Beitrag zur Kernspektroskopie an36Cl,90Y und40K durch Messung der Polarisation von γ-Strahlung nach Neutroneneinfang

The circular polarization ofγ-rays following the capture of polarized thermal neutrons in nuclei was measured. The degree of polarization confirmed the spin 2⁺ for the 0.777 MeV level of⁹⁰Y and the spin 0^? or 3^? for the 0.029 MeV level of⁴⁰K. Further theE2/M1 mixing ratio of the 8.58 MeV decay to the ground state of³⁶Cl was measured.     

Relative measurements of the longitudinal electron polarization in the β-decay of90Y and32P

The ratio of the longitudinal polarization values of⁹⁰Y and³²P was measured at two energies by the method of Møller scattering. The results obtained areP(⁹⁰Y)/P(³²P)=0.992±0.036 at 0.725 MeV electron energy andP(⁹⁰Y)/P(³²P)=0.984±0.030 at 1.0 MeV. For the decay of⁹⁰Y, polarization- and spectrum shape measurements are discussed in the framework of a formfactor coefficient analysis.     

Internal bremsstrahlung from Pr-143

The internal bremsstrahlung (IB) spectrum of¹⁴³Pr is measured in the energy region from 40 to 830 keV by using a multichannel NaI(Tl) scintillation spectrometer and a standard geometrical set up and corrections are applied for various factors. The measured intensity of IB in the investigated energy region is compared with the corresponding theoretical values of Ford and Martin (direct and detour). The present experimental values of IB are coinciding with the direct theory from 40 to 130 keV while from 130 to 500 keV, they are agreeing fairly well with the detour theory. Above 500 keV, the results are deviating positively even from the detour theory.     

The level scheme of91Nb from the reaction90Zr (p, γ)91Nb

The level scheme of⁹¹Nb has been investigated with the reaction⁹⁰Zr(p, γ)⁹¹Nb. Proton energies between 3.0 and 7.2 MeV were used. The γ spectra were taken with Ge(Li) detectors. Primary γ transitions to 36 excited states of⁹¹Nb up to 3.8 MeV excitation energy and many secondary γ transitions from the decay of those states were observed, leading to an extension of the known level scheme. The proton binding energy for⁹¹Nb was determined as (5167± 5) keV. Eleven γ transitions in⁹⁰Zr, part of them new, from the competing reaction⁹⁰Zr(p, p′ γ) were also observed.     

Die Innere Bremsstrahlung beimβ-Zerfall des Y90

The Internal Bremsstrahlung emitted in theβ-decay of Y⁹⁰ was investigated. The spectral yield was measured. Also the angular correlation between electron and IB and the dependence of the IB on electron energy. Calculations ofFelsner, which take into account the Coulomb field of the nucleus, are in consistence with our results.     

Messung der Linearpolarisation der 245 keV-γ-Strahlung in111Cd

A Compton polarimeter for linear polarization measurements ofγ-quanta existing of two thin NaI-crystals is described. The linear polarization correlation of the 171–245 keV cascade in¹¹¹Cd was measured. TheE2-character of the 245 keV quanta follows immediately from this correlation measurement. The mixing ratioδ of the 171 keV quanta was confirmed to beδ ₁=+0.145. The polarization sensitivity of the polarimeter is discussed.     

K conversion coefficients of transitions in87Sr

TheK conversion coefficients of the 388 and 483 keV transitions in⁸⁷Sr populated in the decay of⁸⁷Y have been measured with Ge(Li) and Si(Li) detectors by the NPG method. We find α _K values of 0.162 ± 0.010 and 0.00260 ± 0.00013 for the 388 and 483 keV transitions, respectively.     

Polarization dependence of intersubband absorption and photoconductivity in p-type SiGe quantum wells

We present a detailed study of the polarization dependence of subband absorption and photoconductivity in Si/SiGe quantum wells. For samples with a hole concentration ofp_s2.8×10¹² cm², bothp- ands-polarized absorptions have been observed and transitions to several excited states are clearly identified by comparison with self-consistent Luttinger-Kohn type calculations. The photoconductivity is surprisingly insensitive to the polarization, which indicates the importance of the subsequent transport process on the photocurrent responsitivity.     

Levels of146Ce studied through the decay of high-spin isomer of146La

The decay of 10.0 s high-spin isomer of¹⁴⁶La to levels of¹⁴⁶Ce has been studied using the on-line isotope separator KUR-ISOL. Gamma-ray singles,γ -γ coincidence and conversion-electron spectra have been measured. A level scheme containing 90 levels and 206γ-ray transitions has been constructed for¹⁴⁶Ce, populated in the decay of the high-spin isomer of¹⁴⁶La. Among these, 39 levels are reported for the first time. Spins and parities for some levels are proposed on the basis ofγ-decay mode, logft values and conversion-electron measurements. The band structure of the low-lying levels in¹⁴⁶Ce is discussed.     

Quadrupole moments and the structure of the even titanium and chromium nuclei

The energies of the six circular transitions (n = 13 → n = 12 through n = 8 → n = 7) of the K^?Pb exotic atom have been measured to high precision (typically ～ 50 ppm) using Ge (Li) spectrometers. The data acquisition system was computer controlled and stabilized, the energy calibration spectrum was taken simultaneously with the data spectrum. The experimental energies of the six transitions were corrected for ADC nonlinearities and data-calibration spectrum shifts, as well as the presence of unresolved noncircular transition contaminants. The energies of five of the transitions (13 → 12 through 9 → 8) were computed from quantum electrodynamics, including all significant orders of vacuum polarization, electron screening and nuclear polarization. The mass of the K^? was adjusted to achieve a best fit with the experimental energies: the result was m_K^? = 493.657 ± 0.020 MeV.     

Zirkulare Polarisation von Gamma-Strahlung nach Neutroneneinfang in23Na und31P

The circular polarization ofγ-rays following the capture of polarized thermal neutrons in a target of²³Na and³¹P was measured. The degree of polarization yielded the spinI=2⁺ for the 0.563 MeV level of²⁴Na. For the 6.53 MeVγ-transition from the compound state to the 0.563 MeV level the mixing ratioδ=0.26 _?0.10 ^0.14 between E2 andM1 radiation was deduced. The measurement is consistent with the spinvalueI=2⁺ of the 2.95 keV resonance for thermal neutron-capture of²⁴Na. For³²P we confirmed the earlier spin assignementI=1⁺ for the 1.149 MeV level. An upper limit 0<δ<0.15 for the mixing ratio of the 6.8 MeV capture-γ-transition was established.     

Polarisation und differentieller Wirkungsquerschnitt der Neutronen aus der Reaktion9Be(α,n)12C

The differential cross section and the angular distribution of the polarization of neutrons from the reaction⁹Be(α, n) leading to the ground state of¹²C have been determined at 1.75 and 1.96 MeV energy of theα-particles. The polarization was measured by left-right asymmetry induced by elastic scattering from⁴He. From Blatt, Biedenharn and Simon, Welton theory analysis a set of spectroscopic data has been obtained for five states of the compound nucleus¹³C.     

Messung der zirkularen polarisation von γ-strahlung nach einfang polarisierter thermischer neutronen in kernen

A 70% polarized thermal neutron flux of 6 · 10⁶ s^? was obtained by total reflexion of a 1 m long Co-Fe mirror. Naturel targets of Al, Co, Mo and Sm where exposed to this beam. The measurement of the circular polarization of high energy captureγ-rays yielded some information about nuclear properties: For the transition from the compound state to the ground state in²⁸Al we derived theE2/M1 mixing ratioδ=?2.0 _+1.0 ^?0.5 . In⁹⁶Mo we obtained for the spin of the 2.25 MeV levelJ ^π=2^? or 3^?. If in agreement with theory the spin for this level isJ ^π=3^? the compound state for this decay hasJ ^π=2⁺ for over 50% of the transitions. In accordence with a previous measurement we found for the spins of the doublet in⁶⁰Co at 0.278 and 0.288 MeVJ ^π=3⁺ or 4⁺. For¹⁵⁰Sm we determined the overall circularγ-polarization. The measurement is in agreement with the statistical nuclear model yielding for the compound stateJ ^π=4^?. We confirmed the earlier spin assignementJ ^π=4⁺ for the 0.777 MeV level of¹⁵⁰Sm.     

Relativmessung der longitudinalen β-Polarisation des141Ce

We have measured the longitudinal polarization of the β-particles of¹⁴¹Ce. Whereas Lipnik and Sunier predicted a polarizationP approximate ?0.5v/c we get for an energyE=400 keV a valueP=?(0.91±0.09)v/c. The dependence ofP on the parameterY is discussed.     

Absolutmessung der winkelkorrelation der inneren bremsstrahlung bei Y

The integral angular correlation of the internal bremsstrahlung in the ß-decay of ⁹⁰Y has been measured. The experiments are in better agreement with calculations of Ford and Martin [1], who take into account detour transitions, than with a modified KUB-theory.     

The effects of the microscopical theory of the Coriolis forces on nuclear beta-decay155Eu →155Gd

The wave functions yielded by the microscopical non-adiabatic treatment of the Coriolis interaction proposed in Dubna by Pyatov, Chernej and Baznat have been used in order to calculate the beta decay observables of some allowed transitions of the¹⁵⁵Eu nucleus. The Coriolis interaction effects are important especially for the absoluteft values (an important improvement is obtained) and for theβ-γ circular polarization correlation.     

Nuclear spectroscopy of90Y

The level structure of⁹⁰Y has been studied using the⁹¹Zr(t,α)⁹⁰Y and⁸⁹Y(n,γ)⁹⁰Y reactions. The proton pickup reaction was studied with 17 MeV tritons and a Q3D spectrometer. In the thermal⁸⁹Y(n, γ)⁹⁰Y reactionγ-rays from ≈100 to 6,857 keV were observed. In addition to previously known states and configurations, the ten states of theπ(p 3/2)^?1 v(d 5/2)¹ andπ(f 5/2)^?1 v(d 5/2)¹ configurations are assigned. Also many other new levels are identified from the (n, γ) data. The 0?state of theπ(f 5/2)^?1 v(d 5/2)¹ is assigned at 3,130keV. Finite-range shell model calculations suggest that the tensor force is necessary to reproduce the experimentally observed splittings.     

Spectroscopy of88Y homologous levels

The⁹¹Zr( $z\bar p$ ,α)⁸⁸Y reaction has been studied at incident energy of 22 MeV using a polarized proton source and a Q3D spectrometer. The differential cross sections and asymmetries for transitions to levels of⁸⁸Y homologous to the lowest excitation energy states of⁸⁷Y have been measured and interpreted both in terms of the experimental differential cross sections and asymmetries of the parent⁸⁷Y states and by means of the finite-range distorted wave Born approximation theory using conventional Woods-Saxonα-particle potential. The advantage of the concept of homology consists in having to deal with a uniquel-transfer, that given by the transition to the corresponding parent state. In order to validate the concept of homology as a spectroscopic tool to identify spin, parity and dominant configuration of highly excited states in ( $z\bar p$ ,α) reaction on odd mass target nuclei, shell model calculations have been performed. Several new attributions of spin and parity for⁸⁸Y residual nucleus are proposed.     

Excitation of the analogue of the T> giant dipole resonance of90Zr via the (n,p) reaction

Proton spectra have been measured at lab angles ofθ=0° to 100° for the reaction Zr(n, p)Y at 21.8 MeV incident neutron energy. Spectra over an angular spread of 80° were accumulated simultaneously using a detection system consisting of proportional counterΔE detectors and a curved plastic scintillator as energy detector. Resonant behaviour is observed in the proton spectra for the Zr(n, p)Y reaction but not for the Fe(n, p)Mn reaction. The resonant structure is attributed to the excitation of the analogues ofT _> giant dipole states of Zr. The resonant structure is shown to correspond in position, gross and fine structure, and, in strength and angular dependence of the cross sections, with expectations for the⁹⁰Zr(n, p)⁹⁰Y reaction. DWBA cross sections are derived and fitted to the experimental data with a Lane potential of 150 MeV.     

Messung der Neutronenpolarisation bei der Reaktion12C(d,n 0)13N mit Hilfe der Mott-Schwinger-Streuung

The polarization of neutrons produced in the reaction¹²C(d, n ⁰)¹³N was measured. Deuterons from the Karlsruhe isochronous cyclotron were used to induce this reaction at 51,5 MeV laboratory energy. The degree of polarization was determined by using the special features of Mott-Schwinger scattering. With an uranium scatterer analysing efficiencies of up to 0.92 can be obtained at very small angles (0.23°). The analysing efficiency can be calculated if the differential cross section at 0° and the total cross section is known. These quantities were experimentally determined. The differential cross section for 49.4 MeV neutrons, scattered by uranium, was measured between 0.88° and 2.10°. By an extrapolation the value 43.4±2.6 b/sr was found for the nuclear differential cross section at zero degree. A total cross section ofσ _t=4.80±0.22 b was obtained. The neutron polarization was measured at a reaction angle of 24.5° and the result isP=?0.45±0.07. This value is fairly above the semiclassical 1/3 limit and can be only explained, if spin orbit forces are taken into account. For (d, n) reactions this is the first neutron-polarization measurement above an energy of 20 MeV.