# The Development of Nuclear Science The Development of Scientific Thought in the 20th Century The new radiating material Applications as long as Radioactivity Applications

## The Development of Nuclear Science The Development of Scientific Thought in the 20th Century The new radiating material Applications as long as Radioactivity Applications

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Explanation of natural radioactivity Nobel Prize 1908 The radioactive decay law decay constant; a natural constant as long as each radioactive element. Half life: t1/2 = ln2/ exponential decay with time! 1st example: 22Na 22Na has a half-life of 2.6 years, what is the decay constant Mass number A=22; (dont confuse with activity A(t)!)

radioactive decay laws Activity of radioactive substance A(t) is at any time t proportional to number of radioactive particles N(t) : A(t) = ·N(t) A 22Na source has an activity of 1 Ci = 10-6 Ci, how many 22Na isotopes are contained in the source (1 Ci = 3.7·1010 decays/s) How many grams of 22Na are in the source A gram of isotope with mass number A contains NA isotopes NA Avogadros Number = 6.023·1023 22g of 22Na contains 6.023·1023 isotopes How many particles are in the source after 1 y, 2 y, 20 y Decay in particle number in addition to corresponding activity!

2nd example: Radioactive Decay Plutonium 239Pu, has a half life of 24,360 years. What is the decay constant How much of 1kg 239Pu is left after 100 years The first step: E=m·c2 “It followed from the special theory of relativity that mass in addition to energy are both but different manifestations of the same thing – a somewhat unfamiliar conception as long as the average mind. Furthermore, the equation E is equal to m c-squared, in which energy is put equal to mass, multiplied by the square of the velocity of light, showed that very small amounts of mass may be converted into a very large amount of energy in addition to vice versa. The mass in addition to energy were in fact equivalent, according to the as long as mula mentioned be as long as e. This was demonstrated by Cockcroft in addition to Walton in 1932, experimentally.” Nobel Prize 1921 Albert Einstein Example: Mass-Energy Definition: 1 ton of TNT = 4.184 x 109 joule (J). 1 kg (2.2 lb) of matter converted completely into energy would be equivalent to the energy released by exploding 22 megatons of TNT. 1kg of matter corresponds to an energy of: Nuclear physics units: 1 electron-volt is the energy one electron picks up if accelerated in an electrical potential of one Volt. +1V

The discovery of the neutron By 1932 nucleus was thought to consist of protons in addition to electrons which were emitted in -decay. New Chadwicks experiment revealed a third particle, the neutron Strong Polonium source emitted particles which bombarded Be; radiation was emitted which  based on energy in addition to momentum transfer arguments – could only be neutral particles with similar mass as protons neutrons: BEGIN OF NUCLEAR PHYSICS! Nobel Prize 1935 The model of the nucleus Modern Picture nuclide chart hydrogen isotopes: Z=1 Isotopes: Z=constant, N varies! Isotones: N=constant, Z varies! Isobars: A=constant, Z,N varies! Z=8, O isotopes A=20 isobars N=12 isotones

Energy in Nuclei According to Einsteins as long as mula each nucleus with certain mass m stores energy E=mc2 Proton mp = 1.007596 · 1.66·10-24 g = 1.672·10-24 g Neutron mn = 1.008486 · 1.66·10-24 g = 1.674·10-24 g Carbon m12C = 12.00000 · 1.66·10-24 g = 1.992·10-23 g Uranium m238U= 238.050783 · 1.66·10-24 g = 3.952·10-22 g 1 amu=1/12(M12C)=1.66 · 10-24 g B = (Z · mp+ N · mn- M) · c2 B(12C) = 1.47 · 10-11 J; B/A=1.23 · 10-12 J B(238U) = 2.64 · 10-10 J; B/A=1.21 · 10-12 J Binding energy B of nucleus Breaking up nuclei into their constituents requires energy Nuclear Potential http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/liqdrop.html c2 1 MeV = 1.602·10-13 J Nuclear Binding Energy

Example: Nuclear Binding Energy Conversion of nuclei through fusion or fission leads to release of energy! http://ie.lbl.gov/toimass.html http://nucleardata.nuclear.lu.se/database/masses/ http://www.nndc.bnl.gov/masses/mass.mas03 Nuclear Energy possible through fission in addition to fusion

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