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Natural gamma radiation from IODP Hole 317-U1352C

Publication Date
DOI: 10.1594/pangaea.778471
  • 317-U1352C
  • Canterbury Basin
  • Depth
  • Top/Min
  • Drilling
  • Error
  • Absolute
  • Error
  • Relative
  • Exp317
  • Integrated Ocean Drilling Program / International Ocean Discovery Program
  • Iodp
  • Joides Resolution
  • Natural Gamma Ray
  • Odp Sample Designation
  • Sample Code/Label
  • Time Stamp
  • Physics


Chapter 5 5—1 5. NATURAL GAMMA RADIATION 5.1. Principles PHYSICAL BACKGROUND Source of radiation Natural gamma radiation (NGR) is a useful lithologic parameter because the “primeval” emitters are at secular equilibrium; i.e., radiation at characteristic energies is constant with time (e.g., Adams and Gaspirini, 1970). Radioisotopes with sufficiently long life and that decay to produce an appreciable amount of gamma rays are potassium (40K) with a half-life of 1.3 × 109 years, thorium (232Th) with a half-life of 1.4 × 1010 years, and uranium (238U) with a half-life of 4.4 × 109 years. Minerals that fix K, U, and Th, such as clay minerals, are the principal source of NGR. Other examples include arkosic silt and sandstones, potassium salts, bituminous and alunitic schists, phosphates, certain carbonates, some coals, and acid or acido-basic igneous rocks (Serra, 1984). Units Gamma rays are electromagnetic waves with frequencies between 1019 and 1021 Hz. They are emitted spontaneously from an atomic nucleus during radioactive decay, in packets referred to as photons. The energy transported by a photon is related to the wavelength λ or frequency ν by E = hν = hc/λ (1) where c is the velocity of light, and h is Planck’s constant (6.626 10–34 joule). The energy is expressed in eV (electron-volts). For our purposes, the multiples KeV or MeV are used. Each nuclear species (isotope) emits gamma rays of one or more specific energies. Activity, A, is the rate of radioactive decay and decreases exponentially according to A = λdN = λd N0 e-λdt (2) where λd is the decay constant, and N and N0 are the number of atoms at times t and t0, respectively. The original unit of activity was defined as the number of disintegrations per second occuring in 1 g of 226Ra. In 1950, the Curie (Ci) was redefined as exactly 3.7 × 1010 disintegrations per second. For most purposes, the multiples mCi or µCi are used. Each radioactive species has an intrinsic specific activity (I

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