E2 andE3 transition strengths in some rare-earth nuclei

Coulomb excitation byα-particles of vibrational-like states in even-mass rare-earth nuclei is used to determine the reduced transition probabilitiesB(E2; 0 _gs ⁺ →2 _γ ⁺ ),B(E2; 0 _gs ⁺ →2 _β ⁺ ),B(E2; 2 _gs ⁺ →0 _β ⁺ ) andB(E2; 0 _gs ⁺ →3 _oct ^? ) in¹⁵⁰Nd,^{152, 154}Sm,^{154, 158}Gd,¹⁶⁴Dy and¹⁶⁶Er. TheB(Eλ; 0 _gs ⁺ →I=λ)-values range from 2.4 to 6.5 single-particle units for transitions to the 2 _γ ⁺ -states, 0.8 single-particle units for the 2 _β ⁺ -states and from 14.1 to 21.7 single-particle units for the 3^?-states.     

Level structure of106Mo

The level scheme of the very neutron rich nucleus ₁₀₆ ⁴² Mo₆₄ has been studied for the first time through theβ decay of¹⁰⁶Nb. Six new excited states were observed inγ singles andγ-γ coincidence experiments in addition to the 2⁺, 4⁺ and 6⁺ members of the ground state band. The excitation energies and the deexcitation pattern suggest the interpretation of the levels at 710, 885 and 956 keV as the 2 ₂ ⁺ , 3 ₁ ⁺ and 0 ₂ ⁺ states, respectively. The data support the assumption of a non-axial deformation of¹⁰⁶Mo. A half-life of (1.02±0.05) s has been determined for theβ decay of¹⁰⁶Nb.     

Multiplicities of charged particles prior to fission

Electric monopole transitions between the 0 ₂ ⁺ , 0 ₁ ⁺ and 2 ₂ ⁺ , 2 ₁ ⁺ levels in⁷⁶Se, populated in the decay of⁷⁶Br, were investigated by means of conversion electrons and gammaray spectroscopy. TheK-electron intensity ratios ofE0 andE2 transitions connecting the 0 ₂ ⁺ level to the 0 ₁ ⁺ and 2 ₁ ⁺ levels and of theE0 andE2 components in the 2 ₂ ⁺ →2 ₁ ⁺ transition were determined. The ratioX(E0/E2) of theE0 toE2 reduced transition probabilities and, from the available lifetimes, theE0 strength parameters ρ(E0) were deduced for the two transitions. The results are compared with the predictions of current models.     

Non-statistical effects for inelastic proton amplitudes in49V

The magnitudes and relative signs of inelastic proton-channel amplitudes have been measured for 71 3/2^? resonances in⁴⁹V. The measured quantitiesγ _c ² ,γ _c′ ² , andγ _c γ _c′ provide distributions of reduced widths, distribution of the relative sign between reduced width amplitudes, and correlations between reduced widthsρ(γ _c ² ,γ _c′ ² ) and between amplitudesρ(γ _c ,γ _c′ ). A variety of non-statistical effects are observed, including one case in which the effect occurs only in the signs, and not in the magnitudes of the amplitudes.     

Probing the weak boson sector inγe→Ze

We study possible deviations from the Standard Model in the reactionγe→Ze at a 500 GeVe ⁺ e ^? collider. As a photon source we use a laser backscattered photon beam. We investigate the most generalγZγ andγZZ vertices including operators up to energy-dimension-six which are Lorentz invariant. These vertices require four extra parameters; two are CP-conserving,h ₁ ^γ andh ₁ ^Z , and two are CP-violating,h ₂ ^γ andh ₂ ^Z . We present analytical expressions of the helicity amplitudes for the processγe→Ze for arbitrary values of anomalous couplings. Assuming Standard Model values are actually measured we present the allowed region in the (h ₁ ^γ ,h ₁ ^Z ) plane at the 90% confidence level. We then show how the angular correlation of theZ decay products can be used to extract detailed information on the anomalous (especially CP-violating)γZγ andγZZ couplings.     

On the yrast levels in204Pb

High-spin states in²⁰⁴Pb were populated in the²⁰⁴Hg(α,4n) reaction using α-particles in the energy region 42–51 MeV. Prompt and delayedγ-rays as well as conversion electrons were studied in addition to excitation functions, angular distributions andγ-γ coincidences. In this way a stretched cascade ofγ-rays from a level at 8125.9 keV was found to feed the previously known isomeric 9^? level at 2185.7 keV. Spins and parities were established for levels up to and including a 19^? level at 6098.0 keV. The levels with c= 17^2212; and 19^? at excitation energies of 5664.3 and 6098.0 keV are likely to be due to the simplep ₁ ^2/s-1 i ₁₃ ^2/?3 andf ₅ ^2/?1 i ₁₃ ^2/?3 configurations. The agreement between calculated and experimental energies for all observed levels in the regionJ=9–19 is very good in cases where the empirical two-particle interactions used are satisfactorily well known. Above the 19^? level there are three weakly populated levels at 7402.1, 7849.2 and 8125.9 keV, which are likely to haveJ≥20. None of these energies agrees with the calculated value 7695±20 keV for the 20⁺ state of thei ₁₃ ^2/?4 configuration which has the highest angular momentum produced by the four valence neutron holes. This apparent anomaly can be understood if the yrast levels withJ≥20 have angular momentum contribution from the core. It seems likely that the states at 7402.1, 7849.2 and 8125.9 keV are due to proton core excited states of the typeπh _9/2 h ₁₁ ^2/?1 ×νp ₁ ^2/?2 i ₁₃ ^2/?2 withJ ^π=20⁺ andJ ^π=21⁺ andπh _9/2 h ₁₁ ^2/?1 ×νp ₁ ^2/?1 f ₅ ^2?1 i ₁₃ ^2/?2 withJ ^π=22⁺ or 23⁺, respectively. The state at 8126 keV has the highest energy so far directly observed in a stretched cascade ofγ-rays from the decay of a heavy nucleus produced in (α, xn) reactions.     

The penetration parameter λ of the anomalousM1-conversion of the 482 keV transition in181Ta

Byγ- e _K ^? ande _K ^? -γ TDPAC measurements with the 133 keV–482 keV cascade of¹⁸¹Ta in a polycrystalline beryllium matrix theA ₂(e _K ^? )-coefficient of the 482 keV transition was determined as: A₂(482e _K ^? )=?0.095±0.015. The theoretical value is 6.0 times larger. A remeasurement of the E2/M1 mixing ratio of the same transition by integralγ- γ angular correlation measurements with a system of three 20 ccm Ge(Li)-detectors gave the result:δ(482)=4.96±0.25. Theα _K -coefficient was redetermined as:α _K (482)=0.0246±0.0018. From these data the penetration parameter:λ=157±11 is derived and compared with previously published values and theoretical estimates.     

Detailed Ge(Li)-Ge(Li) coincidence studies of levels in152Sm and152Gd

The decay of 12.4 y¹⁵²Eu to¹⁵²Sm and¹⁵²Gd was studied in a high resolution singles measurement and two 4096×2048 Ge(Li)-Ge(Li) coincidence studies. Forty-five gates were analyzed in order to confirm or establish the placement of the γ rays as well as to accurately determine the intensities of the 12 doublets, which included several not previously reported. A new γ-β interband transition, 4 _γ ⁺ →2 _β ⁺ (561.4 keV), a possible 3 _γ ⁺ →2 _β ⁺ (423.7 keV) transition, and a new 330.9 keV transition between the 4 _γ ⁺ level and theI ^π K=3^?0 octupole level were established from coincidence data. Levels at 1757.0 keV in¹⁵²Sm and 1282.5, 1318.7, and 1692.2 keV in¹⁵²Gd are now established on the basis of coincidence data. These data also establish for the first time the population in the¹⁵²Eu decay levels at 1680.0 and 1047.9 keV in¹⁵²Sm and¹⁵²Gd, respectively, as well as a new level at 1700.8 keV in¹⁵²Sm.     

Gyromagnetic ratios of excited states in186W

The gyromagnetic ratios of the 4 ₁ ⁺ , 6 ₁ ⁺ , and 2 ₂ ⁺ states in¹⁸⁶W were measured relative to that of the 2 ₁ ⁺ level by means of the transient field implantation perturbedγ-ray angular distribution technique. The nuclei in the states of interest were Coulomb excited using a beam of 220-MeV⁶³Cu projectiles and recoiled swiftly through a thin, polarized Fe foil. The present measurements yielded ratiosg(4 ₁ ⁺ )/g(2 ₁ ⁺ )=1.04±0.07,g(6 ₁ ⁺ )/g(2 ₁ ⁺ )=1.03 ±0.20 andg(2 ₂ ⁺ )/g(2 ₁ ⁺ )=0.63±0.13. The sizable disparity between the measuredg-factors of the ground- and excited-band is examined within the context of the interacting boson approximation model.     

Life-times of the 4 1 + -states in134Te and136Xe

The half-lives of the first excited 4⁺-levels in theN=82 isotones ₅₂ ¹³⁴ Te and ₅₄ ¹³⁶ Xe have been determined tot _1/2=(1.50±0.13) ns andt _1/2=(1.32±0.10) ns, respectively, through the measurement of delayedγ,γ-coincidences. The value for¹³⁴Te is in agreement with the assumption that the low lying levels of this nucleus are based mainly on theg ₇ ^{2 /2} proton configuration. In¹³⁶Xe the half-life is unexpectedly small which indicates a more strongly admixed structure of the levels involved in this case.     

Instanton effects on the interaction potential between light quarks and the isomultiplet mass splitting of baryons

On the basis of current assumptions of instanton theory we derive strictly the explicit dependence on the masses and spins of the instanton induced potential between a pair of light quarks in baryons, namelyV ₁₂=γ+β(m _* ^1+α )(m _* ^2+α )η(1-σ ₁ησ ₁), wherem _i ^* andσ _i (i=1.2) are respectively the mass and Pauli spin of theith quark. On the additional basis of the MIT bag model, we obtain γ=c/R ³ and β=b/R ³>0, and α>0 is independent of the radiusR of the baryon. The magnitudes of the parametersb and α are also estimated. The MIT bag model is improved by taking into account this potential. Isomultiplet mass splitting formulas are derived in good agreement with experiment.     

Inclusive production ofK s 0 , K s 0 K s 0 andK *±(892) in\bar pp interactions at 3.0, 3.5, 4.0 and 4.5 GeV/c

InclusiveK _s ⁰ andK _s ⁰ K _s ⁰ production in \(\bar pp\) interactions at 3.0, 3.5, 4.0 and 4.5 GeV/c are studied. Cross sections ofK _s ⁰ , K _s ⁰ K _s ⁰ andK ^*±(892) are presented for each incident momentum. The production ofK _s ⁰ andK ^*±(892) through annihilation process is investigated. It is found that the annihilation process is dominant but decreases with incident momentum. The annihilation process is compared withe ⁺ e ^? interactions. Remarkable similarity between them is found in the \({{x_0 = 2E(K_s^0 )} \mathord{\left/ {\vphantom {{x_0 = 2E(K_s^0 )} {\sqrt s }}} \right. \kern-0em} {\sqrt s }}\) distribution. Events with two detectedK _s ⁰ 's are analyzed. The result shows theK _s ⁰ K _s ⁰ pairs are produced in the central region of c.m. system and there is a clearS ^* signal in theK _s ⁰ K _s ⁰ effective mass distribution.     

High-spin levels in138Ce and140Nd Observed in the (α, 4n γ) reactions

Levels of¹³⁸Ce and¹⁴⁰Nd have been studied using the¹³⁸Ba(α,4nγ)¹³⁸Ce and¹⁴⁰Ce(α, 4nγ)¹⁴⁰Nd reactions. Singleγ-ray spectra,γ-γ coincidence spectra, angular and time distributions with respect to the beam bursts have been measured. A number of higher excited states with excitation energies up to about 5 MeV and with spin value up to 12 are populated in both nuclei. The lower states with spins and parities 7^?, 5^?, 6^? and 10⁺ can be explained by two-quasiparticle neutron configurations of the types (h _11/2 ^?1 ,d _3/2 ^?1 ) 7^? , (h _11/2 ^?1 ,S _1/2 ^?1 ) 5^?, 6^? and (h _11/2 ^?2 ) 10⁺. Several high-spin states observed in¹³⁸Ce and¹⁴⁰Nd can be explained qualitatively as four-quasiparticle states with two-proton-two-neutron configurations. The 3^? state at an energy of 2,137.4 keV is observed in¹³⁸Ce. The evidence for the existence of the low-lying 3^? states in¹⁴⁰Nd at 2,124.0 keV is discussed. Beside the known 9.6 ms (7^?) isomeric state in¹³⁸Ce another state at 3,538.5keV (10⁺) with a half life of about 200 ns has been observed. The observed levels in the¹³⁸Ce and¹⁴⁰Nd nuclei are compared with theoretical predictions using delta force interaction.     

Pion photoproduction on197Au to ground and isomeric states in197Hg

The lifetime of the 331.3 keV 0 ₂ ⁺ state in¹⁰⁰Zr has been measured at the gas-filled recoil separator for fission products JOSEF. By observing the delayed coincidences between theβ-particles populating the level and theE0 conversion electrons from its decay into the ground state, a half-life of 3.37±0.30 ns has been obtained. From the measured lifetime and the relative intensities of the 0 ₂ ⁺ →0 ₁ ⁺ and 0 ₂ ⁺ →2 ₁ ⁺ transitions, values of 0.493±0.015 for theE0 strength parameterρ, and of 16 single particle units forB(E2,2 ₁ ⁺ → 0 ₂ ⁺ ) have been deduced. The enhanced nature of theE0 transitions suggests mixing of the 0 ₁ ⁺ and 0 ₂ ⁺ states which may be estimated by comparing the experimentalB(E2) values for the 2 ₁ ⁺ →0 ₁ ⁺ and 2 ₁ ⁺ →0 ₂ ⁺ transitions with the predictions of the asymmetric VMI model.     

Transition probabilities and the structure of some negative-parity states in126,130Xe and132Ba

The lifetimes of several negative-parity states in^126,130Xe and¹³²Ba have been determined by means of the generalized centroid-shift method. The reactions^124,128Te(α,2n) and¹²²Sn(¹³C, 3n) have been used. Following results were obtained:T _1/2(2758 keV)=1.3±0.2 ns in¹²⁶Xe,T _1/2(2060 keV)=0.20±0.10 ns,T _1/2(2104 keV)=0.50±0.10 ns,T _1/2(2376 keV)=0.30±0.10 ns andT _1/2(2973 keV)=4.6±0.4 ns in¹³⁰Xe as well asT _1/2(2120 keV)=0.40 _?0.10 ^+0.20 ns in¹³²Ba. A systematics of the B(E2; 7 _? ¹ ?5 ₁ ^? ) values in theN=76 nuclei is presented. Electric dipole and quadrupole transition rates are discussed in terms of octupole and quadrupole collectivity. The structure of the 5 ₁ ^? and 7 ₁ ^? states is considered. Nuclear reactions:^124,128Te(α, 2 _n ),E=26 MeV,¹²²Sn (¹³C, 3n),E=53 MeV; measuredE _γ I _γ , γ-r.f. DeducedT _1/2, B(σL) in^126,130Xe and¹³²Ba. Ge detectors. Generalized centroid-shift analysis.     

Winkelkorrelationsmessungen an88Sr

The γγ ande _? ^KL γ directional correlations have been measured for the (898–1836) keV cascade in⁸⁸Sr following the decay of⁸⁸Y. The observed correlation coefficients areA ₂₂(γγ)=?0.0784±0.0042 andA ₂₂(e _? ^KL γ)=0.0102±0.0046. The γγ experiment is consistent with a mixing ratio δ(γ)=0.009±0.005 for the 898 keV transition. Using the result of thee _? ^KL γ experiment the most probable value of the ratio of the penetration matrix element to the normal γ-ray matrix element was determined to be η=0.03±0.30 showing a normal conversion process. This penetration parameter agrees with a hindrance factorH _W(E1)=2.1 · 10^?3 for theE1 transition.     

Properties of the 69 150 Tm81 6− β-decaying isomer

Decay experiments for¹⁴⁸Ho 6^? and¹⁵⁰Tm 6^? were carried out at the GSI On-line mass separator using 5 MeV/A⁵⁸Ni-beams on⁹⁴Mo and⁹⁶Ru targets. Gammaγ-andγX-coincidences established the¹⁵⁰Tm 6^? decay scheme, and e^? gave firm I ^π assignments for¹⁴⁸Dy and¹⁵⁰Er levels fed in the decays. It was found that the previously unknown 6 ₁ ^? state in¹⁵⁰Er receives significantβ-strength, which strongly suggestsπh _11/2 νs ₁ ^2/?1 character for the¹⁵⁰Tm 6^? isomer. The results are discussed in terms of the expected GT strength function. Shell model calculations for theπh ₁₁ ^2/4 yrast states are presented.     

Extension to velocity dependent gauge transformations

In previous papers it was shown that in phase space a generator of gauge transformations for a singular Lagrangian \(L(q,\dot q)\) is given byG[ε^α]=ε _k ^α φ _α ^k (q,p,t) where φ _α ^k are first class constraints andG is subjected to a stationarity condition. A non-trivial extension from velocity (or momentum) independent gauge transformations to velocity dependent ones is realized, by replacing gauge functions ε^α(t) with momentum dependent functions ε^α(q,p,t), as long asG satisfies the stationarity condition. Inversely, it is proved in a classical framework that, within velocity dependent gauge transformations, all generators of gauge transformations can be expressed in terms of the linear combinations of φ _α ^k .     

Theoretical evidence for di-molecular rotational behaviour in the hypernuclei ∑ 8 Li and ∑ 8 Be

We have performed microscopic cluster studies of light∑-hypernuclei based on effective nucleon-nucleon and two different sigma-nucleon interactions. Our calculation confirms a bound 0⁺ state in _∑ ⁴ He and _∑ ⁴ H, but reveals no evidence for levels in other partial waves. We have investigated the _∑ ⁸ Li and _∑ ⁸ Be hypernuclei in a microscopic 3-cluster approach. For both hypernuclei, our calculation shows that the lowest levels in the partial wavesJ=0–4 are bound or quasibound states of collective nature and show a strong α _∑ ⁴ H and α + _∑ ⁴ He clustering. These levels form a sequence of states which can be well interpreted as arising from a rotatingα+ _∑ ⁴ H orα+ _∑ ⁴ He di-molecule. Our results are compared to those of similar studies for lightΛ-hypernuclei which do not show evidence for this kind of collective degrees of freedom.     

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.