Seniority inverted yrast states observed in 69 153 Tm84

Through an in-beam study of the ₆₉ ¹⁵³ Tm₈₄ nucleus we have identified the πh ₁₁ ^2/5 /2νf ₇ ^2/2 and πh ₁₁ ^2/5 νf_7/2h_9/2 7-valence particle configurations up to their fully aligned spins of 47/2^? and 51/2^?. Shell model calculations predict that in the πh ₁₁ ^2/5 νf_7/2h_9/2 configuration, contrary to the π ₁₁ ^2/5 νf ₇ ^2/2 case, the h_11/2 proton seniority does not increase regularly with spin. This seniority inversion is verified by the data.     

High spin shell model excitations in149Gd

The high spin level structure of the three-neutron nucleus¹⁴⁹Gd has been investigated by in-beamγ-ray and electron spectroscopy with (α, xn) reactions. The observed levels are characterized as members of the shell model multipletsνf ₇ ^2/3 ,νh _9/2 f ₇ ^2/2 ,νf ₇ ^2/3 ×3^?,νh _9/2 f ₇ ^2/2 ×3^?, and tentativelyνf ₇ ^2/3 ×(3^?)². The energies of theν f ₇ ^2/3 states agree only moderately with those calculated using empirical two-nucleon interactions taken from¹⁴⁸Gd, which indicates the importance of long range contributions already atN=85.     

Search for the K L 0 → π0ν \tilde v decay at the INEP U-70 accelerator: The KLOD project

The rare decay K _L ⁰ → π⁰ν $ \tilde v $ branching ratio measurement is one of the clearest Standard Model test. Calculations based on the SM predict Br(K _L ⁰ → π⁰ν $ \tilde v $ ) ≈ 2.8 × 10^?11, but the most accurate experimental value Br(K _L ⁰ → π⁰ν $ \tilde v $ ) < 6.7 × 10^?8 (90% C.L.). We present design of a new experimental setup KLOD (U-70 accelerator, IHEP, Protvino) for K _L ⁰ → π⁰ν $ \tilde v $ branching ratio measurement. Sensitivity of the KLOD experiment will be enough for registration of 2.4 events K _L ⁰ → π⁰ν $ \tilde v $ for every 10 days of the data taking (according to SM predictions).     

Yrast states in the π- particle ν- hole nucleus 65 146 Tb81

The nucleus ¹⁴⁶Tb was studied from in beam γγ-and conversion electron measurements. The level scheme was established up to ～5MeV above the (πh_11/2 vd _3/2 ^?1 )_5? β-isomer. In addition to the known (πh_11/2 vh _11/2 ^?1 )₁₀₊ E3-isomer, the 8⁺ and 11⁺ members of this configuration were located. The levels at the yrast line are dominated by the couplings of the πh_11/2 vh _11/2 ^?1 valence nucleons to the collective 3^? octupole state and to the πh_11/2d _5/2 ^?1 and πh_11/2g _7/2 ^?1 particle-hole excitations of ¹⁴⁶Gd.     

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 magnetic moment of the 10+ isomer in140Ce andE1 transitions inN=82 isotones caused by outer subshell configurations

Using the reaction¹³⁸Ba(α,2n)¹⁴⁰Ce the magnetic moment of the 10 ₁ ⁺ isomer atE _x =3714.7 keV in theN=82 nucleus¹⁴⁰Ce has been determined by means of the TDPAD method toμ=+10.3(4)μ _N . Measuredg-factors in¹⁴⁰Ce are compared to calculations within the shell model with configuration mixing. For the 10 ₁ ⁺ isomer in¹⁴⁰Ce the four proton configuration π(1g ₇ ^2/2 ,2d ₅ ^2/2 ) has been found to be dominant. From theg-factor measurement strong contributions of multiparticle excitations to thegp2d _3/2,π3s ₁ ² or π1h ₁₁ ² shells and admixtures of neutron excitations to the wave function of the 10 ₁ ⁺ state could be excluded. The strongE1γ-branch of the deexcitation of the 10 ₁ ⁺ isomer in¹⁴⁰Ce can be explained by means of small admixtures of configurations which contain the outer subshell excitationsπ2f _7/2 andπ1h _9/2. On this basisE1 transitions experimentally observed in theN=82 nuclei¹⁴⁰Ce,¹⁴¹Pr and¹⁴⁵Eu may be understood.     

Particle × phonon multiplets in 65 147 Tb82

High-spin states of¹¹⁵Sb were studied by inbeamγ-ray spectroscopy using the⁸⁹Y (²⁹Si, 2pn) fusionevaporation reaction at a beam energy of 108 MeV. The experiments includedγ-γ coincidence and directional correlation of oriented nuclei (DCO) ratio measurements using six BGO Compton suppressed Ge detectors. An intruderΔJ=2 rotational band has been identified for the first time and it is interpreted as the h_11/2 proton coupled to a two particle-two hole (2p ? 2h) deformed state of the¹¹⁴Sn core. A ΔJ=1 rotational band based on the 2p ? 1h, π{g ₇ ^2/2 ?g ₉ ^2/?1 }, configuration has been extended to the 29/2⁺ state at an excitation energy of 5241 keV.     

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.     

New screening doublets in x-ray satellite spectra

Recent scrutiny of the relevant data available at present on x-ray satellite spectra in theK, L andM regions revealed the existence of two new satellite pairsα″α′ andα″α′ ₃ ′ in theKα satellite group, three pairsα′ ₂ α″,α′ ₂ α^VI andα? α ^IV in theLα satellite group, twoLβ ₂ satellite groups; viz.,β ₂ ^(b) (β ₂ ^I ,β ₂ ^II β ₂ ^(c) ) andβ ₂ ^(c) (β ₂ ^I β ₂ ^II ), two pairsγ′₁ γ′₂ andγ′₁ γ′_2′ in theLγ satellite group and also a pairβ _II β _III in theMβ satellites, which are all found to be governed by the screening doublet relationship,Δ(v/R)^1/2=constant.     

High-spin states in206Bi populated in the205Tl(α, 3n) reaction

Using alpha-particles in the energy range 35–51MeV and in-beam gamma ray and conversion electron spectroscopy techniques the reaction²⁰⁵Tl(α, 3n)²⁰⁶Bi was studied. A 15±1ns isomeric 15⁺ state was found at an excitation energy of 3147keV in²⁰⁶Bi. The main configuration of the isomeric state is suggested to beπh _9/2 vp ₁ ^2/?1 i ₁₃ ^2/?2 . The isomeric state decays mainly through a stretched cascade of five gamma rays to the previously known 0.88ms 10^? state of theπh _9/2 vi ₁₃ ^2/?1 (j ^?2)₀₊ configuration at an excitation energy of 1045 keV. A shell model calculation of the yrast states has been performed and it is found that the calculation agrees fairly well with the experiments. The average deviation between experimental and calculated energies for the yrast states with angular momenta in the region 6–18 is +4keV and the root mean square deviation is 22 keV.     

g-factors of rotational states in176Hf,177Hf,and180Hf

g-factors of rotational states in¹⁷⁶Hf and¹⁸⁰Hf were measured with the twelve detector IPAC-apparatus of our laboratory [1]. The natural radioactivity 3.78·10¹⁰y¹⁷⁶Lu and the 5.5 h isomer^180mHf were used which populate the ground-state rotational bands of¹⁷⁶Hf and¹⁸⁰Hf. The integral rotations ofγ-γ directional correlations in strong external magnetic fields and in static hyperfine fields of (Lu→Hf)Fe₂ and HfFe₂ were observed. The following results were obtained: $$\begin{array}{l} ^{176} Hf: g\left( {4_1^ + } \right) = + 0.334\left( {38} \right) \\ ^{180} Hf: g\left( {2_1^ + } \right) = + 0.305\left( {14} \right) \\ g\left( {4_1^ + } \right) = + 0.358\left( {43} \right) \\ {{ g\left( {6_1^ + } \right)} \mathord{\left/ {\vphantom {{ g\left( {6_1^ + } \right)} {g\left( {4_1^ + } \right)}}} \right. \kern-\nulldelimiterspace} {g\left( {4_1^ + } \right)}} = + 0.95\left( {12} \right) \\ \end{array}$$ . The hyperfine field in (Lu→Hf)Fe₂ was calibrated by observing the integral rotation of the 9/2^? first excited state of¹⁷⁷Hf populated in the decay of 6.7d¹⁷⁷Lu. Theg-factor of this state was redetermined in an external magnetic field as $$^{177} Hf: g\left( {{9 \mathord{\left/ {\vphantom {9 {2^ - }}} \right. \kern-\nulldelimiterspace} {2^ - }}} \right) = + 0.228\left( 7 \right)$$ . Finally theg-factor of the 2 ₁ ⁺ state of¹⁷⁶Hf was derived from the measuredg(2 ₁ ⁺ ) of¹⁸⁰Hf by use of the precisely known ratiog(2 ₁ ⁺ ,¹⁷⁶Hf)/g(2 ₁ ⁺ ,¹⁸⁰Hf) [2] as $$^{176} Hf: g\left( {2_1^ + } \right) = + 0.315\left( {30} \right)$$ .     

Two-nucleon excitations in 66 148 Dy82 from Gamow-Teller decay of the 67 148 Ho81 6− isomer

Two-particle excitations in the two-proton nucleus¹⁴⁸Dy populated inβ-decay of 10-s ¹⁴⁸Ho(6^?) were investigated throughγ-ray measurements following on-line mass separation. Theπh _11/2s_1/2 two-proton doublet and the (vh _9/2 s ₁ ^2/?1 )5^? neutron particle hole configuration are firmly identified, and theπh _11/2 d ₅ ^2/?1 and πh_11/2D_3/2 multiplets are also observed. The results suggest dominantπh _11/2vs ₁ ^2/?1 character for the¹⁴⁸Ho 6^?-isomer.     

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.     

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.     

Magnetic moments of the 2 1 + states in102, 104Mo

Theg factors of the first excited 2⁺ levels in the neutron-rich nuclei¹⁰²Mo and¹⁰⁴Mo have been studied through the measurement of the perturbed angular correlations for theγ-γ cascades between the 0 ₂ ⁺ -2 ₁ ⁺ -0 ₁ ⁺ level sequences. The results of g=0.42±0.07 for¹⁰²Mo and ofg= _?0.11 ^+0.12 for¹⁰⁴Mo agree with the prediction of the vibrational-rotational model. In terms of IBA, with the assumption ofN _π=3 for the Mo isotopes which takes into consideration a two particle, two-hole excitation across the Z=40 subshell, the proton-bosong factor is deduced to beg _π=1.00±0.23. It is shown that this value provides evidence for subshell effects in¹⁰⁰Zr.     

Remeasurement of the lifetime of the 4 1 + -state of156Gd and recalculation of itsg-factor

The half-life of the 4 ₁ ⁺ -state of¹⁵⁶Gd has been remeasured by the delayed coincidence technique. The excellent time resolution which can now be achieved by use of small BaF₂ detectors allows a more reliable determination than with previously applied methods. The resultT _1/2(¹⁵⁶Gd,4 ₁ ⁺ )=108(2) ps is smaller than previously published data, but it fits well into the systematics of theB(E2) values of the rotational transitions of this nucleus. A recalculation of the previously measuredg-factor of the same state givesg(¹⁵⁶Gd,4 ₁ ⁺ ) =0.327(19). This value is still smaller than theg-factor of the 2 ₁ ⁺ state, but the magnitude of the reduction can now easier be interpreted by nuclear structure calculations.     

Study of the centrally producedK 1 0 K ± π∓ system at 85 GeV/c

We have analyzed theK ₁ ⁰ K ^± π^? system in the reactions π⁺/pp→π⁺/p(K ₁ ⁰ K ^± π^?)p. A spin-parity analysis of theK ₁ ⁰ K ^± π^? system in the “4C” channel confirms the existence of the 1⁺⁺ E meson which decays mainly throughK ^* \(\bar K\) . The data allow the presence of a 0^?+ wave at a level of 14% of theE/ι signal. The production ofD andE mesons in the channels where theK ₁ ⁰ K ^± π^? system is produced along with a π⁰ or π⁺π^? system is suppressed.     

g-factor of the 4 1 + rotational state of160Dy

By use of Ge-detectors of the OSIRIS-collaboration [1] in connection with the 12 detector IPAC apparatus of our laboratory [2] a precise measurement of theg-factor of the 4 ₁ ⁺ rotational state of¹⁶⁰Dy was performed. The directional correlations of the threeγ-γ cascades, 1003-197 keV, 1103-197 keV and 1115-197 keV, which are weakly populated in the decay of 72.3 d¹⁶⁰Tb were observed simultaneously. The integral rotations in the static hyperfine field of DyTb at 4.2 K were measured. Theg-factorg(4 ₁ ⁺ )=+0.350(20) was derived. By comparison with the magnetic splitting of the 2 ₁ ⁺ rotational state observed in the same environment by a Mössbauer experiment [3] the ratio of the twog-factors was derived as g(4 ₁ ⁺ )/g(2 ₁ ⁺ )=+ 0.91(5). For the high energy lines we derived from the measured directional correlations the E1/M2 mixing parameters: δ(1003 keV)=+0.005(4); δ(1103 keV)=?0.020(22), and δ(1115 keV)=+0.010(4)     

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.