Effects of Pulsed Ionizing Radiation on Some Selected Quartz Oscillator Crystals

The effects of high-energy ionizing radiation on the behavior and output frequency of electronic oscillators, whose frequency-determining elements were quartz crystals operating in the vicinity of 5 Mc, have been studied. Both fundamental- and fifth-overtone crystals were studied over a dose range from 3,000 rads (Si) to 2 Mrads (Si). The crystals studied were of two types: (1) standard commercial precision crystals fabricated from natural quartz with Q's of approximately 2.5 × 106 for the fifth overtone and 4 × 105 for the fundamental, and (2) special fifth-overtone crystals fabricated from swept pure Z-growth synthetic quartz. The natural quartz showed much larger changes in frequency and transient loss of Q than the swept synthetic crystals. The crystals were incorporated into commercial precision oscillator circuits and maintained in a temperature-controlled oven. The radiation doses (both 25-MeV electrons and 10-MeV peak bremsstrahlung gamma rays) were provided by the General Atomic electron linear accelerator. The radiation was collimated to irradiate only the crystal. The oscillator output signal was monitored with an oscilloscope during and after the radiation burst, and the frequency was measured by cycle counting for 10-or 100-sec time intervals. The precision of the frequency measurements was ±2 parts in 108 for the 10-sec intervals and ±2 parts in 109 for the 100-sec intervals. Electrons and gamma rays were shown to have the same effect on the crystals; therefore, most of the work was done with electrons because of the convenience of accumulating large doses in 4.5-psec pulses.     

Rapid Annealing of Frequency Change in Crystal Resonators Following Pulsed X-Irradiation

A transient negative frequency change in AT-cut 125 MHz 5th overtone quartz resonators has been observed following exposure to an intense burst of x-rays. All natural, Z-growth synthetic, and swept Z-growth synthetic resonators suffer a significant initial negative frequency offset. At room temperature, the transient frequency change in natural quartz anneals in approximately ten minutes to a relatively stable negative offset. For the synthetic quartz resonators, appreciable annealing of the initial negative offset continues for a longer period, finally arriving at an offset which may be positive in the case of the Z-growth synthetic but negligibly small for swept Z-growth synthetic. The transient frequency change is attributed to a relaxation process, which anneals above 165°K (Stage I). This annealable relaxation is superposed on a more stable part (Stage II) which is removed only by heating the crystal well above room temperature. The kinetics of Stage I annealing obeys a t-2 relationship and is interpreted in terms of a one-dimensional diffusion limited annealing of uncorrelated defects. In particular, it is proposed that the annealing involves the trapping of monovalent cations, most probably H+, at substitutional aluminum sites in the crystal lattice. The activation energy governing the diffusion of the defect to the trapping center is estimated to be 0.80 ± 0.05 eV.     

Transient Change in Q and Frequency of At-Cut Quartz Resonators Following Exposure to Pulse X-Rays

Study of the transient behavior of AT-cut quartz resonators following pulse irradiation has been extended. In addition to 125 MHz 5th overtone crystal units previously reported, both 32 MHz and 5 MHz 5th overtone units have been studied using several different oscillator circuits, one of which is designed to give the transient resistance at series resonance, RS, as well as frequency as a function of time after pulse exposure. RS is proportional to the acoustic loss, i.e., Q-1, of the resonator. With but one notable exception, the annealing kinetics of the transient frequency offset following pulse irradiation obeys a t-? relationship over three to four decades in time, indicative of a 1D diffusion limited trapping of uncorrelated mobile cation impurities in the crystal lattice. The most significant observations of the post-irradiation behavior of RS is the relatively large RS increase in natural quartz resonators. The transient increase anneals asymptotically to a relatively stable RS value which is somewhat higher than the pre-irradiation RS. The transient and steady-state post-irradiation change in RS is frequency dependent and, based upon the underlying model, should also be temperature dependent. The increase of RS in 5 MHz natural quartz resonators exposed to 104 Rad from the Sandia Laboratories' Hermes II facility is 30 times its pre-irradiation value at 0.2 sec after burst. However, RS for 32 MHz crystal units at .2 sec after exposure to 4 × 104 Rad typically increases only a factor of 2 times the pre-irradiation value.     

MeV ion damage in III–V semiconductors: Saturation and thermal annealing of strain in GaAs and GaP crystals

MeV ion irradiation of GaAs crystals at room temperature has shown that the lattice strain perpendicular to the sample surface saturates to ∼ 0.4% for 〈100〉 cut and ∼ 0.3% for 〈111〉 and 〈110〉 cut crystals with zero parallel strain in all cases. In this paper, the thermal recovery behavior of the saturated strain in GaAs (100) is presented for a 15 min isochronal annealing. The recovery of strain depth profile is shown explicitly by a dynamical theory analysis of the X-ray rocking curves taken after each annealing step. The isochronal recovery behavior of strain suggests that a spectrum of activation energies is involved in the thermal migration of defects in the saturated surface layer. This also suggests that many kinds of antisite defect complexes exist in the surface layer. The strain and related defects are also shown to saturate in MeV ion bombarded GaP (100) crystals. This may indicate that all the primary defects (interstitials, vacancies, and antisite defects) saturate under MeV ion irradiation of III–V compounds, and support the proposed ion-lattice single collision model of defect production and saturation under MeV ion irradiation. The linewidths of X-ray rocking curves obtained from GaP crystals bombarded at room temperature and at 490 K indicate that low-temperature recovery stage defects cause major crystal distortion in III–V compounds. Also presented are the isochronal annealing behaviors of lattice strain, X-ray broadening, and peak reflecting power of room temperature irradiated GaP (100) crystals.     

Total sputtering yields of solids under MeV-energy Si ion bombardment

Total sputtering yields have been measured for SiO₂ and Cu targets bombarded with Si ions at an incident energy between 500 keV and 5.0 MeV using a quartz crystal microbalance technique. In order to measure total yields accurately, we have developed a beam modulation technique to avoid the effect of thermal drift. In the MeV energy range, an ion penetrates through thin SiO₂ and Cu targets and is implanted into a quartz crystal. Therefore, the thickness of these layers deposited on quartz crystals was carefully controlled to avoid damage of quartz crystal by incident ions. As a result, total sputtering yields of SiO₂ increased with incident Si ion energy, while those of the Cu target decreased. The total yields of the SiO₂ target were represented well by a power low of the electronic stopping power.     

Thermal annealing of fission tracks in synthetic apatites

Synthetic analogues of poor-silicated natural apatites have been doped with uranium. These minerals have been irradiated with a thermal neutron dose in the aim to induce the ²³⁵U fission and to obtain a fission track population. Thermal annealing experiments have been performed on the fission track population and allow us to compare the ability of the synthetic minerals to anneal such nuclear damages with their natural analogues. The thermal of the fission tracks in the synthetic minerals need more time and/or higher temperature to reach the same annealing rate as in the natural analogues. The alpha damage present in the natural analogues seems to enhance the thermal annealing of fission tracks.     

Permanent Radiation Effects in Swept and Unswept Optical Grade Synthetic Quartz at Resonators

Permanent changes in the frequency versus temperature characteristics of unswept and swept optical grade synthetic quartz AT resonators which are caused by fast neutron and Co60 irradiations have been investigated. Neutron damage shifts the frequency versus temperature characteristics of the unswept resonators upwards in frequency across the entire zero to + 120°C temperature range at a rate of 0.56 × 10-15 ppm per N/cm2, which is the smallest value yet reported in the literature. The observed erratic results for swept resonators were attributed to effects of ionizing radiation accompanying the neutron fluence and led to the Co60> investigation. The unswept optical grade quartz was found to provide AT resonators which are more resistant to ionizing radiation than any other unswept material yet investigated in the literature. Appreciable amounts of acoustically active defects attributed to Na inpurities which were apparently gaded during sweeping were indicated by the Co results for the swept devices and made the swept devices useless as radiation resistant resonators.     

Recombination Effect as Component of Residual Defect in Silicon Surface Barrier Detector

The thermal conductivity of graphite components used as in-core components in high-temperature gascooled reactors (HTGRs) is reduced by neutron irradiation during reactor operation. The reduction in thermal conductivity is expected to be reversed by thermal annealing when the irradiated graphite component is heated above its original irradiation temperature. In this study, to develop an evaluation model for the thermal annealing effect on the thermal conductivity of IG-110 graphite for the HTGRs, the thermal annealing effect evaluated quantitatively at irradiation temperatures of up to 1,200°C and neutron fluences of up to 1.5 dpa. Moreover, the thermal conductivity of IG-110 graphite was calculated by using a modified thermal resistance model considering the thermal annealing effect. The following results were obtained. (1) The thermal annealing effect on the thermal conductivity of IG-110 graphite could be evaluated quantitatively and a thermal annealing model was developed based on the experimental results at irradiation temperatures of up to 1,200°C and neutron fluences of up to 1.5 dpa. (2) The thermal conductivities of IG-110 graphite calculated by using the modified thermal resistance model considering the thermal annealing effect showed good agreement with experimental measurements. This study has shown that it is possible to evaluate the annealed thermal conductivity of IG-110 graphite by using the modified thermal resistance model at irradiation temperatures of 550–1150°C and irradiation fluences of up to 1.5 dpa.     

Thermal quenching of thermoluminescence in quartz samples of various origin

The effect of thermal quenching stands among the most important properties in the thermoluminescence (TL) of quartz on which many applications of TL are based. Since the quartz samples used in various applications are all of different origin it is useful to investigate whether the values of the thermal quenching parameters, i.e. the activation energy for thermal quenching W and a parameter C which describes the ratio of non-radiative to radiative luminescence transitions, evaluated mainly in specific quartz samples can be extrapolated to quartz samples of unknown origin as well as to quartz samples which are annealed at high temperatures. In the present work the TL glow curve of a series of un-annealed and annealed natural and synthetic quartz samples were studied as a function of the heating rate between 0.25 K/s and 16 K/s. Using an indirect fitting method it was found that the thermal quenching parameters W and C in most of the quartz samples are very similar to the values accepted in the literature. Furthermore, in some cases the thermal quenching parameters W and C are not the same for all TL glow-peaks in the same glow-curve. Finally, the strong external treatment of annealing the quartz samples at very high temperature can also influence at least one of the thermal quenching parameters.     

Elaboration de monocristaux de zirconium α et etude de leur perfection cristalline

The methods depending on critical straining followed by α-phase annealing, or on thermal cycling across the allotropie transformation temperature, do not enable the production of large zirconium crystals of predetermined orientation. A method based on localised phase transformation in a controlled thermal gradient has been successfully developed: it permits the preparation of crystals up to 100 mm long in favourable cases. A study of the mechanism of formation of an α monocrystal from a β monocrystal has led to a recognition of the parameters which determine the growth of the desired monocrystals. An analysis of the crystal orientations obtained has established the optimal conditions for obtaining orientations close to a desired one. X-ray methods have been used to examine the perfection of the crystals: some were strongly polygonised but others had overall misorientations of less than 10^?2 degree.     

Thermal and Injection Annealing of Neutron-Irradiated p-Type Silicon between 76°K and 300°K

Measurements of minority carrier lifetime damage constant and divacancy growth following neutron irradiation at 76°K have been used to characterize further the annealing of neutron damage in silicon below 300°K. It has been shown that electron injection into p-type silicon at 76°K causes recovery of the neutron induced defect clusters with the simultaneous appearance of divacancies. Comparison of isochronal annealing curves of damage constant taken with and without prior injection at 76°K illustrates the nature of cluster annealing below 300°K. The thermal annealing results are shown to agree with previous annealing measurements of the carrier removal rate.     

用正电子湮没实验研究PbWO4新型闪烁晶体绿光发光机理

通过正电子湮没寿命谱研究ＰｂＷＯ４晶体退火处理前后缺陷的变化,发现氧退火后,晶体正电子寿命值τ２变小,正电子捕获率ｋ增大,真空退火反之。并且ＰｂＷＯ４晶体氧退火后发光主峰位从４４０ｎｍ称到４８５ｎｍ的绿光处,而真空退火晶体发射谱谱形并未变化。从不同退火处理对晶体的影响,提出了ＰｂＷＯ４晶体中铅空位形成ＷＯ３＋Ｏ＾－发绿光的发光模型。     

Recrystallisation of amorphous natural brannerite through annealing: The effect of radiation damage on the chemical durability of brannerite

An amorphous natural brannerite sample was chosen to study the annealing of the radiation damage through thermal recrystallisation, and subsequently to evaluate the effect of radiation damage on its aqueous durability. Microstructural characterisation of the natural brannerite revealed minor alteration along the rim of the crystal and within cracks. The formation of UO₂ particles and soluble Pb–Ca-rich aluminosilicate glass is responsible for the higher U and Pb releases from the recrystallised brannerite. In general, natural brannerite has been shown to be resistant to dissolution over geological time, therefore minor brannerite inclusions in ceramic formulations for immobilisation of actinide-rich radioactive wastes should not have a detrimental effect on the long-term chemical durability of the wasteforms.     

Reducing edge effects and improving position resolution in positionsensitive NaI(TI) detectors

Large two-dimensional position sensitive NaI(Tl) crystals used in positron emission tomographs and elsewhere normally have gaps or inactive, unusable areas at the edges. Experiments aimed at reducing these edge effects have been performed. Unencapsulated crystals have been used to test the feasibility of optically coupling crystals together to decrease gap size. Other experiments increased the sampling of the scintillation light at the edges in order to obtain better position sensitivity. In addition, the edges were treated to reduce unwanted reflections and increase the position sensitive area. Experiments aimed at improving the position resolution throughout the crystal, as well as at the edges, were performed     

Annealing Characteristics of Neutron Irradiated Silicon Transistors

When a transistor is subjected to neutron irradiation, a component of base current proportional to neutron fluence is induced. From the effects of annealing on the base and collector currents, the conclusion was drawn that there is an apparent difference in the annealing characteristics between the neutral and the space-charge regions of the semiconductor device. This study of the anomalous annealing indicates that the neutron-induced component of base current is a result of one, or a combination, of the following mechanisms: a quasi-tunneling recombination phenomena in the emitter-base space-charge region, or an influence of the p-n junction electric field on the formation, annealing, and electronic behavior of the neutron-induced defect centers. A field dependence of the formation and annealing of the neutron-induced defects appears to be present both during the introduction and annealing of the neutron-induced defect centers. It could not be finally determined whether or not the quasitunneling phenomena occurred although it can be shown on theoretical grounds that it is possible for such phenomena to occur. The annealing characteristics of the defects, as represented by changes in the collector and base currents, have been obtained. Three sets of devices were irradiated and then annealed, with one set having a forward bias during annealing, one set having no bias, and one set having a reverse bias. The dependence of the field on annealing is present but appears quite complex.     

Paleothermometry of NaCl as evidenced from thermoluminescence data

The firing temperature of ancient ceramic artifacts, i.e. the paleothermometry of these materials has been estimated by various techniques including thermoluminescence (TL) and, more recently, Optically Stimulated Luminescence (OSL) where the OSL response of quartz to firing temperature is used. In this work we report the paleothermometry of sodium chloride (NaCl) by studying the TL response of the material as a function of annealing temperatures in the range of 100–500 °C. Annealing/measurement has been done in a commercial TL/OSL reader (Model No. Risø TL/OSL reader TL-DA-15) in a nitrogen atmosphere.Sodium chloride (NaCl) has been selected as the candidate to test the feasibility of the technique since in this system TL peaks are correlated with the thermal annealing of F-centers unlike the case of quartz where a one to one correlation with all the glow peaks and thermal annealing of defects has not been possible.     

Dependence of damage efficiency of ions in diamond on electronic stopping

Natural diamond single crystals were irradiated at room temperature with 75 keV carbon and 80 keV argon ions at fluences exceeding the graphitization dose. The resulting damage depth profiles before and after rapid annealing at 1500 K were obtained by -particle channeling analysis. Measurements were done both at back- and forward scattering angles using conventional surface barrier detectors and an electrostatic analyzer system, respectively. Boundary positions of the graphitic layers were determined and compared with the corresponding depth-dependent elastic and inelastic energy deposition graphs to extract critical damage energy densities. The obtained values increase strongly with inelastic energy deposition rate, indicating a significant reduction of the ions’ damage efficiency due to irradiation induced annealing by electronic stopping.     

Simulations of thermally transferred OSL signals in quartz: Accuracy and precision of the protocols for equivalent dose evaluation

Thermally-transferred optically stimulated luminescence (TT-OSL) signals in sedimentary quartz have been the subject of several recent studies, due to the potential shown by these signals to increase the range of luminescence dating by an order of magnitude. Based on these signals, a single aliquot protocol termed the ReSAR protocol has been developed and tested experimentally. This paper presents extensive numerical simulations of this ReSAR protocol. The purpose of the simulations is to investigate several aspects of the ReSAR protocol which are believed to cause difficulties during application of the protocol. Furthermore, several modified versions of the ReSAR protocol are simulated, and their relative accuracy and precision are compared. The simulations are carried out using a recently published kinetic model for quartz, consisting of 11 energy levels. One hundred random variants of the natural samples were generated by keeping the transition probabilities between energy levels fixed, while allowing simultaneous random variations of the concentrations of the 11 energy levels. The relative intrinsic accuracy and precision of the protocols are simulated by calculating the equivalent dose (ED) within the model, for a given natural burial dose of the sample. The complete sequence of steps undertaken in several versions of the dating protocols is simulated. The relative intrinsic precision of these techniques is estimated by fitting Gaussian probability functions to the resulting simulated distribution of ED values. New simulations are presented for commonly used OSL sensitivity tests, consisting of successive cycles of sample irradiation with the same dose, followed by measurements of the sensitivity corrected L/T signals. We investigate several experimental factors which may be affecting both the intrinsic precision and intrinsic accuracy of the ReSAR protocol. The results of the simulation show that the four different published versions of the ReSAR protocol can reproduce accurately the natural doses in the range 0-400 Gy with approximately the same intrinsic precision and accuracy of ∼1-5%. However, these protocols underestimate doses above 400 Gy; possible sources of this underestimation are investigated. Two possible explanations are suggested for the modeled underestimations, possible thermal instability of the TT-OSL traps, and the presence of thermally unstable medium OSL components in the model.     

高能氧离子注入LN晶体光波导的色心形成

采用高能氧离子注入同成分铌酸锂(LN)晶体中制备离子注入光波导,对制备的光波导进行(200°C–500°C)不同温度的退火处理。采用常规光谱法对退火后的光波导进行光吸收谱研究。研究发现,氧离子注入后会使LN晶体中的锂离子发生缺失,进一步偏离化学剂量比;随氧离子注入剂量的增加,锂离子缺失的现象会加重。研究还发现离子注入后样品的吸收强度增加,注入剂量增大,其光吸收强度也提高,说明经离子注入后产生的色心点缺陷数目随注入剂量而增加。研究表明,主要的吸收色心缺陷有氧空位、激化子、间隙原子缺陷及反位Nb离子捕获电子等缺陷,由于这些色心缺陷的共同作用,导致了氧离子注入LN晶体的光吸收强度的加强。在实验的退火温度范围内,这些色心缺陷消除程度不显著,在LN晶体采用氧离子注入形成的光波导具有优良的温度稳定性。     

He implantation in cubic zirconia: Deleterious effect of thermal annealing

This study investigates the microstructural modifications induced in cubic zirconia by He implantation at high concentration (∼4 at.%). The effect of post-implantation thermal annealing on the crystal stability is particularly addressed. For this purpose, three complementary analysis techniques, namely RBS/C, XRD and TEM, have been used. The structure of as-implanted crystals appears weakly defective, the damage very likely consisting of interstitial-type defects and helium-vacancy clusters. These defects induce a tensile elastic strain gradient with a depth distribution that overlaps the He depth profile. After annealing at 800 °C, a partial strain relaxation is observed, but the crystalline structure is strongly altered due to the formation of helium bubbles and elongated fractures.