Directional Correlation Measurements Research Articles

Decay of Nb 94 and Nb 94m

Gamma rays in Mo 94 following the decay of Nb 94 have been studied using coincidence and directional correlation measurements. The 700 keV transition was found to be in coincidence with the 873 keV gamma ray. The intensity of the crossover transition of 1573 keV was found to be less than 0.1 % of the 873 keV gamma ray intensity. The directional correlation of the 700 keV – 873 keV cascade was measured and the corrected expansion coefficients were found to be A 2 = 0.0965 ± 0.0076 and A 4 = 0.019 ± 0.011. These data indicate spins of 4 and 2 for the 1573 keV and 873 keV levels, respectively. Gamma rays following the decay of Nb 94m were studied with proportional and scintillation counters. The conversion coefficient α K of the 42 keV gamma ray in the decay of 6.6 min Nb 94m was measured to be 1600 ± 350 and the branching ratio of the transition from Nb 94m to the 873 keV level of Mo 94 was found to be 0.19 ± 0.03 %. The intensity ratio of the 600 keV beta ray to the 1.3 MeV beta ray in the decay of Nb 94m was determined to be 3.0 ± 0.6 %. These measurements support a spin and parity of 3- for the isomeric state.

Decay of105Ag

Levels of105Pd excited from theK-capture decay of105Ag have been investigated with the help of a Nal(Tl) sum γ-spectrometer and logft values for these transitions have been estimated. Eesults of γ-γ directional correlation measurements and a level scheme are also presented.

Directional correlation measurements in xenon-132

The directional correlations of six different gamma-ray cascades involving the 670, 1443, 1960, 2400, 2630 and 2840 keV levels have been studied. By a comparison of the experimental coefficients obtained by least square analysis of the data with theoretical coefficients for various possible sequences, the spins of these levels and the mixing ratios of the transitions involving these levels have been determined. The proposed spins are 1443 (4), 1960 (3 or 4), 2400 (4), 2630 (3) and 2840 (3). The spin assignment of 3 for the 2630 keV level strengthens the suggestions that this level is of octupole vibrational origin.

Direction and polarization angular correlations of gamma-ray cascades in Pb 208

Polarization-direction and directional angular correlation measurements have been made on three of the most prominent gamma-ray cascades in Pb 208 following the beta decay of Tl 208. In combination with other information, the results lead to specific electromagnetic transition parameters and to spin and parity assignments for four of the excited levels in Pb 208. The results of existing internal conversion measurements are found to agree with those computed from the present transition assignments and mixing ratios, provided finite nuclear size (without penetration effects) is taken into account.

Gamma-gamma directional correlations in Pt 192

Measurements of gamma-gamma directional correlation have been made of the 468 keV-316 keV, 300keV-300 keV, 600 keV-300 keV, 588 keV-613 keV, 885 keV-316 keV and 1065 keV-316 keV cascades in Pt 192 following the β-decay of Ir 192. The two first mentioned cascades are a composite of several cascades. Our measurements, in combination with multipole measurements of gamma rays carried out by other investigators prove that the levels at 784 keV, 921 keV and 1201 keV have spins and parities 4 +, 3 + and 4 +, respectively. It is probable that the two last mentioned levels belong to a rotational band, the head of which is the γ-vibrational level with 2 +, K = 2 and energy 613 keV. For the 1381 keV level we can report 3 +, 3 − or 4 −.

The character of the 1315 keV state in Yb 174

The electron capture decay of Lu 174 which populates levels of 76.5 and 1315 keV in Yb 174 has been re-investigated. A measurement of the K-conversion coefficient of the 1238±7 keV transition was made, and a directional correlation measurement performed on the 1238 keV−76.5 keV cascade. The data were most consistent with an assignment of 2 − for the 1315 keV level in Yb 174.

Polarization Correlation Measurements onEu154

The spins and parities of the 1400- and 1723-kev levels in ${\mathrm{Gd}}^{154}$ are discussed on the basis of the polarization-directional correlation measurements on the 1277-123 and 725-998 kev gamma-gamma cascades following the $\ensuremath{\beta}$ decay of ${\mathrm{Eu}}^{154}$. In the case of the 1277-123-kev cascade, directional correlation measurements and the polarization correlation measurements of the 1277-kev gamma ray are made with liquid and solid sources. An attenuation in the anistropy of directional correlation and in the degree of linear polarization correlation has been observed in both the sources, the attenuation in the solid source being greater. In the 725-998 kev cascade, the polarization of either of the two radiations has been measured in two separate experiments. On the basis of these measurements, the spins and parities of both the 1400- and the 1723-kev levels in ${\mathrm{Gd}}^{154}$ are assigned ${2}^{\ensuremath{-}}$. The performance of the apparatus has been checked by measuring the polarization correlations of known cascades in ${\mathrm{Ni}}^{60}$, ${\mathrm{Ti}}^{46}$, ${\mathrm{Pd}}^{106}$, and ${\mathrm{Sr}}^{88}$.

3.14-hr Isomeric Level inY90

s produced in Y/sup 90/ by thermal neutron irradiation of Y/sup 89/. The thermal capture cross section for the production of the isomer was measured to be 1.0 plus or minus 0.2 mb. The decay of the isomeric level is characterized by the emission of two cascade gamma rays of 0.482 and 0.203 Mev. Conversion coefficient measurements indicated that the isomeric level at 0.685- Mev decays by M4 or E5 radiation to an intermediate level at 0.203 Mev followed by a predominantly M1 transition to the ground state of Y/sup 90/. Gamma-gamma directional correlation measurements and internal conversion measurements indicated that the level at 0.203 Mev has spin 3 with odd parity and that the level at 0.685 Mev has spin 7 or 8 with even parity. A shell-model configuration of (g/sub 9/2/ d/sub 5// /sub 2/) was assigned to the isomeric state. (auth)

Level Structure of Nd144

The energies and spins of lower excited levels in Nd 144 have been established by studies of the beta decay of Ce 144 –Pr 144 and the electron capture decay of Pm 144 . The experiments include the energy and relative intensity measurements, and directional correlation measurements of gamma rays by several NaI (T1) scintillation counters. The level of Nd 144 is populated at the 695 keV and 2190 keV from decay of Pr 144 , and the 695 keV, 1310 keV, and 1780 keV from the decay of Pm 144 . The levels at the 1220 keV and the 1560 keV which have been found by the neutron capture gamma ray measurements could not be found in both decay in the limit of about one percent.

Directional Correlation Measurements inHf178

Measurements of the directional correlations of the 1335-93 kev, 1345-93 kev, and 1390-93 kev $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ cascades in ${\mathrm{Hf}}^{178}$ have been made, using a liquid source of 21-day ${\mathrm{W}}^{178}$ in equilibrium with 9.3-min ${\mathrm{Ta}}^{178}$. It is shown that the data support the tentative spin assignments of Gallagher et al. The 1390-kev $\ensuremath{\gamma}$ ray is found to be almost pure quadrupole radiation. If the spin and parity of the 1430-kev level is 1+, as suggested by Gallagher et al., the multipolarity of the 1335-kev $\ensuremath{\gamma}$ ray is determined by our measurements to be mainly $M1$. Using these results, the amount of $E0$ radiation in the 1309-kev transition has been estimated. It is found that approximately 70% of the 1390-kev $K$-conversion electrons are due to monopole transitions.

Gamma-Gamma Directional Correlations inNd147

Directional correlation measurements have been made on the 320- to 92-kev and 280-to 320-kev gamma-ray cascades in ${\mathrm{Pm}}^{147}$ following the decay of 11.1-day ${\mathrm{Nd}}^{147}$ with a coincidence scintillation spectrometer using NaI detectors. The observed correlation functions are: $W(\ensuremath{\theta})=1\ensuremath{-}(0.1030\ifmmode\pm\else\textpm\fi{}0.0298)$ ${P}_{2}(cos\ensuremath{\theta})+(0.0107\ifmmode\pm\else\textpm\fi{}0.0099)$ ${P}_{4}(cos\ensuremath{\theta})$, and $W(\ensuremath{\theta})=1+(0.0710\ifmmode\pm\else\textpm\fi{}0.0162)$ ${P}_{2}(cos\ensuremath{\theta})\ensuremath{-}(0.0126\ifmmode\pm\else\textpm\fi{}0.0103)$ ${P}_{4}(cos\ensuremath{\theta})$, respectively, for the two cascades. The energy levels of ${\mathrm{Pm}}^{147}$ at ground state, 92 kev, 410 kev, and 690 kev were found to be ${\frac{7}{2}}^{+}$, ${\frac{7}{2}}^{+}$, ${\frac{7}{2}}^{+}$, and ${\frac{5}{2}}^{+}$, respectively. It was found that the 92-kev gamma ray has a mixture of (95\ifmmode\pm\else\textpm\fi{}2)% $M1$ and (5\ifmmode\pm\else\textpm\fi{}2)% $E2$ with ${\ensuremath{\delta}}_{92}=+(0.229\ifmmode\pm\else\textpm\fi{}0.143)$, the 320-kev gamma ray has a mixture of 1% $M1$ and 99% $E2$ with ${\ensuremath{\delta}}_{320}=+9.95\ifmmode\pm\else\textpm\fi{}0.11$, and the 280-kev gamma ray has a mixture of 99% $M1$ and 1% $E2$ with ${\ensuremath{\delta}}_{280}=\ensuremath{-}0.11\ifmmode\pm\else\textpm\fi{}0.11$.

Gamma-Gamma Directional Correlations inCs133

Directional correlation measurements were made on the 356 to S2 kev, 301 to 82 kev, and 8O to 82 kev gammagamma cascades in Cs/sup 133/ following the decay of 8-year half-life Ba/sup 133/ with a coincidence scintillation spectrometer using NaI detectors. The observed correlation functions are: W( theta ) = 1. + (0.042 theta 0.005) P/sub 2/ (cos theta ) - (0.0041 plus or minus

Levels in Gd 156 fed by the decay of 15-day Eu 156

Radiations following the decay of 15-day Eu 156 have been studied using the techniques of coincidence scintillation spectrometry and 4π beta counting. Twenty-eight gamma rays were identified as transitions from excited levels in Gd 156. The energies of these gamma rays, along with their coincidence relationships, indicate that levels are present in the daughter nucleide at 89, 290, 520, 1150, 1240,1250, 1320, 1360, 1960, 2030, 2180 and 2200 keV, Gamma-gamma directional correlation measurements have been made leading to spin assignments for the levels at 1320, 1960 and 2030 keV.

Directional and Polarization Correlation Studies in the Decay of 5-hourSb118

Directional and polarization correlation measurements have been carried out on the gamma rays accompanying the decay of 5-hour ${\mathrm{Sb}}^{118}$. These measurements lead to the following spin and parity assignments for excited levels in ${\mathrm{Sn}}^{118}$: 1.22 Mev (${2}^{+}$), 2.25 Mev (${4}^{+}$), and 2.51 Mev (${5}^{\ensuremath{-}}$). A search for positrons was made, and an upper limit on positron emission was set at 0.2% of the 1.22-Mev decays, giving a lower limit of 2500 hours for the partial half-life of positron emission to any of the excited levels in ${\mathrm{Sn}}^{118}$. The level scheme is discussed in terms of various nuclear models.

Level Structure ofEu153

Gamma rays in ${\mathrm{Eu}}^{153}$ following the decay of ${\mathrm{Sm}}^{153}$ and ${\mathrm{Gd}}^{153}$ have been studied using coincidence and angular correlation methods. Results for the strong transitions are in agreement with the decay scheme given by McCutchen. Measurements were made of spectra of gamma rays in coincidence with the x-ray, 70-kev, and the 97-kev and 103-kev transitions in the decay of ${\mathrm{Gd}}^{153}$, and with eight energy regions in the decay of ${\mathrm{Sm}}^{153}$. A number of new, weak transitions were observed in the decay of ${\mathrm{Sm}}^{153}$, and a consistent decay scheme is proposed. Directional correlation measurements were made on the 70 kev-103 kev cascade from the decay of ${\mathrm{Sm}}^{153}$ and from the decay of ${\mathrm{Gd}}^{153}$. Possible spin assignments are discussed.

Radioactive Decay ofPm143,Pm144, andPm146

The decay of ${\mathrm{Pm}}^{143}$, ${\mathrm{Pm}}^{144}$, and ${\mathrm{Pm}}^{146}$ has been studied with permanent magnet spectrographs, an intermediate-image beta spectrometer, and scintillation counters. Results on the electron-capture decay of ${\mathrm{Pm}}^{143}$ and ${\mathrm{Pm}}^{144}$ confirm the findings of previous investigators. The results of gamma-gamma directional correlation measurements are consistent with the spin assignments for the ${\mathrm{Nd}}^{144}$ levels made by Ofer. ${\mathrm{Pm}}^{146}$ (${T}_{\frac{1}{2}}\ensuremath{\sim}710$ days) is found to decay both by beta emission to a level of 749 kev in ${\mathrm{Sm}}^{146}$ and by electron capture to levels of 453 and 1198 kev in ${\mathrm{Nd}}^{146}$. The percentage branchings are 35%, 35%, and 30%, respectively. Gamma-ray transitions of 453 and 745 kev in cascade in ${\mathrm{Nd}}^{146}$ and 749 kev in ${\mathrm{Sm}}^{146}$ are observed. The end-point energy for the beta-decay branch is measured to be 779 kev. Directional correlation and internal conversion coefficient measurements are most consistent with a 3+ assignment for the 1198-kev level in ${\mathrm{Nd}}^{146}$, with a 2+ assignment being possible, but less likely, since the cross-over transition is absent or extremely weak.

Evidence forO+and1−Levels inU234Populated in the One-Minute Beta Decay ofPa234

A directional correlation measurement has been performed on the 250-kev vs (751+795)-kev composite cascade in ${\mathrm{U}}^{234}$ following the 24-day beta decay of ${\mathrm{Th}}^{234}$ and the subsequent one-minute beta decay of ${\mathrm{Pa}}^{234}$. The "770"-kev (751+795 kev) composite photopeak spectrum coincident with the 250-kev gamma ray was displayed on a multichannel pulse-height analyzer for different positions of the scintillation counters. From these spectra the directional correlations between the 250-kev gamma ray and the lower and upper sides of the 770-kev composite line were measured. The results together with other measurements are consistent with assignments of multipolarity $E1$ to the 250-, 751-, and 795-kev gamma rays and spin and parity assignments ${0}^{+}$-${1}^{\ensuremath{-}}$-${2}^{+}$ and ${0}^{+}$-${1}^{\ensuremath{-}}$-${0}^{+}$ to the levels involved in the 250-751 kev and 250-795 kev gamma-gamma cascades, respectively. Thus new levels are proposed at 795 and 1046 kev with spin and parity ${1}^{\ensuremath{-}}$ and ${0}^{+}$, respectively.

Decay of 45-DayFe59

The gamma rays following the decay of 45-day ${\mathrm{Fe}}^{59}$ have been studied using the techniques of gamma-ray scintillation spectrometry, including $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ directional correlation measurements. In addition to the previously reported 0.192-, 1.10-, and 1.29-Mev gamma rays, two additional gamma rays having energies of 0.145 and 0.337 Mev were observed. These latter two arise from a state at 1.43 Mev in ${\mathrm{Co}}^{59}$. All gamma rays were observed to decay with a half-life of 45\ifmmode\pm\else\textpm\fi{}5 days. Directional correlation measurements on the 0.14-1.29 Mev and 0.19-1.10 Mev cascades were performed. The results of these measurements, together with the gamma-ray relative intensities, suggest an assignment of \textonehalf{}- to the 1.43-Mev state in ${\mathrm{Co}}^{59}$.

Directional Correlation of the Gamma Rays inW182

Directional correlation measurements were performed on seven cascades involving the gamma rays in W/sup 182/. The angular momenta of the excited states and the character of the gamma transitions which were determined by the correlation measurements are in good agreement with the values as determined by previous investigators. There is evidence for the exisience of three rotational bands with the possibility of a fourth band in W/sup 182/. The nature of these rotational bands is explained in terms of the BohrMottelson model for spheroidal nuclei. The levels are characterized by the quantum numbers (K. I, pi ). After correction for x-ray interference the 1.222 Mev--0.068Mev correlation results in a spin of 3 to the 1.290-Mev level. The 0.068-Mev garnma ray is essentially pure dipole radiation. The results of the 1.231 Mev--0.100-Mev correlation are in good agreement with spin 3 to the 1.331Mev level with a quadrupole content of 2 plus or minus 0.5% for the 1.231-Mev radiation. The 0.152 Mev-1.222-Mev correlation is only in agreement with an assignment of spin 3 to the 1.374-Mev level with a quadrupole content of less than 0.5% for the 0.152-Mev transition. The 0.152 Mev-1.122Mev correlation yields a quadrupole content of (3-11% or 94-- 99%)more » for the 1.122-Mev transition. The 0.222 Mev1.231 Mev, 0.264 Mev-1.222-Mev correlations are in good agreement with the assignment of spin 4 to the 1.554-Mev level. However, spins of 3 or 5 for the 1.554-Mev level are also in agreement with the oorrelation data. (auth)« less

Decay ofSm155

${\mathrm{Sm}}^{155}$ was found to decay to ${\mathrm{Eu}}^{155}$ with a half-life of 21.9\ifmmode\pm\else\textpm\fi{}0.2 minutes. Internal conversion electrons corresponding to the gamma rays in ${\mathrm{Eu}}^{155}$ were observed in a magnetic spectrometer. The gamma ray spectrum was studied with a well crystal. The spectra of gamma rays coincident with the x ray, 104-kev, 142-kev, and 246-kev gamma rays were observed. A number of new, weak transitions are proposed. Directional correlation measurements were made on the 142-kev---104-kev cascade. Possible spin assignments are discussed.