Der Zerfall des 1,5 min-Isomers Co54m

Co^54m (T _1/2=1.43 min) was produced in iron-foils by irradiation with_dE=19 MeV deuterons. The gamma ray spectrum was investigated using a NaJ(Tl) scintillation spectrometer, a coincidence circuit and a Ge(Li)-counter. There were observed three gamma rays having the following energies and intensities per Co_54m decay: 411 keV (0.97±0.07), 1130keV (0.98±0.05), 1407 keV (1.00±0.05). The directional correlation between the pairs of gamma rays were determined. These results correspond to spin and parityJ _π=2⁺ for the 1407 keV,J _π=4⁺ for the 2537 keV, andJ _π=6⁺ for the 2948 keV energy level of Fe⁵⁴. The last-mentioned level was not excited in previous scattering experiments. Our results are compatible withE=210keV andJ _π=6⁺ or 7⁺ of the isomeric state of Co^54m .     

Level structure of <Superscript>164</Superscript>Dy from the (<Emphasis Type="Italic">n</Emphasis>, <Emphasis Type="Italic">n</Emphasis>′γ) reaction

By employing a beam of reactor fast neutrons, gamma-ray spectra and angular distributions of gamma rays with respect to the neutron-beam axis were measured in the reaction ¹⁶⁴Dy(n, n′γ). The scheme of levels and gamma transitions in ¹⁶⁴Dy was composed on the basis of data published earlier and new levels, rotational bands, gamma transitions, and multipole-mixing parameters. It is concluded that the scheme of J = 0–4 levels is complete up to the excitation energy of 1.95 MeV. The commonly accepted rule in constructing K _n ^π = 0₂ ⁺ and 1₁ ⁺ rotational bands is found to be violated. The nature of the 2⁺ level at the energy of 1796.68 keV is discussed.     

Verzweigungsverhältnisse und Konversionskoeffizienten von angeregten Zuständen des208Tl

The branching ratios of theγ rays of the second and fourth excited states of²⁰⁸Tl have been investigated by coincidence measurements between the α rays of²¹²Bi and subsequent 40keVγ ray. The detectors employed were a silicon surface barrier counter for α particles, and a 1.5 in ×2 mm NaJ (Tl) crystal forγ rays. It has been found that (75.6±3.7)% of all transitions of the 328 keV state and (94±7)% of all transitions of the (492 keV+473 keV) states populate the first excited state of²⁰⁸Tl. The 40 keV state is excited to (3.4±0.3)% by transitions of higher excited states relative to the direct excitation by α particles. The number of α particles with energyE _α = 6.047 MeV and the number of subsequent 40keVγ rays resulted in a conversion coefficient α(40keV)=22.55± 0.46. Similarly coincidence measurements between Tl-x rays and α particles have been used to determine theK- conversion coefficients α_K(328 keV)=0.31±0.03 and α_K(492 keV+ 473keV)=0.100±0.015. The experimental results are in good agreement with the theoretical values ofSliv.     

Excited energy levels in U235

The transitions and levels in U²³⁵ populated by Pu²³⁹ alpha decay have been studied by alpha fine-structure investigations, alpha-gamma and gamma-gamma coincidence measurements. The spectra revealed the existence of at least 17 alpha groups and 24 gamma transitions which could be accounted for by 21 excited levels in U²³⁵. The results are discussed within the framework of the unified model. The proposed level scheme exhibits a level density about twice as high as predicted by the Nilsson theory. This result is in fair agreement with the predictions of the superfluid model ofSolov'ev.     

Gamma transitions in the decay of195mPt

The gamma transitions in the decay of^195mPt were investigated by the use of high resolution double focusing beta-ray spectrometer. Conversion electrons were observed for transition of energy 79.94±0.32 keV and ascribed for the first time to the decay of 4.2 d^195mPt. This confirmed that the 209 keV level decays either by the 208.81 keV transition (98%) or by a 79.94 keV–128.51 keV cascade (2%). The multipolarity assignment for each transition in¹⁹⁵Pt was obtained by comparing the measured conversion line intensity ratios with the theoretical line intensity ratios ofSliv andBand. Two gamma transitions of nearly equal energy 129 and 130 keV could be detected, the first found to be pureE2 transition while the latter hasM4 character. The mixing ratio of some gamma-rays have been determined and some discrepancies were found. The data were discussed on the light of Coulomb excitation results.     

Radioactive decay of Os191 and Os191m

Beta and gamma spectra of Os¹⁹¹ were studied using a magnetic double-focusing beta-spectrometer and a scintillation spectrometer. The isomeric state Os^191m decays through the 74·4 ± 0·1 keV (E3/M4=50) transition with a half-lifeT _1/2=13·0 ± 0·5 hours. A continuous beta spectrum withE _max=147 ± 3 keV and the gamma transitions 41·83 ± 0·05 keV (E3), 82·5 ± 0·3 keV and 129·4 ± 0·1 keV (70%M1 + 30%E2) were observed in the decay of the ground state of Os¹⁹¹. The conversion coefficient of the last transition was determined as 1·94 ±± — 0·10. Gamma transitions with energies of 47 keV and 185·8 keV were not observed.     

Der radioaktive Zerfall des Fe61

Fe⁶¹(T _1/2=5.95 min) was produced irradiating Ni⁶⁴ and natural nickelfoils with fast neutrons in the reaction Ni⁶⁴(n, α)Fe⁶¹; Fe was chemical seperated. The gamma and beta spectrum were investigated with Ge(Li)-counters, NaJ(Tl) and plastic scintillation spectrometers. Fe⁶¹ emits five gamma rays having the energies and intensities per Fe⁶¹ decay: 121 keV (0.064), 177 keV (0.027), 298 keV (0.293), 1025 keV (0.461), 1202 keV (0.539). Threeγγ-cascades could be identified: 121–177 keV, 121–1202 keV, 298–1025 keV. Inγ β-coincidence measurements the maximal beta energy was determined:E _βmax=2.86 MeV. A decay sceme Fe⁶¹-Co⁶¹ was constructed: Fe⁶¹, spin and parityJ ^π=3/2^?, decays by means of allowed beta decay to three excited states of Co⁶¹: 1323 keV (1/2^?), 1202 keV (3/2^?), 1025 keV (5/2^?). The energies and intensities per Fe⁶¹ decay of the three beta decay modes are: 2.56 MeV (0.367), 2.68 MeV (0.495), 2.86 MeV (0.138). — A 88 keV gamma ray (T_1/2=33 sec) was observed coming from the Co⁶³ decay.     

Untersuchung des Zerfalls von134Cs durch γ-γ-Winkelkorrelationsmessungen

γ-γ-angular correlation measurements with Ge(Li) detectors and NaJ(Tl) detectors provided theE2/M1 mixing ratios of the following gamma transitions: 3 ₁ ⁺ →2 ₂ ⁺ (475.3 keV), 2 ₂ ⁺ →2 ₁ ⁺ (563.3 keV), 4 ₂ ⁺ →4 ₁ ⁺ (569.4 keV), 3 ₁ ⁺ →2 ₁ ⁺ (1,039 keV). The angular correlation measurements were only consistent with spin 3 of the 1,643 keV level. The half life of the 1,401 keV level was determined by delayed coincidence techniques to beT _1/2 (1,401 keV)≦30 ps.     

Mössbauer effect and nuclear moments of the 75 keV state of Dy161 and the 81 keV state of Dy162

The Mössbauer effect of theγ rays from the 74.5 keV state of Dy¹⁶¹ and the 80.7 keV state of Dy¹⁶² has been investigated. From hyperfine splitting patterns the magnetic moments μ(75 keV)=?(0.39±0.04) nm, μ(81 keV)=+(0.74±0.08) nm and the quadrupole momentQ(75 keV)=+(1.4±0.2)b have been determined. For the odd neutron nucleus Dy¹⁶¹ an effective spin g factorg _{s, eff}=0.76 g_{s, free} is deduced for the 75 keV level.     

Investigations of Properties of <Superscript>89</Superscript>Y Levels with Reactor Fast Neutrons

By employing a beam of reactor fast neutrons, the spectrum of gamma rays up to an energy of 4.6MeV and their angular distributions with respect to the neutron-beamaxis aremeasured in the reaction ⁸⁹Y(n, n'γ). The multipolarities and multipole-mixture parameters for 34 gamma transitions and the spin–parities J^π of states excited in this reaction are determined. The lifetimes of the lowest 32 levels of 89Y were measured by the Doppler shift attenuation method, and the reduced probabilities for the respective gamma transitions were calculated. Levels of the K^π = +5/2⁺ and K^π = ?7/2⁺ bands associated with, respectively, prolate and oblate deformation shapes are found in ⁸⁹Y at low excitation energies.     

Half-life measurements of the 86.6 keV level in233Pa and 59.6 keV level in237Np

The half-lives of the 86.6 keV level in²³³Pa and the 59.6 keV level in²³⁷Np have been measured. A silicon surface barrier alpha detector and a NaI(Tl) gammadetector were used. The decay time spectrum of alpha-gamma coincidences obtained from a start-stop type of time-to-pulse height converter was recorded on a 2048-channel analyser. Analysis of the data gave the following half-life values: $$\begin{gathered} T_{\frac{1}{2}} :^{233} Pa (86.6 keV level) = (37.4 \pm 0.4) ns \hfill \\ T_{\frac{1}{2}} :^{237} Np (59.6 keV level) = (66.7 \pm 0.7) ns \hfill \\ \end{gathered}$$ . Using the experimental levelT _1/2's, partial gamma-ray half-lives have been calculated for the 86.6- and the 29.6-keV transitions (from the 86.6 keV level) in²³³Pa and the 59.6- and the 26.36-keV transitions (from the 59.6 keV level) in²³⁷Np. The results are compared with the single particle and the Nilsson estimates.     

Study of131Ba decay

Singles and coincidence spectra of gamma rays emitted in the decay of¹³¹Ba(11.8d) have been studied with improved statistics. The existence of the level at 1342.07 keV and gamma transitions at 82.58, 461.22, 562.87, 703.53, 1046.4, 1125.97, 1170.53, 1208.43 and 1342.02 keV have been confirmed. Thirteen previously unreported gamma rays at 390.1, 474.2, 506.1, 517.5, 533.7, 596.5, 657.6, 745.5, 757.0, 785.92, 840.9, 1037.0 and 1218.30 keV have been identified and seven new coincidence relations are reported. The level at 596.4 keV is proposed based on coincidence evidence and the level at 657.6 keV is tentatively proposed on the basis of energy differences. All the 62 gamma rays observed in this study have been placed into the decay scheme.     

Basic parameters of the gamma-decay process and properties of the <Superscript>174</Superscript>Yb nucleus that manifest themselves in radiative resonance-and thermal-neutron capture

An independent analysis of available data on the intensities of primary gamma rays from the capture of ≈2-keV neutrons by a ¹⁷³Yb nucleus is performed. The distribution of the scatter of these intensities around the average value is approximated in various intervals of energies of primary gamma transitions. An extrapolation of the distributions obtained in this way to zero detection threshold for the intensity of a primary gamma transition makes it possible to estimate, independently of other experimental procedures, the expected number of levels of both parities for spins in the range J = 1–4 and the total possible sum of partial widths with respect to electric and magnetic dipole gamma transitions to levels whose excitation energies extend up to about 4 MeV. The results obtained in this way for the level density and the sum of radiative strength functions confirm the characteristic features of analogous data extracted from the intensities of two-step gamma-ray cascades initiated by radiative thermal-neutron capture by 40 ≤ A ≤ 200 nuclei and also make it possible to assess the sign and magnitude of their systematic uncertainty associated with a very strong dependence of radiative strength functions for cascade gamma transitions on the structure of the excited level, at least for excitation energies below half the neutron binding energy. A comparison with model concepts of the level density reveals that the ¹⁷⁴Yb nucleus is in a superfluid states for the bulk of excited levels, at least below 3.5 to 4 MeV.     

Gammaübergänge und Energieniveaus in Dy 165

220 neutron capture Gamma rays of Dy 165 were measured with the Risø curved crystal spectrometer. The intense transitions permitted the construction of a level scheme for this oddN nucleus. The rotational bandsK=7/2⁺[633],K=1/2^?[521] andK=5/2^?[512] were precisely localized, including the spin 11/2 states. Gammavibrational bands built on these Nilsson orbits were observed with their band heads at 538.6, 573.5 and 570.2 keV. TheI=5/2 term at 533 keV can be considered as the 5/2^?[523] Nilsson state. The branching ratios allowed the determination of (g _K?g^R)²-factors for the [633], [521] and [512] bands and yieldedE 1-hindrance factors.     

РАСПАД Ag108m

The -spectrum of the long-living isomer of Ag¹⁰⁸ (T_1/25 years) was studied by means of Ge(Li) semiconductor detectors. Eight gamma transitions were found with energies of 79.5, 405.7, 433.7, 613.5, 633.0, 722.6, 836.5 and 1020 keV and correspanding relative intensities of 0.083, 0.008,1, 1.05, 0.0018,1.02,0.0006 and 0.010. The conversion coefficients and multipolarities were determined for transitions of 79.5, 613.5 and 722.6 keV. In the decay scheme of Ag^108m the sequence of the levels 4⁺ (1047 keV) and 0⁺ (1049 keV) is given and the existence of the levels 1454 keV and 1469 keV is confirmed. Spin and parity 2^– were ascribed to the 80 keV level of Ag¹⁰⁸ on the basis of the multipolarity of the 79.5 keV transition.     

Die γ-Spektren von Tc95, Tc95m und Tc96

Theγ spectra of Tc⁹⁵ (20 h), Tc^95m (62 d), and Tc⁹⁶ (4.3 d) have been investigated using Li-drifted germanium counters. The observedγ transitions in the decay of Tc⁹⁵ and Tc^95m are in agreement with earlier investigations except for 6 transitions at 204, 680, and 840 keV in Tc⁹⁵ and at 970, 1390, and 1630 keV in Tc^95m reported previously which have not been confirmed. In the spectrum of Tc⁹⁶ new transitions at 437, 462, 1094, 1200, and 1505 keV have been identified. The level scheme of Mo⁹⁶ is discussed in respect of these results.     

Levels and transitions in125Te

Gamma transitions and levels of¹²⁵Te following the decay of¹²⁵Sb have been studied using Ge(Li) detector and NaI(Tl)-NaI(Tl) sum-coincidence spectrometer incorporated with a fast-slow coincidence circuit. In all, twenty five gamma rays have been reported, out of which two weak gamma rays with energies 366·0 and 402·0 keV have been observed and confirmed for the first time. These gamma rays have been fitted by assigning a new level of 402 keV energy. An ambiguous transition of energy 122·1 keV has also been confirmed. No evidence was found for the existence of 145·9, 315·0, 489·8, and 497·4 keV transitions. The accurate intensities for various transitions have been determined.     

Konversionselektronen und Multipolordnungen von Übergängen in Dy165

The spectrum of internal conversion electrons emitted by Dy¹⁶⁵ after thermal neutron capture was measured with the beta spectrometer at the reactor FRM. 225 conversion lines were found between 0 keV and 7 MeV. They correspond to 193 transitions. The multipolarities of most transitions were determined. The result of this measurement is in good agreement with the level scheme proposed bySchult et al. Eighteen additional levels with energies up to 3 MeV are proposed. A new 3/2^?-rotational band with its band head at 1103.30 keV has been disclosed. The level scheme contains 39% of the complete decay of the capture state. The multipolarities of 6 transitions following the beta decay of Dy¹⁶⁵ to Ho¹⁶⁵ are given.     

Experimental search for the effect of resonant environment on the Mössbauer absorption of gamma rays by <Superscript>57</Superscript>Fe

Due to the virtual photon exchange between atomic nuclei and the field of zero-point electromagnetic oscillations, some nuclei of a given sample are in a virtual excited state with the lifetime ～?/E, where E is the energy of nuclear level. For ⁵⁷Fe nuclei, whose first excited state has an energy of 14.4 keV, this time is equal to ～4.6×10^?20 s. If a thin ⁵⁷Fe Mössbauer gamma-ray absorber is surrounded by a thick screen of the same atoms, the number of virtual excited nuclei in the absorber decreases and, at first glance, it should more strongly absorb Mössbauer gamma rays emitted by an external source and passing through the absorber. In this work, the ratio of the intensities of 14.4-keV gamma rays emitted by the ⁵⁷Fe nuclide and passing through the thin resonant absorber is measured in the absence and presence of the resonant screen around the absorber. Comparison shows that these ratios measured for the gamma source at rest and in the oscillating state differ by 0.00123±0.00075. This value should be treated as the upper limit for the desired effect under these experimental conditions.     

Niederenergetische Gammalinien vom Neutroneneinfang in Lu 175 und Lu 176

The low energy gamma-rays from neutron-capture in Lu 175 and Lu 176 have been investigated by means of the bent crystal-spectrometer at the DR-3-reactor at Risø. From the transitions in Lu 177 3 rotational bands have been determined. The levels of the (404)K=7/2⁺ groundstate rotational band are: 121,62 keV (I=9/2), 268,79keV (I=11/2), 440,66 keV (I=13/2), 636,22 keV (I=15/2), 854,34 keV (I=17/2). The level-sequence of the (514)K=9/2^?-band is: 150,39 keV (I=9/2), 288,99 keV (I=11/2), 451,49 keV (I=13/2), 637,05 keV (I=15/2) and 844,88 keV (I=17/2). At 457,92 keV is the basis for the (402)K=5/2⁺-band the higher levels of which are 552,05 keV (I=7/2), 671,89 keV (I=9/2), 816,63 keV (I=11/2), 985,23 keV (I=13/2), 1176,73keV (I=15/2) and probably 1389,5 keV (I=17/2). The energies of the levels apart from the 1389 keV-level have an accuracy of 7×10^?5. The energy differences between the 3 bands agree very well with the values expected from the Bohr-Mottelson-formulaE=A·I(I+1)+B·I ²(I+1)². The calculated branching-ratios within the 3 bands are in fairly good agreement with the experimental values. Theg _K -factors have been determined for 2 bands: It was found that for the (514)-bandg _K =1,16±0,04 and for the (402)-bandg _K =1,33±0,07.