Energy levels of136Pm and136Nd via beta decay of136Sm and136Pm

¹³⁶Pm and¹³⁶Nd were studied using theβ decay of¹³⁶Sm and¹³⁶Pm. The radioactive nuclei were produced by the⁹²Mo (⁴⁸Ti,xpyn) and¹¹²Sn (²⁸Si,xpyn) reactions. The UNISOR isotope separator enabled mass identification. The previously unknown level scheme of¹³⁶Pm was constructed and the half-life of¹³⁶Sm was determined to be 47±2 s. Six new levels and thirteen newγ-ray transitions have been added to the level scheme of¹³⁶Nd.     

OnE0 transitions in the decay of152Eu m (9.3 h)

The conversion electron spectrum of the decay of¹⁵²Eu ^m (9.3 h) has been specially investigated forE0 transitions with the aid of a magnetic spectrometer and coincidence techniques. Besides the knownE0 transitions of 685 keV in¹⁵²Sm and 615 keV in¹⁵²Gd two further pureE0 transitions of 432 keV and 1048 keV have been observed. It is shown that theseE0 transitions are identical with those observed previously in the decay of¹⁵²Tb. NoE0 transitions could be found from a 0⁺ state of 1083 keV in¹⁵²Sm. The measured intensities together with the gamma spectrum measured by Barretteet al. give a consistent decay scheme of¹⁵²Eu ^m . Furthermore the half-life of the 0⁺ level at 615 keV in¹⁵²Gd was measured using the method of “delayed coincidences”. The result was (0.2≦t _1/2≦2.1)×10^?10 s. From this theE0 transition probability for the level was derived as (0.3≦W _K (E0)≦3.7)× 10⁹ s^?1 and theρ-value as 0.10≦¦ρ¦≦0.36. The results are discussed within the framework of the collective model.     

Structure of even-even138Nd from the decay of138Pm

The structure of¹³⁸Nd is investigated through theβ ⁺-decay of¹³⁸Pm, whose decay half-life is measured to be 3.24±0.05 min. A level structure comprising 27 excited states and 52 transitions is constructed. With the help of deducedft values and internal conversion coefficients, spin-parity assignments are made to many states in¹³⁸Nd and to the ground states of¹³⁸Pm. From the positron end-point energy measurement, the total decay energy is determined to be 5.4±0.2 MeV, which is compared with the predictions of several mass formulae and with the decay energy systematics of theN=77 isotones. The structure of¹³⁸Nd is discussed in the light of nuclear systematics of theN=78 isotones.     

The decay of 8.7 min237Pa

The beta and gamma radiations of²³⁷Pa have been investigated employing semiconductor and scintillation spectrometers and coincidence techniques. Sources of²³⁷Pa were obtained after bombardments of²³⁸U with bremsstrahlung and 14-MeV neutrons and subsequent chemical separation. From the total of 18γ-rays following the decay of 8.7±0.2 min²³⁷Pa 17 transitions, representing 99.9% of theγ-ray intensity, could be placed in a level scheme of²³⁷U. AQ _β- value of 2.25±0.1 MeV has been determined.     

Levels in152Gd and152Sm populated by the decay of152Eu

The energy level schemes of¹⁵²Gd and¹⁵²Sm have been established on the basis of singlesγ-spectra, andγ- γ coincidence measurements. Ge(Li) detectors were used to study the gamma spectra produced in the EC/β⁺ and β^? decays of¹⁵²Eu to¹⁵²Sm and¹⁵²Gd, respectively. Thirteen new transitions are reported and data from eleven coincidence gates enabled five new levels to be suggested. Relative intensities and logf t values were calculated and spin/parities deduced. Comparisons are made with new predictions of the Interacting Boson Model.     

Seniority isomerism in theN]=82 isotone152Yb; Favouredβ transitionsπh 11/2→vh 9/2

The reaction⁵⁸Ni→⁹⁶Ru has been investigated withγ spectroscopic methods and pulsed-beam techniques. A level scheme of the magic nucleus¹⁵²Yb has been established. The half-life of the isomeric 10⁺ state was found to be 39±5 μs. The result is discussed in the frame-work of the seniority scheme. Theory and experiment show excellent agreement for the half-lives of the 10⁺ states in theN=82 isotones¹⁴⁸Dy,¹⁵⁰Er and [¹⁵²Yb. A level scheme of¹⁵¹Tm, consisting of ten excited states, has been established.β-decay schemes of [¹⁵²Yb (3.2±0.3 s),¹⁵²Tm^(m) (8.0±1.0 s) and¹⁵¹Tm (3.8±0.8 s) have been derived. The logft value of theβ transition¹⁵²Yb (0⁰)→¹⁵²Tm (1⁺) has been determined to be about 3.4. It was found that theft values of the favouredβ transitions 0⁺→1⁺ in theβ decays of [¹⁴⁸Dy,¹⁵⁰Er and¹⁵²Yb are almost inversely proportional to the numbers of protons out of theh _11/2 subshell.     

The decay of 31 sec98Zr, 2.9 sec98Nb and 51 min98Nb

TheΒ- andγ-radiations of⁹⁸Zr and^{98m, g} Nb have been investigated employing scintillation and semiconductor spectrometers and coincidence techniques. Sources of⁹⁸Nb were produced by the⁹⁸Mo(n, p)⁹⁸Nb reaction, sources of⁹⁸Zr by fission of²³⁵U with thermal neutrons applying chemical separations. For⁹⁸Zr, a half-life of 30.7±0.4 sec and aQ _β-value of 2.3±0.2 MeV were obtained, for the⁹⁸Nb isomers, half-lives of 2.86±0.06 sec and 51.3±0.4 min, andQ _β-values of 4.8±0.2 MeV and 4.5±0.2 MeV, respectively. Noγ-rays were observed in the decay of⁹⁸Zr. The decay of 2.9 sec⁹⁸Nb was found to involve 11γ-ray transitions. In the decay of 51 min⁹⁸Nb, 54γ-transitions were detected. Spin and parity of 1⁺ and 4^? were deduced for the isomeric states of⁹⁸Nb.     

Structure of140Pm from beta decay of140Sm

The structure of¹⁴⁰Pm is investigated through the beta decay of¹⁴⁰Sm, whose half-life is measured to be (14.7 ± 0.2) m. A level structure comprising 41 transitions among 17 excited states is constructed. Using the deduced ft values and measured internal conversion coefficients, spin-parity assignments to several states in¹⁴⁰Pm were made. From beta end-point measurement, the total decay energy is deduced to beQ _EC =3.4±0.3 MeV, which is compared with the predictions of several mass formulae. The systematics of the odd-Z, N=79 isotones are discussed.     

States inN=80140Nd populated in the decay of140Pm

The level structure of theN=80,¹⁴⁰Nd has been investigated through the beta decay of^140m Pm and^140g Pm, whose decay half-lives were measured to be 5.95±0.05 min and 9.1±0.5 sec, respectively. Decay schemes for the two isomers have been constructed fromγ-ray measurements. With the help of the beta decayft values and internal conversion electron measurements, spins and parities were deduced for levels in¹⁴⁰Nd. Among the levels a 7^? state at 2222.0 keV and a 5^? state at 2273.3 keV are identified as two-neutron quasiparticle states. The (ie233-01) for^140m Pm and^140g Pm have been deduced as 7^? and 1⁺, respectively. From beta end-point measurements, the decay energies of the two isomers have been determined asQ _EC=6.48±0.07 MeV^140m (Pm) andQ _EC=6.08±0.10 MeV (^140gPm). The results are discussed in the light of nuclear systematics of theN=79 and 80 isotones.     

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.     

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.     

Lifetime measurements and particle-core coupling calculations in144Sm

Applying the generalized centroid shift method in the¹⁴²Nd(α, 2n)¹⁴⁴Sm reaction the following half-lives have been measured:T _1/2(3,376 keV)=(1.6±0.2) ns,T _1/2(3,460 keV) =(0.5±0.2) ns andT _1/2(5,150 keV)≦0.3 ns. Level energies and electromagnetic transition rates have been calculated within a particle-core coupling approach that is based on the shell model with configuration mixing. The persistence ofl-forbiddenness of M1 transitions between rather complex configurations could be confirmed.     

Level structure of170Er observed in the decay of the 2.76 min170Ho

TheΒ ^?-decay of the longer-lived¹⁷⁰Ho isomer produced through the¹⁷⁰Er(n, p)¹⁷⁰Ho reaction has been investigated by using a versastile detector and coincidence equipment. The half-life andΒ ^?-decay energy were determined to beT _1/2=2.76±0.05 min andQ _β =3.85±0.15 MeV, respectively. In addition to the ground state band and some higher energy levels, the proposed level scheme of¹⁷⁰Er contains 11 states between 1.0 and 1.6 MeV (6 new ones), which are connected mutually by previously unknown low-energy transitions. Spin and/or parity assignments based mainly on coincidence data and multipolarity determinations are suggested for most of these states. By using systematic considerations and the nuclear projection model calculations several bands withK≧2 can be assigned tentatively. As a side result the half-life of¹⁶⁹Ho was determined to be 4.7 ±0.2 min.     

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.     

Der β-Zerfall des208Tl

An iron-free intermediate-imageβ-ray spectrometer was used to investigate theβ-decay of²⁰⁸T1 in coincidence with the 2.615 MeVγ-ray of²⁰⁸Pb. Fourβ-groups were found, three of which were previously known. The fourth group has an endpoint energy of 0.64±0.03 MeV and an intensity of (4.5±1.5)%. It is supposed that this transition is still complex and feeds a group of levels around the known 4.3 MeV level of²⁰⁸Pb. Noβ-ray of maximum energy 1.032 MeV to the 3.961 MeV level could be found.     

Spin-flipβ − decay of even-even deformed nuclei110Ru and112Ru

Neutron-rich nuclides¹¹⁰Ru and¹¹²Ru produced in symmetric fission of²³⁸U by 20 MeV protons have been studied at the IGISOL facility by means ofβ-ray,γ-ray and conversion electron spectroscopy. A total of 12 and 6γ-transitions were observed in the decays of¹¹⁰Ru and¹¹²Ru, respectively. Multipolarities were determined for a few transitions. The beta decay half-life was determined to be 11.6±0.6 s for¹¹⁰Ru and 1.75±0.07 s for¹¹²Ru. As a side product, a new value of 2.1±0.3 s for theβ half-life of the¹¹²Rh 1⁺ state was obtained. The decay energy measured with the plastic scintillator was 2.81 ±0.05 MeV for¹¹⁰Ru and 4.52 ±0.08 MeV for¹¹²Ru. The beta decay schemes of¹¹⁰Ru and¹¹²Ru isotopes indicate that the main fraction of their beta strength resides in two 0⁺→1⁺ spin-flip transitions with their logf t values between 4.4 and 4.7. The decay energies and the energies of the 1⁺ GT states are compared with the macroscopic-microscopic model calculations. The observed GT-strengths are discussed in the framework of the deformed single-particle model.     

Konversionskoeffizient von69m Zn und Fluoreszenzausbeute von Zink

The decay of^69m Zn and⁶⁹Zn has been investigated using a radioactive source obtained by irradiating a sample of 99%⁶⁸ZnO with neutrons. Theβ-spectrum of⁶⁹Zn and the conversion electrons of the^69m Zn decay have been studied with an anthracene scintillation spectrometer of the split crystal type. The measured value of the conversion coefficient of^69m Zn is α=0.054±0.003. With this result and those obtained by measurement of theγ-ray spectra of^69m Zn with NaI(Tl) scintillation crystals, theK-fluorescent yield of Zn has been determined to be ω_K=0.45±0.04.     

Half-life of the 89.83 keV level in152Eu

The half-life of the 89.83 keV level in¹⁵²Eu was measured in the¹⁵¹Eu(n, γ)¹⁵²Eu reaction to be 381±19 nsec. This results in the determination of the absolute transition probabilities of the 89.83 keVE1+M2 transition to the ground state, yielding hindrance factors relative to the Weisskopf estimateF _W(E1)=(2.3 ± 0.4) × 10⁶ andF _W=0.20±0.08.     

Identification of152Ce

Although the¹⁵²Ce isotope, the heaviest one of cerium, was once reported as identified, it was pointed out later on that the assignment should be corrected and¹⁵²Ce is still unknown. The search for¹⁵²Ce has been carried out again in the present report. From γ-ray spectra of mass separated fission products produced by KUR-ISOL, the Pr-K X-rays and two γ-rays are assigned to be generated by the ß-decay of¹⁵²Ce. The half-life is determined to be 1.4(2) s, which is a little shorter than theoretical predictions, 2.2 s and 2.1 s.     

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.