TheEC-decay of170Tm

The spectrum ofK X-rays andγ-rays following the decay of¹⁷⁰Tm has been reinvestigated using a high resolution Si(Li) detector. The intensities of theEC-branches from the ground state of¹⁷⁰Tm to the ground state as well as to the first excited level in¹⁷⁰Er have been measured. The total intensity of theEC-decay is (0.25 ± 0.05)% of all¹⁷⁰Tm disintegrations with (0.18 ± 0.05)% leading to the ground state and (0.07±0.02)% leading to the first excited level of¹⁷⁰Er. The energy of the de-excitingγ-ray has been determined to (78.7±0.5) keV. Its intensity is (0.28 ± 0.06)% of that of the 84.3 keVγ-ray in¹⁷⁰Yb.     

Levels in182W populated in the decay of182Ta

Theγ-rays emitted in theβ-decay of¹⁸²Ta have been reinvestigated with improved statistics in attempting to clarify the reported new levels at 1460.41, 1592.98, 1620.36, 1712.29 and 1762.91 keV in¹⁸²W observed in theβ-decay of¹⁸²Ta. The present study demonstrated that the fifteen newγ-rays, which were used to support the existence of the five new levels, are not relevant to theγ-decay of¹⁸²Ta. Therefore the five new levels are not populated in this decay. Additionally, theγ-ray with an energy of 1035.6 keV (0 ₂ ⁺ →2 ₁ ⁺ ) deexciting theβ-band head in¹⁸²W is observed for the first time in the present decay study and the previous tentative placement of the 351.0 keVγ-ray in the level scheme is confirmed by the present coincidence measurements.     

Theβ-decay of100Y: Discovery of a very low lying 0+ state in100Zr

Theβ-decay of¹⁰⁰Y has been investigated at the gas filled recoil separator JOSEF by means ofγ-ray and conversion electron spectroscopy. Twoβ-decay modes, of half lives 0.94±0.03 s and 0.55±0.15 s, have been observed. Using Xγ-, Xce-, γγ- andγce-coincidences the level scheme of¹⁰⁰Zr has been constructed. An excited 0 ₂ ⁺ state at 331.3 keV has been discovered in this nucleus. Theβ-decay from the 0.55 s decay mode in¹⁰⁰Y shows a strong preference for the ground state compared to the 0 ₂ ⁺ state in¹⁰⁰Zr. The structure of¹⁰⁰Zr and the nature of the 0 ₂ ⁺ level is discussed in the light of the present results.     

Theβ-decays of99Y and99Zr and the level schemes of99Zr and99Nb

Theβ-decays of⁹⁹Y and⁹⁹Zr have been investigated with the two recoil fission product separators JOSEF and LOHENGRIN. Half-lives of 1.51±0.08s and 2.1±0.1s respectively, have been determined. Aβ-decaying isomeric state has been observed in⁹⁹Y. The level schemes of ₄₀ ⁹⁹ Zr₅₉ and ₄₁ ⁹⁹ Nb₅₈ have been established fromγ-ray spectroscopy. Absoluteγ-intensities have been obtained by means of two independent techniques. Halflives of 293±10 ns for the 251.9 keV state and 10.2±1.5 ns for the 614.0 or 667.2 keV level in⁹⁹Zr have been measured through delayedβ,γ- andγ,γ-coincidence experiments. Values for the spins and parities of the low lying levels in⁹⁹Zr are proposed in accordance with the systematics of lighter odd Zr isotopes. Spins and partities are assigned to some levels in⁹⁹Nb fromγ,γ-angular correlation measurements. In this nucleus there is evidence for three-particle configurations of some excited states, where the odd proton is coupled to two neutrons which are in different orbits.     

Lifetime measurements on excited states in100Rh

Lifetime measurements of three excited states in¹⁰⁰Rh populated by the decay of¹⁰⁰Pd have been carried out. A two parameter delayedγ-γ-coincidence experiment using an intrinsic Ge and a plastic scintillation detector resulted in the following values:T _1/2(32.72 keV,¹⁰⁰Rh)=(27.6 ±0.6) nsT _1/2(74.8keV,¹⁰⁰Rh)=(213.6±2) nsT _1/2(158.8 keV,¹⁰⁰Rh)<0.5 ns. For the levels at 32.72 keV and 158.8 keV no former values are known.     

The β-decay of98Y and the level scheme of98Zr

Study of theβ-decay of⁹⁸Y and of the level scheme of⁹⁸Zr was undertaken by the use of the two recoil fission product separators JOSEF and LOHENGRIN. Twoβ-decay modes have been detected for⁹⁸Y, the half-lives of which are 0.65±0.05 s and 2.0±0.2 s. The spins and parities of the two states which undergoβ-decay are proposed to be 1⁺ and 4^?, respectively, with the configurations (π1g _9/2)(ν1g _7/2) and (π2p _1/2 (ν1g _7/2). The measuredQ _β -value is 7300±400 keV for the 0.65 s decay. The level scheme of⁹⁸Zr was deduced fromγ,γ-coincidence data. Absoluteγ-intensities were obtained from two independent measurements. The half-life of the first excited state of⁹⁸Zr at 853.0 keV with spin and parity 0⁺ was determined through delayedγ, e^?-measurements to be 63 ±7ns. No indication of the coexistence of two different nuclear shapes of⁹⁸Zr was found.     

Structure of the highly deformed nucleus101Sr63 and evidence for identical K=3/2 bands

The low-energy level scheme of theN=63 nucleus¹⁰¹Sr has been obtained from a β-decay study of¹⁰¹Rb. The ν[532]5/2 and ν[411]3/2 orbitals are well established as the ground state and a band head at 271.2keV, respectively. The general properties of the level scheme indicate a quadrupole deformation ofβ ? 0.4, confirming the unique feature of saturation of deformation inN ≥ 60 Sr isotopes. The energies of theK=3/2 intraband transitions in the odd-neutron neighbours⁹⁹Sr₆₁ and¹⁰¹Sr₆₃ are very similar. More generally, the identical bands at low spin in^98–101Sr nuclei are correlated with the mass-independent moments of inertia in this region.     

States of167Ho from the decay of neutron rich nuclide167Dy

Theβ ^?-decay of ₆₆ ¹⁶⁷ Dy produced through the fast neutron reaction¹⁷⁰Er(n, α)¹⁶⁷Dy has been investigated by using several kinds of detectors and a high-capacity two-parameter recording system. The half-life andβ ^?-decay energy of¹⁶⁷Dy were determined to beT _1/2 = 6.20 ± 0.08min andQ _β-=2.35±0.06, respectively. The observed level scheme of ₆₇ ¹⁶⁷ Ho (completely unknown previously) contains 12 states, among them a 6.0±0.1 μsM2 isomer at 259.3 keV. On the basis of theoretical and systematic considerations combined with multipole determinations, the following Nilsson model assignments are proposed for the lowest states of¹⁶⁷Ho: 0 keV (7?/2 [523]), 259.3 keV (3+/2[411]), 319.8 keV (5/2 3+/2[411]), 392.5 keV (1+/2[411]), 410.0 keV (3/2 1+/2[411]), 569.7 keV (3?/2{7?/2[523], 2⁺}). Theβ-decay proceeds mainly to the proposed gamma-vibrational state at 569.7 keV with an anomalously low logft value 5.4, indicating similarity between the microscopic structures of this state and the famous ¦K ₀?2¦ gamma vibration of¹⁶⁵Ho.     

Search for missing predicted high-spin states in28Si

New shell model calculations have predicted several high-spin (I ^π=5⁺ and 6⁺) levels in²⁸Si near 10 MeV excitation energy which are missing from or ambiguous in existing experimental studies. Angular distributions, linear polarizations and Doppler-shifts ofγ-rays have been measured for theγ-decay of theE _p=1,911 and 2,073 KeV resonances of the²⁷Al(p, γ) reaction in an attempt to discover these missing states or confirm the discrepancies between experiment and theory. The excitation energies and spin-parities of the resonances were determined as 13,424.4±0.2 keV,I ^π=5⁺ and 13,582.3±0.5 keV,I ^π=6⁺. States populated in theγ-decay of these resonances were assigned spins and parities as follows: 11,777 keV,I ^π=5⁺; 11,331 keV,I ^π=6⁺; 10,417 keV,I ^π=5⁺; 9,417 keV,I ^π=4⁺ and 8,945 keV,I ^π=5⁺. On the basis ofγ-ray transition rates T=1 is assigned to the 13,424 keV level and T=0 to the 10,417 and 11,777 keV levels. With the new data excellent agreement is achieved between the experimental spectrum of²⁸Si and the new shell model predictions. These data provide evidence for aK ^π=3⁺ rotational band comprised by the 6,276, 6,889, 8,945 and 11,331 keV levels. This band emerges also from the shell model wave functions as do theK ^π=0⁺ bands based on the ground state and the 6,691 keV state.     

The collective structure of106,108Ru

Levels in^106,108Ru have been studied by measuringγγ coincidences andγγ directional correlations of theγ-rays following theβ ^?-decay of 36 s¹⁰⁶Tc and 5 s¹⁰⁸Tc. Tc activities were separated chemically from the fission products of thermal neutron induced fission of²³⁹Pu by the continuously running system “SISAK 2” and theγ-radiation was measured on-line. An extended level scheme for¹⁰⁸Ru, spin assignments,E2/M1 multipole mixing ratios andB(E2) ratios for¹⁰⁶Ru and¹⁰⁸Ru have been obtained. The collective structure of the two nuclei is discussed in the framework of different nuclear models.     

The decay of105Tc to levels in105Ru

Theβ ^?-decay of 7.6-min¹⁰⁵Tc has been investigated byβ- andγ-ray singles and coincidence measurements. The activities have been produced by thermal-neutron-induced fission of²³⁵U or²³⁹Pu and subsequent chemical separation of the technetium fraction from the fission product mixture. AQ _β-value of 3.2±0.2 MeV has been determined. In a delayed coincidence experiment the lifetime of the first excited state in¹⁰⁵Ru at 20.55 keV has been measured to be 340±15 nsec. A level scheme of¹⁰⁵Ru is proposed and compared with the results of recent nuclear reaction studies like¹⁰⁴Ru(d, p) and¹⁰⁴Ru(n, γ). From beta branching ratios to levels in¹⁰⁵Ru, ground state spin and parity of 5/2⁺ can be suggested for¹⁰⁵Tc in accordance with the trend observed in neutron rich technetium isotopes.     

On the assignment of high-spin cascades to98Rh and98Pd isotopes

Isotopic assignment of high-spin cascades in⁹⁸Rh and⁹⁸Pd have unambigously been obtained by a suitable combination of the⁹⁶Ru(α, xn yp) and the⁹⁹Ru(d, xn yp) reactions. As a result the band headed by the 841.3 keV line was assigned to⁹⁸Rh and the one headed by the 862.6 keVγ-ray has been found to belong to⁹⁸Pd. In the case of⁹⁸Rh the band is based on the (2⁺) ground state.     

Activation measurement of the3He(4He,γ)7Be reaction

The energy integrated absolute cross section of the³He(⁴He,γ)⁷Be reaction has been determined by an activation measurement, using the branching of the⁷Be 53.44d β-decay to the 478 keV state in⁷Li and its subsequentγ-decay. Depending on the branching ratio used (10.4% or 15.4%) we obtain a zero-energy nuclear cross section factor ofS(0)=0.56±0.03 keV·barn orS(0)=0.38±0.03 keV·barn, respectively.     

A Si(Li) detector system for conversion coefficient measurements and application to the decays of51Cr and87Y

An electron detector system with a 3 mm × 100 mm² Si(Li) detector with a cooled FET and vacuum air lock for changing sources was constructed. The absolute efficiency was measured as a function of energy for use in the measurement ofK conversion coefficients. With the Si(Li) and a Ge(Li) detector, theK conversion coefficient of the 320 keV transition in⁵¹V was measured to be 0.00156 ± 0.00008 where theK conversion coefficients of the 661 and 279 keV transitions in¹³⁷Ba and²⁰³Tl were used as standards. From absolute detection efficiency measurements, theK conversion coefficients of the 388 and 483 keV transitions in⁸⁷Sr were measured to be 0.16 ± 0.02 and 0.0024 ± 0.0003, respectively.     

The decay of115 mIn

The decay of^115m In has been investigated using accurate counting methods. The emission rate of conversion electrons plusβ ^?-particles was determined with a 4π proportional flow counter. The total andK-shell internal conversion coefficients of the 336 keVγ-ray in¹¹⁵In were measured by the electron X-ray coincidence method using combinations of a Si surface barrier with a NaI(Tl) detector and of a magneticβ-spectrometer with a high energy resolution Si(Li) detector, respectively. The conversion ratioR=K/(L+M+...) was deduced from electron spectra recorded with the magneticβ-spectrometer. The 336 keVγ-ray emission rate of all used sources was determined with a calibrated NaI(Tl)γ-ray spectrometer. A Ge(Li) detector has been used to determine the relative intensity of the 497 keVγ-ray in¹¹⁵Sn. As results have been deduced the 336 keVγ-ray emission per decay (N _γ1/N ₀=(45.9 ± 0.1)%), the total internal conversion coefficient (α=1.073 ± 0.014), theK-shell internal conversion coefficient (α _K=0.843±0.012), the conversion ratioR=3.63±0.07, theβ ^?-transition per decay going to the ground state (N _β1/N ₀=(5.0 ± 0.7)%) and to the first excited level in¹¹⁵Sn¹¹⁵Sn(N _β2/N ₀=(0.047 ± 0.002)%), and the 497 keVγ-ray emission (N _γ2/N _γ1=(0.103 ± 0.004)%). From the obtained internal conversion data it follows that the 336 keVγ-ray transition is ofM4 character with anE5 admixture of less than (3.5±1.5)%. The half-life of the isomeric state¹¹⁵ mIn has been determined with four different methods. The result isT _1/2=(4.486±0.004) h.     

Measurements of someK-internal conversion coefficients near threshold

TheK-internal conversion coefficients have been measured by the XPG technique for a number of low energyγ-ray transitions whose energies do not exceed theK-binding energies by more than 4 keV. Using Si(Li) detectors in singles and coincidence arrangements, the following results were obtained: 63.1 keV El in¹⁶⁹Tm(α_K=1.02±0.15), 72.0 keV E1 in¹⁸⁷Re (0.75±0.05), 57.8 keV M1 in¹⁶²Ho (11.42±0.67), 56.6 keV M1 in¹⁶⁴Ho (12.04±0.70), and 67.1 keV M1 in¹⁷⁴Lu(10.25±0.58). The experimental results are compared with the theoretical calculations which include transition energies down to 1 keV above threshold.     

Multipole mixing ratios of transitions in168Er

Time-integral and time-differentialγ-γ directional correlation measurements were performed for cascades in¹⁶⁸Er populated from the electron-capture decay of¹⁶⁸Tm(87d). The¹⁶⁸Tm source was dissolved in HF acid to minimize extranuclear perturbations. The results of the time-differential experiment for the 448-99.3 keV and 448-198 keV cascades showed agreement with time dependent interaction and gaveλ ₂(1094)=(0.79±0.09) ×10⁷ sec^?1. The attenuation factors for the 80 keV level were determined asG ₂₂ (80)=0.90±0.01 and G₄₄(80)=0.94±0.01. OnlyI=4 spin value for the 1094 keV level is consistent with our measurements. The 632, 731, 741, and 816 keV transitions connecting theK=2⁺ andK = 0⁺ rotational bands were found to be of almost pureE2 character. The 99.3, 198, 547, 720, 830, and 1277 keV transitions are of practically pureE1 multipolarity. The 448 keVMl transition has (0.8 _?0.4 ^+2.0 )%E2 admixture. The results for the 1014?80keV cascade give (23±4)%E3 component in the 1014 keV transition.     

The electron capture decay of125I and145Pm

The productP _K ω _K of theK-capture probability and theK-fluorescence yieldω _K was measured in the EC decay of 17.7 y¹⁴⁵Pm and 60.14d¹²⁵I by means ofK x-ray-γ-ray coincidences with semiconductor detectors. Accepting a best value ofω _K =0.920 forZ=60 from the literature, values ofP _K =0.606±0.025 and 0.554±0.025 for decay of¹⁴⁵Pm to the 67.2 and 72.4 keV levels in¹⁴⁵Nd, respectively, were determined, from which the application of EC theory givesQ _EC=153±4 keV to the ground state. TheP _K ω _K ratio to the 67.2 and 72.4 keV levels also was determined independently to be 1.11±0.01, which serves as a good check on theγ-ray-gatedP _K values. Theγ-ray energies were determined more accurately to be 72.4±0.1 and 67.2±0.1 keV, together with a ratio of their relative intensities,I _72.4/I _67.2=3.35±0.09. In the decay of¹²⁵I, a value ofP _K ω _K =0.699±0.030 was measured, and by using an independent determination ofQ _EC=178±2 keV to the ground-state from the literature, a value ofP _K=0.801 is calculated from allowed EC theory, from whichω _K =0.873±0.017 atZ=52 is obtained. This value is in good agreement with theoretical values and with a value of 0.875±0.028 predicted by the best fit curve of Bambyneket al.     

Spectroscopy of excited states in212Po,210Pb,and213At employing18O induced few-nucleon transfer reactions

γ-ray spectroscopic techniques have been applied to measure properties of excited states (E ^*<2MeV) in²¹⁰Pb,²¹²Po, and²¹³At after populating these neutron rich (N=128) nuclei via¹⁸O induced few-nucleon transfer reactions on²⁰⁸Pb and²⁰⁹Bi targets. In²¹²Po an isomeric state is located atE ^*=1,477 keV with a halflife oft _1/2=14.7±0.3 ns. This state is interpreted to be the 8⁺ yrast level which decays to the ground state via the measured $$8^ + \left( {121.1 keV} \right)6^ + \left( {223.3 keV} \right)4^ + \left( {405.1 keV} \right)2^ + \left( {727.8 keV} \right)0^ + $$ γ-cascade.α-decay (E _α≈10.2 MeV) of the isomer is also observed. In²¹⁰Pb the time spectra for members of the 4⁺ (297.8keV) 2⁺ (799.4keV)0⁺ γ-cascade show a delayed component with a halflife oft _1/2=152±13 ns which is attributed to the known 8⁺ yrast state atE ^*=1.27 MeV. For²¹³At first results on theγ-decay of excited states are presented.     

Decay of the 4.2-min152Pm into levels of152Sm

After bombardments of enriched¹⁵²Sm with 14-MeV neutrons, three isomers of¹²⁵Pm reaction, have been observed with half-lives of 4.2±0.2 min, 7.5±0.2 min and 15.0±1.0 min. Sources of pure 4.2-min¹⁵²Pm were obtained by separating the promethium from its parent 11-min¹⁵²Nd produced by thermal-neutron induced fission of²³⁵U. The beta and gamma radiations of the 4.2-min¹⁵²Pm have been investigated using semiconductor and scintillation spectrometers. Most of theγ-ray transitions could be placed in a level scheme for 152Sm. Especially interesting is a level at 1083 keV for which the assignmentI ^π=0⁺ is proposed. In a 4πβγ experiment, the ground state feeding of¹⁵²Sm in theβ ^?-decay of the 4.2-min¹⁵²Pm has been measured to be 61% of allβ-ray transitions. AQ _β-value of 3.4±0.2 MeV has been obtained.