keV Cascade Research Articles

Displacement Cascades. Dynamics and Atomic Structure

AbstractThe seminal ideas of Seeger, in 1958 and 1962, on the nature of a displacement cascade (DC) in irradiated crystalline materials have played an important role in the field of radiation damage. This paper first reviews the early history of displacement spikes, replacement collision sequences (RCSs), “diluted” or depleted zones and thermal spikes. Then the use is discussed of molecular dynamics (MD) simulations and field‐ion microscopy as techniques by which one can study the dynamics of the formation of DCs and the spatial array of point defects — on an atomic scale — associated with quiescent DCs, respectively. These techniques demonstrate quantitatively that a DC consists of a vacancy‐rich core surrounded by a distribution of self‐interstitial atoms (SIAs) — the latter are predominately created by RCSs. Recent results on the application of MD to the behavior of 5 keV cascades in copper are presented. Some of the results of the application of field‐ion microscopy to the study of DCs in tungsten are reviewed, and compared with the MD results.

A six-detector high-resolution PAC spectrometer

A new high-resolution PAC spectrometer using six detectors equipped with fast BaF 2 scintillators is presented. As compared with a conventional four detector arrangement, for the same source activity, this spectrometer allows to reduce the time of experiments by a factor of about 1.8. The random coincidence rate is considerably reduced by using a “slow fast” circuitry. The time resolution is ⋍ 0.5 ns for the 181Ta 133–482 keV cascade.

Study of the radioactive decay of192Ir

Theβ − and electron capture decays of192Ir to the levels of192Pt and192Os respectively have been investigated to verify the existence of some of weak gamma transitions reported earlier. Gamma-gamma directional correlation measurements have been done for 13-cascades. Multipole admixture of 201, 283, 485 keV gamma transitions in192Os and 296, 308, 416, 604 keV gamma transitions in192Pt have been deduced. A spin value of 4+ has been reaffirmed on the basis of almost zero intensity of 1201 keV gamma ray (4+→0+) and 416→(468)→316 keV cascade directional correlation measurements.

Nuclear quadrupole interaction at133Cs in some barium compounds

Nuclear quadrupole interaction frequencies at133Cs following the electron-capture decay of133Ba for BaSO4, Ba/BrO3/2 and Ba/NO3/2 were obtained by measuring the perturbation of 356–81 keV cascade of133Ba. Nuclear quadrupole interaction frequencies for BaSO4 and Ba/BrO3/2 are 17.2 Mrad sec−1 and 14.6 Mrad sec−1, respectively, while no perturbation of 356–81 keV cascade was observed in case of Ba/NO3/2. Further the possibility of any after-effects of electron-capture decay is ruled out through the measurement of 276–161 keV gamma-gamma directional correlation.

Hyperfine-field measurements inCr Rh andCr Re alloys using perturbed angular correlation technique

The hyperfine fields on111Cd probe nuclei in Cr (1 at% Rh), Cr (0.3 at% Rh) and Cr (0.5 at% Re) matrices are measured using time-differential perturbed (γ−γ) angular correlation of 173–247 keV cascade in the decay of111In to the levels in111Cd. The sources prepared by ion implantation of111In (2.81 d) activity followed by appropriate annealing procedure were found to be of good quality. The addition of impurities, located to the right of chromium in the periodic table such as Rh and Re, to the chromium matrix increases the electron to atom ratio, resulting in an increase in the magnetic moment compared to pure chromium. This in turn is expected to result in an increase in the hyperfine fields at probe nuclei in these alloys. The measured hyperfine fields are in qualitative agreement with the expected changes in these alloys.

Gamma-Gamma Directional Correlations in 160Dy

The gamma-gamma directional correlation coefficients of 16 cascades in 160 Dy following the decay of 160 Tb ( t 1/2 =72.1 d) have been measured using a Ge(Li)-NaI(Tl) coincidence set-up (2 τ≈6 n sec). Out of these, the correlation coefficients of the 310-962, 338-962, 392-(879)-87, 1003-(197)-87, 1103-(197)-87 and 1115-197 keV cascades have been measured for the first time. From these correlation measurements the spin value of 4 - has been confirmed for the 1386.5 keV level. The multipole mixing ratios of the 1003, 1103, 1115, 1200 and 1312 keV transitions in 160 Dy have been determined for the first time.

Internal conversion studies in the decay of84mRb

The relative gamma intensities of the 216, 248 and 464 keV transitions in the decay of 84mRb were determined. The K-conversion coefficients of the 216 and 248 keV transitions were obtained as 0.74(4) and 0.033(3), respectively, using coincidence methods. These values of alpha K are consistent with assigning the 248 keV transition as pure E2 and the 216 keV transition as M3+E4. From the relative gamma intensities of the 216-248 keV cascade, the total conversion coefficient of the 216 keV transition was evaluated as 0.93(6), assuming that alpha T for the 248 keV transition was 0.038(3). The average adopted values of the M3 and E4 contributions to the 216 keV transition were obtained a 0.58(9) and 0.42(9), respectively. The transition probability for the 248 keV transition showed an E2 enhancement of 86(17) over the Weisskopf estimate. In addition, the reduced transition probability of this transition was found to be of the same order of magnitude as the 2+ to 0+ transitions in the neighbouring even-even nuclei, suggesting the possibility of core excitation in 84Rb.

Quadrupole interaction studies of graphite indium chloride using time-differential perturbed angular correlations

The technique of time-differential perturbed angular correlations has been applied to the study of quadrupole interactions in graphite intercalated with indium chloride. Indeed, these experiments represent the first application of this particular spectroscopic technique to graphite intercalation systems. With 111In incorporated as a probe, γ-γ angular correlation measurements were performed on the 173–247 keV cascade in the daughter product 111Cd. Information on quadrupole interactions was obtained from Fourier analysis of the data and by comparison with theoretical fits based on standard angular correlation theory. Three sites are found for intercalated InCl 3: two of these correspond to static electric field gradient interactions, which for a Grafoil sample yielded mean values of v q (1) = 57.8 ± 0.8 MHz and v q (2) = 267 ± 5 MHz; it is suggested that the third, time-dependent component represents a site to which electron transfer is inhibited. The possibility that signals may have been observed from adsorbed as opposed to intercalated InCl 3 was eliminated by comparison with measurements on Spheron 6 carbon black.

TDPAC studies on181Hf implanted into diamond

181Hf ions were implanted at (900±10)K into (100) cleaved single crystal diamonds. After subsequent annealing residence site parameters were determined for the implanted ions employing the γ(133 keV)−γ(482 keV) cascade in181Ta in TDPAC technique. Fractions of 5% each were determined that experience axially symmetric electric field gradients (EFG) Vzz(1)=5.5×1017 V cm−2 and Vzz(2)=9.6×1017 V cm−2, respectively. The bulk of the ions are strongly disturbed by still higher electric field gradients.

Perturbed angular correlation and Mössbauer study of the hydrogen distribution near Ru, Rh and Pd in palladium hydride

Mossbauer experiments with the 90 keV resonance of99Ru as well as PAC measurements using the 353 and 528 keV - 90 keV cascades in99Ru and the 84 keV - 75 keV cascade in100Rh were combined in a study of the hyperfine interactions produced by the hydrogen distribution near Ru, Rh and Pd atoms in Β-PdHx (0.6≲x≲1.0). The electric field gradients produced by the non-cubic nearest neighbour hydrogen distribution were found to be very small. This shows that the protons are very strongly shielded and justifies an interpretation of the Mossbauer spectra in terms of isomer shift distributions only. By combining the two methods one thus can obtain a rather detailed picture of the hydrogen distribution near the probe atoms.

TDPAC study of indium oxide

TDPAC measurements on polycristalline indium oxide powder using the well known 174–245 keV cascade of111In were performed at different temperatures. In accordance with X-ray diffraction data,111In was observed in two sites which are clearly distinguishable by the coordinations of the nearest neighbor oxygen ions. A calculation of the ionic electric field gradient produced by these gave fair agreement with the experimental ratio of the two field gradients, the asymmetry parameters and the relative fraction of In ions at both sites. The observed quadrupole interaction parameters are very similar to the ones found in the internal oxidation of In in Ag and AgIn alloys.

Triple gamma ray directional correlation in 154Gd

An experiment to measure the triple gamma ray directional correlation is described. One NaI(Tl) and two Ge(Li) detectors were employed under computer control. Total and accidental counts were accumulated simultaneously by use of two ADCs. The apparatus was used to study the 723-873-123 keV cascade following the beta decay of 154Eu. Procedures for determination of accidental coincidences, correction for finite detector solid angle, and correction for attenuation of the correlation due to the finite lifetime of an excited state differ from double correlation procedures. Double correlation studies were also made to confirm the consistency of the measurements and to determine the attenuation factors for the radioactive source employed here. Results that were both internally consistent and in accordance with prior studies of this decay were obtained, with δ(873) = −6.9 (+1.8, −3.4) on the basis of the triple correlation experiment; δ = −10.2±0.8 on the basis of supporting double correlation experiments.

The Decay of Ag-105g

The level structure of Pd-105 has been studied from the decay of Ag-105g. The energies and intensities of 50 gamma rays have been precisely measured using a 64.1 c.c. Ge(Li) detector (FWHM=2.1 keV at 1.33 MeV). The gamma ray singles spectrum measurements confirm the existence of the 158.93, 167.5, 202.17, 216.11, 382.5, 486.65, 576.64, 583.01, 844.34, 860.20, 921.23, 929.01 and 1124.90 keV gamma rays in the decay of Ag-105g. However, the 270.5, 564.39, 580.13, 610.0, 640.5, 709.8, 768.9 and 796.25 keV weak transitions reported by earlier workers could not be observed in the present investigations. Also the ?-? directional correlation coefficients for 7 cascades in Pd-105 have been measured. Out of these, the 361-(447)-280 and 807-280 keV cascades have been attempted for the first time. From these correlation measurements spin value of 1/2+ has been confirmed for the 673.03 keV level. Also these measurements have been used to deduce the multipole mixing ratios of seven transitions in Pd-105.

The Level Structure of 105Pd

The structure of 105 Pd levels populated in the decay of 41.29d 105 Ag has been investigated using a 64.1 cc Ge(Li) detector in singles mode and a 64.1 cc Ge(Li)–7.6 cm×7.6 cm NaI(Tl) detector set-up in coincidence mode. The gamma ray singles spectrum measurements confirm the existence of 158.93, 167.5, 202.17, 216.11, 382.5, 486.65, 576.64, 583.01, 844.34, 860.20, 921.23, 929.01 and 1124.90 keV gamma rays in the decay of 105g Ag. However, the 270.5, 564.39, 580.13, 610.0, 640.5, 709.8, 768.9 and 796.25 keV weak transitions reported by earlier workers could not be observed in present investigations. The γ-γ directional correlation coefficients for 7 cascades in 105 Pd have been measured. Out of these the 361–(447)–280 and 807–280 keV cascades have been attempted for the first time. From these correlation measurements the spin value of 1/2 + has been confirmed for the 673.03 keV level and found the multipole mixing ratios of various transitions in 105 Pd.

The Gamma-Gamma Angular Correlation Studies in 132Xe

The gamma-gamma angular correlations on 17 cascades in 132 Xe from the decay of 132 I have been measured using a Ge(Li)–NaI(Tl) coincidence set-up. Out of these, the correlation coefficients of the 363–772, 650–(523)–772, 877–(523)–772, 910–772 and 910–(772)–668 keV cascades have been measured for the first time. These measurements have been used to deduce the multipole mixing ratios of 11 transitions in 132 Xe. The results are: δ(363)=-0.023±0.023, δ(523)=-0.23±0.16, δ(630)=6.1 -2.5 +6.5 , δ(650)=-0.16±0.11, δ(877)=-1.2±0.5, δ(955)=-0.033±0.033, δ(1136)=0.45±0.05, δ(1173)=-0.6±0.4 or -2.0 -6.0 +0.9 , δ(1372)=0.02±0.07, δ(1399)=0.04±0.02 and δ(1442)=-0.02±0.03. The directional correlation results have also been used to deduce the spin value of 4 + to each of the 1962.9, 2394.9 and 2840.5 keV levels and those of 3 + and 3 + or 5 + to the 2669.9 and 2350.7 keV levels respectively.

The Decay of 99Mo

The decay of 67h 99 Mo to the levels of 99 Tc has been studied with Ge(Li), Ge and Si(Li) detectors. Some new gamma rays of energies of 38, 163.4, 319.8, 321.0, 352.9, 599.6, 727.07 and 1082.2 keV have been observed. One new level at 163.4 keV is suggested and two controversial levels at energies 726.7 and 1081.4 keV have been confirmed. The directional correlation system has been used to measure the 740–181, 740–(40)–140, 961–181 and 822–(40)–140 keV cascades. These measurements confirm 3/2 + , 5/2 - and 1/2 - spin assignments for 921.0, 1004.2 and 1142.1 keV levels. The mixing ratios of 40.585, 140.511, 739.7, 823.1 and 961.0 keV gamma rays have been obtained as \(\text{M1}+{\leqslant}6.25{\times}10^{-2}\)% E2, M1+9±1% E2, E2+8.0±1% M1, E1±1% M2 and M2+E2, respectively.

Level structure of the 89-neutron nucleus 153Gd : (I). Levels and gamma-transitions in 153Gd excited in the decay of 153Tb

Investigations of the properties of 153Gd excited states populated in 153Tb decay were continued. The following measurements were performed: coincidence spectra e −γ with L41, K93 + L52, K110, K129 + L87 + L88 and K195 + L152 keV conversion electron lines, angular correlations of high energy γ-cascades going through the 109.7 keV level, delayed e −γ and e −e − coincidence spectra to determine the half-lives of 41.5, 93.3, 109.7, 129.1,183.5, 212.0 and 216.1 keV states, R(135°, ± B) parameters of IPAC for the 102–110 and 83–129 keV cascades using 153Tb sources implanted into Fe foil. A decay scheme of 153Tb containing 50 excited levels is proposed. Their spins, parities, log ƒt and, for low-lying levels, also the mean half-lives have been determined. An estimation of the g-factors of the 109.7 and 129.1 keV levels has been given. On the basis of half-lives of investigated states absolute values of reduced γ-transition probabilities for these states have been calculated. The structure of the ground state of 153Gd is discussed.

Ordered alloys reveal fundamental mechanisms of neutron damage production

Ordered alloys have historically played an important role in investigating basic mechanisms of neutron irradiation damage. We have been particularly active in this field at Argonne National Laboratory, and in this paper we will review four different areas of our experimentation using ordered alloys. We will briefly review and critically re-examine our magnetic saturation measurements performed on Ni 3Mn during neutron irradiations. Disordering during thermal-neutron bombardment at 5 K uniquely revealed the existence, number and average length of replacement collision sequences. Confirmation of our analysis by others will be presented; some refinements will be introduced; comparisons with recent molecular-dynamic calculations will be drawn; and the (n, γ) recoil spectrum in Ni 3Mn will be reanalyzed. Overall, we conclude that 112 to 150 〈110〉 replacements occur, within one or two sequences, per (n, γ) recoil with an average energy of 492 eV. Similar measuremens on Ni 3Mn during fast-neutron bombardment at 5 K yielded the total number of replacements per typical 30 keV cascade and demonstrated that very few interstitials were produced at large distances from the cascade by 〈110〉 replacement sequences. We will discuss our very recent results on high-resolution TEM measurements of disordered zones in fast-neutron irradiated Cu 3 Au. These results have been compared with damage calculations for the accurately measured fast-neutron flux and energy spectrum in CP5 and reveal the spatial characteristics of the deposited energy in individual cascades. Resistivity measurements of Cu 3Au during fast-neutron bombardment at 150°C have revealed both the disordering process within cascades and ordering by irradiation-enhanced vacancy diffusion. These experiments provide a means of comparing different neutron energy spectra and studying irradiation-enhanced diffusion in a system amenable to theoretical treatments.

Measurements of perturbed directional correlations in gaseous H 275Se/He sources

The integral PAC attenuation coefficients G 2(∞) of the 121–279 keV cascade in 75As were measured, dependent on the pressure of He as a buffer gas in the system H 2 75Se/He. A rough estimate of the corresponding cross section is given.

Gamma-gamma directional correlation study of model membranes

Measurements of the perturbed gamma-gamma directional correlation were made for the 173-247 keV cascade in 111Cd at the In ion site in dipalmitoylphosphatidylcholine liposomes. A time-dependent electric quadrupole interaction was observed. Below the order in equilibrium fluid phase transition temperature the exponential damping coefficient was lambda 2 = 0.033 +/- 0.007 ns-1. Above the transition temperature the coefficient was lambda 2 = 0.015 +/- 0.006 ns-1 indicating a twofold increase in molecular mobility in the disordered phase. Absolute values for the motional correlation time, tau c, were estimated to be on the order of a few nanoseconds. The presence of cholesterol was found to cause no significant difference in the molecular mobility of the phosphatidylcholine head groups in the ordered and fluid states.