COSMIC RADIATION AND
AND NATURAL RADIOELEMENTS
IN NATURE

Primary Cosmic Radiation

  • stable charged particles that have been accelerated to enormous energies by astrophysical sources somewhere in our universe

70% Protons

20% Alpha particles

0.7% Li, Be, B ions

1.7% C, Ni, O ions

residual 0.6% Z>10

Sun

  • Non-isotropic
  • Energy <10e4 GeV
  • Flux solar dependent

Galaxies

  • Isotropic
  • Energy 10e4 - 10e10 GeV
  • Flux solar independent

Secondary Reaction

  • the collision of pions results of formation of large
    number of electrons, neutrons, protons and photons

Radioelements in Nature

  • all natural materials (rain water, lakes, sea)
    has low concentration of radioactive nuclides

Cosmogenic

  • formed from cosmic radiation

Primordial

  • liferime comparable
    to earth formation

Anthropogenic

  • nature by man modern technique

Survey

  • cosmic radiation reacts with Nitrogen & Oxygen gas, Ar etc. resulting production of some radionuclide (long-lived and short-lived)

Tritium

  • 2500 tritium atoms per second per square meter of earth surface
  • has half-life of 12.33 yrs
  • incorporated with water, enter hydrological cycle
  • Define by using DU (Deuterium Unit)

Carbon-14

  • Most important is between thermalized neutrons from cosmic radiaitons and nitrogen atoms
  • The half-life is 5715 yrs

Elements in natural Radioactive
Decay Series

Thorium

  • occurs with 100% isotopic abundance
  • Specific activity of 4.06 Mbq/kg (half-life through alpha decay)

Uranium

  • 4n + 2 series
  • U-238 with natural abundance of 99.3%
  • Undergoes alpha decay with half-life of 4.46x10^9 yr.
  • The stable end product of uranium is Pb-206
  • The uranium decay series provides the most important isotopes (radium, radon & polonium) can be isolated in the processing of uranium minerals.

Actinium

  • 4n + 3 series
  • Begin with U-235, with half-life of 7.04x10^8 yr and a specific activity of 8x10^4 MBq/kg
  • The stable end product is Pb-207
  • Most important isotope: protactinium, actinium, francium, astatine.

Neptunium

  • 4n + 1 series
  • Parent species: Np-237, with half-life of 2.14x10^6 yr.
  • The end product of the neptunium series is Bi-209

Plutonium

  • Long live plutonium isotope Pu-244
  • Decay through alpha emission and spontaneous fission with half-life of 8.26x10^7 yr.

Age Determination

Dating by C-14

  • produced at a constant rate
  • after organism incorporating the biological material died, no exchange occurs between carbon atoms of material and those of the surrounding

Dating by Kr-Ar

  • Radioactive isotope K-40 present only 0.0117% in natural potassium.
  • It half-life is of the same magnitude of the age of the earth
  • K/Ar ratio can be used to determine ages of the oldest K-containing minerals.

Dating by Rb-Sr

  • one of the most reliable methods for geologic age
    determinations

Dating by Re-Os

  • Re-187, Os-186 and Os-187 has been used to measure the age of meteorites.

Dating by U-238

  • more reliable than the helium method
  • since the lifetime of uranium isotopes U-238 and U-235 are different, the isotopic ratio between their end products Pb-206 and Pb-207 can also be used for age determination.

Nuclear Weapons

  • banned since 1963
  • Total release of radiation up to 2x10^20 Bq fission products.
  • Most of the fission products: Sr-90, Cs-137 and Pu

Nuclear Power Plant Accidents

  • In 1979, partial melt-down occured at Three Mile Island power station in Pennsylvania
  • Xe, Kr and some Iodine were released.
  • In 2011, the Fukushima Daichi accident occurred.
  • Causing a release of a total up to 900 PBq to the air.
  • Chernobyl released a total of 5200 PBq to the air.