1 atomic structure protons 1 1 p (1.007276 amu) neutrons 1 0 n (1.008665 amu) electrons (0.0005486...
TRANSCRIPT
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Atomic StructureAtomic StructureProtons 1
1p(1.007276 amu)
Neutrons 10n
(1.008665 amu)Electrons(0.0005486 amu)
Neon-20 2010Ne
(19.992434 amu)
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Nucleus of the AtomNucleus of the Atom
The nucleus contains protons and neutrons
All atoms of the same element contain the same number of protons
Isotopes of an element can have differing numbers of neutrons
Isotopes having a nearly equal number of protons and neutrons are most likely to be stable
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Nuclear Shorthand and Nuclear Shorthand and DefinitionsDefinitions
Mass Number: (A) # Protons + #Neutrons Atomic Number: (Z) # Protons
(the atomic number defines the element)
Isotope: Nuclides of an element with the same atomic number (number of protons) but differing numbers of neutrons
THE ATOM The nucleus structure
– protons and neutrons = nucleons– Z protons with a positive electric charge
(1.6 10-19 C) – neutrons with no charge (neutral)– number of nucleons = mass number A
The extranucleus structure – Z electrons (light particles with electric charge)
equal to proton charge but negative
Particle Symbol Mass Energy Charge (kg) (MeV)----------------------------------------------------------Proton p 1.672*10-27 938.2 +Neutron n 1.675*10 -27 939.2 0Electron e 0.911*10 -30 0.511 -
Identification of an Isotope
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Question #1Question #1
A P32 atom has 15 protons in the nucleus. How many neutrons does it have?
a. 15
b. 16
c. 17
d. 18
IONIZATION-EXCITATION
Energy
characteristicradiation
Auger-electron
DEEXCITATION
THE NUCLEUSENERGY LEVELS
The nucleons can occupy different energy levels and the nucleus can be present in a ground state or in an excited state. An excited state can be reached by adding energy to the nucleus. At deexcitation the nucleus will emit the excess of energy by particle emission or by electromagnetic radiation. In this case the electromagnetic radiation is called a gamma ray. The energy of the gamma ray will be the difference in energies between the different energy levels in the nucleus.
Occupied levels
~8 MeV
0 MeV
ENERGY
Particle emission
Gamma ray
DeexcitationExcitation
EnergyEnergy particlesphotons
NUCLEAR EXCITATION
alpha-particlebeta-particle
Gamma radiation
NUCLEARDEEXCITATION
INTERNAL CONVERSION
characteristicradiation
conversionelectron
Radioactive decay
IAEA Training Material on Radiation Protection in Nuclear Medicine
STABLE NUCLIDES
long rangedelectrostatic
forces
short rangednuclear forces
p
p
n
Line of stability
Stable and unstable nuclides
Too manyneutronsfor stability
Too manyprotonsfor stability
RADIOACTIVE DECAYFissionThe nucleus is divided into two parts, fission fragments. and3-4 neutrons. Examples: Cf-252 (spontaneous), U-235 (induced)
-decayThe nucleus emits an -particle (He-4). Examples: Ra-226, Rn-222
-decayToo many neutrons results in -decay. n=>p++e-+. Example:H-3, C-14, I-131.Too many protons results in -decayp+=>n+ e++ Examples: O-16, F-18 or electron capture (EC). p+ + e-=>n+ Examples: I-125, Tl-201
86226
84222
24Ra Rn+
Multiple & prefixes (Activity)Multiple Prefix Abbreviation
1 - Bq
1 000 000 Mega (M) MBq
1 000 000 000 Giga (G) GBq
1 000 000 000 000 Tera (T) TBq
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Types of Ionizing Radiation: Alpha, Beta, & Types of Ionizing Radiation: Alpha, Beta, & GammaGamma
Alpha ParticleAlpha Particle
Beta ParticleBeta Particle
Large Mass (nuclei) – HeliumLarge Mass (nuclei) – HeliumAtom with a +2 chargeAtom with a +2 charge
Small Mass - Small Mass - ElectronElectron(subatomic (subatomic particleparticle))
Gamma PhotonGamma Photonand X-Raysand X-Rays
No MassNo Mass(Electromagnetic(Electromagnetic Radiation)Radiation)
+
+
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Penetrating Power of Radiations
Penetrating Power of Radiations
Alpha
Beta
Gamma and X-rays
Paper Plastic Lead
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Radioactivity UnitsRadioactivity UnitsActivity = Rate of decay of a radioactive sample or the
number of atoms that decay per unit time
1 Curie (Ci) = 3.7x1010 dps
or 2.22 x 1012 dpm
1 millicurie (mCi) = 3.7 x 107 dps or 2.22 x 109 dpm
1 microcurie (Ci) = 3.7 x 104 dps or 2.22x106 dpm
1 Becquerel (Bq) = 1 disintegration per second
Specific Activity: amount of radioactivity in a given mass or volume, e.g. μCi/ml
or mCi/mg
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Half-LifeHalf-Life
The time required for theamount of radioactive materialto decrease by one-half
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Half-Life: I-131 Half-Life: I-131
8 day half-life
0 8 16 24 321.0 ½ ¼ 1/8 1/16
20 mCi 10 mCi 5 mCi 2.5 mCi 1.25 mCi
It is impossible to know at what time a certain radioactive nucleuswill decay. It is, however possible to determine the probability l of decay in a certain time. In a sample of N nuclei the number of decays per unit time is then:
2lnT
eN=N(t)
Ndt
dN
2/1
t-0
RADIOACTIVE DECAY
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Activity CalculationsActivity Calculations
A = Aoe-t
(λ = ln 2 ÷ T½ = 0.693/ T½)
Phosphorus-32 has a half-life of 14.3 days. How much is left of a one millicurie shipment after 30 days?
A = 1 mCi × e-(0.693/14.3 d) x 30 d
A = 0.234 mCi