nuclear energy and radiation

04/12/23 Physics 31: Nuclear Energy; Effects and Uses of Radiation - Christopher Chui

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Physics 31: Nuclear Energy - Effects and Uses of Radiation

Christopher Chui


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Nuclear Reactions and the Transmutation of Elements

Nuclear reaction: n + 147N14

6C + p Conservation of energy: a + X Y + b Reaction energy, Q-value=(Ma+MX-Mb-MY)c2

If Q>0, the reaction is exothermic or exoergic If Q<0, the reaction is enthermic or endoergic Neutron capture: n + 238

92U 23992U

Beta decay: 23992U 239

93Np + e- + Beta decay: 239

93Np 23994Pu + e- +


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Nuclear Fission & Nuclear Reactor Neutron bombards: n + 235

92U14156Ba + 92

36Kr + 3n Energy/fission = (0.9MeV/nucleon)

(236nucleon)~200MeV Sustaining chain reaction bomb or nuclear reactor In nuclear reactors, moderators such as heavy water

or graphite (C-12) to slow down reactions Critical mass must be maintained for nuclear fission Control rods are used to maintain critical mass Delayed neutrons allow control rods to operate A breeder reactor breeds new fuel, 239

94Pu, from 23892U


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Fusion Nuclear fusion builds larger nuclei by combining

smaller nuclei, up to about A ~ 60 Producing deuterium: n + 1

1H + 21H + 2.22 MeV

Fusion reactor: 21H + 2

1H 31H + 1

1H + 4.03 MeV


1H 32He + n + 3.27 MeV


1H 42He + n + 17.59 MeV

Temperatures required for fusion to occur ~108 K Two forms of fusion reactors: magnetic

confinement and inertial confinement


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Magnetic and Inertial Confinement Fusion Russian tokamak uses two magnetic fields to

confine plasma Lawson criterion: ion density x time > 3x1020 s/m3

Temperatures of 4x108 K have been obtained Inertial confinement: deuterium and tritium pellets

are bombarded with several high power lasers. Lawson criterion was achieved, but not hot enough

NOVA lasers deliver 105J in 10-9 s1014W, which is more all US power plant capacity


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Radiation Damage

Ionizing radiation are charged particles which ionize atoms or molecules of any object

Alpha and beta rays have energies of 1 Mev and atoms and molecules ionize at ~10 eV

Damage to cells due to ionization All forms of radiation can ionize atoms by knocking

out electrons Damage to DNA is more serious: somatic and

genetic


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Dosimetry-1 Strength of a source at a given time is source

activity 1 Ci = 3.70 x 1010 disintegrations/sec 1 Bq = 1 disintegration/sec Source activity = N/t = N = 0.693N / T1/2

Absorbed dose is the effect on the absorbing matter. 1 R = 1.6x1012 ion pairs/gm of dry air

1 R = 0.878 x 10-2 J/kg of air 1 rad = 1.00 x 10-2 J/kg in any absorbing material 1 Gy = 1 J/kg = 100 rad


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Dosimetry-2

Relative biological effectiveness or quality factor is the number of rads of X or g radiation that produces the same biological damage as 1 rad of radiation

Effective dose in rem = dose in rad x QF Effective dose in Sv = dose in Gy x QF We all receive a low-level natural

radiation~0.36rem/yr. Government allows 0.5rem/yr Radiation film badge monitors radiation absorbed Radiation sickness includes nausea, fatigue, etc


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Radiation Therapy and Tracers The treatment of disease, mainly cancer, using 60

27Co or X-rays in the range of 200 keV to 5 MeV

The diagnosis of disease, such as 13153I, 99m

43Tc Tracers are isotopes for research in biology and medicine.

146C or 3

1H are tagged to molecules to study pathway Autoradiography uses film to detect isotopes Single photon emission tomography uses camera to image

whole body patients Positron emission tomography uses positron emitters, 11

6C, 13

7N, and 189F. After absorption, are emitted and detected

PET and SPET give images related to biochemistry, metabolism, and function, while X-ray CT scans give anatomy


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NMR and MRI NMR requires a ring circular magnetic field and

and RF coil. A RF pulse of EM radiation is applied to the sample. If hf = E = kBT, then the photons will be absorbed, exciting many nucleiresonance

For 11H, f = 42.58 MHz for a field BT = 1.0 T

NMI is to image NMR to give 2D and 3D images Typical resolutions: X-rays ½ mm; nuclear

medicine 1 cm; SPET 1 cm; PET 3-5 mm, NMR ½ -1 mm; ultrasound 2 mm

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