keV Cascade Research Articles

Level structure and gamma-gamma directional-correlation studies in147Pm

The level structure of147Pm is studied with a high-efficiency sum coincidence spectrometer. The levels at 182, 320 and 725 keV are confirmed and their decay modes are also proposed. The gamma-gamma directional correlations involving the (194–531) and (595–91) keV cascades in147Pm are studied. The spin of the 725 keV level is established to be 5/2+. The mixing ratios for the 194 and 595 keV gamma transitions are estimated to be δ=−3.65±0.84 and 0.27±0.11, respectively. The half-life of the 686 keV level determined by a slope method employing a delayed-coincidence technique isT1/2=(0.22±0.01) ns. The experimentalM1 andE2 transition probabilities of the gamma-rays following the decay of the 686, 531, 410 and 91 keV levels are compared with the single-particle estimates.

Gamma-Gamma Directional Correlation in the Decay of 168Tm

Time-integral and time-differential gamma-gamma directional correlation measurements were performed for cascades in 168 Er populated from the decay of 168 Tm (90d.). The mixing parameters of most of the intense gamma-rays have been determined more precisely than ever. Some ambiguities concerning to the directional correlation coefficients of the 447–198 keV and 447–830 keV cascades were well removed. The directional correlation coefficients of these cascades were determined as A 22 =0.009 ±0.003 and -0.067 ±0.008, respectively, and A 44 ≈0 for both. The mixing parameters of the 198-, 447- and 830-keV gamma-rays were determined as δ(198)=0.13 ±0.02, δ(447)=0.09 ±0.01 and δ(830)=0.05 ±0.03, respectively. The transition probabilities of the gamma-rays deexciting the 1094-keV level are deduced on the basis of this work.

Electric quadrupole interaction and its temperature variation at100Rh in Be metal

The nuclear quadrupole interaction at the100Rh probe nucleus in a Be host is measured from 4.2–968 K using time-differential perturbed γ-γ angular correlations of the 84–75 keV cascade in the de-excitation of100Rh. The sources were prepared by recoilimplanting the parent100Pd activity produced in a heavy-ion reaction. The temperature variation of the electric field gradient can nicely be fitted by aT3/2 law.

Determination of solid angle corrections for precise gamma-gamma directional correlation experiments with Ge-detectors

An experimental method is described to determine angle dependent attenuation factors due to the finite solid angle in gamma-gamma directional correlations with Ge-detectors. The correction factors have been calculated a.o. for the 622-512 keV (0 +−2 +−0 +) cascade in 106Pd. Data from a correlation experiment on this cascade have been fitted to the factors and produced A 2 and A 4 anisotropy coefficients within 1% of the theoretical values. Angle independent correction factors obtained from Monte-Carlo calculations and from a horizontal scan method have been used in a comparison with the mentioned results. This comparison has shown that differences of more than 10% can arise by using these methods. An extended measurement yielded A 2 and A 4 coefficients for the (0 +−2 +−0 +) cascade in 106Pd. The values are: A 2 = 0.356(2) and A 4 = 1.143(3), very close to the theoretical ones.

Level Structure of82Kr

The level structure of 82 Kr, from the decay of 35.3 h 82 Br, has been investigated using a 64.1 cc Ge(Li) detector (FWHM≈2.1 keV at 1.33 MeV) in singles mode and Ge(Li)–NaI(Tl) (64.1 cc and 3''×3'' respectively) detector set-up in coincidence mode (2τ=6 nsec). These measurements confirmed the existence of 129.22, 180.5, 280.8, 332.5, 470.28, 735.7, 1 173.3, 1427.2 and 1871.7 keV weak gamma ray transitions, while the 345.65, 599.5, 625.5, 692.7, 726.8 and 932.1 keV gamma rays reported earlier, could not be observed. The gamma-gamma directional correlation measurements have been done on 15 cascades, out of which the 221–(606)–1044, 273–1014, 606–1044 and 221–1650 keV cascades have been attempted for the first time. Based on these measurements, the spin 3 + has been confirmed for the 2426.79 keV level in 82 Kr. Also the multipole admixtures in the 221.34, 273.45, 606.30, 619.07, 698.32, 827.81, 1007.57, 1043.98, 1317.46 and 1650.28 keV gamma transitions have been evaluated.

Angular correlation measurements of207Bi

Gamma-gamma angular correlation measurements of the 569·65 keV–1063·63 keV cascade in the decay of207Bi were carried out with two NaI (Tl) detectors of size (3″×3″) and (1·5″×1″). Graphical methods of Arns and Wiedenbeck (Phys. Rev.111 (1958), 1631) were applied in determining the mixing ratio of gamma 1063·63 keV transition. The parametric plot was done by the method described by C. F. Colman (Nucl. Phys.5 (1958), 495). The mixing ratio of gamma 1063·63 keV transition was thus found to be $$|\delta | = 0.036_{ - 0.064}^{ + 0.034} .$$ .

Sudden change of quadrupole moment between the first [formula omitted]− states of 197Hg and 199Hg

Low-temperature time differential perturbed angular correlation experiments with the 164 keV-134 keV cascade of 197mHg in a zinc matrix give evidence that the hitherto accepted value of the quadrupole moment of the first 5 2 − state of 197Hg is erroneous. A new value is derived from a time differential perturbed angular correlation experiment with the 374 keV−158 keV cascade of 199mHg implanted into a Be single crystal and comparison with an analogous experiment for 197mHg. Taking Q( 5 2 −, 199Hg) = +0.95(7) b we derive |Q( 5 2 −, 197Hg)¦= 0.081(6) b . This change of quadrupole moment is discussed in the framework of the shell model.

Simulations of Cascade Damage in Silicon

In an effort to better understand radiation damage to electronic materials, we use the binary-collision simulation code MARLOWE to model displacement cascades in silicon. We examine the average number of displacements produced by knock-on atoms as a function of their energy. The resulting vacancy-interstitial pairs are classified according to separation radius. We also examine a few particular cases of 100 keV cascades in silicon in order to highlight the importance that channeling has on the shape of displacement cascades.

The structure of the low-lying energy levels in 187Re

Gamma radiations and conversion electrons in the decay of 23.9 h 187W to 187Re have been investigated using Ge(Li) detectors and a Si(Li)-Ge(Li) conversion electron spectrometer. Forty-one γ-ray lines are observed, including seven new lines. Gamma-gamma angular correlations of the 551.57−134.25, 479.56−72.02, 479.56−(72.02)−134.25, 72.02−134.25 and 246.33−618.35 keV cascades have been measured. From the measurements of the conversion coefficients and the γ-γ angular correlations, the E2/M1 mixing ratios were determined as δ(134.25) = 0.184 ± 0.003, δ(238.82) < |0.9|, −2.0 < δ(246.33) < −0.2, δ(589.12) = |0.58 +∞ −0.58|, −1.5 〈 δ(618.35)−0.4 and δ(772.85) = |0.41 +0.28 −0.41|. Theoretical calculations based on the Nilsson model in which Coriolis coupling and quasiparticle-phonon and rotation-vibration interactions are taken into consideration have been performed. The low-lying levels could be assigned to the Nilsson states mixed with the quadrupole vibrations: β vibration (K = Ω) and γ ± vibration ( K = Ω ± 2). Good agreement between experimental and calculated energy levels was obtained and the calculated mixing ratios were consistent with experimental results.

The application of dynamical computer models to high energy cascades

A modification of the quasi-dynamical computer code ADDES has been developed to allow for the simulation of defect production in high energy cascades. In the first of a two-stage modeling process, the cascade is allowed to develop until no atom has more than a relatively high cut-off energy. As atoms fall below the cut-off, they are tagged and removed from consideration during the remainder of the development. The second stage is the evaluation of defect production by energetic atoms tagged in the first stage using a defect yield function determined from dynamical simulations of low energy events. This code is used to simulate defect production in 10 keV cascades in several directions in copper, and the results are compared with those of the binary collision code MARLOWE. Good agreement is obtained when an effective recombination radius of 2.2 lattice parameters is assumed.

Low-lying energy levels in 166Ho

The properties of some low-excited states of 166Ho have been studied using thin, high resolution Ge detectors. The relative intensities of γ-lines were determined. The directional angular correlation measurements for the 28.23–54.24 keV cascade are in agreement with the 1 −(M1)2 −(E2)0 − spin sequence. The magnetic moment μ = 0.068 ± 0.010 μ N of the 54.24 keV level was determined by integral perturbed angular correlation (IPAC) in an external magnetic field. This value can be explained by the configuration mixing due to the Coriolis interaction.

Energy levels and γ-ray transitions in 147Pm

Gamma rays emitted in the decay of 147Nd have been studied using Ge(Li) detectors as singles and coincidence spectrometers. Four new γ-rays of 53.1, 81.15, 149.4 and 191.24 keV have been detected and all incorporated into the decay scheme. Angular correlation measurements for the 275–319, 275–411 and 272–408 keV cascades have yielded the following result: A 2(275–319) = 0.006(2), A 4(275–319) = 0.005(5), A 2(215–411) = −0.013(17), A 4(275–411) = −0.008(30), A 2(272–408) = −0.283(10) and A 4(272−408) = 0.015(18). From these coefficients the E2/M1 mixing ratios of the 272 and 275 keV γ-transitions have been determined to be 0.10(3) and 0.107(7), respectively, and the spin of the 680.43 keV level to be 7 2 . Theoretical calculations on the intermediate coupling model for harmonic and anharmonic potential functions have been carried out and better agreement with experiment has been obtained for the anharmonic potential function.

Level Structure of124Te

The level structure of 124 Te has been investigated by studying gamma rays emitted following the beta decay of 124 Sb to the excited states of 124 Te. The intensities of 70 gamma rays observed in this decay have been measured with a better precision than known earlier. The existence of the gamma rays with energies of 1248.62 and 1731.4 keV has been confirmed, whereas the 159.4, 185.4, 385.9, 476.6, 498.4, 553.8, 997.0, 1163.2, 1388.7, 1505.6, 1557, 1950.4, 2151.5 and 2274.0 keV gamma transitions reported earlier have not been observed in the present investigations. The gamma-gamma angular correlation measurements for nine cascades populated in this decay have been done out of which 791-(646)-603 keV cascade has been attempted for the first time. From these measurements, the multipole admixtures in the 714, 723, 791, 968, 1045, 1368, 1691 and 2091 keV transitions have been obtained. These angular correlation studies have enabled us to assign 2 + and 3 - characters to the levels at 2039.5 and 2694.0 keV res...

The Level Structure of Tm169

The energies and intensities of various gamma ray transitions in Tm 169 nuclide populated in the electron capture decay of Yb 169 have been measured using a 64.1 cc. Ge(Li) detector coupled with 4096 channel analyser. The coincidence measurements have been made using Ge(Li)–NaI(Tl) slow-fast coincidence set up. The singles and coincidence measurements confirm the existance of 285, 295, 304.0, 328.0, 336.5, 354.7, 370.8, 579.5 and 600.3 keV γ-transitions from the decay of Yb 169 . The presence of 718.5 keV level in the level scheme of Tm 169 is also confirmed from the electron capture decay of Yb 169 . In addition to the energy and intensity measurements, gamma-gamma angular correlation measurements on five cascades, namely 198–118, 198–110, 261–110, 177–130 and 177–(21)–110 keV have been done using Ge(Li)–NaI(Tl) fast coincidence set up. Out of these, the 261–110 keV cascade has been attempted for the first time. On the basis of these measurements, the multipole mixing in 261, 198, 177, 130 and 110 keV γ-...

Properties of the 635.4 keV level in171Tm

The properties of some high excited states of171Tm have been studied using Ge(Li) detectors. The directional angular correlation measurements for 277.4-210.5 keV cascade are in agreement with the spins of the 635.4 keV© and 912.8 keV(5/2) levels. The magnetic momentμ=(1.15±0.21)μN of the 635.4 keV level was determined by integral perturbed angular correlation (IPAC) in external magnetic field.

Levels ofPb200and isomers

In-beam measurements of internal-conversion electrons and ..gamma.. rays from /sup 1/98Hg(..cap alpha..,2n)/sup 2/00Pb are reported. The most recent yrast level scheme, used by several other groups, is found to be in error since the 480-ns state is not primarily deexcited by an 84-keV transition. This transition must instead be less-than-tilde 43 keV. The primary deexcitation of the 158-ns state must be less-than-tilde - 50 keV. The 778-keV high-spin transition is measured as E1. The multipole orders of the transitions in the 245 ..-->.. 420 ..-->.. 462 ..-->.. 1026 keV cascade are measured as E2, E1, E2, and E2, respectively.

Gamma-gamma directional correlation study in92Zr

The gamma-gamma directional correlation of the 2+′-2+-0+, 913(Iγ=1.69)-934(Iγ =100)keV cascade in92Nb decay has been investigated with a NaI-Ge(Li) system. Our results yieldδ=−0.013 −0.024 +0.041 . This is one of a very few cases where the second 2+ to first 2+ transition is not predominatelyE2. This may be related to the closed neutron shell, as earlier suggested. [Radioactivity92Zr; measuredγ-γ(θ), deducedδ]

Nuclear level structure of low lying levels of109Cd

Nuclear level structure of low lying levels of109Cd from109In decay has been investigated by gamma-gamma angular correlation experiments using a Ge(Li)-NaI(Tl) fast coincidence arrangement. From the measurement on the 347.4−326.3, 347.4–650.1, 287.7–650.1, 203.3–420.5, 203.3–619.3 keV cascades spin-parity assignments of 5/2+,1/2+,7/2+,5/2+, 7/2+,5/2+,9/2+, and 9/2+, have been made to the ground, 59.5, 203.3, 347.4, 623.8, 673.7, 822.5 and 997.5 keV states, respectively, of109Cd. The results have been discussed and compared with the previous works.

Effect of source preparation technique on the differential angular correlation of the 133–482 keV cascade in 181Ta

By using a standardised method of source preparation and an ultra-fast coincidence circuit the differential angular correlation of the 133–482 keV cascade in 181Ta using sources of Hf(OH) 4 in HF, HClO 4, HCl, HNO 3, H 2SO 4, and CH 3COOH medium has been measured. The results are (1) no attenuation in HF, (2) λ 2=(4.0±0.3) × 10 7 s −1, λ 4=(6.6±2.8) × 10 7 s −1 in HClO 4, (3) λ 2=(7.8±0.3) × 10 7 s −1, λ 4(13.0±1.8) × 10 7 s −1 in HCl,(4) λ 2=(9.5±0.5) × 10 7 s −1, λ 4=(11.4±3.9) × 10 7 s −1 in HNO 3, (5) λ 2=(26.1±0.2) × 10 7 s −1 in H 2SO 4, and (6) a two-exponential decay in CH 3COOH medium with λ 1 2=(4.1±0.2) × × 10 8 s −1 and λ 2 2=(0.14±0.02) × 10 8 s −1. The experiments in HClO 4 and HNO 3 medium are new. The other results are compared with the nature and magnitude of the results obtained by other workers in terms of the chemistry of Hf-ions in solution.

The nuclear structure of 151Pm in the low excitation region < 1 MeV

The level scheme of 151Pm populated by the β-decay of 12 min 151Nd has been studied using Ge(Li) detectors as singles and coincidence γ-ray spectrometers. Most of the new γ-rays have been included in a partial level scheme of 151Pm involving four new levels. Angular correlation measurements on the 170.752–255.678 keV and 170.752–138.882 keV cascades have been made with the result A 2 = 0.088±0.005 and −0.02 – +0.05, respectively. A PAC measurement on the 170.752–255.678 keV cascade has yielded the g-factor of the 255.676 keV level as g = 1.18 ±0.16. A Nilsson-model calculation including Coriolis coupling has been made and the experimental level energies have been well reproduced by the Nilsson orbitais [413]↓, [411]↑, [420]↑, [532]↑, [541]↑ and [550]↑. Theoretical transition rates, E2/M1 mixing ratios, branching ratios and g-factors are in good agreement with experimental values.