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Decay Scheme of the Isomers of Te129
Abstract
The decay of 70-min Te129 and 33-day Te129m has been studied using a beta-ray spectrometer, scintillation spectrometers, and coincidence techniques. The 70-min activity, studied in equilibrium with Te129m and also independently, was seen to emit gamma rays of energies 27, 205, 245, 275, 350, 455, 550, 625, 755, 810, 825, 960, 1080, and 1235 keV. From coincidence relationships among these gamma rays, it was concluded that levels at 27, 275, 350 or 755, 482, 550, 810, 1105, and 1235 keV are excited in the decay of the 70-min activity. Te129m was observed to decay by the emission of gamma rays of energies 550, 695, 720, and 830 keV in addition to the 106-keV isomeric transition. These gamma rays were attributed to the excitation of levels at 695, 830, 1385, and 1415 keV. The Fermi plot of the beta spectrum of Te129m studied with a Siegbahn-Slätis spectrometer showed beta groups with end-point energies of 1595, 1452, 976, and 690 keV. From beta-gamma coincidence measurements it was concluded that 1595 keV is the end-point energy of the beta transition from Te129m to the ground state of I129 while 1452 keV is the end-point energy of the beta transition from the 70-min activity to the 27-keV level. Comparison of the total intensities of the beta transitions from Te129m and Te129 showed that the isomeric transition takes place with a branching ratio of 0.64. The ft values for the various beta groups were found from their relative intensities and spin assignments to various levels were made on this basis.
The 1983 evaluation of A = 129 (83Ha46) has been updated using experimental decay and reaction data received by the cutoff date noted below.Cutoff Date:All data available before December 31, 1995, have been considered for inclusion in this evaluation.General Policies and Organization of Material:See the January issue of Nuclear Data Sheets.Acknowledgments:The author would like to thank the staff of the Nuclear Data Center, Japan Atomic Energy Research Institute, for their support. The many useful comments and suggetions by the reviewer and Editor-in-Chief, are gratefully appreciated. I also thank T. Tamura for his helpful comments, and Y. Kidachi for her aid in the preparation of this evaluation.
The radiations from I129 have been restudied using a Ge(Li) detector, scintillation detectors and coincidence and sum-coincidence techniques. The Te129m source was prepared by the irradiation of enriched Te128 with thermal neutrons, followed by chemical separation. Using a 4 keV resolution Ge(Li) detector, gamma rays were found at energies of 27, 208, 250, 278, 280, 343, 345, 460, 487, 532, 557, 573, 624, 673, 697, 730, 742, 804, 819, 837, 848, 982, 1022, 1050, 1083, 1112, 1233, 1262 and 1400 keV. From coincidence and sum-coincidence studies on these transitions, it was concluded that excited levels are populated at 27, 278, 343, 487, 557, 697, 730, 831, 846, 1022, 1050, 1083, 1112, 1262, 1378, 1404 and 1427 keV. Gamma-ray intensities were calculated from the Ge(Li) spectra.
The quantum radiations emitted in the decay of Te129m-Te129 have been investigated with application of a Ge(Li) detector, scintillation counters, coincidence techniques, and multichannel analysis. In addition to the well-known 27-keV gamma ray, twenty-three others have been detected at energies of 205, 250, 273, 277, 340, 448, 455, 482, 523, 548, 550, 630, 660, 698, 725, 770, 797, 810, 835, 945, 1085, 1112, and 1222 keV. Thus, six pairs of gamma rays are present which exhibit within each pair an energy difference of 27 keV. Excited states in I129 are established at 27, 277, 482, 550, 725, 797, and 1112 keV by this energy difference. Additional excited states are found at 837, 1065, 1222, and 1385 keV by coincidence experiments.
At low excitation energies a "constant nuclear temperature" representation of nuclear-level densities is used, and at high excitation energies the regular Fermi gas formula is adopted. A method is developed for determining the parameters of the Fermi gas formula by using both the pairing and the shell-correction energies found by Cameron and Elkin for their semiempirical atomic mass formula in its exponential form. This procedure determines level densities at neutron-binding-energy excitations subject to an average factor error of 1.8. Methods are also developed for determining the parameters for the lower-energy formula in such a way that it best fits the lower-energy levels and joins smoothly to the Fermi gas formula. Correlations of the resulting parameters with shell and pairing effects are found. A composite prescription is given for calculating level densities in nuclei for which no experimental information is known. Tables give level density parameters for a wide variety of nuclei for which some experimental information is known. Some of the derivations of the Fermi gas formula in the literature were found to be slightly incorrect, so new derivations are presented in Appendixes.
Penetration factors lambda are calculated for l-forbidden M1 transitions for the nuclei 119,121,125Sb 129,131I, 143pr and 147,149Pm. The penetration matrix elements Me are calculated in a unified model, according to the general formulae of Church and Weneser. Gamma transition matrix elements Mgamma are calculated from experimental half-lives and total conversion coefficients. Where experimental K-conversion coefficients and L-subshell ratios are available, experimental penetration factors lambda are determined from these data. The L-subshell ratios are re-analysed with the use of the penetration effects.
The Mössbauer effect of the 26.8-keV transition in I129 has been studied in a number of iodine compounds. The following results have been obtained: (a) The isomeric shifts for the alkali iodides were found to be linearly dependent on the number of 5p holes in the iodine ion. From this dependency, a calibration of the isomeric shift scale in terms of the 5s-electron density was obtained. The s and p populations inferred from these data are in sharp disagreement with those predicted by the simple theory of electronegativity. An explanation for this discrepancy is given. (b) From the calibration mentioned under (a), a relative change of nuclear radius DeltaRR=(R26.8- Rgnd)Rgnd=3×10-5 is computed. (c) The isomeric shifts for some iodates indicate that their 5s-electron density is about 18% larger than that of the iodides. This increase is caused by the partial removal of 5p electrons from iodine in the I-O bonds, which results in reduced screening of the 5s electrons. The shift for potassium periodate implies that the 5s-electron density is decreased by 33% compared to the iodate. This decrease is attributed mainly to the sp hybridization of the I-O bonds in KIO4. The average charge removed per I-O bond, calculated from the isomeric shifts of the iodates and periodate, is 0.61 e. (d) The quadrupole splitting of KIO3 was used to determine the I129 quadrupole ratio, Q26.8Qgnd=1.23+/-0.02. The asymmetry of the iodate spectrum and the sign of the quadrupole moment show that the sign of the iodate field gradient is negative. The values of the quadrupole coupling constant, eqQ, at 80°K for KIO3 and NH4 IO3 are in agreement with nuclear-magnetic-resonance results and eqQ127=1030+/-20 Mc/sec for Ba(IOa)2. (e) The recoilless fraction f was found to deviate from 0.26 by less than 25% for all alkali iodides at 80°K.
The half-life of the 26.8 keV level in I129 has been measured by the delayed coincidence (logarithmic slope) method and is found to be in good agreement with some of the earlier measurements.
The decay of Sb129 has been studied with Li-drifted germanium and scintillation spectrometers. Singles and beta-gamma and gamma-gamma coincidence spectra were observed. Gamma rays with energies 180, 296, 358, 410, 523, 544, 652, 683, 760, 813, 876, 916, 967, 1028, 1048, 1240, 1300, 1520, 1730, 1840 and 2070 keV, and beta branches with end-point energies 0.58, 0.70, 1.06, 1.55, 1.82 and 2.24 MeV were found. The relative intensities of these gamma and beta rays were estimated. The half-life of Sb129 was determined to be 4.35± 0.05 h. The present data are consistent with a level scheme with states at 544, 813, 1227, 1637, 1729, 1841 and 2064 keV.
Normalized expansion coefficients A22 = -0.0148 +/- 0.0029 and A44 = -0.0068 +/- 0.0043 have been found for the angular correlation of the 460 keV-27.7 keV cascade in 129I, in contradiction with some earlier measurements. These results are consistent with a spin 3/2 or 5/2 assignment of the 487 keV level. For both spins the E2/M1 mixing ratio of the 460 keV transition is given. Unfortunately, no conclusion can be drawn about the sign of the mixing ratio of the 27.7 keV transition. Present address: Development Laboratories, N.V. Philips Gloeilampenfabrieken, Drachten.
Gamma rays emitted in the decay of 70 min 129gTe and 33 d 129mTe have been investigated with Ge(Li) and NaI(Tl) detectors. Results of Ge(Li)-NaI(Tl) coincidence studies, coupled with relative intensity measurements for both isomers, suggest a decay scheme considerably different from those recently proposed by other workers. Excited levels are placed in 129I at 27.7, 278.4, 487.4, 559.8, 696.0, 729.8, 829.8, 844.7, 1050, 1111.4, 1260, 1291, and 1402 keV. Beta decay of 129gTe feeds all of these except the ones at 696.0, 729.8, 768.9, 844.7, 1050 and 1402 keV. Beta transitions form 129mTe populate all of the latter set of levels and the ground state. The I.T. branching fraction of 129mTe is about 72%. With some exceptions the levels of 129I agree rather well with those predicted by Kisslinger and Sorensen. Considerable evidence for the previously suggested hindrance of beta-decay caused by phonon mixing of the wave functions has been observed. This work was supported in part by the U.S. Atomic Energy Commission under Contract No. AT(30-1)-905.
The properties of the first excited state of I129 have been studied with a mass-separated Te129m source. The energy of this state, as determined from the conversion-electron spectrum, is Egamma=27.72+/-0.06 keV. This differs considerably from the often quoted value of 26.8 keV, but it agrees very well with the value recently published by Bemis and Fransson. An accurate half-life value T12=16.8+/-0.2 nsec was determined from delayed betae- coincidences. A total conversion coefficient alpha=5.3+/-0.3 was obtained from the relative intensities of the 27.7-keV gamma rays and the 27.4-keV x rays that accompany the isomeric transition in Te129. The contributions of these rays were separated by comparing Mössbauer spectra obtained with the 70-min and 33-day activities of Te129. Some remarks are made about the relative merits of these activities for use in Mössbauer sources.
The decay of 129mTe and 129gTe to levels in 129I has been studied using Ge(Li) detectors for high-resolution γ-ray spectroscopy with some supporting data from NaI(Tl) detectors in coincidence. A total of 46 gamma rays is accounted for by 16 excited states (one tentative) in 129I up to 1401.6 keV. These include ten new gamma rays not previously reported, a new level in 129I at 1282.1 keV () and a probable new level at 1204.2 keV () (values of Jπ in parentheses). The decay scheme was arrived at primarily on the basis of precise γ-ray energy determinations (to ±50 eV in many cases and never worse than ±200 eV). Beta-decay log ƒt values were determined from our γ-ray intensity balances coupled with published β-branchings. Most-probable spins and parities were deduced based on the γ-ray branching, the log ƒt value and published angular correlations of other workers. The state predicted by Kisslinger and Sorensen in the region of 200 eV and observed in 125I and 127I is not seen; we find log ƒt≧10.6 for the allowed β-decay from 129gTe to such a level. We likewise find no evidence for the state at ≈ 930 keV as predicted by Kisslinger and Sorensen; the allowed β-decay to this state would have log ƒt ≧ 11.0.
Coincidence and gamma-gamma angular correlation measurements are made for five cascades of 129I, namely, 455-27, 275-275, 205-275, 720-695 and 555-830 keV. The corresponding correlation functions obtained are W(θ) = 1−(0.160±0.033)P2(cosθ)+(0.022±0.060)P4(cosθ), W(θ) = 1+(0.039±0.007)P2(cosθ)−(0.009±0.008)P4(cosθ), W(θ) = 1−(0.104±0.012)P2(cosθ)−(0.010±0.021)P4(cosθ), W(θ) = 1 (within 1%), W(θ) = 1−(0.167±0.036)P2(cosθ)+(0.060±0.080)P4(cosθ).The results indicate spins of for the levels at 275, 482, 550, 695, 830, 1385 and 1415 keV, respectively. The E2/M1 mixing ratio for the 27 keV l-forbidden M1 transition is discussed.
The experimental results from various decays and reactions for the A=129 mass chain have been compiled and evaluated. Adopted values for the level and decay properties are tabulated. Inconsistencies and discrepancies are noted.
The de-excitation γ-ray spectra of 127I, 129I and 133Cs have been studied following Coulomb excitation with 6.0 to 11.0 MeV α-particles. The γ-ray energies, branching ratios and B(E2) values have been determined and angular distribution measurements have been used to assign the spin value of to the 696 keV level in 129I and the 633 keV level in 133Cs. The results have been compared with recent calculations based on the intermediate coupling: unified nuclear model.
The experimental nuclear spectroscopic data for known nuclides of mass number 50 (Cl,Ar,K,Ca,Sc,Ti,V, Cr,Mn,Fe,Co,Ni) have been evaluated and presented together with Adopted properties for levels and γ rays. This evaluation has been carried out about 15 years after the previous one by Thomas Burrows (1995Bu29). Except for 50Sc and 50V, extensive new data have become available for all the other nuclides in the intervening years. The data for 50Sc and 50V have also been checked again in detail and several changes made. No data are yet available for excited states in 50Cl, 50Ar and 50Ni. This work supersedes earlier evaluations (1995Bu29, 1990Bu18, 1984Al29, 1976Au07) of A=50 nuclides.
The literature pertaining to nuclei in the A = 129 mass chain has been examined and the experimental data summarized in the present compilation. A minimum of numerical data is included.Few definitive spin and parity assignments could be made. Decay data for 129Ba indicate the existence of two isomers with nearly equal half-lives. Using unpublished results, the compilers propose these to consist of the g.s., Jπ = 1/2+, and a level at 0.2771 MeV, Jπ = (11/2−).Efforts have been made to indicte apparent discrepancies in the data. The present compilation might serve as a basis for choosing definitive experiments to augment our knowledge of nuclei in this mass chain.
The energy spectra of the odd-proton nucleides 121, 125Sb, 129, 131I, 143Pr and 147, 149Pm, and of the doubly even nucleides 142Ce, 144Nd and 146Sm are described in terms of the unified model in intermediate coupling. The phonon energy of the core, the coupling strength between phonon excitations and single-particle motion, the single-particle energies and the strength of the residual interaction between the single particles are all considered as free parameters and are determined in a least-squares fitting procedure. With the wave functions thus obtained, electromagnetic (M1 and E2) moments and transition rates are calculated. Effective gs factors are determined in a fitting procedure to known magnetic moments; customary effective charges for neutron and proton are used.
The decay of Cd115m was studied by using NaI(Tl) scintillation counters and a 4π beta scintillation spectrometer. The following gamma rays were observed: 0.485±0.007, 0.935±0.014, 1.14±0.017, and 1.29±0.019 Mev. The 0.485- and 0.935-Mev gammas were found to be in coincidence. There were no gammas in coincidence with the 1.29-Mev gamma. The end-point energy of the ground-state beta transition was determined to be 1.631±0.016 Mev. The shapes and end-point energies of the beta groups in coincidence with the 0.935- and the 1.29-Mev gammas were measured. The former has a ΔI=2, yes, character; and the latter appears to have an allowed or statistical shape; the end-point energies are 0.687±0.008 Mev and 0.335±0.010 Mev, respectively.
The energy levels of I129 have been studied through the β− decay of Te129m and Te129 employing two NaI (Tl) scintillation spectrometers in coincidence arrangement. In addition to confirming the presence of the previously known gamma rays of energies 27, 212, 475, 720 and 1120 keV, evidence is found for seven new gamma rays. The new gamma rays have energies of 448, 450, 625, 693, 1073, 1320 and 1520 keV. From the coincidence experiments a probable energy level scheme for I129 is proposed.
The j-j coupling shell model implies the existence of certain geometrical relations among the spectra of neighboring nuclei. We have considered one such relationship between states of a nucleus that is one proton or neutron away from a closed shell with states of the corresponding closed-shell nucleus. Use of this relationship has enabled us to predict excited-state spins for several nuclei, most of which are in the vicinity of mass number 60. In two cases we predict the existence of states that have not been observed.
A coincidence scintillation spectrometer was used to study the decay of the 9.3-hour Te127 isomer and the 72-minute Te129 isomer. The Te127 isomer was found to decay by a simple beta ray with an end-point energy of 0.683+/-0.010 Mev. The beta-ray spectrum of the Te129 isomer consists of two beta groups with end-point energies of 1.46+/-0.01 and 1.01+/-0.02 Mev. Two gamma rays with energies of 0.450+/-0.005 and 0.035 Mev were observed, and they were found to be in coincidence. The 0.450-Mev gamma ray was shown to be in coincidence with the 1.01-Mev beta ray, and the 0.035-Mev gamma ray was shown to be in coincidence with the 1.46-Mev beta ray. The results are consistent with level assignments based on the shell model of the nucleus.
The gamma rays of Te131 and Te129 have been investigated by means of a crystal spectrometer.
Summary If a radioactive source emitting cascadeγ-rays is placed between two well-matched NaI crystal and multiplier units and pulses from the two units are added electronically,
one would get, in the added spectrum, a peak corresponding to the sum of the energies of the cascadeγ-rays. If the pulses in one of the units are analysed in coincidence with the final sum peak, one would get only the photo-peaks
of the cascadeγ-rays. This “sum-coincidence” technique has been applied to the study of theγ-rays of Sc46, Sm153 and Eu154. In Eu154 decay, the cascade emission of 320 Kev., 1280 Kev. and 123 Kev.γ-rays has been established; and it has been shown that there is a level in Gd154 at 1850 Kev. which is fed byβ
−-emission from Eu154 to the extent of about 3%.
The possibility of describing some excited states of odd-$A$ nuclei in terms of excitations of the even-even core is investigated. No assumption is made on the nature of the core excitation, but certain relations involving electromagnetic transitions and moments are deduced. These seem to fit well some data available on ${\mathrm{Ag}}^{107}$, ${\mathrm{Ag}}^{109}$, ${\mathrm{Au}}^{197}$, ${\mathrm{Hg}}^{199}$, ${\mathrm{Tl}}^{203}$, and ${\mathrm{Tl}}^{205}$. More experimental data are required to test the validity of this picture in other cases.
The disintegration of Te129 has been investigated with the help of a magnetic lens spectrometer, permanent field spectrometer with photographic recording, and scintillation counters. The half-lives of the isomeric states in the parent were found to be 41 days and 74 minutes, respectively. The 74-minute state decays to I129 with the emission of beta-ray groups whose end-point energies and relative abundances are 1.453 Mev (71%), 0.989 Mev (15%), 0.69 Mev (4%), and 0.29 Mev (10%). Gamma rays of 0.027, 0.21, 0.475, 0.72, and 1.12 Mev were found. The 41-day state decays, for the most part, to the 74-minute state of Te129 with the emission of a highly internally converted gamma ray of energy 106.3±0.1 kev for which the K/L ratio is unity. A beta-ray transition, of low intensity, from the 41-day state of Te129 to the ground state of the product is postulated. Gamma-gamma and beta-gamma coincidence experiments using scintillation spectrometers served to indicate the probable level scheme of I129. A discussion of the disintegration scheme is given suggesting probable spins and parities of the levels.
Energy levels of I¹²ⷠand I¹²⹠isotopes are calculated on ; the basis of the unified model. Agreement with observed levels is obtained for I/; sup 129/, but there are discrepancies in the case of I¹²â·. (auth);
The low energy gamma spectrum and decay scheme of a Eu¹â´â¹ source ; and the transmission through a Sm¹ⴠabsorber as a function of source ; velocity are presented. The occurrence of resonant absorption shows that at ; least part of the 22-kev radiation results from a transition to the ground state. ; A lower limit to the actual mean life of the state is 4 x 10â»â¹ seconds. ; Assuming M1 transition, the total conversion coefficient is 12, and the lower ; limit to mean life against gamma transition is 5 x 10â»â¸ seconds. (H.D.R.);
The decay of Cd115m has been investigated with scintillation and magnetic spectrometers along with the coincidence technique. Gamma rays of 485-, 930-, 1125-, 1285-, and 1430-keV energy have been observed and their intensities have been calculated from the analysis of the gamma spectrum. Weak-intensity gamma rays of energies 160, 310, 650, and 890 keV have been observed in the coincidence spectra. The shape of the beta transition to the ground state deviates from the statistical shape and the correction factor for this is calculated. The beta spectrum in coincidence with 930-keV gamma ray has been shown to have a unique first-forbidden shape. A decay scheme consistent with these results is presented.
The lifetime of the 26.8-kev level in I¹²⹠was measured as 26.8 ; plus or minus 1.5 nsec from the delay distribution of the 26.8-kev gamma rays ; that follow excitation of the level by BETA particles of maximum energy 1.45 ; Mev. (H.D.R.);
A new method has been developed to measure the spectra of gamma radiation emitted in cascade disintegrations. Use is made of a two-crystal scintillation spectrometer and a gated multi-channel analysing device. The pulses produced by summing the outputs of the two crystal-photomultiplier combinations are selected by a single-channel differential discriminator. The output of this differential discriminator gates the multi-channel analyser whenever the sum pulse corresponds to the release in the crystals of the full energy available in the cascade. The spectrum displayed is that of either of the two detectors. The most important features of the technique are:1.(a) only “full-energy” peaks are detected;2.(b) improved resolution is obtained especially at higher gamma-ray energies;3.(c) one γ-γ or p-γ-γ angular correlation experiment determines the angular correlation of the gamma rays of all double cascades deexciting a given level.Details of operation and typical spectra are presented. It is suggested that the technique be called the “sum-coincidence” method.