Nuclear orientation of82Br implanted into Fe

Nuclear orientation measurements are used to determine the hyperfine hamiltonian for⁸²Br implanted into Fe single crystals (dose 5×10¹⁴/cm^–2 implant energy 80 keV). Using a model based upon channeling measurements a good fit to the temperature-dependent gamma anisotropy is obtained for a pure magnetic interaction experienced by the 36±5% of Br which implants substitutionally of magnitudeB _hf (substitutional)=840±120 kG, withB _hf (non-substitutional)<150 kG. This hamiltonian is used to deduce unknown multipole mixing ratios in the daughter⁸²Kr decay. Hyperfine field systematics are shown to indicate a substitutionalFeBr field of 1000 kG, and the origins of this field and the smaller interstitial interaction are discussed.     

NMR-ON on196,197m,198,198m,200mAu in Fe and Ni

The zero-field hyperfine splitting frequencies of a series of Au isotopes in Fe and Ni have been determined with nuclear magnetic resonance on oriented nuclei. The results are:. For¹⁹⁸Au(2^–) in Fe the quadrupole splitting could be resolved. The results are ¦g_NB_HF/h|=259.48 (3) MHz and e²qp/h=–2.08(4) MHz. Our measurements show that most hyperfine splittings published on these isotopes have been incorrect. The quadrupole splitting of¹⁹⁸AuFe disagrees in magnitudeand sign from the value reported by single-passage NMR on oriented nuclei. The following nuclear quantities are deduced: (^197mAu,11/2^–)=5.98(9) _N; (^198mAu, 12^–)=5.85(9) _N; (^200mAu, 12^–)=5.90(9) _N; Q(¹⁹⁸Au,2^–)/Q(¹⁹⁹Au, 3/2⁺)=1.37(3). Our measurements show further that the non-contact hyperfine field for Au in Ni is smaller than assumed previously, and that the magnetic hyperfine splitting frequency of¹⁹⁷AuFe known from NMR is inconsistent with the magnetic hyperfine splitting frequencies of^{198, 199}AuFe.     

NMR-ON measurements of187WFe,182,183,186ReNi,186ReFe and203PbFe

The magnetic hyperfine splitting frequencies of¹⁸⁷WFe,¹⁸²Re(j ^π=2⁺)Ni,¹⁸³ReNi,¹⁸⁶ReNi,¹⁸⁶ReFe and²⁰³PbFe in a zero external magnetic field have been determined by the NMR-ON method at about 7 mK as 225.56(6), 130.9(1), 98.17(4), 136.6(4), 1007.0(3) and 58.43(3) MHz, respectively. With the knowng-factors ofg(¹⁸⁶Re, 1⁻)=1.739(3) andg(²⁰³Pb, 5/2⁻)=0.27456(20), the following hyperfine fields were deduced:B _HF(¹⁸⁶ReNi)=−103.05(35) kG;B _HF(¹⁸⁶ReFe)=−759.7(13) kG;B _HF(²⁰³PbFe)=+279.18(25) kG. Taking hyperfine anomalies into account, theg-factor of¹⁸³Re was deduced as |g(¹⁸³Re, 5/2⁺)|=1.267(6). With the assumption of Knight shift factorK=0, theg-factors of¹⁸²Re and¹⁸⁷W and the hyperfine field of¹⁸⁷WFe were determined as |g(¹⁸²Re, 2⁺)|=1.63(5), |g(¹⁸⁷W, 3/2⁻)|=0.414(10) andB _HF(¹⁸⁷WFe) =−714(18) kG. The large hyperfine anomaly was deduced to be¹⁸³W Δ¹⁸⁷W =−0.124(22).     

Nuclear orientation and NMR/ON on implanted114mIn in Fe and Co

Nuclear orientation and NMR/ON of^114mIn implanted into Fe at an energy of 80 keV and dose of 3–5×10¹⁴ cm^–2 is reported. The zero applied field resonance frequencyv ₀=203.65(6) MHz is combined with the recently determinedB _hf(InFe) of 286.8(3) kG to yield (^114mIn)=+4.658(14) nm. The nuclear spin-lattice relaxation time for^114mIn in iron is measured to be 88(18) s at 18 mK and the applied field dependence of the NMR/ON resonance frequency gives the Knight shift for the system as –2.4(6)%. The absence of measurable nuclear orientation in similarly prepared^114mInCo sources is discussed.     

The magnetic hyperfine field at Hg impurities in ferromagnetic Gd

The magnetic hyperfine field at dilute Hg impurities in Gd has been investigated by the conversion electron (e ^–)--time differential perturbed angular correlation (TDPAC) technique. The radioactivities^197m Hg and¹⁹⁹Tl were implanted into Gd foils by means of an isotope separator. TDPAC measurements were performed with the 165 keV-L-conversion electron—134 keV--cascade of¹⁹⁷Hg at different temperatures and with the 334 keV--158 keV-K-conversion electron cascade of¹⁹⁹Hg at 200 K.The regular site occupation probabilities were found to be 15(3)% for an annealed^197m HgGd sample and 29(5)% in unannealed¹⁹⁹TlGd samples.From the magnetic hyperfine interaction frequencies measured for the regular sites at 200 K the magnetic hyperfine fields |H _hf(¹⁹⁷HgGd; 200 K)|=256(13) kG and |H _hf(¹⁹⁹HgGd; 200 K)|=267(7) kG were deduced.On leave from the University of Lisboa, Portugal     

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

Gyromagnetic ratios of first 2⁺ states in^{126, 128, 130, 132}Xe 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 /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.     

The semileptonic decay fraction ofB-mesons in the light of interfering amplitudes

Consequences of the interference between spectator amplitudes for the lifetimes and semileptonic decay fractions ofB ⁰ andB ⁺ mesons are discussed. Extracting these amplitudes from a fit to 11 exclusive hadronicB decay fractions we finda ₁=1.05±0.03±0.10,a ₂=+0.227±0.012±0.022, an inclusive semileptonic decay fraction of (11.2±0.5±1.7)%, and a lifetime ratio (B ⁺)/(B ⁰)=0.83±0.01±0.01.Supported under DOE grant number DE-FG02-91-ER40690     

The183Re ground state dipole moment and nuclear spin-lattice relaxation of Re in Fe

The hyperfine interaction of the system¹⁸³Re(70d)Fe has been investigated with the NMR/ON technique. With the hyperfine field valueB _hf(ReFe)=–76.0(1.5) T the ground state magnetic moment was determined as: (5/2⁺,¹⁸³Re)=+3.12(6) _N. The field dependent nuclear spin-lattice relaxation time has been measured. The result for the high-field relaxation rateR _exp=1.65(5)·10^–15 T ²s K^–1 is explained in terms of indirect spin-wave interaction.     

Magnetic moment of the 2140.2 keV 5− state in136Ba

We have determined theg-factor of the 2140.2 keV 5^– state of¹³⁶Ba using the timeintegral perturbed angular correlation (IPAC) method at an external magnetic field of 17.0 kG;g=–0.38±0.04. The half-lives of the 2140.2 keV 5^– and 2207.1 keV 6⁺ states were redetermined to be 1.5±0.1 ns and 3.1±0.1 ns, respectively. The radioactive source of¹³⁶Cs was prepared by the¹³⁸Ba(, pn) reaction.     

Nuclear magnetic resonance on oriented76,77,82Br in Fe

Nuclear magnetic resonance on oriented^76,77,82BrFe has been measured using recoil-implanted samples. The magnetic hyperfine splitting frequency of⁸²BrFe in a zero external magnetic field has been determined to be 201.90(3) MHz. The resonances of⁷⁶BrFe and⁷⁷BrFe were also observed in an external magnetic field of 0.2 T asv(⁷⁶BrFe)=340.9(3) MHz andv(⁷⁷BrFe)=403.5(2) MHz. With the known values of theg-factors, the hyperfine fields have been deduced:B _HF(⁸²BrFe)=81.397(27) T,B _HF(⁷⁶BrFe)=81.38(7) T. Theg-factor of⁷⁷Br was determined to be |0.6487(4)|.     

Nuclear spin lattice relaxation of191mIr in Fe

Thermal cycling of the lattice temperature was used to determine the nuclear spin lattice relaxation of^191m IrFe in polarizing fields of 0.05 to 1.3 T. At low temperatures, the relaxation time is not very much shorter than the lifetime of^191m Ir. In the first part of the paper, the master equation formalism is extended to include a finite lifetime. Our result for the reduced relaxation constant, ² C _K =(1.48±0.11)·10¹⁴ K s^–1 T^–2 (high field limit) is in serious disagreement with that of a spin echo measurement of¹⁹³IrFe, but fits much better into the general systematics. A comparison of relaxation rates for 3d-, 4d-, and 5d-impurities in Fe is given. As a by-product, a Kapitza conductivity constant ofl _K =1.5 mW cm^–2 K^–4±30% was found between Fe and dilute³He/⁴He.     

The dependence of the neutron temperature on the geometric parameter for water and loose diphenyl

The dependence of the neutron temperatureT _n on the geometric parameterB ² was measured by the pulse method in water and loose diphenyl. The measurements were made on a moderator poisoned by cadmium sulphate, a substance whose absorption cross-section is non 1/v.The following results were obtained: For waterT _n [eV]=–(0·00391±0·00045)B ² [cm^–2]+(0·02537±0·00035) for loose diphenyl:T _n [eV]=–(0·01014±0·00152)B ² [cm^–2]+(0·02518±0·00054).We are indebted to J. Jirou and J. Jadavan for their assistance in the measurements, the accelerator operation and electronic apparatus maintenance.     

The hyperfine field on carbon in iron

Integral perturbed angular correlation experiments have been carried out on recoilimplanted¹⁵C nuclei in iron. The 739 keV5/2⁺ level of¹⁵C was populated via the¹⁴C(d, p)¹⁵C^* reaction. Using the known g-factor and lifetime of the state, effective internal fields of –12.4±1.1 kG and –10.9±1.5 kG were determined at room temperature and 77 K, respectively. A conduction electron polarization hyperfine field of about –20 kG was deduced from the data.Work supported in part by the National Science Foundation.     

ИжМЕРЕНИЕ пОльРИжАцИИ пРОтОНОВ с ЁНЕРгИЕИ 6,7 MeV пРИ РАссЕьНИИ НА УглЕРОДЕ

A carbon polarimeter for proton polarization measurements at energies higher than 4 MeV has been designed. Considerable transmission has been attained by using a thick polarimeter target and larger scattering solid angles. The effective polarization value at the region ofE _p from 4·6 to 6·0 MeV varies only slightly with energy and attains an average value ofP _eff–0·8. Solid state detectors were used for proton recording. The instrument calibration curve was determined by means of a triple experiment.The angular distribution of polarized protons scattered elastically has been measured at an energy of 6·7 MeV and in an angle range of _lab form 30 to 120. This distribution has two minima ofP(40_lab)=–056±0·03 andP(100_lab)=–088±0·06 and one maximum ofP(70_lab)=+1·03±0·04.     

Volume and grain boundary diffusion of implanted 113Sn in aluminium

Volume and grain boundary diffusion of ¹¹³Sn in aluminium was investigated with the radiotracer method. The implantation technique was used for tracer deposition to avoid problems of tracer hold-up caused by the oxide layer always present on aluminium. The diffusion penetration was chosen large enough to permit serial sectioning of samples with the aid of a microtome.The temperature dependence of the volume diffusivity was determined as D(T)=4.54×10^–5×exp[–(114.5±1.2)kJmol^–1/RT] m ² s ^–1. This confirms previous measurements from our group which already showed that Sn is the fastest foreign metal diffusor so far investigated in aluminium.Grain boundary diffusion of ¹¹³Sn in Al polycrystals was measured in the type-B kinetic regime. The grain boundary diffusion product P=sD _gb (s=segregation factor, =grain boundary width, D _gb=grain boundary diffusivity) was found to be strongly affected by the impurity content of aluminium. For Al polycrystals of 99.9992% nominal purity we obtained P _5N(T)=1.08×10^–8exp [–(96.9±7.5) kJ mol^–1/RT] m³ s^–1 and for less pure Al polycrystals of 99.99% nominal purity P _4N(T)=3.0×10^–10 exp [–(90.1±4.2) kJ mol^–1/RT] m³ s^–1 was determined. The grain boundary diffusion product in the purer material is more than one order of magnitude higher than in the less pure material. Very likely this is an effect of co-segregation of non-diffusant impurities into the grain boundaries.     

Gadolinium as a ferromagnetic host for IMPAC experiments

The properties of ferromagnetic Gd as a host for IMPAC measurements have been investigated. The transient and internal magnetic fields at Cd, Nd, Sm, Dy, Er, Yb and Hf nuclei recoil implanted into polarized Gd at 80 K have been studied by the IMPAC technique. All available experimental transient field data for Gd have been analysed in the framework of the Lindhard-Winther theory. Empirical values of the parametersv _p andC _ion C _atom have been deduced which give good agreement between experiments and theory. Internal magnetic fields at rare-earth nuclei in magnetized Gd at 80 K have been deduced. The results areH _h.f. (NdGd)=?1370±440 kG,H _h.f.(SmGd)=?1440±120 kG,H _h.f.(DyGd)=1410±400 kG,H _h.f.(ErGd)=2310±420 kG andH _h.f.(YbGd)=?216±32 kG. The signs of these fields are, except for Yb which is in a 2⁺ ionic state, consistent with a ferromagnetic coupling between the 4f spins of the implanted ion and the Gd host. The deduced internal field at Hf in Gd is ?440±90 kG. The observed time-dependent interactions for rare-earth nuclei in ferromagnetic Gd are consistent with the Abragam-Pound theory. For the Cd isotopes,g-factors of the first 2⁺ states were deduced from the experiments. The results areg(¹¹⁰Cd)=0.49±0.11,g(¹¹⁴Cd)=0.34±0.09 andg(¹¹⁶Cd)=0.41±0.11. The use of transient magnetic fields forg-factor measurements on high-spin rotational states is discussed.     

The electric field gradient for Gd in gadolinium metal

We have examined the temperture dependence of the efg for GdGd above the Curie point. Using anI =10⁺ isomer in¹⁴⁴Gd as a probe nucleus, we find a weakT ^3/2 dependence withB=(1.5±0.4) 10^–5 K^–3/2. The absolute value of the efg at 332 K was measured by Coulomb excitation of 2⁺ states in^{156, 158, 160}Gd, yielding |eq(332 K)|=(3.43±0.14) 10¹⁷ V/cm². A possible small deviation from theT ^3/2 temperature dependence of the efg for ferromagnetic Gd is discussed.     

Magnetic hyperfine fields of Zr in nickel and iron measured by the DPAD method

The magnetic hyperfine fields of Zr in nickel and iron were measured by the DPAD method. Using the 8⁺ isomeric states in⁹⁰Zr and⁸⁸Zr these fields were found to beH _hf(ZrNi)=–4.65(10) T andH _hf(ZrFe)=–27.4(4) T, respectively.     

Nuclear orientation of154EuFe,166TmGd and169YbFe and169YbGd

Nuclear orientation measurements at low temperatures have been carried out on radioactive isotopes of¹⁵⁴Eu and¹⁶⁹Yb in Fe and of¹⁶⁶Tm and¹⁶⁹Yb in Gd. Gamma-rays from¹⁶⁹YbGd, obtained by the decay of implanted and melted sample of¹⁶⁹IuGd, were observed to have smaller anisotropies of opposite signs compared with those from¹⁶⁹YbFe. This may indicate that for Yb polarized in Gd electric quadrupole interaction is comparable with magnetic dipole one. Mixing ratios of the transitions in¹⁵⁴Gd,¹⁶⁶Er and¹⁶⁹Tm have been made for two levels in¹⁶⁶Er. Our analysis showed that the 3^– to 3⁺ beta decay to the 1128 keV level in¹⁵⁴Gd has 65(20)% j=0.     

Magnetic hyperfine field of K,Ca and Ti in iron

The magnetic hyperfine field for K, Ca, Ti in iron has been measured by means of time differential observation of the perturbed angular distribution of gamma rays emitted in the reactions³⁷Cl(,n)⁴⁰K,³⁹K(, p)⁴²Ca and⁴²Ca(, n)⁴⁵Ti. The valuesH _hf(0)=–66 (6)kG, –96(4) kG, –122(15) kG, respectively, were extrapolated at 0°K. In the case of calcium the presence of a satellite field was confirmed with a strength of –45(4)kG. In the case of potassium most of the implanted nuclei do not contribute to the Larmor precession.