Spins und γ-Multipolordnungen beim Zerfall Fe59→Co59

In the decay of Fe⁵⁹ the following quantities have been measured:γ-ray intensities, conversion coefficients andβ-(circularly polarizedγ) correlations. The conversion coefficients were found to be: for the 1.10 MeVγ-transition, α_tot.=(1.36±0.10)·10^?4 and for the 1.29 MeVγ-transition, α_tot.=(1.07±0.08)·10^?4. The asymmetry parameterA of the correlationβ(0.27 MeV)?γ(1.29 MeV) were measured to beA= ?0.17±0.10, and forβ(0.46 MeV)?γ(1.10 MeV),A=?0.13±0.04. From these data and publishedγ?γ angular correlation measurements the following spins of Co⁵⁹ levels could be deduced: 1.10 MeV,I=5/2^?; 1.29 MeV,I=5/2^?; and 1.43 MeV,I=3/2^?. The two strongβ-ray groups are pure Gamow-Teller transitions (ΔI=1). The multipolarities of all fiveγ-rays are given.     

Zerfallsschema und β-Spektrum des MsTh1 (Ra228)

Theβ-spectrum of MsTh1 (Ra²²⁸) has been measured in a proportional counter in 2π — and in 4π-geometry. Comparison of these measurements shows that there are no conversion electrons. Theβ-decay of MsTh 1 therefore leads in all cases to the ground level of MsTh2. The Kurie plot is straight from 15 keV up to the upper energy limit ofE ₀=55±3 keV (logft=5·6). The result has been checked by a search for photons emitted by the MsTh1. Noγ-rays and no X-rays have been found. The measurements had to be made with a relatively large amount of natural Ra²²⁶ in the sources. — The results do not agree with those ofLecoin, Perey, Teillac andRiou, who proposed a complex decay sheme for MsTh1.     

Verzweigungsverhältnisse undβ +-Maximalenergie beim Zerfall von Ag108

The branching ratios of Ag¹⁰⁸ have been remeasured with scintillation spectrometers. There is evidence for a weak 177 keV-β ^?-branch going to the 1473 keV level of Cd¹⁰⁸, followed by aγ-γ-cascade of (841+632)keV. Spin and parity 2+ of this level are supported by logft=4.7 of theβ ^?-branch. Theβ ⁺-spectrum has been measured for the first time yielding an end point energy of (880±25)keV, in agreement with the value derived from theK/β ⁺ratio.     

Der Zerfall des Mn52m

Mn^52m(T _1/2=21 m) was produced by irradiating iron-foiles with deuterons ofE _d =9 MeV. Coincidences ofγ-rays with the main 1434 keV-transition had been sought for with the aid of a scintillation fast-slow-coincidence circuit. There was no evidence ofγ-lines which had been found earlier byKatoh et al. atγ-energies 700, 940, 1020, 1150, 1370, 1520 keV. If these transitions exist, their relative intensities are less than 0.7% (700 keV) and 0.3% (all others) per decay of Mn^52m.     

Der Zerfall des Co55,T 1/2=18h

Co⁵⁵ T ^1/2=18 h) was produced by bombarding iron-foiles with 9 MeV deuterons.γ-spectra from the decay of Co⁵⁵ have been investigated using a scintillation fast-slow-coincidence circuit and a Li-drifted Ge-counter. 18γ-transitions were observed having the following energies in keV and intensities per Co⁵⁵-decay:γ ₁=95 (0.006),γ ₂=413 (0.016),γ ₃=475 (0.12),γ ₄=645 (0.005),γ ₅=750 (0.002),γ ₆=810 (0.025),γ ₇=900 (0.024),γ ₈=940 (0.80),γ ₉=985 (0.009),γ ₁₀=1055 (0.005),γ ₁₁=1210 (0.01),γ ₁₂=1320 (0.065),γ ₁₃=1375 (0.042),γ ₁₄=1410 (0.13),γ ₁₅=1600 (0.001),γ ₁₆=1800 (0.0006),γ ₁₇=2160 (0.001),γ ₁₈=2310 (0.0042).     

Messung von zwei β-γ-Richtungskorrelationen im Zerfall von J126

In the decay of J¹²⁶ twoβ-γ directional correlations have been measured. The 0.865MeVβ-0.386 MeVγ correlation shows a big anisotropy; the reduced coefficient ?/(p ²/W) has a mean value of 0.0419±0.0005 and is not quite energy independent. The 0.385 MeVβ-0.86 MeVγ correlation is isotropic within about 2%. Therefore the 0.386 MeV 2⁺ state and the 0.86 MeV 2⁺ state in Xe¹²⁶ may not be described by differences in collective properties only.     

Energieverteilung und Wirkungsquerschnitt der Photoprotonen aus N15

The energy spectra of photo protons from highly enriched N¹⁵ were investigated with the bremsstrahlung from the Heidelberg betatron running at six different endpoint energies between 19 and 30.5 MeV. The protons were detected at 90° to theγ-beam by means of a CsJ-spectrometer with pulse shape discrimination. The energy spectra show pronounced maxima atE _p =3.2; 4.6; 9.5 and 13.3 MeV. Proton yields are given as a function of endpoint energy, the yield value atE ₀=30.5 MeV being (7.0±0.8) μb/MeV · ster. Because the first excited state in the daughter nucleus C¹⁴ lies 6.09 MeV above the groundstate, the cross section for groundstate transitions of the process N¹⁵(γ, p)C¹⁴ could be derived from the upper 6 MeV of the single proton spectra. The main contribution to the cross section comes from the region between 18 and 26 MeV excitation energy with maxima at 19.5; 20.4; 22.7 and 24.5 MeV. A “pygmy resonance” occurs at 15.2 MeV with further less pronounced structures at 13.6 and 17.0 MeV. The integrated cross section for groundstate transitions up to 30.5 MeV is (22±3) MeVmb assuming isotropic angular distribution. The ratios of protons from transitions to excited states and from the (γ, n p)-reaction to those of groundstate transitions rise from 0.45 atE ₀=24.5 MeV to 0.70 atE ₀=30.5 MeV.     

Der Zerfall Co58m →Co58g

Co^58m , Co^58g and Co⁵⁵ were obtained by radiating nickel-foiles with deuterons of energies 11,5 MeV and 2,07 MeV. The γ-radiation was measured with NaJ scintillation spectrometers. For the isomeric transition of Co^58m was determinedT _1/2=(9.15±0.1)h,T _γ=(25±1)keV,α _K=2200±300 and α_L+M=1100±300. From these values it follows, that the radiation is ofM3-type. Twoγ-energies of 95 keV and 1322 keV were found belonging to Co⁵⁵.     

Elektron-Photon-Kaskaden in Blei

A Monte-Carlo program has been used for the calculation of electron-photon cascade showers in lead. Bremsstrahlung, electron-electron scattering, multiple scattering, ionization loss, pair creation, Compton effect, and photoelectric effect are taken into account, with empirically corrected values for the cross-sections of these processes. Electrons are followed down toE _e =1,5 MeV and photons toE _γ =0,25. After a comparison of the Monte-Carlo results with available experimental data, the following distributions for electrons and photons are presented for primary electrons incident on lead with energiesE ₀=100, 200, 400 and 1000 MeV and depthst ranging from 0,5 to 25X ₀:

1. 1.
   Number of particles as function of deptht for various cut-off energiesE betweenE _e (orE _γ resp.) up toE=0,9·E ₀. Interpolation formulas are given for the height and position of the maxima of the distributions mentioned before.     
   
   

Untersuchungen über den nichtresonanten Anteil der Li7 (p,γ)-Strahlung

The angular distributions of the 17,6 MeVγ-rays from the reaction Li⁷(p,γ) Be⁸ have been measured betweenE _p=0,4 MeV andE _p=0,65 MeV. The known strong asymmetry resulting from interference of the 441 keV-resonance radiation and the nonresonant radiation, and a cos² Θ-term, slowly increasing with energy have been observed. According to our results the nonresonant radiation is predominantly due tos-wave capture, but in addition to this a small contribution ofp-waves must be considered.     

Deviation from the standard model in the decay <Emphasis Type="Italic">π</Emphasis><Superscript>+</Superscript> → <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">νγ</Emphasis>

A precise investigation of radiative pion decay (π⁺ → e⁺νγ) in a pion beam from the meson factory of the Paul Scherrer Institute (Switzerland) was performed by the PIBETA Collaboration with the aid of the PIBETA detector. This resulted in finding 41 601 events of radiative pion decay in three kinematical regions. The absolute values of the branching ratio for radiative pion decay were determined in each of these regions. To a precision approximately four times higher than that known previously, the ratio of the axial-vector to the vector form factor was found to be γ ≡ F _A /F _V = 0.443 (15), the latter being fixed at F _V = 0.0259. The number of events found in the kinematical region specified by photon energies of E_γ > 55.6 MeV, positron energies of E _e > 20.0 MeV, and angles of θ_{γ, e} > 40° between the momenta of the corresponding particles (B region) was 5233. In region B, the measured branching ratio for radiative pion decay, R_π→evγ(expt) = 11.6(3) × 10^?8, proved to be smaller by eight standard deviations than that which follows from the Standard Model, R_π→evγ (theor) = 14.34(1) × 10^?8.     

Ausbeuteverhältnisse einiger durch Kernphotoreaktionen in Cer und Silber erzeugter Aktivitäten

Samples of metallic silver and cerium-oxide have been irradiated with 31 MeV and 34 MeV bremsstrahlung. Relative yields of the induced activities have been obtained by counting the emitted gamma-quanta or byβ-counting. The yield ratio Y [Ag¹⁰⁷ (γ, n) Ag^106m ]/Y [Ag¹⁰⁷ (γ, n) Ag^106g ] for 34 MeV bremsstrahlung was found to be (0.08±0.02). The corresponding ratio Y [Ce¹⁴⁰ (γ, n) Ce^139m ]/Y [Ce¹⁴⁰ (γ, n) Ce^139g ] at 31 MeV was (0.19±0.01).     

Zerfallsschemata, β-Matrixelemente und γ-Multipolordnungen für die Übergänge Co56→Fe56 und J131→Xe131

In the decay of Co⁵⁶ the following quantities have been measured:γ-ray intensities,β-γ directional correlation, andβ-(circularly polarizedγ) correlation. The directional correlation anisotropy was found to be, forβ energies above 300 keV,A ₂=0.5±0.4 per cent, corresponding to small or vanishing twice forbidden contributions to the allowed decay. The asymmetry parameterA of theβ-(circularly polarizedγ) correlation was measured to beA=?0.01±0.05 which implies a ratiox between Fermi and Gamow-Teller contributions to the decay ofx=?0.10±0.07, in agreement with the isospin selection rule. In the decay of J¹³¹ the following quantities have been measured: shape of the 606 keVβ-ray group,γ-ray intensities, conversion coefficients, andβ-(circularly polarizedγ) correlations. The measuredK/L ratio of the 364 keVγ-transition,K/L=6.0±0.2, is compatible with the conversion tables of Sliv and Band only. The multipolarities of theγ rays of 364, 637, and 723 keV were deduced. The 606 keVβ-364 keVγ cascade was used as a new calibration standard for analysers of circularly polarizedγ-rays.     

Über die mathematische Struktur und eine Klasse strenger Lösungen der Jordanschen erweiterten Gravitationstheorie

Theβ-α. angular correlationW(Θ)=1+a cosΘ+cos² Θ of the decay of Li⁸ was measured for average electron energies ofE _β ≈5 MeV, 11 MeV and 12 MeV. The experiment yields an anisotropyA=(0·0036±0·0011)·E _β (MeV)^?1. This result is in good agreement with the results of the other groups. The measurements were performed in a counting chamber separated from the activation room simultaneously for two sealer positionsΘ=90° and 180°. The result is discussed in terms of the CVC-theory, taking into account the second forbidden Fermi-matrixelements (‖M1‖) and (‖E2‖).     

Der β-Zerfall des208Tl

An iron-free intermediate-imageβ-ray spectrometer was used to investigate theβ-decay of²⁰⁸T1 in coincidence with the 2.615 MeVγ-ray of²⁰⁸Pb. Fourβ-groups were found, three of which were previously known. The fourth group has an endpoint energy of 0.64±0.03 MeV and an intensity of (4.5±1.5)%. It is supposed that this transition is still complex and feeds a group of levels around the known 4.3 MeV level of²⁰⁸Pb. Noβ-ray of maximum energy 1.032 MeV to the 3.961 MeV level could be found.     

Die Konversion des Hg199m

Hg^199m was produced from natural HgO by fastn irradiation. The cascade decay was investigated with scintillation spectrometers by application of the summing technique. The following results were obtained: half-lifeT _1/2=(43±0,5) min; energy of the isomeric transitionE _γ1=(375±3)keV; conversion coefficients α _K375=3,05±0,25; α_total=5,45±0,25; yielding the multipole order of the isomeric transition to beM4+(25±15)%E5; energy of the second transitionE _γ2=(159±2)keV; conversion coefficients α _K159=0,30±0,03; α_total=0,9±0,1, confirming the multipolarityE2 of this transition.     

Zum Kernphotoeffekt am Ar40 und Ar38

Liquid Argon was irradiated with bremsstrahlung from 18 to 31 MeV endpoint energy in steps of 2 MeV. The yields of the reactions Ar⁴⁰(γ, n)+(γ, p) and Ar³⁸(γ, n) were measured by detecting the 269a and the 35d rest activity with a low-level-counter. Cross section curves for the (γ, n)-processes could be found from the yield values, and they allowed together withσ _N, σ(γ, p) andσ(γ, np) a determination ofσ(γ, 2n) and σ_γabs for Ar⁴⁰. The integrated cross section forσ(γ, n) from threshold to 33 MeV yields (200±40) MeVmb for Ar⁴⁰ and (210±40) MeVmb for Ar³⁸, the corresponding value for σ_γabs being (450±60) MeVmb for Ar⁴⁰.     

Angular correlation measurements in the Be9(d,p, γ)Be10 reaction

Thep-γ angular correlations in the Be⁹(d, p, γ)Be¹⁰ reaction have been measured in the reaction plane atE _d =1.3, 1.5, 1.9, 2.3 and 2.45 MeV for proton anglesθ _p =35°, 80° and 120°. The anisotropy of the angular correlations measured forθ _p =35° is independent of deuteron energy. A systematic shift of the symmetry axis from the recoil direction has been observed. The shift is 20.5° at E_d=2.45 MeV. The anisotropy decreases with increasing proton angle and vanishes atθ _p =120°.     

Investigation of giant-dipole-resonance decay in the (<Emphasis Type="Italic">γ, n</Emphasis>) reactions on <Superscript>52</Superscript>Cr and <Superscript>51</Superscript>V nuclei

The cross sections for the emission of fast neutrons (? _n > 3.7 MeV) in the reactions ⁵²Cr(γ, n)⁵¹Cr and ⁵¹V(γ, n)⁵⁰V at incident-photon energies in the range between 16.0 and 25.8 MeV were studied. The neutron energy spectra were measured at the bremsstrahlung-photon endpoint energies of 18.5, 21.0, and 23.0 MeV for the ⁵²Cr and ⁵¹V nuclei and at the bremsstrahlung-photon energy of 25.5 MeV for the ⁵¹V nucleus. Special features of giant-dipole-resonance decay that are associated with the existence of a structure in photoneutron cross sections and spectra are discussed.     

Angular correlation measurements in the Cr53(p,n γ)Mn53 reaction

Then-γ angular correlation measurements for the Cr⁵³(p, nγ) Mn⁵³ reaction were performed atE _p=2.3, 2.4 and 2.5 MeV. The neutron detector was located in the reaction plane atθ _n=45?, 90? and 120? and perpendicularly to this plane atθ _n=Φ=90?. The experimental results obtained are in good agreement with predictions of the statistical compound-nucleus theory.