Induced modifications of kaolinite under ionizing radiation: an infrared spectroscopic study

Radiation effects on kaolinite were investigated using He⁺ ions of 1.5 MeV at radiation doses up to 4.3 × 10⁸ Gy, which are comparable to the doses expected for clay barriers in high-level nuclear waste repositories. The concentration of paramagnetic radiation-induced defects in kaolinite reaches 2 × 10¹⁶ spins/mg (400 at. ppm), as determined by electron paramagnetic resonance spectroscopy. The broadening of X-ray diffraction patterns and transmission infrared (IR) absorption bands is mostly related to the structural strain induced by radiation-induced point defects. The broadening of IR absorption spectra is analyzed using an autocorrelation approach and is related to a change in the distribution of vibrational frequencies due to crystal heterogeneities. We theoretically analyze how the effective dielectric properties of kaolinite samples depend on macroscopic parameters and how irradiation can modify some of them. Irradiation leads to an increase in the electronic polarizability of kaolinite particles, related to the accumulation of radiation-induced electronic point defects.     

Water in silicate glasses: An infrared spectroscopic study

Infrared and near-infrared transmission spectra have been taken on 19 volcanic and synthetic silicate glasses with known H₂O contents (0.06–6.9 wt. %). Absorption peaks were observed at wavelengths of 1.41 m, 1.91 m, 2.22 m, 2.53 m, and 2.8 m. These peaks have been attributed to the first overtone of the OH stretching vibration, the combination stretching+bending mode of H₂O molecules, the combination stretching+bending mode of X-OH groups, a combination mode of the fundamental OH stretch+a low energy lattice vibration, and the fundamental OH stretching mode, respectively. Molar absorptivities of the peaks have been determined to be 0.2, 1.8, 1.0, 0.9, and 67 l/mol-cm. These values apply over the full range of glass compositions studied (albite, rhyolite, basalt).Quantitative determinations of total H₂O contents and of the concentrations of molecular water and hydroxyl groups in silicate glasses are possible using these molar absorptivities, although they are limited in their accuracy by the accuracy of the reported water contents of the glasses used to calibrate these molar absorptivities. The most important uses of this technique may stem from its applicability to microsamples (100 m) and to the determination of the concentrations of hydroxyl groups and molecular water in quenched silicate melts.Hydroxyl groups are the dominant hydrogen-bearing species in water-bearing glasses at low total water contents, but molecular H₂O was detected in all samples with 0.5 weight percent total water. The concentration of hydroxyl groups increases rapidly with total water content at low total water contents, but more slowly at higher (>3 wt. %) total water contents; it may level off or even decrease at high total water contents. The concentration of molecular water increases slowly at low total water contents and more rapidly at high total water contents. More water is dissolved as molecular water than as hydroxyl groups at total water contents greater than 4 wt. %. Molecular water in these glasses is probably structurally bound rather than present as fluid inclusions as a separate phase, since ice bands were not observed in spectra taken at 78K and since samples were free of visible bubbles.It is proposed that the speciation of water in silicate glass formed by rapid quenching from melt equilibrated at high temperatures reflects that of the melt. According to this hypothesis, neither high water contents nor high pressures are needed to stabilize substantial quantities of molecular water in melts. This hypothesis, that water dissolves in silicate melts as both molecular water and hydroxyl groups in proportions similar to those measured in waterbearing glasses, can explain the variations in viscosity, electrical conductivity, diffusivity of water, diffusivity of cesium, and phase relationships that are observed in melts as functions of total water content. It also explains the observation that at vapor-saturation at high pressures, where most of the dissolved water is expected to be present as molecular water, water solubilities are similar for all melts but that at low pressures and water contents, where most dissolved water is present in dissociated form as hydroxyl groups, vapor-saturated water solubilities differ for different melt compositions. The linear relationship between water fugacity and the square of the mole fraction of total dissolved water observed for silicate melts at low water contents and the observed deviations from this linear relationship at high total water contents can be accounted for by this hypothesis.     

Hydroxyl stretching in phyllosilicates at high pressures and temperatures: an infrared spectroscopic study

The hydroxyl stretching frequencies of four phyllosilicates have been measured at high pressures and temperatures using an externally heated diamond-anvil cell and synchrotron infrared spectroscopy. Spectra were measured up to 26, 31, 21 and 8 GPa at room temperature for samples of talc, pyrophyllite, muscovite and 10-Å phase, respectively. Spectra were also measured in the range 273–500 K at ambient pressure for all samples and at 8–9 GPa for talc and pyrophyllite. The frequency of the Mg₃OH band in talc increases with pressure due to the absence of hydrogen bonding. The different orientation of the hydroxyl group in pyrophyllite and muscovite leads to hydrogen bonding and a decrease in the frequency of the Al₂OH band with pressure. 10-Å phase is approximately equivalent to talc with the addition of interlayer H₂O. In a spectrum of a sample synthesised for 143 h, two hydroxyl stretching bands are clearly resolved on compression. One is the same as the Mg₃OH band in talc, indicating the presence of intra-layer hydroxyl in a talc-like environment with no hydrogen bonding. The other, which separates from the talc-like band at 1 GPa, is associated with intra-layer hydroxyl that is hydrogen bonded to interlayer H₂O. There are equivalent bands in high-pressure spectra of a sample of deuterated 10-Å phase, synthesised for 400 h. This sample shows a greater extent of hydrogen bonding at ambient pressure than the 143 h sample. For all of the phases studied, increasing temperature leads to a decrease in frequency for every hydroxyl stretching vibration, both at low and high pressures. The shifts in frequency with temperature are an order of magnitude greater than the shifts with pressure when normalised to previously measured structural parameters.     

Structural states of natural potassium feldspar: An infrared spectroscopic study

Natural samples of K-feldspar representing various states of Al, Si order were characterised using X-ray methods, transmission electron microscopy, and Fourier transform infrared spectroscopy. Line profiles of infrared absorption bands were observed to show strong correlation with the degree of Al, Si order present. In particular, the absorption frequencies of the 540 cm^?1 and 640 cm^?1 bands were seen to vary by ca. 10 cm^?1 between sanidine and microcline, with modulated samples respresenting intermediate behaviour. Linewidths of these modes also decrease by ca. 50% in this series. The experimental results are discussed within the framework of Hard Mode Infrared Spectroscopy (HMIS), and it is shown that the absorption frequencies vary with the short range order parameter τ = (4t₁-1)² and the symmetry breaking order parameter describing Al, Si order, Q _od=(t₁ 0?t₁ m)/Q _od=(t₁ 0+t₁ m), where t₁ is the average Al occupancy on the T₁ sites and t₁ o and t₁ m are the individual site occupancies of the T₁ o and T₁ m sites, respectively. The structural state of orthoclase is characterised by strain-induced modulations with large spatial variations of the modulation wavelength. No such modulations were observed in the degree of local Al, Si order. Sanidine shows mode hardening in excess of the extrapolated effect of symmetry breaking Al, Si order, which is presumably related to nonsymmetry breaking ordering between T₁ and T₂ sites and/or as yet unobserved short range order of the symmetry breaking ordering scheme. The possibility of an additional phase transition in K-feldspar at temperatures above 1300 K is discussed.     

Volatile characteristics of peralkaline rhyolites from Kenya: an ion microprobe,infrared spectroscopic and hydrogen isotope study

Peralkaline rhyolites of the Greater Olkaria Volcanic Complex, Kenya Rift Valley, were derived from separated, though closely related, magma chambers. Ion microprobe analyses of glass inclusions in quartz phenocrysts show pre-eruptive water contents of up to 3.4 wt% contrasting with previous estimates that the magmas were anhydrous. The values approach predicted solubility levels corresponding to water saturation at low crustal pressures (1 kbar). The glass matrices of the rhyolites have low water contents, ranging from 0.07 to 0.46 wt%, suggesting significant degassing during, or prior to, eruption. Infrared measurements of the matrix glasses show variation in the relative proportions of the two hydrous species dissolved in the glasses. The amount of molecular water, determined semi-quantitatively, apparently increases with increased fluorine content and peralkalinity. This suggests a competition between hydroxyl groups and fluoride ions for similar sites within the melt structure. The mechanism of degassing has been investigated using hydrogen isotopes. The range of D values in most rocks can be produced by varied degrees of open-system degassing of rhyolite melt initially in equilibrium with water of a fixed, or limited, D value. There is evidence to suggest that closed-system degassing may also have been a significant component in some rhyolites. The exact mechanisms of degassing remain uncertain. Particular problems include the relative contribution of open-and closed-system degassing during eruption and the initial vapour compositions and solubility relationships.     

An infrared and Raman spectroscopic study of gypsum at high pressures

 We present Raman and infrared spectra of gypsum to 21 GPa at 300 K. Our measurements encompass the internal modes of the (SO₄)⁻⁴ group that lie between 400 and 1150 cm⁻¹, hydroxyl-stretching vibrations between 3200 and 3600 cm⁻¹, and a libration and bending vibrations of the molecular H₂O group. All vibrations of the sulfate group have positive pressure shifts, while the hydroxyl-stretching and -bending vibrations have a mixture of positive and negative pressure shifts: the effect of pressure on the hydrogen bonding of the water molecule thus appears to be complex. Near 5 GPa, the two infrared-active bending vibrations of the water molecule coalesce, and the morphology of the hydroxyl-stretching region of the spectrum shifts dramatically. This behavior is consistent with a pressure-induced phase transition in gypsum in the vicinity of 5–6 GPa, which is observed to be reversible on decompression to zero pressure. The spectral observations are consistent with the onset of increased disorder in the position of the water molecule in gypsum: the sulfate vibrations are largely unaffected by this transition. The Raman-active symmetric stretch of the sulfate group undergoes an apparent splitting near 4 GPa, which is interpreted to be produced by Fermi resonance with an overtone of the symmetric bending vibration. The average mode Grüneisen parameter of the 20 vibrational modes we sample is less than 0.05, in contrast to the bulk thermal Grüneisen parameter of 1.20. Accordingly, the vibrations of both water and sulfate units within gypsum are highly insensitive to volumetric compaction. Therefore, in spite of the changes in the bonding of the water unit near 5 GPa, metastably compressed gypsum maintains strongly bound molecular-like units to over 20 GPa at 300 K. Received: 31 July 2000 / Accepted: 5 April 2001     

Thermal expansion and decomposition of jarosite: a high-temperature neutron diffraction study

The structure of deuterated jarosite, KFe₃(SO₄)₂(OD)₆, was investigated using time-of-flight neutron diffraction up to its dehydroxylation temperature. Rietveld analysis reveals that with increasing temperature, its c dimension expands at a rate ~10 times greater than that for a. This anisotropy of thermal expansion is due to rapid increase in the thickness of the (001) sheet of [Fe(O,OH)₆] octahedra and [SO₄] tetrahedra with increasing temperature. Fitting of the measured cell volumes yields a coefficient of thermal expansion, α = α₀ + α₁ T, where α₀ = 1.01 × 10⁻⁴ K⁻¹ and α₁ = −1.15 × 10⁻⁷ K⁻². On heating, the hydrogen bonds, O1···D–O3, through which the (001) octahedral–tetrahedral sheets are held together, become weakened, as reflected by an increase in the D···O1 distance and a concomitant decrease in the O3–D distance with increasing temperature. On further heating to 575 K, jarosite starts to decompose into nanocrystalline yavapaiite and hematite (as well as water vapor), a direct result of the breaking of the hydrogen bonds that hold the jarosite structure together.     

On the presence of hydrous defects in differently coloured wulfenites (PbMoO4): an infrared and optical spectroscopic study

Several samples of wulfenite, PbMoO₄, varying in colour from colourless to yellow, orange and red, have been characterised by means of IR and optical absorption spectroscopy and by microprobe analyses. A distinct pleochroic band group with absorption maxima centred at 3,380 and 3,150 cm^?1 can be seen in the IR spectra of wulfenite single-crystals, indicating the presence of hydroxyl groups. The pleochroic and thermal behaviour of the OH stretching bands along with deuteration experiments, as well as results obtained from synthetic flux-grown samples, exclude the presence of submicroscopic hydrous mineral inclusions as their primary origin. The pleochroic scheme and the band positions were used to postulate a model for the OH incorporation mode, based on the assumption of vacancies on Mo and Pb sites in the structure of this ‘nominally anhydrous mineral’. Optical absorption spectra of coloured natural samples show a broad and polarised band around 23,000–24,000 cm^?1, preceding the fundamental UV absorption edge, which has been identified as the reason for the colour of the mineral. The comparison with synthetic PbMoO₄ single-crystals, doped with variable amounts of Cr⁶⁺, yielded conclusive evidence that trace amounts of the CrO₄ ^2? anion group, substituting for MoO₄ ^2?, determine the variable colour. Besides, in one sample, trace amounts of Nd³⁺ have been spectroscopically identified.     

An infrared spectroscopic and single-crystal X-ray study of malayaite, CaSnSiO5

Powder infrared spectroscopy and X-ray diffraction techniques on single crystals were used to study the thermal behaviour of malayaite, CaSnSiO₅. Infrared spectra show a discontinuity in the temperature evolution of phonon frequencies and absorbance near 500 K. However, crystal structure data collected at 300, 450, 550, 670, and 750 K show no evidence of a symmetry-breaking phase transition and no split positions. The most obvious change with heating is a tumbling motion of the SnO₆ octahedra and an increase of the anisotropic displacement factors of Ca. The thermal evolution of the mean-square vibrational amplitude of the Ca atom shows a pronounced change in slope near 500 K. The evidence suggests that the 500 K anomaly in malayaite is more similar in character to the 825 K (β-γ) transition as opposed to the 496 K (α-β) transition in synthetic titanite. Received: 26 March 1998 / Revised, accepted: 23 December 1998     

含白云石天然碳酸盐岩在中红外波段的辐射特性研究

利用红外发射光谱研究了含白云石天然碳酸盐岩及主要组成矿物的红外发射光谱特征,探究了影响其红外辐射性能的因素。X射线衍射(XRD)和微区拉曼光谱(Raman)结果显示白云石(70%)、方解石(25%)和石英(5%)是该天然碳酸盐的主要组成物相。基于黑体辐射定律以及在80℃时、400～2 000 cm-1各矿物的辐射能量谱,显示碳酸盐岩、白云石、方解石和石英的发射率依次减少(1. 010、1. 000、0. 997、0. 958),白云石是碳酸盐岩红外辐射性能的主要贡献者。在本文研究的温度和波长范围内,含白云石碳酸盐岩中主要组成矿物的热容是温度的函数,白云石高的热容有利于提高整体的热辐射性能;矿物颗粒直径对热辐射的传播有一定的影响,颗粒直径接近于辐射波长时热辐射出现衰减导致发射率降低;当化学键(C—O键、Si—O键)的振动出现在发射光谱窄的发射带范围内(1 350～1 500 cm-1和950～1 275 cm-1)则会导致相对较高的辐射能和发射率。     

Solar absorption infrared spectroscopic measurements over Mexico City: Methane enhancements

In this work, the experiment for performing solar-absorption infrared measurements from the atmospheric observatory of the Universidad Nacional Autónoma de México (UNAM) located at the university campus in Mexico City is described. The Fourier transform infrared (FTIR) spectrometer and solar-tracking system have been operating since June 2010, and from the recorded spectra the total column amounts of several atmospheric gases can be derived. The current study presents the results obtained for methane (CH₄), an important pollutant involved in ozone production and a rapidly increasing greenhouse gas. The total column amounts, retrieved with high temporal resolution, present a large dispersion and day-to-day variability. A mean value of 2.88 × 10¹⁹ molecules/cm² (1.829 ppm), with a 95% confidence interval between 2.62 and 3.14 × 10¹⁹ molecules/cm², has been obtained for the period from June 2010 to December 2011. No clear annual cycle can be determined from the monthly means due to the large variability in the measurements, suggesting a significant effect of local emissions on the natural background concentrations. Some days with extraordinary enhancements are presented and a simple back trajectory analysis points to a predominant source direction from the northeast of the measurement site. The methane-contaminated air masses passing over the UNAM atmospheric observatory, however, originate presumably not from one but several dispersed sources. A more detailed analysis with modeling of the dynamics of these air masses is required.     

Thermally induced phase transitions in tridymite: an infrared spectroscopy study

The temperature dependence of the infrared active modes of meteoritic and synthetic tridymite have been investigated between 23 K and 1073 K in IR absorption and IR emission experiments. At room temperature both tridymite samples consist of a mixture of low temperature forms, in different proportions, due to the grinding. The sequence of phase transitions in Steinbach tridymite deduced from the IR data agrees well with recent X-ray and calorimetry studies using identical samples (Cellai et al. 1994). The previously suspected structural phase transition P6₃22P6₃/mmc is confirmed by the disappearance of the 470 cm^-1 mode and a temperature anomaly of the spectral shift of the 790 cm^-1 mode. Changes in the infrared spectra of synthetic tridymite give a different sequence of phase transitions from those of the meteoritic sample, consistent with the structural phase transitions observed in a ²⁹Si MAS NMR investigation using the same sample (Xiao et al. 1993).     

A high pressure infrared spectroscopic study of PbCO3-cerussite: constraints on the structure of the post-aragonite phase

We have measured the infrared spectrum of aragonite-structured PbCO₃-cerussite to 41 GPa at 300 K in the diamond anvil cell. We observed a phase transition from an orthorhombic to a trigonal structure beginning at ~15 GPa, manifested by a splitting of the ν₂-out-of-plane bending vibration and a broadening and dramatic decrease in amplitude of the ν₁-symmetric stretching vibration of the carbonate group. While the locations of the ν₁-symmetric stretching and ν₄-in-plane bending bands are similar between the low- and high-pressure phases, their mode shifts and peak shapes change markedly near the transition. In particular, the ν₁ symmetric stretch has an essentially zero pressure shift in the high pressure phase, and its dramatically enhanced peak width indicates that it may be symmetry forbidden. The decreased mode shifts of the carbonate vibrations after the phase transition suggest that the carbonate group is less compressible in the new structure. The spectral changes observed are consistent with a small, trigonal unit cell, with space group ${P\bar{3}{1c}}$ and two formula units, instead of a previously proposed orthorhombic cell with sixteen formula units. This structure is identical to that of the high-pressure phase of BaCO₃, and likely CaCO₃ as well. Our results thus indicate that the post-aragonite, high-pressure phase of divalent-cation carbonates may be a comparatively high-symmetry trigonal structure.     

Thermal decomposition of NH4-analcime

The thermal decomposition of ammonium-exchanged natural analcime is characterized by gas chromatography, IR spectroscopy and X-ray diffraction. The de-ammoniation and dehydroxylation proceed in parallel throughout the decomposition, which evidences the instability of the protonated analcime framework. The mechanism of degassing of NH₄-analcime changes throughout its decomposition. At the initial step, the mechanism of de-ammoniation consists in thermal dissociation of NH₄⁺ molecule onto NH₃ and proton (framework OH group) and diffusion of NH₃ out of the structure. Subsequent decomposition and removal of the OH groups lead to a progressive loss of crystallinity. At this step, an apparent activation energy for NH₃ desorption is estimated to be 145(±13) kJ mol^–1. This value is within the upper limit of the activation energy characteristic for the NH₃ desorption from proton centres in large-pore zeolites. At the final step, the adsorption of NH₃ and protons onto the defect centres in the amorphosed aluminosilicate framework results in a significant increase of an apparent activation energy for the de-ammoniation and dehydroxylation up to 270(±20) kJ mol^–1.     

Vibrational spectroscopic investigation of the goethite thermal decomposition products

Goethite, hematite and intermediate products of goetite thermal decomposition were studied by IR and Raman spectroscopy to identify these products used as catalysts of some chemical reactions. The presence of a small number of OH-groups in the products of the decomposition up to 900–1000° C was supposed to hinder the formation of perfect hematite structure. The hypothesis concerning C _3v ⁶ space group of protohematite indistinguishable from D _3d ⁶ space group of hematite by X-Ray diffraction was suggested. This hypothesis explains both the additional lines in IR and Raman spectra compared to hematite spectra and the same position of peaks in X-Ray diffraction picture.     

The effect of silica activity on the incorporation mechanisms of water in synthetic forsterite: a polarised infrared spectroscopic study

Pure forsterite crystals were grown from hydrous melts using controlled cooling experiments at 2.0 GPa and varying the bulk Mg/Si ratio from 2.0 to 1.5. Oriented single crystals were then studied by polarised infrared spectroscopy. The spectra of the samples with the lowest silica activity (aSiO₂) contain the main OH bands in the range 3,620–3,450 cm^–1 only. In contrast, the spectra of the samples synthesised with the highest aSiO₂ contain additional pleochroic bands at 3,160, 3,220 and 3,600 cm^–1. The variations are interpreted in terms of protonated silicon vacancies being dominant at low aSiO₂ and Mg vacancies dominant at high aSiO₂. Xenolithic mantle olivines generally do not have the spectrum expected for orthopyroxene buffered conditions, suggesting that they re-equilibrated with their host melts during ascent, but mantle olivine from the Zabargad peridotite massif probably is in equilibrium with the coexisting orthopyroxene.Editorial responsibility: T.L. Grove     

State of water molecules and silanol groups in opal minerals: a near infrared spectroscopic study of opals from Slovakia

Recently, near infrared spectroscopy in combination with double derivative technique has been effectively used by Christy (Vib Spectrosc 54:42–49, 2010) to study and differentiate between free and hydrogen bonded silanol groups on silica gel surface. The method has given some insight into the type of functionalities, their location in silica gel samples, and the way the water molecules bind onto the silanol groups. The important information in this respect comes from the overtones of the OH groups of water molecules hydrogen-bonded to free silanol groups, and hydrogen-bonded silanol groups absorbing in the region 5,500–5,100 cm⁻¹. Chemically, opal minerals are hydrated silica and the same approach was adapted to study the state of water molecules, silanol functionalities, and their locations in opal samples from Slovakia. Twenty opal samples classified into CT and A classes and one quartz sample were used in this work. The samples were crushed using a hydraulic press and powderized. Each sample was then subjected to evacuation process to remove surface-adsorbed water at 200°C, and the near infrared spectrum of each sample was measured using a Perkin Elmer NTS FT-NIR spectrometer equipped with a transflectance accessory and a DTGS detector. The samples were also heated to 750°C to remove the hydrogen-bonded silanol groups on the surface to reveal their locality. Second derivative profiles of the near infrared reflectance spectra were obtained using the instrument’s software and used in the detailed analysis of the samples. The analysis of the near infrared spectra and their second derivative profiles had the aim in finding relationships between the surface chemical structure and the classification of opal samples. The dry opal samples were also tested for their surface adsorption effectivity toward water molecules. The results indicate that the opal samples contain (1) surface-adsorbed water, (2) free and hydrogen-bonded silanol groups on the surface, (3) trapped water molecules in the bulk, and (4) free and hydrogen-bonded silanol groups in the cavity surfaces in the bulk. A part of the water molecules in the bulk of opal minerals are found as free molecules and the rest are found in hydrogen-bonded state to either free or vicinal or geminal silanol groups.     

Radio-colouration of diamond: a spectroscopic study

We have undertaken a study of the common green or orange-brown spots at the surface of rough diamond specimens, which are caused by alpha particles emanating from radioactive sources outside the diamond. Richly coloured haloes represent elevated levels of structural damage, indicated by strong broadening of the main Raman band of diamond, intense strain birefringence, and up-doming of spots due to their extensive volume expansion. Green radio-colouration was analogously generated through the irradiation of diamond with 8.8 MeV helium ions. The generation of readily visible radio-colouration was observed after irradiating diamond with ≥10¹⁵ He ions per cm². The accumulation of such a high number of alpha particles requires irradiation of the diamond from a radioactive source over long periods of time, presumably hundreds of millions of years in many cases. In the samples irradiated with He ions, amorphisation was observed in volume areas where the defect density exceeded 5 × 10^?3 Å^?3 (or 0.03 dpa; displacements per target atom). In contrast, graphitisation as a direct result of the ion irradiation was not observed. The green colouration transformed to brown at moderate annealing temperatures (here 450 °C). The colour transformation is associated with only partial recovery of the radiation damage. The colour change is mainly due to the destruction of the GR1 centre, explained by trapping of vacancies at A defects to form the H3 centre. An activation energy of ~2.4 ± 0.2 eV was determined for the GR1 reduction. The H3 centre, in turn, causes intense yellowish-green photoluminescence under ultraviolet illumination. Radio-colouration and associated H3 photoluminescence are due to point defects created by the ions irradiated, whereas lattice ionisation is of minor importance. This is concluded from the depth distribution of the colouration and the photoluminescence intensity (which corresponds to the defect density but not the ionisation distribution pattern). The effect of the implanted He ions themselves on the colour and photoluminescence seems to be negligible, as radio-colouration and H3 emission were analogously produced through irradiation of diamond with C ions. The photoluminescence emission becomes observable at extremely low defect densities on the order of 10^?6 Å^?3 (or 0.000006 dpa) and is suppressed at moderate defect densities of ~5 × 10^?4 Å^?3 (or ~0.003 dpa). Intensely brown-coloured diamond hence does not show the H3 emission anymore. Anneals up to 1,600 °C has reduced considerably irradiation damage and radio-colouration, but the structural reconstitution of the diamond (and its de-colouration) was still incomplete.