questions - university of notre damensl/lectures/nuclear_warfare/2012/nuclear-warfare-4... ·...
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Questions
1. Radioactive material emits radiation dangerous for your health. What is the half life of a radioactive source?
2. How do decay constant and half life correspond to each other?
3. You increase the decay constant for a radioactive nucleus. What is the effect of the half life?
Terminology of nuclear energy
Mass number: number of protons and neutrons in nucleusE=mc2: energy corresponds to massBinding energy: mass difference between mass of nucleus and mass of the single nucleons (protons and neutrons)Isotopes: nuclei with identical number of protons ZIsobares: nuclei with identical atomic number AIsotones: nuclei with identical number of neutrons
The first step: E=m·c2
"It followed from the special theory ofrelativity that mass and energy are bothbut different manifestations of the samething - a somewhat unfamiliarconceptionn for the average mind.Furthermore, the equation E is equal tom c-squared, in which energy is putequal to mass, multiplied by the squareof the velocity of light, showed that verysmall amounts of mass may be convertedinto a very large amount of energy andvice versa. The mass and energy were infact equivalent, according to the formulamentioned before. This wasdemonstrated by Cockcroft & Walton in1932, experimentally."
Nobel Prize 1921
Albert Einstein
Example: Mass-Energy
smc
smkgJmcE 8
22 10311
JsmkgsmkgE 16
21628 1091091031
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: JeV 19106.11 1 electron-volt is the energy one electron picks up if accelerated in an electrical potential of one Volt.
+1V
By 1932 a nucleus was thought to consist of protons and electrons, which were emitted in the β-decay. Chadwick’s experiment revealed a third particle, the neutron
Strong Polonium source emitted α particles which bombarded Be;radiation was emitted which – based on energy and momentumtransfer arguments - could only be neutral particles with similar mass as protons neutrons: BEGIN OF NUCLEAR PHYSICS!
The discovery of the neutron
Nobel Prize 1935
np
011 H
011 H
The model of the nucleus
Nucleus with Z protons (p) and N neutrons (n) with a total mass number A=Z+N
Hydrogen: 1 p, 0,1 n
Helium: 2 p, 1,2 n
Lithium: 3 p, 3,4 n
Carbon: 6 p, 6,7 n
Sodium: 11 p, 11,12 n …
Uranium: 92 p, 143,146 n
242 He
011 H
6126C
363 Li
7136C
14623892U
121 D
132 He
473 Li
14323592U
112211 Na 12
2311 Na
N
Z
hydrogen isotopes: Z=1Isotopes: Z=constant, N varies!Isotones: N=constant, Z varies!Isobars: A=constant, Z,N varies!
Modern Picturenuclide chart
Z=8, Oisotopes
A=20isobars
N=12 isotones
Impact of Z and NAdding a proton (electron)
Carbon to Nitrogen
Gold to Mercury
Subtracting or adding neutrons
nucleus becomes unstable anddecays by internally convertingneutrons to protons (beta-decay)!
- decayn p+e-+
+ decayp n+e++
_
Energy in NucleiAccording to Einstein’s formula, each nucleus with a certain mass m stores energy: E=mc2
Proton mp = 1.007596 · 1.66·10-24 g = 1.672·10-24 gNeutron mn = 1.008486 · 1.66·10-24 g = 1.674·10-24 gCarbon m12C = 12.00000 · 1.66·10-24 g = 1.992·10-23 gLead m208Pb = 207.797665 · 1.66·10-24 g = 3.449·10-22 gUranium m238U = 238.050783 · 1.66·10-24 g = 3.952·10-22 g
1 amu=1/12(m12C)=1.66 · 10-24 gBreaking up nuclei into their constituents requires energy
http://ie.lbl.gov/toimass.htmlhttp://www.nndc.bnl.gov/masses/mass.mas03
Binding energy of a nucleusB = (Z · mp+ N · mn- M) · c2Binding energy B
of nucleus
nucleon
JA
CB
Jsmkg
smgsmg
smggg
cmmmCBCnp
1212
112
112
821625
28232424
212
1017.1
10404.110404.110404.1/1091056.1
/10310992.110674.1610672.16
66 12
nucleon
JA
UB
Jsmkg
smgsmg
smggg
cmmmUBUnp
12238
102
102
721624
28222424
2238
10145.1
10725.210725.210725.2/1091003.3
/10310952.310674.114610672.192
14692 238
Nuclear Potential
MeVaMeVaMeVaMeVaMeVa
oddNZAoddNZAaevenNZAaA
ZAaAZZaAaAaB
psymcsv
pp
symcsv
34;23;72.0;8.16;5.15
);(0);,();,(
21
3/43/4
23/13/2
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/liqdrop.html#c2
1 MeV = 1.602·10-13 J
Nuclear Binding Energy
Mass number A
1 MeV = 1.602·10-13 J
Binding energy normalized to mass number B/A
Nuclear Decay Processes
A B+bA(b)B14C(-)14N234U(α)230Th
Decay energy is released in kinetic energy of emittedparticles or in electromagnetic gamma radiation energy
JeVMeVQ
MeVMeVMeVMeVQ
BBBQBBBQcmcmmQ
U
U
ThHeUUAbBd
AbBd
127
22
104.81025.55.52
5.52128.12755296.28325.1779
234
234
2304234234
JeV 19106.11
Political developments in Europe
Economic instabilities, and theeconomic downturn worldwidetriggered by Black Fridaystrengthened the radical rightwing National Socialist PartyNSDAP party in Germany,which ran on a social andnational platform.
Democratic partiesRight wing partiesLeft wing parties
In January 1933 the party leader Adolf Hitler was appointed by
President Hindenburg asnew German Chancellor
-Reichstagsbrand-27 February 1933
The Reichstag building, seat of the German parliament, burns after being seton fire. This enabled Adolf Hitler to seize power under the pretext of protectingthe nation from threats to its security. (Photo credit: U.S. National Archives)
This Decree of the Reich President for the Protection of the People and State abrogates the following constitutional protections: • Free expression of opinion • Freedom of the press • Right of assembly and association • Right to privacy of postal communications • Protection against unlawful searches & seizures • Individual property rights • States' right of self-government
A supplemental decree creates the SA (Storm Troops) and SS (Special Security) Federal police agencies.
Consequences for Science and Academia
Minister of Education tookmore flexible stand. Jewishscientists were allowed to holdtemporary assistant posts, butthey were facing increasingadministrative difficulties.
KWI under Planck tried firstto remain independent but gotmore involved in war relatedresearch during WW-II.
KWI for Physics in Berlin with van de Graaff Accelerator tower in front
Removal from all Jewish faculty members from their posts(Law of restoration of Career Civil Service 1933). Many ofthe leading figures emigrated. Bernhard Rust became the new
Nuclear Reactions and Energy Release
a
A
Frederic Joliot and Irene Curie at Parishad observed the first nuclear reaction.Enrico Fermi showed the existence ofneutron induced reactions, whichproduce artificial radioactivity.Nuclear reactions can produce energyQ > 0 exothermicor need energy Q < 0 endothermic
A(a,b)B Q = (mA+ ma- mB- mb)·c2
Q = BB+ Bb- BA-BB
Nobel Prize 1938
difference of masses in entranceand exit channel determines Q
Q value of nuclear reaction process
a
A
b
B
A+a B+bA(a,b)B
projectile
target
product
recoil
reactioncendothermi0reactionexothermic0
22
BBBBQcmmcmmQ
aAbB
aAbB
Example: Nuclear Binding Energy
isotope B (J)
2H 3.34131·10-13
4He 4.53297·10-12
12C 1.47643·10-11
119Pd 1.59643·10-10
238U 2.88631·10-10
JJJQ
UBPdBPdBQ
QPdU
JJJQHBHBHeBQ
QHeHH
111010146
2389273
1194673
11946
7311946146
23892
121213
2242
421
211
21
1006542.31059633.121088631.2
)()()(
2
108647.31053295.41034131.32)()(2)(
Conversion of nuclei through fusion or fission leads to release of energy!
http://ie.lbl.gov/toimass.htmlhttp://nucleardata.nuclear.lu.se/database/masses/http://www.nndc.bnl.gov/masses/mass.mas03
Nuclear Energy possible through fission and fusion
The most stable nucleus is 56Fe