Test 2-Ch. 24 Nuclear Reactions Flashcard

Nuclear Reactions

-Reactions are accompanied by relatively large changes in energy and measurable changes in mass

-reaction rates depend only on number of nuclei and rarely based on the compound in which it occurs

Isotopes

atoms with the characteristic number of protons of the element but different numbers of neutrons

-in nature, the isotopes of the element are present in specific proportions

Intensity of Radiation
Directly proportional to the concentration of the element in the mineral, not to the nature of the mineral or compound, and is unaffected by temp, pressure or any other physical conditions
Alpha Decay

Helium 2+ ion expelled

change in mass is -4

change in protons is -2

change in charge is -2
-Every element beyond Bi(z = 83) is radioactive and exhibits alpha decay

Beta Decay

nucleus changes to a proton and a negative beta particle

change in mass = 0

change in protons = +1

change in charge = -1

Positron Emission

a proton changes to a neutron and a positive beta particle

change in mass = 0

change in protons = -1

change in charge = +1

Electron Capture

An electron and proton are changed into a neutron

change in mass = 0

change in proton = -1

change in charge = +1

 

 

Gamma Emission
excited nucleus goes to a stable nucleus and emits a gamma photon
Nuclear Stability- Odd or Even?

-elements with an even z usually have a larger number of stable nuclides than elements with and odd z.

-only four nuclides with odd N and odd z are stable: H(2/1), Li(6/3),B(10/5),N(14/7)

Predicting Mode of Decay

-Neutron-rich nuclides= undergo beta decay

-Proton rich nuclides= undergo beta emission or electron capture

-Heavy nuclides(Z>83) undergo Alpha decay

Decay Rate (A)
Decay rate(A) = -(delta nuclei)/(delta t)
Unit of Radioactivity
1 curie(Ci) = 3.7*10^10 d/s (one disintegration per second)
Decay Constant k

-larger the decay constant, the higher decay rate

A= (-delta nuclei)/(delta t) = k*nuclei

*ln(nuclei(t)/nuclei(0)) = -kt

*nuclei(t) = nuclei(0)*e^(-kt)

 

Radioactive Decay Process

It is a first-order process

-in the case of nuclear decay the number of nuclei is considered rather than their concentrations

Half-life

-the number of nuclei remaining is halved after each half-life

-t(1/2) = ln2/k

*dependent of number of nuclei

Activity at Time = t

A(t) = A(0)*e^(-k*t)

 

Radioactive Dating Equation
t = (1/k)*ln(A(0)/A(t))
half-life of carbon 14
= 5730 yrs
12C/14C after an organism dies
the ratio in a dead organism steadily increases because 14C decreases as it decays
Einstein’s Equation

E = mc^2

Delta(E) = Delta(m)*c^2

Nuclear Binding Energy
The energy required to break 1 mol of atoms into neutrons and hydrogen atoms = the enegy to break 1 mol of nuclei into individual nucleons
Electron Vold (eV)

The energy an electron acquires when it moves thru a delta(V) of 1 volt

;

1 eV = 1.602E-19J

;

MeV or Mega eV
1 MeV = 10^6 eV = 1.602E-13 J
1 amu to eVs
1 amu = 931.5E6 eV = 931.5 MeV

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