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.     

Experimental determination of penetration parameter forM1 conversion,and theE2 admixtures for 77 and 191 keV transitions in197Au

TheL-subshell conversion for 77 keV transition andK,L ₁,L ₂-shell conversion for 191 keV transition in¹⁹⁷Au, as well asK-shell conversion transition of 158 keV in¹⁹⁹Hg were measured by means of Π√2-iron free electron spectrometer. Relative gamma-ray intensities have been determined by Ge(Li) spectrometer. From these measurements the α _K conversion coefficient value has been deduced for 191 keV transition as α_K(191 keV)=0.86±0.03. This value shows that the spin of the level at 268 keV in¹⁹⁷Au is 3/2⁺. For the penetration parameter (λ) and intensity ratio \(\left( {\delta ^2 = \frac{{\left\langle {E2} \right\rangle ^2 }}{{\left\langle {MI} \right\rangle ^2 }}} \right)\) the following values are obtained: $$\begin{gathered} \lambda = 3.4 \pm _{1.5}^{1.9} \delta ^2 = 0.11 \pm 0.03for 77 keV transition \hfill \\ \lambda = 3.2 \pm _{0.6}^{0.8} \delta ^2 = 0.17 \pm 0.04for 191 keV transition. \hfill \\ \end{gathered} $$ The agreement of these results with the predictions of De Shalit model is discussed.     

Reevaluation of the conversion coefficient of the 14.4 keV transition in57Fe

Existing values of the conversion coefficient of the 14.4 keV transition in⁵⁷Fe have been reevaluated using newK-shell fluorescence yields and recent decay scheme information. Previous disagreements are removed and the mean values found are α _T =8.26±0.19, α _K =7.37±0.17.     

Half-life measurements of intrinsic states in deformed odd-mass nuclei

The half-lives of the following intrinsic states in deformed odd-mass nuclei has been measured by delayed coincidences with a time-to-amplitude converter:

1. 5/2 5/2⁺[642] at 86.5 keV in¹⁵⁵Gd:T _1/2=6.7±0.3 ns, which results in the determination of theE1,ΔK=1 transition probability to the ground state 3/2 3/2^?[521] and first rotational state 5/2 3/2^?[521], yielding hindrance factors ofF _N ≈5.5 and ≈1.8 (F _W =3.1×10⁴ and 2.3×10⁴) respectively.
2. (3) 5/2 5/2^?[512] at 191.4 keV in¹⁶⁹Yb:T _1/2=3.35±0.15 ns and at 122.39 keV in¹⁷¹Yb:T _1/2=265±20 ns which results in the determination of the transition probabilities of theE1,ΔK=1 transitions to the ground states 7/2 7/2⁺[633], of theK-forbiddenM1 transitions to the 5/2 and 3/2 1/2^?[521] and of theE2 transitions to the 5/2, 3/2 and 1/2 1/2^?[521] states in both nuclei.

TheE1 transition probabilities are compared to the transitions between the same Nilsson states in¹⁷³Yb and¹⁷⁵Hf discussing the influence of the position of the Fermi surface — obtained from recent stripping and pick-up reactions — on these transition probabilities. Additional information on the decay scheme of¹⁷¹Lu→¹⁷¹Yb is obtained by delayed coincidence measurements. For testing the used time-to-amplitude converter the well known half-lives of the 482 keV level in¹⁸¹Ta (T _1/2=10.4±0.3 ns) and of the 279 keV level in²⁰³Tl (T _1/2=0.285 ±0.015 ns) were measured, in good agreement with other measurements.     

Study of Er171 decay by means of an electron-gamma coincidence technique

The decay scheme of Er¹⁷¹ (7.8 h) has been reinvestigated by means of an electron-gamma coincidence spectrometer and a scintillation spectrometer with a transistorized RIDL-400 channel analyser. A careful unfolding of the high energy region of the gamma-ray spectrum revealed the presence of photopeaks at energies of approximately 371, 404, 543, 572, 618, 675, 738, 796, 869, 910 and 962 keV. The existence of 32 transitions in Tm¹⁷¹ was confirmed. Also, it is proved that the 277, 362 keV transitions are in coincidence with the 210 keV and that the 175 keV transition is in coincidence with the 86 keV transition. We revealed the doubt for the existence of the 166, 210, 236, 277 and 419 keV transitions. From coincidence and single counting rates the followingK-conversion coefficients of the 111, 116, 124, 296 and 308 keV transitions were determined to be: α _K (111)=1.561±0.062, α _K (116)=0.699±0.035, α _K (124)=0.608±0.024, α _K (296)=0.0197±0.0010, α _K (308)=0.0183±0.0009, which give the 116, 124 keV transitions an electric quadrupole character; the 111 keV transition a magnetic dipole character withE2/M1 equal 0.4528; and the 296, 308 keV transitions an electric dipole character withM2/E1 equal 0.0058 and 0.0071 respectively.     

Messung des Elektroneneinfangs am Kern176m Lu

The electron capture of^176m Lu to the ground state and to the first excited state of¹⁷⁶Yb has been observed by measuring the YbK x-rays and the 82,2 keV gamma-rays from the gamma decay of the first excited state in¹⁷⁶Yb. With the data of the 88,36 keV gammarays following the beta decay of^176m Lu to the first excited state of¹⁷⁶Hf the electron capture/beta decay ratio of^176m Lu was found to be (0,95±0,16)·10^?4. The electron capture branching ratio to the ground state and to the first excited state of¹⁷⁶Yb was found to be 40/60±30%. By analyzing the 88,36keV gamma-rays and the HfKx-rays the halflife of^176m Lu was evaluated to be 3,66±0,04 h. The value for theK-conversion coefficient of the 88,36keV transition was determined from the x-ray/gamma-ray ratio to be 1,19±0,09.     

Internal conversion studies of the 114 keV transition in175Lu

Measurements of the conversion line intensities, the directional correlation and the conversion probability for the 114 keVM1+E2 transition in¹⁷⁵Lu are reported. TheE2 admixture, determined from relativeK andL intensities, is (19.2±0.2)%. The theoreticalL _I internal conversion coefficient is found to be about 8% too low relative theK,L _II andL _III conversion coefficients.     

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.     

In-beam study of174Lu isomers

Levels in¹⁷⁴Lu have been investigated using the¹⁷⁶Yb(p,3n) reaction. Prompt and delayedγ-ray spectra have been observed with a 0.56-cm³ Ge(Li) detector by a multispectrum analysis method. The half-life and decay mode of two isomeric levels, one at 240.8keV (395±15ns) and the other at 365.1keV (145±3ns) have been firmly established. Hindrance factors are discussed. New delayed transitions in¹⁷⁵Lu are also noted.     

Penetration effects in the internal conversion process of the 204 keV transition in205Tl

Penetration effects have been detected in²⁰⁵Tl by measuring theK, L and (M+N+...) internal conversion coefficients of the 204 keV, 3/2⁺→l/2⁺ transition. From the resulting values α _K =0.29±0.04, α _L =0.132±0.006 and α _M+N+...=0.0397±0.0034 the penetration parameter and the mixing ratio have been deduced to be λ=13.1±2.7 andδ ²=1.40±0.46, respectively.     

The investigation of the reaction22Na(n,p)22Ne for a neutron energy to 1,000 eV

TheK-internal conversion coefficient of the 205 keV (7/2⁺→5/2⁺) transition in¹⁰⁷Cd was determined. From the measured value α _K =0.0552±0.0009 and the known value of theE2/M1 mixing ratio δ² a value of 6.3±1.5 was deduced for the penetration parameterλ. Information derived on effective gyromagnetic ratios in the frame of an extreme single particle model is briefly discussed.     

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.     

Multipole mixing ratios of transitions in175Lu populated from the decay of175Hf

Electron capture decay of¹⁷⁵Hf(70 d) provides a possibility for unambiguous determination of the sign and magnitude of multipole mixing ratios for 89 keV and 114 keV transitions in¹⁷⁵Lu. This is because both gamma rays are in coincidence with the 230 keV transition which is of a pureE2 character. The results of theγ —γ directional correlation measurements, in terms ofE2/M1 mixing ratiosδ, areδ ₈₉ = 0.11±0.07 andδ ₁₁₄ = 0.465±0.005. In addition the directional correlation measurements of the 89γ- 343γ and 319γ-114γ cascades yieldδ ₃₄₃ = 0.08±0.07 andδ ₃₁₉ = ?0.152±0.015.Radioactivity ¹⁷⁵Hf from¹⁷⁴Hf(n, γ); measuredγ —γ(θ) deducedδ(E2/M1); Ge(Li) detectors.     

Decay of the first excited state at 13.3 keV in73Ge

Singles and coincidence measurements of the 13.3 keV transition of⁷³Ge are reported. The total andK conversion coefficients of this gamma-ray and the half-life of this level have been determined. The results are: α _T =1095±55; α _K =312±30;T _1/2=2.98±0.05 μs.     

AnomalousK-conversion coefficient of the 124keV transition in131Cs

The absoluteK-conversion coefficients of the 496 keV-124 keV cascadeγ-rays in¹³¹Cs have been determined from angular correlation experiments using a new approach. The value ofα _K =0.0100±0.0007 obtained for the 496 keV transition is in excellent agreement with the theory whereas a strong case is presented for the existence of an anomalous nuclear-structure-dependent conversion coefficient for the 124 keV transition. TheK-conversion coefficient for this transition has been measured to be 0.742±0.077 giving a value of 1.25±0.13 for the ratioα _K ^(expet) /α _K ^(theory) . The result is interpreted as being due to the presence of electric monopole,E0, electron transition. A value of 0.26±0.14 has been obtained for theE0/E2 electron conversion ratio and the absolute value of the electric monopole matrix element has been determined to be 0.07±0.02.     

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.     

Niederenergetische Gammalinien vom Neutroneneinfang in Lu 175 und Lu 176

The low energy gamma-rays from neutron-capture in Lu 175 and Lu 176 have been investigated by means of the bent crystal-spectrometer at the DR-3-reactor at Risø. From the transitions in Lu 177 3 rotational bands have been determined. The levels of the (404)K=7/2⁺ groundstate rotational band are: 121,62 keV (I=9/2), 268,79keV (I=11/2), 440,66 keV (I=13/2), 636,22 keV (I=15/2), 854,34 keV (I=17/2). The level-sequence of the (514)K=9/2^?-band is: 150,39 keV (I=9/2), 288,99 keV (I=11/2), 451,49 keV (I=13/2), 637,05 keV (I=15/2) and 844,88 keV (I=17/2). At 457,92 keV is the basis for the (402)K=5/2⁺-band the higher levels of which are 552,05 keV (I=7/2), 671,89 keV (I=9/2), 816,63 keV (I=11/2), 985,23 keV (I=13/2), 1176,73keV (I=15/2) and probably 1389,5 keV (I=17/2). The energies of the levels apart from the 1389 keV-level have an accuracy of 7×10^?5. The energy differences between the 3 bands agree very well with the values expected from the Bohr-Mottelson-formulaE=A·I(I+1)+B·I ²(I+1)². The calculated branching-ratios within the 3 bands are in fairly good agreement with the experimental values. Theg _K -factors have been determined for 2 bands: It was found that for the (514)-bandg _K =1,16±0,04 and for the (402)-bandg _K =1,33±0,07.     

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.     

K-conversion coefficient of the 53.3 keV transition and\frac{K}{{L + M}}-ratio of the 13.34 keV transition in73Ge

TheK-conversion coefficient of the 53.3 keV transition in⁷³Ge was measured by coincidence techniques to be αk ₁=7.1 ± 0.6 indicating very good agreement with heory forM2-radiation. The \(\frac{K}{{L + M}}\) -ratio of the 13.34 keV transition to the ground state was determined using the same techniques. The resulting value \(\left( {\frac{K}{{L + M}}} \right)_2 \) =0.36 ± 0.03 supports theE2-character of this radiation and therefore a spin assignment of \(\frac{5}{2}\) for the 13.34 keV level. The measured lifetime of this transition (T _1,2=(2.95 ± 0.05) μsec) corresponds to a factor of 15 greater than the Weisskopf estimation for a pureE2-transition. A short discussion of a possible transfer of the collectivity of the⁷²Ge-nucleus to the⁷³Ge-nucleus is given.     

Collective contributions to E1, ΔK=1 matrix elements in odd-odd deformed nuclei

The half-life of the 184.3 keV state in¹⁶⁵Dy has been remeasured asT _1/2=1.0±0.1 ns in order to deduce a reliable value for the transition matrix element of the depopulatingE l,ΔK=1 transition. Experimental E1,ΔK=1 transition matrix elements in odd-odd deformed nuclei are found to be systematically larger than similar values in adjacent odd-A isotones. This effect is supposed to be associated with higher-order vibrational admixtures coupled via RPC andp— n interaction mixings.