Die radioaktiven Substanzen und die geologische Forschung

Hamberg, Axel

doi:10.1080/11035891309449550

Cited by 31 publications

(5 citation statements)

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“…Zircon is not always completely crystalline, but commonly occurs in a partly or completely amorphous (metamict) state (Holland and Gottfried 1955;Chakoumakos et al 1987;Murakami et al 1991;Weber 1990) due to radiation damage resulting from e-decay events (Hamberg 1914;Ewing et al 1987;Weber 1993;Weber et al 1994). Average U concentrations in zircon vary from 5 to 4000 ppm, and average Th concentrations vary from 2 to 2000 ppm; thus, in periods of hundreds of…”

Section: Introductionmentioning

confidence: 97%

Energetics of radiation damage in natural zircon (ZrSiO4)

1994

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Abstract. Transposed temperature drop calorimetry at 1000 ~ was performed on natural zircons (ZrSiO4) from Sri Lanka that were partially to completely metamict due to e-decay event damage (0.06 to 11.7x l02s e-decay events/mg). The enthalpy of annealing at room temperature (AH ..... 1) varies sigmoidally as a function of radiation dose. AH ..... l reaches a saturation plateau at radiation doses greater than 5 x 1015 a-decay events/mg. The annealing of several samples to a crystalline structure with broadened diffraction peaks does not significantly affect the enthalpy of annealing. The large magnitude of the enthalpy of annealing plateau, -59 __ 3 kJ/mol, suggests that the damage to the structure is pervasive on the scale of ~ngstroms, consistent with the loss of mid-range order characteristic of a glass. The energetics are consistent with, but do not require, chemical heterogeneity caused by micro-domains of amorphous SiO2-rich and ZrO2-rich regions in the metamict state.

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Section: Introductionmentioning

confidence: 97%

Energetics of radiation damage in natural zircon (ZrSiO4)

1994

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“…Metamict minerals were judged amorphous because of their conchoidal fracture and isotropic optical properties, but well developed crystal faces proved that they were originally crystalline. Hamburg 1914 was the first to suggest that metamictization is a radiationinduced phase transition caused by alpha decay of radionuclides in the U and Th decay series. X-ray diffraction studies confirmed that metamict minerals were either amorphous or very finely crystalline (e.g., Vegard 1916).…”

Section: Introductionmentioning

confidence: 98%

Alpha-decay damage in minerals of the pyrochlore group

1988

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Abstract. X-ray diffraction analysis and transmission electron microscopy have been used to study the effects of alpha-decay damage in pyrochlore group minerals, characterized by the general formula A1 ,~BzO6(O,OH,F)I -n'pH20.As defined by the XRD intensity ratio I/Io, both the saturation dose (for which I/Io =0.1-0.0) and the dose which signifies the initial loss of crystallinity (for which I/Io = 1.0-0.8) increase as a function of geologic age. The increase is attributed to annealing of isolated alpha-recoil tracks back to the original crystalline structure. The tracks have calculated mean lives, za, on the order of 108 years. In contrast, minerals which remain crystalline (e.g., uraninite, UO2) despite doses of up to 1018 alpha-events/mg have mean alpha-recoil track lives ~ 104 years (Eyal and Fleischer 1985).After correcting the calculated dose for annealing of alpha-recoil damage, I/Io is observed to decrease exponentially to zero over the dose range 0.02-1.0 x 1016 alphaevents/rag. The relationship between I/Io and "corrected" dose was used to calculate an average alpha-recoil track diameter of 4.6 nm, in which < 2600 atoms are displaced. XRD line broadening due to strain dominates the first half of the crystalline-to-metamict transition, reaching a maximum of 0.003, then decreasing to < 0.001. Line broadening due to decreasing crystallite size dominates the latter half of the transition. Estimated crystallite dimensions decrease from 450 nm to < 15 nm prior to reaching the fully metamict state. With increasing dose HRTEM images of microlites from the Harding pegmatite sequentially exhibit: 1) mottled diffraction contrast, 2) isolated 1-5 nm aperiodic areas, 3) coexisting aperiodic and crystalline areas, 4) relict" islands" of crystalline material in an aperiodic matrix, and 5) complete loss of lattice fringe periodicity. With no consideration given to alpha-recoil track fading, the transition covers a dose range of 0.04-1.7x 1017 alpha-events/mg. Using a value of za=108 years, this dose range is corrected down to 0.02-1.2 x 10 ~6 alpha-events/mg.The metamict state is characterized by a range of M-M and M-O distances which give rise to bands of diffuse scattering centered at 0.30 nm and 0.18 nm, respectively, in x-ray and electron diffraction patterns. Random image contrast shown by HRTEM is consistent with a random network type structure, an interpretation supported by EX-AFS/XANES studies (Greegor et al. 1985a(Greegor et al. , b, 1987. The structure of metamict pyrochlore consists of an aperiodic framework of corner-sharing B--O polyhedra. Compared to the crystalline precursor, the metamict state displays a reduced M-O coordination number and mean bond length, increased distortion of the B-site, and a slight increase in the average M-M distance.

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“…Metamictisation is defined as the amorphous state of a substance that has lost its periodic structure (Brøgger, 1893). Metamictisation is a radiation-induced, periodic-to-aperiodic phase transition caused by α-particles from the U or Th decay series (Hamberg, 1914). Damage by α-decay has two components that occur simultaneously.…”

Section: Introductionmentioning

confidence: 99%

The importance of cation–cation repulsion in the zircon–reidite phase transition and radiation-damaged zircon

Tokuda

Yoshiasa

Kojitani

et al. 2019

MinMag

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Single crystals of synthetic reidite and natural radiation-damaged zircon from Okueyama, Japan were investigated using X-ray diffraction. The pressure-induced zircon–reidite transition is described by the twisting and translations of SiO4 tetrahedra with disappearance of the SiO4–ZrO8 shared edges. The lattice of radiation-damaged zircons expands mainly from α-decays of radioactive elements such as U and Th. Although old radiation-damaged zircons show anomolous lattice distortion, young radiation-damaged zircons do not show such distortions. These distortions are caused by thermal recovery that suppresses the Si4+–Zr4+ repulsion between the SiO4 tetrahedron and ZrO8 dodecahedron. These changes in structure can be understood by considering the cation–cation repulsion between the SiO4–ZrO8 shared edges.

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Die radioaktiven Substanzen und die geologische Forschung

Abstract: o l a 3 ~~11igsreriniigen wie die rc-Stralilen, n-erden aber ron einer 5)))m clickan Aliuiiini~uii~~latte oder voii einer 1 w i i i dicken Bleiplntte einigerniassen rollstiindig absorbiert ; die 7-Strnhlen sind analog niit den starli dnrchdringenden l Show more

Cited by 31 publications

References 0 publications

Energetics of radiation damage in natural zircon (ZrSiO4)

Energetics of radiation damage in natural zircon (ZrSiO4)

Alpha-decay damage in minerals of the pyrochlore group

The importance of cation–cation repulsion in the zircon–reidite phase transition and radiation-damaged zircon

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