Radioactivity

Pregunta	Respuesta
Transmutation	atoms being converted to atoms of another element
Nuclide	particular nucleus (specific composition) each isotope of an element has a different nuclide
Notation for neutron	1 N 0
Notation for proton	1 P 1
Notation for an electron	0 e -1
Radioactive Decay	when a nuclide is unstable and spontaneously emits radiation
What does NOT affect the intensity of radiation?	temperature, pressure, or other physical and chemical conditions
Alpha Particles	α
Beta Particles	high-speed electrons; β
Gamma rays	very high-energy photons; γ
What happens when a nuclide decays?	forms a daughter nuclide of lower energy
Alpha decay	loss of an α particle from the nucleus; A decreases by 4 and Z decreases by 2 in the daughter nuclide
Beta decay	ejection of a β- particle from the nucleus; a neutron is converted to a proton and a β- particle is expelled; Z increases by 1 unit
Positron emission	β+ particle is emitted from the nucleus; proton is converted to a neutron and a positron is emitted; Z decreases by 1 unit
Positron	the antiparticle of the electron
Electron capture	occurs when the nucleus interacts with an electron in a low atomic energy level; proton is transformed into a neutron
Gamma emission	the radiation of high-energy Y photons; usually occurs together with other forms of radioactive decay; different Y photons of different energies can be emitted as the nucleus returns to group state
What two factors determine the stability of a nuclide?	1. the number of neutrons (N), the number of protons (Z), and their ratio (N/Z) 2. the total mass of the nuclide
Band of stability	produced by a plot of numbers of neutrons vs. number of protons for all stable nuclides
As Z increases, the N/Z for a stable nuclei gradually _________.	increases
All nuclides with Z > ___ are unstable	83
If the N/Z ratio is too HIGH...	neutrons are converted to protons via beta decay
If the N/Z ratio is too LOW...	protons are converted to neutrons via positron emission or electron capture
Electrostatic Repulsive Forces	protons experience these forces within the nucleus which destabilize the nucleus
Strong Force	exists between all nucleons, contracts the weaker repulsive forces
What leads to greater stability?	the pairing of spins between nucleons
Elements with an _____ number of protons (Z) have a larger number of stable nuclides	even
Nuclide type: neutron-rich Description: high N/Z Mode of Decay: β- decay (lowers N/Z)	..
Nuclide type: proton-rich Description: low N/Z Mode of Decay: β+ emission or e- capture (increases N/Z)	.
Nuclide Type: heavy nuclides Description: Z > 83 Mode of Decay: α decay (reduces both Z & N	.
Decay Series	when all of the radioactive nuclides that are produced one after the other until a stable nuclide is made
What are three ways to detect radioactivity?	1. can expose light-protected films 2. can ionize the air 3. give off flash of light when interacting with specific chemicals
1 Ci (curie) = 3.70e10 d/s	measures radioactivity
The rate of radioactive decay (activity-A) is proportional to the ________.	number of nuclei present (N) A=kN
Radioactive decay follows ________	first-order kinetics
rate constant = ___________	decay constant (k)
The larger the k value, the _________ the activity of the substance	higher
Half-Life	the time taken for half the nuclei in a sample to decay ln(Nt/N0)=-kt Nt=N0e-kt ln(N0/Nt)=kt
Half-Life of 14C	t1/2=ln2/k
Radioisotopes	can be used to determine the ages of certain objects
Radiocarbon Dating	measures the relative amounts of 14C and 12C in materials of biological origin
The mass of the nucleus is less than....	the combined masses of the nucleons
Mass always __________ when nucleons form a nucleus	lost (the lost mass is released as energy)
Nuclear Binding Energy	energy required to break 1 mol of nuclei into individual nucleons
Electron Volt (eV)	way to express binding energy
nucleus + nuclear binding energy --> nucleons	,
1 amu = 931.5e6 eV = 931.5 MeV	.
The binding energy/nucleon peaks at elements with a mass number ________.	A = 60 (nuclides become more stable with increasing number up to around 60 nucleons, after which stability decreases)
Nuclear Fission	- heavier nucleus splits into lighter ones using neutron bombardment to start the process -releases energy and generates more high-energy neutrons, which causes further fission to occur -the fission process becomes self-sustaining by a chain reaction
Nuclear Fusion	-lighter nuclei can combine to form a heavier nucleus -requires high energy input to initiate the process -
Critical Mass	mass required to achieve a self-sustaining chain reaction

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