Suche nach Zweiquantenprozessen beim Zerfall von Xe131m

The decay of Xe^131m was investigated in order to detect nuclear double decay processes, in which the transition energy is distributed either between twoγ-quanta or between oneγ-quantum and oneK-conversion electron or between twoK-conversion electrons. By analyzing the emittedγ-radiation in a two-dimensional way an upper limit of 2.2 · 10^?5 was derived for the ratio of theγγ- toγ-transition probability. An investigation of theγ-spectrum in coincidence withK-quanta yielded an upper limit of 3 · 10^?2 for the rate ofe _Kγ-transitions relative toγ-transitions. The simultaneous emission of twoK-quanta was actually observed. These doubleK-quanta result either from the doubleK-conversion that was sought or from the internal conversion of the internal Compton-effect. For the doubleK-electron emission toγ-emission probability a value of (3.6±0.7) · 10^?3 was obtained. TheK-conversion coefficient and the half-life of Xe^131m were measured to be 32.1±0.4 and 11.94±0.04 d, respectively.     

Suche nach Strahlungsprozessen zweiter Ordnung beim Zerfall von Ag109m

The decay of an excited state by the emission of twoγ-quanta (γ γ-transitions) or two conversion electrons (e e-transitions) or oneγ-quantum and one conversion electron (γ e-transitions) is expected as a second order radiation process. The decay of Ag^109m was examined for such events using a special arrangement of two NaJ-scintillation counters in coincidence. The energies of coincident quanta were displayed on the two axes of an “X-Y”-Oscilloscope respectively. For the ratio ofγ γ-transitions to one-quantum transitions an upper limit of\(\frac{{W_{\gamma \gamma } }}{{W_\gamma }} \leqq 1,9 \cdot 10^{ - 5} \) was obtained. Furthermore theγ-spectrum in coincidence withK X-rays was studied. From these measurementse e- andγ e-transition rates can be calculated for the case ofK shell conversion. The results obtained are:

$$\frac{{W_{^e K^e K} }}{{W_\gamma }} = \left( {8,1_{ - 1,7}^{ + 0,6} } \right) \cdot 10^{ - 3} and\frac{{W_{\gamma ^e K} }}{{W_\gamma }}< 1,5 \cdot 10^{ - 3} .$$     

Untersuchungen an Zinn und Indium-Zinn-Legierungen im supraleitenden Zustand mit Hilfe des Mössbauer-Effekts

The recoilless nuclear resonance absorption of the 23.8 keV-γ-line of¹¹⁹Sn was measured in a transmission experiment. The measurements were performed with tin and tin-indium alloys, as a function of temperature above and below the transition points of superconductivity (2 ?K<T<6 ?K). The Lamb-Moessbauer-factors, the Debye-temperatures, and an upper limit of the quadrupol interaction were calculated from the data. Within the experimental accuracy there is no evidence for a difference of the quantities mentioned above in the normal and super-conducting state down toT=0.6T _c . The data for the isomeric shift yield a constants-electron density within the nucleus in the two states within 2·10^?4 down toT=0.8T _c .     

Method for taking into account hard-photon emission in four-fermion processes

A method for taking into account hard-photon emission in four-fermion processes proceeding in the s channel is described. The application of this method is exemplified by numerically estimating one-loop electroweak corrections to observables (cross sections and asymmetries) of the reaction e^?e⁺ → μ^?μ⁺(γ) involving longitudinally polarized electrons and proceeding at energies below the Z-resonance energy.     

Die isomeren Atomkerne: Yb169m,Yb175m,Yb177m

Short lived isomers of Yb were produced by neutron irradiation of enriched isotopes and have been investigated with the aid of scintillation spectrometers. Yb^169m decays with a half-life ofT _1/2=(46±2) sec emitting only L-radiation. This decay is assumed to be the same as the E 3-transition of 24 keV following the electron capture of Lu¹⁶⁹. Yb^175m [T _1/2=(0,072±0,005) sec] emitsγ-rays of (495±15) keV. The measured K-conversion coefficientα _{K 495}=0,24±0,04 and the total conversion coefficientα _{4 5}=0,6±0,3 indicate the transition to be M3. Yb^177m [T _1/2=(6,4±0,1) sec] decays by a cascade of twoγ-rays. The isomeric (228±3) keV-transition is followed by a (104±1,5) keV-radiation. The measured conversion coefficients areα _{K 228}=4,1±0,4 andα _{K 228}=6,5±0,5 for the first transition andα _{K 104}=0,39±0,05 andα ₁₀₄=0,51±0,05 for the second, indicating a M3-E1-cascade. For the M 3-transition the measured coefficients agree well with those calculated for a nucleus of finite size, but they differ by a factor of 1,5 for the E1-transition.     

Untersuchung des Magnesium-27-Zerfalls

Theγ-rays of the decay of Mg²⁷ were investigated with NaJ-crystals, andγ-γ-cascades had been sought for by a fast-slow-coincidence circuit. A method for an exact measuring of the random-coincidence spectrum and a stabilisation method of the multiplier gain is described. The twoγ-lines of 808 keV and 988 keV in coincidence with the 842 keVγ-line and the 817 keVγ-line in coincidence with the 1013 keVγ-line, reported by other authors, could not be observed. If these transitions exist, their intensity would be less than 10^?3 per decay.     

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).     

Die Faktoren der inneren Umwandlung beim35Br80m (4,4 Std)

The intensities of the 37keV- and 49keV-γ-rays of Br^80m have been measured with the aid of Na J-scintillation spectrometers and compared with the intensity of the conversion electrons registered by an anthracene split crystal spectrometer. It was possible to separate the 49 keV-γ-radiation from the intense 37 keV-line by selctive absorption with balanced Sm- and Gd-filters. The internal conversion coefficientsα(49 keV)=298±30 andα (37 keV)=1,59±0,10 are in good agreement with the calculated values for M₃- and E₁-transitions. The half life was measured yielding a value ofT _1/2=(4,40±0,05) h.     

Proximity effect of a superconductor on an antiferromagnetic metal

There should be two contributions to the pair breaking energy in an antiferromagnetic metal. The first, already discussed byde Gennes andSarma, is due to disorder on the magnetic sites. The second is a temperature dependent contribution from electron magnon scattering. This term is calculated for the temperature rangeT _N(J/μ)²?T?T _N and found to be of orderT ²/T _N. (T _N = Néel temperature,μ = Fermi energy,J = exchange coupling between conduction electrons and magnetic ions.)     

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.     

Population and current noise in semiconductor laser junctions

The population noise in a semiconductor laser is calculated by means of the quantum mechanical Langevin method. The resulting population noise is given by 〈δ N _c ² 〉=(T _c/2) (rate in+rate out)+K(¯n), whereN _c is the total number of electrons in the conduction band in the active region,T _c is a relaxation time. The first expression is the usual shot noise term. The transition rates are the sum of the rates due to the light field, the pumping and the spontaneous emission. The last termK(¯ n) is caused by the light field fluctuations;¯n is the mean number of photons in the laser mode.K(¯ n) consists of two parts: a) The main part is proportional to the intensity noise of the light field, which increases below but near threshold and gets constant above threshold. b) There is a second term due to the fact that parts of the fluctuations of the population and of the light field are correlated. — The noise spectrumS _I(ω) of the junction currentI is calculated for low frequencies. Beyond the usual shot noise termS _I(0)=2eI, additional noise is found in and above the threshold region, a) mainly because of the fluctuations of the light field in the laser mode and b) to a small amount, because the absorption processes due to the laser photons weaken the forward current, which is carried by emission processes, while the absorption noise adds to the emission noise.     

<Superscript>14</Superscript>N Nuclear Magnetic Resonance and Relaxation in the Paramagnetic Region of Uranium Mononitride

The spin susceptibility of a polycrystalline sample of uranium mononitride UN is studied by measuring the ¹⁴N NMR line shift, spin–lattice relaxation rates of the nuclear spin, and static magnetic susceptibility in the temperature region of 1.5T_N < T < 7T_N A joint analysis of the results obtained has revealed the temperature dependence of the characteristic energy of spin fluctuations of the uranium 5f electrons: Γ_nmr(T) ∝ T^0.54(4) close to the dependence Γ(T) ∝ T^0.5 characteristic of concentrated Kondo systems above the coherent state formation temperature.     

Using a chiral anomaly to determine the number of colors

The N_c dependence of PPPγ vertices, where P is a pseudoscalar meson and N_c is the number of colors, is analyzed with allowance for the N_c dependence of the quark charges. It is shown that the reactions Kγ → Kπ and π^±γ → π^±η and the decay η → π⁺π^?γ are the best processes for determining N_c. The cross section σ(π^?γ → π^?η) as measured by using the VES facility at IHEP agrees with the value of N_c=3.     

Die Lebensdauer des 23/2-Dreiteilchenniveaus des Hafnium 177 und sein Zerfall durchK-verbotene Gamma-Übergänge

An isomeric state of Hf¹⁷⁷ withT _1/2=(1,12±0,10)s was found by a fast chemical separation of the hafnium daughter from the 155d Lu^177m activity. We measured the same half-life by observing the delayedβ-γ-coincidences. A systematic investigation of the whole region 5s≧T _1/2≧10^?7s by the technique of delayed coincidences gave no further isomerism. We assign the observed half-life to the 23/2 three particle state of Hf¹⁷⁷ at 1315 keV and assume that the second hypothetical three particle state at 1337 keV does not exist. The 21/2 rotational state of theK=9/2 band is populated by a strongly converted 14,16 keVγ-transition from the isomeric state at 1315 keV. The 14,16 keVM _I andN _I conversion lines were observed by use of a double focusing magneticβ-spectrometer. The isomerism is caused by theK-selection rule. The retardation of the following threeγ-transitions by different degrees ofK-forbiddeness is discussed. The pulse height spectrum, measured by means of a Li-drifted Ge-detector, does not show the 36,52 keV-γ-transition which was previously assumed to populate the 1301keV-state. In addition to the knownγ-transitions we found a 40,9 keV-line. This is probably the transition between the 1301,1 keV and the 1260,3 keV-states.     

Electron–phonon heat exchange in quasi-two-dimensional nanolayers

We study the heat power P transferred between electrons and phonons in thin metallic films deposited on free-standing dielectric membranes. The temperature range is typically below 1 K, such that the wavelengths of the excited phonon modes in the system is large enough so that the picture of a quasi-two-dimensional phonon gas is applicable. Moreover, due to the quantization of the components of the electron wavevectors perpendicular to the metal film’s surface, the electrons spectrum forms also quasi two-dimensional sub-bands, as in a quantum well (QW). We describe in detail the contribution to the electron–phonon energy exchange of different electron scattering channels, as well as of different types of phonon modes. We find that heat flux oscillates strongly with thickness of the film d while having a much smoother variation with temperature (T _e for the electrons temperature and T _ph for the phonons temperature), so that one obtains a ridge-like landscape in the two coordinates, (d, T _e ) or (d, T _ph ), with crests and valleys aligned roughly parallel to the temperature axis. For the valley regions we find P ∝ T _e ^3.5 – T _ph ^3.5 . From valley to crest, P increases by more than one order of magnitude and on the crests P cannot be represented by a simple power law. The strong dependence of P on d is indicative of the formation of the QW state and can be useful in controlling the heat transfer between electrons and crystal lattice in nano-electronic devices. Nevertheless, due to the small value of the Fermi wavelength in metals, the surface imperfections of the metallic films can reduce the magnitude of the oscillations of P vs. d, so this effect might be easier to observe experimentally in doped semiconductors.     

The S34 (p, γ) Cl35 reaction and energy levels of the Cl35 nucleus

A method is presented to eliminate quantitatively the decay time of the radioactive source and all systematic errors caused by the instability of the associated electronics. The essential part of this procedure is a versatile method to measure the random coincidences together with the sum of true and random coincidences under the same experimental conditions for both quantities. The proposed method is applied toγ-γ-directional correlation measurements with a five detector apparatus. The construction and function of the device is illustrated. Test measurements with⁶⁰Co prove the usefulness of the method and the capability of the apparatus. The investigation of twoγ-γ-cascades in the decay of¹²⁴Sb gives the following values for the coefficients of the correlation function 1,69-0,603 MeV-cascade:A ₂=?0,065±0,003A ₄=+0,001±0,005 2,09-0,603 MeV-cascade:A ₂=?0,056±0,008A ₄=+ 0,006±0,008     

Investigation of the dependence of the e<Subscript>0</Subscript>-electron yield on the radioactive decay location in <Superscript>64</Superscript>Cu sources

The yields of near-zero-energy e₀ electrons from sources of different thickness in the ⁶⁴Cu decay have been measured. At small thicknesses of the ⁶⁴Cu source, the e₀-electron yield Y _e sharply increases and is qualitatively described by the dependence Y _e ～ r ^?2, where r is the distance from the point of charge formation to the source surface.     

Kern-Isomerie bei In116

The short lived indium isomer produced by thermal neutron capture is confirmed to be In¹¹⁶. A new determination of half-live andγ energy yieldsT _1/2=(2.17α0.07) sec andE _γ=(164±1) keV. From measurement of theK shell conversion coefficient follows that the multipolarity of the transition isE 3, leading to a spin and parity assignment of 8^? for the isomeric level.     

Die Störung der Resonanzstreuung von γ-Strahlung einer Kr79-Quelle an Br79 durch gaskinetische Stöße in der Quelle

γ-quanta emitted by gaseous Kr⁷⁹-sources were scattered resonantly from Br⁷⁹-nuclei. By increasing the density in the source the effective cross section for resonance scattering was influenced due to gaskinetic collisions of the recoiling Br⁷⁹-nuclei with atoms before emission of theγ-quantum. The cross section for gaskinetic collisions was determined to beσ _st=(12.0±1.8) 10^?16 cm² in agreement with the theoretical value obtained from a hard sphere model. This technique, similar to the usual “Doppler shift technique”, yields, if combined with the measurement of the absolute cross section for resonance scattering, spin and lifetime of the levels at 398 and 606 keV. The resonance scattering from the 834 keV level shows an unexpected behaviour in complete contradiction to the hard sphere model, indicating that the velocity of the recoiling nuclei is increased in a dense source atmosphere.