existence of enhanced transient fields acting on fast recoiling ions leaving the magnetized Fe foil and stopping in Cu. In such measurements the contributions from the static field and from the normal Lindhardt-Winther field are eliminated. The possible use of this technique for measurements of magnetic moments of short-lived states is discussed. An experiment in which the /sup 56/Fe ions recoiled into vacuum through the polarized foil was also carried out. In this case a strong attenuation of the angular correlation was observed; however, no excessive precession was seen, as would be observable if polarized hf fields persisted in vacuum for a substantial part of the nuclear lifetime. (AIP)

Measurements of the Magnetic Hyperfine Fields at Hg in Fe, Co, and Ni Hosts by thee−−γTime-Differential Perturbed-Angular-Correlation Method

The $^{197m}\mathrm{Hg}$ radioactivity was implanted into pure-Fe, -Co, and -Ni hosts with the help of an isotope separator. These ferromagnetic hosts produce strong magnetic hyperfine interactions at the nuclear site of the Hg atoms. These hyperfine interactions were studied by time-differential measurements of the 165-keV $L$-conversion ${e}^{\ensuremath{-}}$-134-keV $\ensuremath{\gamma}$ angular correlation. Measurements with both nonmagnetized and magnetized foils were performed. By use of the quite accurately known g factor of the 134-keV state of $^{197}\mathrm{Hg}$, the magnetic hyperfine fields $|{H}_{\mathrm{int}}|=692\ifmmode\pm\else\textpm\fi{}55,483\ifmmode\pm\else\textpm\fi{}40, \mathrm{and} 103\ifmmode\pm\else\textpm\fi{}8$ kG for the Fe, Co, and Ni lattices, respectively, were deduced.

Capture of polarized electrons by deuterons emerging from a magnetized nickel foil

The spin polarization observed by Kaminsky in the neutrals of a deuteron beam emerging from a ferromagnetic single-crystal nickel foil is attributed to electrons captured in the tail of the surface electron distribution.

Nuclear-Orientation Study of the First-ForbiddenβDecays ofAu198

Using a ${\mathrm{He}}^{3}$-${\mathrm{He}}^{4}$ dilution refrigerator coupled with adiabatic demagnetization, ${\mathrm{Au}}^{198}$ has been polarized in a magnetized Fe foil at 5 mK. By measuring the directional distribution of the $\ensuremath{\gamma}$ rays emitted following the ${2}^{\ensuremath{-}}$\ensuremath{\rightarrow}${2}^{+}$ first-forbidden $\ensuremath{\beta}$ decays to ${\mathrm{Hg}}^{198}$, the $\ensuremath{\beta}$ dealignment parameters ${U}_{2}$ and ${U}_{4}$ have been determined. For the 0.96-MeV transition, we find ${U}_{2}=0.795\ifmmode\pm\else\textpm\fi{}0.007$ and ${U}_{4}=0.347\ifmmode\pm\else\textpm\fi{}0.03$. This implies that about 60% of the total decays carry off no angular momentum, about 39% carry off one unit of angular momentum, while 1% \ifmmode\pm\else\textpm\fi{}1% carry off two units of angular momentum. For the 0.29-MeV transition, we find ${U}_{2}=1.047\ifmmode\pm\else\textpm\fi{}0.054$, implying that less than 1% of the decays carry off one or two units of angular momentum.

Energy-Loss Straggling of a Helical Electron Beam in a Magnetized Foil

The energy-loss process of a helical negatron or positron beam of a few MeV in a thin magnetized foil was studied. The straggling distributions were derived, taking into account spin-dependent terms of the M\"oller and Bhabha cross sections. These terms affect the shape of the straggling distributions by an amount which increases with increasing energy losses. Numerical calculations were carried out in some typical cases, which are of interest with a view to using the spin-polarization effect as a means of measuring the helicity of $\ensuremath{\beta}$ rays.

Annihilation into two photons of lepton pairs including anomalous magnetic moment and polarization effects

The high-energy y-ray source from electron-positron pair annihilation has been discussed by several authors (~,2) and looks most attractive for the bubble chamber (3.~). The use of magnetized supermendur foil (~) for polarized electrons will make it possible to obtain polarized high-energy photons from the pair-annihilation process. GATTO (~) analysed the two-quantum annihilation of the electron-positron pair, including a form factor to test qnantum electrodynamics with colliding-beam experiments. The purpose of this note is to report the results of a calculation of matrix elements for annihilation into two photons of lepton pairs with anomalous magnetic moment and polarization effects taken into account. A form factor which can be thought of as a product of a form factor for the vertex and a form factor for the propagator (6) is also included. The mass terms which are usually omitted not without justification for high-energy lepton pairs are included in the present calculation so that the results can be applied to both lowand high-energy experiments. The matrix elements for annihilation into two photons of a lepton pair with anomalous magnetic moments are given by

Search for Parity Admixture in the 57.5-keV Gamma Transition ofHf180m

The possible explanation of the anomalous $L$-conversion coefficients of the 57.5-keV $K$-forbidden transition of ${\mathrm{Hf}}^{180m}$ as due to a parity mixture ($E1+M1$) would imply a circular polarization of the $\ensuremath{\gamma}$ rays of 56%. By measuring the transmission of the radiation through a magnetized foil of Supermendur, a circular polarization of (5.9\ifmmode\pm\else\textpm\fi{}6.1)% was obtained. We conclude that the anomaly found for the conversion coefficients is probably due to penetration effects.

A measurement of the e + polarisation in muon decay: The e + annihilation method

The experimental design for measuring the e/sup +/ polarization in mu / sup +/ decay by e/sup +/ annihilation in magnetized iron foil is described. From measurements based on two foil orientations, a value of P/sub (e/sup +/)= (105 plus or minus 30)% was obtained, which is consistent with predictions of the (V- A) theory of weak interactions. (L.B.S.)

Measurements on the Longitudinal Polarization of Beta Rays fromP32,Y90,Pr144,Au198, andBi210(RaE)

The polarization of the beta rays from five negatron emitters were studied by the method of Moller scattering in a magnetized NiFe foil. The scattered incident electron and the recoil electron from the target foil are detected in coincidence by two scintillation counters. The difference between the coincidence counting rates for the two directions of foil magnetization divided by the average rate gives a quantitative measure of the longitudinal polarization of the incident beta rays. Our experimental results are as follows: P/sup 32/, P = - (0.94 plus or minus 0.06)v/c; Y/sup 90/ P = - (0.86 plus or minus 0.06)v/c; Pr/sup 144/P = - (0.90 plus or minus 0.22)v/c; Au/sup 198/ P =- (0.98 plus or minus 0.18) x v/c; and for RaE, P=- (0.69 plus or minus 0.10)v/ c. The first four results may indicate a polarization magnitude slightly less than full -v/c. The differences are, however, within the range of possible systematic errors. The result obtained with RaE is significantly lower than the average of the other four results. This indicates a departure from --v/c polarization for this nuclide. (auth)