Atomic and Nuclear Phenomena Flashcards
Photoelectric effect
When light of sufficiently high frequency is incident on metal in a vacuum, the metal emits electrons
When light’s frequency is above the threshold frequency of metal, the magnitude of the resulting current is
Directly proportional to the intensity/amplitude of the light
Threshold frequency (fT)
The minimum frequency of light that causes ejection of elections
Energy of a photon
E=hf
Maximum kinetic energy of ejected electron
Kmax=hf-W
W= Work function of metal
Work function
Minimum energy required to eject electron
W=hfT
Fluorescence
If a flurescent substance is excited with UV light, it will glow
Light returns to original state in 2+ steps which involves less energy, and lower frequency photon is emitted (sometimes within visible)
Mass defect
Mass of a nucleus is smaller than protons and neutrons due to E=mc^2
Small mass emits huge energy
Strong nuclear force
Attraction of replusive electromagnetic forces that overcomes repulsion of protons
Nucleon
protons and neutron
Binding energy
Nucleons must get close together and bonded system has lower energy than unbonded system
E=mc^2
Weak nuclear force
a lot less strong than strong nuclear forces
Mass defect is
The mass contributed by the binding energy in the nucleus
Binding energy is greatest for
Intermediate sized atoms
Isotopic notation
Atomic number (protons) bottom Mass number (protons + neutrons) top
Fusion
When small nuclei combine to form larger nucleus
Fission
Large nucleus splits into smaller nucleus, rarely spontaneous
Induced by absorption of low energy neutron
Radioactive decay
Spontaneous decay of nuclei emitting particles
Alpha decay
emission of a-particle which is 4,2He nucleus (2 protons, 2 neutrons, 0 electrons)
Carries a double charge
Do not penetrate shielding and interact with matter easily
Charge of alpha particles
+2
What will alpha particles cause a loss of
4 from mass number
2 from atomic number
Beta decay
B-particle is an electron
Emitted when a neutrons decays into a proton and antineutrino
What does a neutron decays into
Proton and antineutrino (v)
Is b radiation penetrating?
Yes
Positron
Mass of electron,but has a positive charge also a neutrino
B emission causes
Addition of proton to atomic number
During positron emission
Mass number will be less the positrons emitted
Gamma decay
Gamma ray emitted (high energy photons0
No change in mass number or atomic number
Electron capture
Reverse B- decay
Forms a proton from neutron to emit
Atomic number -1
Rate of nuclei decay
Delta(n)/Delta (t)=-(decay constant)(n)
Exponential decay
n=no(e)^-constant(t)
Decay constant
0.693/half life
How to find mass defect for e=mc^2
mulitply amu amount times the amount of protons and neutrons
Add together and subtract isotope nucleus weight
