Conversion electron measurements in the decay of156Tb

The conversion electron spectrum from the decay of¹⁵⁶Tb to¹⁵⁶Gd was measured with an iron, double-focusing spectrometer. TheK conversion coefficient of the 1222.4 keV transition was measured relative to theK conversion coefficient of the 661.6 keV transition in¹³⁷Cs and found to be 0.00174±0.00013. This result was used to normalize electron and gamma-ray data to obtain theK conversion coefficients of 33 transitions in¹⁵⁶Gd. The 1009.6 and 1040.6 keV transitions have largeE0 components.     

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.     

High resolution studies of transitions in the decay chain146Gd to146Eu to146Sm

Transitions in¹⁴⁶Eu and¹⁴⁶Sm were studied using a double-focussing beta-ray spectrometer and a Ge(Li) detector. Internal conversion and gamma-ray intensities were determined. The internal conversion spectrum of the three 155, 115 and 116 keV cascading transitions in¹⁴⁶Eu was studied for all subshells.K-,L- andM-subshell ratios were determined andE2/M1 mixing ratios were deduced for these three transitions. Intensities from theN- andO+P-shells were determined and compared to theoretical calculations. All internal conversion intensities were found to be in agreement with theoretical data for pureM1 character with smallE2 admixtures for all the three transitions. Selected parts of the internal conversion spectrum of the transitions in¹⁴⁶Sm were restudied at 0.06% momentum resolution. This study was mainly concentrated on four transition doublets feeding and deexciting the close lying levels at 1,380 and 1,381 keV. A new transition with 702.20 keV energy was detected in the 702–703 keV transition group. Internal conversion coefficients were deduced using reported gamma-ray intensities. Multipole characters of the transitions were deduced and used as a basis for a discussion of the spins and parities of the lower lying excited states of¹⁴⁶Sm.     

InternalK-conversion coefficients of transitions in182W

TheK-conversion coefficients of seven low energy transitions (～100–400 keV) in¹⁸²W following the decay of¹⁸²Ta have been determined by the NPG method using the newly reported γ-ray intensities measured by Ge(Li) detectors. The results are compared with theoretical values deduced from the tabulations of Rose, Sliv and Band, and Pauli. The weak peak corresponding to theK-conversion line of the 351.3 keV transition could be observed in accordance with the previous investigations, however the existance of the previously reported 146.3 keV transition could not be confirmed. Also theK-conversion line of the recently reported 110.4 transition could not be observed.     

Asymmetry parameters in183W and182W using mice detection with a crystal monochromator

Using exceptionally high intensity Mössbauer sources (～ 1–100 Ci) of¹⁸²Ta and¹⁸³Ta, we have measured the Mössbauer effect for the 46.5 and 99.1 keV transitions of¹⁸³W and the 100.1 keV transition of¹⁸²W. Using a microfoil internal conversion electron (MICE) /1/ detector capable of operation at low temperatures, and a LiF crystal monochromator, we obtain effects of nearly 600% for the 46.5 keV transition and 3 1/2% and 6% for the other two cases, while standard transmission measurements typically yield much smaller signal-to-background ratios. With this technique we have measured the asymmetry term in the conversion electron spectra. To our present level of accuracy the results are in agreement with theoretical calculations of interference parameters /2/. Our results do not agree with earlier measurements /3/ on this transition, which are grossly at variance with theoretical calculations of the interference parameter.     

Mössbauer conversion spectroscopy: Measurements on the first excited states of180, 182W and145Pm

The Mössbauer Conversion (MBC) Spectroscopy and criteria for its useful application are discussed and compared with other MB-techniques. By help of the MBC spectroscopy the isomer shift of the first excited state in¹⁸²W was measured and a change in radius ?0.05 · 10^?4>Δ 〈r ²〉/〈r ²〉>?0.28 · 10^?4 derived. The ratio of quadrupole moments of first excited states in¹⁸⁰W and¹⁸²W turns out to be¹⁸⁰ Q/¹⁸² Q=0.976 (30). Due to the excellent statistical quality of the spectra the interference parameter of the 100keVE2 transition in¹⁸²W could be determined to 2β=0.0165(9) for theL-shell. The MB-effect for the 61 keV transition in the instable¹⁴⁵Pm has been detected for the first time. A widthΛ _exp=2.15(58) mm/s was obtained.     

Nuclear orientation of152,154Tb in gadolinium

The anisotropy in the directional distribution of gamma-rays from the decay of^152,154Tb oriented in a gadolinium matrix at low temperatures, has been measured at the angles of 0 and π/2 with respect to the applied magnetic field direction at temperature of (15±1) mK. Unambiguous values of spin have been deduced for several levels in¹⁵²Gd. Multipole mixing ratios of many gamma-ray transitions occurring in¹⁵²Gd have been found and results are compared with the similar transitions in^150,154,156Gd and they are discussed in terms of the rotational-vibrational model and dynamic deformation theory based on the Strutinsky method. Our results confirm the spin value of 0 for 21·4 h isomer in¹⁵⁴Tb and they establish the spin value of 3 for the 2277·0 and 2336·1 keV levels and the spin value of 4 for the 2416·3 keV level in¹⁵⁴Gd.     

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 charge radii of198Pt-183Pt

The reactions⁵⁸Ni+¹⁰²Pd→¹⁶⁰W and⁵⁸Ni+¹⁰⁶Cd→¹⁶⁴Os were investigated to search for new decay data of neutron deficient nuclei. Excitation energies of the compound nuclei covered a range from 47 to 89 MeV. Velocity separation of the evaporation residues and position time correlations with the a decays of the implanted nuclei were used. The following new decay data were measured:¹⁶²Os (E_α=(6611 ±30) keV, T_1/2=(1.9±0.7) ms);¹⁵⁸W (T_1/2=(0.9±0.3) ms);¹⁵⁸m_W (E=1.88 MeV, E_α=(8280±30) keV, T_1/2=(0.01-1) ms);^155mLu (E_α=(5575±10) keV); β decay of¹⁵⁶Ta (T_1/2 > 10 ms) to the 8⁺ yrast isomer in¹⁵⁶Hf. A cross section of 5μb was measured for the new isotope¹⁵⁶Ta produced in a p3n evaporation channel from¹⁶⁰W at 64 MeV excitation energy.     

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.     

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.     

Internal conversion coefficients of the transitions in Tm169

The conversion electron spectrum of Tm¹⁶⁹ has been measured by an iron-yoke double focusing spectrometer. Gamma-ray energies and gamma-ray intensities were measured by a bent crystal spectrometer. Conversion coefficients and conversion ratios were determined from the electron and gamma intensities. The conversion process of the retardedM 1 transitions of 177 keV and 198 keV was found to be normal, in agreement with our earlier directional correlation results. No penetration effects were found in the conversion process of the retarded 63 keVE1 transition.     

K conversion coefficients of transitions in87Sr

TheK conversion coefficients of the 388 and 483 keV transitions in⁸⁷Sr populated in the decay of⁸⁷Y have been measured with Ge(Li) and Si(Li) detectors by the NPG method. We find α _K values of 0.162 ± 0.010 and 0.00260 ± 0.00013 for the 388 and 483 keV transitions, respectively.     

Gamma-ray polarization and nuclear orientation measurements on182TaFe

The results of combined measurements of the directional distribution and the linear polarization of gamma-rays from oriented¹⁸²TaFe are reported. Construction and calibration of a Compton polarimeter based on a single planar Ge(Li) detector are described. The degree of the linear polarization and multipole mixing ratios for many gamma-transitions in¹⁸²W have been deduced. A triple multipole mixingE1+M2+E3 of the 1,274 keV transition has been obtained withδ ₁(M2/E1)=+0.36(10) andδ ₂(E3/E1)=?0.28(12). Results are discussed in the framework of the rotational model. Strong evidence of the octupole vibrational nature of the 1,289 keV level in¹⁸²W has been found.     

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.     

Mixing ratios in67Zn determined by gamma-gamma angular correlations

The gamma-gamma angular correlations of the 209.0–184.6, 494.3–393.6, 494.3–300.2 and 703.6–184.6 keV cascades in⁶⁷Zn have been measured. Mixing ratios of the 209.0, 300.2, 393.6 and 703.6 keV transitions are deduced. A spectroscopic study could not confirm the existence of a recently proposed level at 710 keV.     

On the newly proposed levels in152Gd and152Sm

It is shown that there is no evidence for the existence of levels at 1312.41, 1485.67 and 1698.34 keV in¹⁵²Gd and at 1436.65 and 1681.56 keV in¹⁵²Sm, which were recently claimed to be observed in the decay of¹⁵²Eu(3^–, 15 y).Work supported in part by the Natural Science Fund of China and in part by the Department of Science and Technology of China Nuclear Energy Industry Corporation     

Are the GSI positron electron lines due to internally converted E0 transitions?

We have searched for excited 0⁺ states in¹⁸⁰Hf and¹⁸²W with one-proton transfer reactions on¹⁸¹Ta targets. Such a state could give rise to internally pair converted transitions to the ground state which would not be accompanied by ground state gamma transitions. No state was found to explain the e⁺-e^? sum energy lines observed in²³⁸U+¹⁸¹Ta collisions at the GSI.     

High resolutionL- andM-subshell internal conversion studies of low energy transitions in149Sm and151Eu

The internal conversion subshell intensities of the (21.529±0.014) keV transition in¹⁵¹Eu and the (22.494±0.011) keV transition in¹⁴⁹Sm have been determined in a high resolution investigation using a double-focussing iron-core spectrometer. The subshell ratios yielded unambiguousM1+E2 multipole mixtures for both transitions. δ²(E2/M1) for the 21.53 keV transition was determined to be (8.8±0.7)·10^?4 and for the 22.49 keV transition to be (5.5±1.2)·10^?3.     

AbsoluteE0 andE2 transition rates and collective states in116Sn

AbsoluteE0 andE2 transition rates in¹¹⁶Sn have been measured using several newly developed techniques. ManyE2 transitions are observed to have a collective character withB(E2) values of up to 60 W.u. The presence of deformed excited states in¹¹⁶Sn is discussed in view of the results obtained.