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COSMIC RADIATION AND AND NATURAL RADIOELEMENTS IN NATURE (Primary Cosmic…
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
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
Primordial
liferime comparable
to earth formation
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.
Anthropogenic
nature by man modern technique
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.
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.