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Uranium Isotopes: Their History, Uses and Threats Arghya Chakravorty1 Michael Bojazi1 Bradley S. Meyer1 1Department
of Physics and Astronomy, Clemson University, Clemson - SC
ABSTRACT:
Radioactive actinides play significant roles in driving the geophysical activities in a habitable planet like ours which has subsequently helped life evolve and flourish on it. Our understanding of their properties have allowed us to harness them for our own purposes, but not without dangers to ourselves. We review here the role they’ve played since the formation of galaxies and eventually explore why they pose threats to our existence. Uranium from primary r-process[2]
How could it all have started? [1] •
Some 100,000,000 years into the “BIG-BANG”, the primordial gas, containing H and He and “NO” METALLICITY, formed proto-galactic clumps which condensed to form the first generation of stars.
• r-nuclei like U, Th in our Solar system most likely formed in environments that experienced freeze-out from equilibrium due to temperature drop and subsequent slowing down of charged particle reactions. • However neutron and light-nuclei captures on iron-group “seed” nuclei must have continued.
•
Enrichment within them and their eventual death ejected newer/heavier elements that formed the progeny stars and their planetary systems with higher metallicity.
• The sites must have been neutron-rich, at least 100 free neutrons per seed nucleus at the time of freeze-out must have been present, which is evident from formation of 238U from seed nuclei with A ~ 50-100.
•
Subsequent supernovae (SN) events enriched the Interstellar Medium (ISM) causing formation of elements and their isotopes by fusion of H/He in the core of stars or by rapid/slow capture of neutrons (r,s-process) or protons (p-process).
• The process was endowed with continuous 1n-capture, 1n-disintegration and β-decay reactions.
Actinides like Uranium, Thorium formed via r-process nucleosynthesis in which seed nuclei at Fe56 peak rapidly captured neutron capture than they β decayed.
Uranium isotopes that entered our Solar system (U234,U235, U238) were also progenies of higher mass nuclei that decayed on their own or by fission with elementary particles
•
• In all Earth-like planets, activities.
Radionuclide
dominates
Half-life ( x 109 yrs.)
in
radiogenic
40K
1.28
232Th
14.10
124.0 (80%)
235U
0.70
0.22 (1.34%)**
4.47
Meltdown and Radio Toxicity [11]
30.8 (49.36%)**
• % of the mantle concentration at the time of SS formation left today [4]
•
I131, Sr90 and Cs137 pose major immediate threats after a meltdown due to relatively shorter half-lives.
•
Volatile I131 and Cs137 sublimate due to immense heat and rise to the stratosphere.
•
They then “fall out” and are deposited on plants or are inhaled or ingested by animals. Eventually enter the food-chain.
•
Results into Acute Radiation Syndrome (ARS) / Radiation Sickness within 24 hours from the accident.
** U235/U238 dropped from 0.263 to 0.007 (by 97%) in earth’s lifetime
Mining Uranium : Uranium Ore (U3O8) today is mined from the crust
which has 99% U238 and 0.7% U235. The ore is enriched by centrifugation to raise the U235 concentration from 0.7% to 3 - 5% (enough for power plants; >90% for Nuclear Bombs)
56 +
140Xe 54 235U
92 +
92Kr + 36
3
1n 0
+ 94Sr38+ 2 1n0
β137 Cs
Radio Nuclide
Nuclear Fission 141Ba
53
+ 89Y39 + 16 1n0
137Cs 55
Source of Irradiation
+ 96Rb37 + 3 1n0
Usual dosage [7] (Gy; 1 Gy=100 rad)
Primordial radionuclides on earth’s crust
1 mGy
CT-scan
15-20 mGy
Cosmic rays from a Transatlantic flight
0.02 mGy
Nuclear Fallouts
Close to 2Gy
Half-Life [5]
Controlled in
8.02 days 6.57 hrs. 15.7 M-years
2.833 6.333 0.900
Uncontrolled
Cs 137 Mo 99 Tc 99 Sr 90 Pm 147
30.17 years 2.75 days 211 K-Years 28.9 years 2.62 years
6.090 6.100 6.051 5.752 2.271
Power Reactors
in Bombs and nuclear accidents
Iodine is transferred via Sodium Iodide Symporter (NIS) channel protein across the Basolateral membrane and then via Pendrin into Follicle colloid [12]
The thyroid gland absorbs Iodine from the plasma in the form of Iodide ions (I-). The process is called Iodine Trapping
Avg energy ~ 0.18 MeV Max energy ~ 0.81 MeV
131I 53
β-
131Xe
* 54 Excited daughter
γ
131 I
90 Sr
β-
53
β38
56
• Potassium Chemistry • Readily Soluble in water
131 Xe 54
• Deposits on Vegetation • Dissolves in the blood
137 Ba
55
Yield (%) [5] by thermal neutron fission of U235
I 131 I 135 I 129
1n 0
131I
+ γ 4He + 238U 238Pa 238U + e- + v e 1n + 237U γ + 238U
• The unceasing decay thereafter has brought these numbers to even lower levels making U235 almost negligible when it comes to accounting for radioisotopes that drive the radiogenic heating on earth.
Concentration in Earth’s Mantle Today (ppb) / (%*) 36.9 (7.96%)
238U
242Pu
• At the time of the formation of the Solar System, for every 1,000,000,000 Si atom, there were only 20 atoms of U238 and 6 atoms of U235.
• The figure shows the evolution of the mass-fractions of the two isotopes in the progenitor gas that formed the solar system fitted to the present condition of the solar annular gas. 235U
+ γ 4He + 235U 1n + 234U γ + 235U 235Pa 235U + e- + v e 235Np 235U + e+ + v e
• However, the abundance of U235/U238 with respect to Si28 decreased exponentially after an initial increase since the formation of galaxy as predicted by the model.
• Using Clayton Model [3] it can be shown that owing to its higher decay rate , U235 has almost always been scarcer than U238 (0.984 vs 0.155/Gyr) since the formation of our galaxy.
U238
239Pu
β90
Y 39
90Zr 40
• Calcium Chemistry • Dissolves in Milk
Major Nuclear Fallout incidents [6] • • • •
Chernobyl accident, 1986 Japan Atomic Bomb Blast, 1945 Nevada and Marshall Island Nuclear Bomb Testing, 1950-1960s Fukushima Nuclear Meltdown, 2011.
Cannot distinguish between a stable Iodine (I127) and its radioactive isotopes (I131,I125,I129) [12]
131Xe
54 Stable Daughter
Inside, it binds to tyrosines of Thyroglobulin protein - the precursor for the synthesis of thyroid hormones. It is called the “Organification Of Iodide”
Synthesis of Thyroid hormones - Triiodothyronine (T3) -Thyroxine (T4).
DNA damage induced by ionizing radiations [10] •
I131 concentrated in the gland emits the hazardous β-rays that can penetrate ~ 0.125” to yield the non-carcinogenic Xe131.
The powerful β-rays [9] •
β-rays transfer energy to local tissues/cells especially affecting the nucleus of the cell than its cytoplasm – High Linear Energy transfer (LET).
•
They cause DNA single/double strand breaks (SSB/DSB) through disrupting bonds or ionization of bases.
•
Along its “track”, the high-LET cause localized but dense free radical concentration which are chemically very reactive and cause damage due to radiation.
•
SSBs are repaired relatively efficiently over the DSBs by the natural DNA repair mechanism. Erroneous DSB repair generally lead to mutations.
•
β-rays from I131 create 180,000 ion-pairs/cm inside the tissues against 250/cm in air. Its track-length is reduced to < 400 mm against ~ 30cm in air leading to severe localized damages to the DNA.
•
These mutations are expressed , if the cell survives, in the offsprings and over generations leading to genetic disorders namely Thyroid cancer, Grave’s disease - common amongst Chernobyl, Nagasaki, Hiroshima inhabitants even today.
Homology Model of h-NIS (Phyre) [8] [1] L Saleh et al, J. Phys. G: Nucl. Part. Phys. 32 (2006) 681–712 [2] B. S. Meyer, Annu. Rev. Astron. Astrophys. (1994). 32: 153-90 [3] D.D. Clayton, Nucleosynthesis: Challenges and New Developments, University of Chicago Press, Chicago (1985), p. 65 [4] E.A. Frank et al., Icarus 243 (2014) 274–286. [5] Https://en.wikipedia.org/wiki/Fission product yield [6] Institute of Medicine (US) Committee on Thyroid Screening Related to I-131 Exposure; National Research Council (US) Committee on Exposure of the American People to I-131 from the Nevada Atomic Bomb Tests. Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests: Review of the National Cancer Institute Report and Public Health Implications. Washington (DC): National Academies Press (US); 1999.
[7] Web-Article: Fallout from Nuclear Weapons Tests and Cancer Risks [8] Kelley LA et al. Nature Protocols 10, 845-858 (2015). [9] Nuclear Technology, Author: Joseph A. Angelo, Greenwood Publishing Group, Jan 1, 2004, Pg: 195. [10] Eyvazzadeh et al. Cell J. 2015; 17(1): 99-110. [11] Web-Article: Worldwide Effects of Nuclear War. (http://www.atomicarchive.com/Docs/Effects/wenw_chp2.shtml) [12] Levy et al. FEBS Lett 429: 36–40, (1998)
