CHEM 1405 Concept Review: Nuclear Reactions

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Common forms of Radioactive Decay

Alpha Decay: Radioactive decay that releases a high energy helium nucleus referred to as an “alpha particle.”

General formula for Alpha Decay:  $^x_yA\:\longrightarrow\:^{x-4}_{y-2}B\:+\:^4_2\alpha$

Beta Decay:  Radioactive decay that releases a high energy electron referred to as a “beta particle.”

General formula for Beta Decay:  $^x_yA\:\longrightarrow\:^x_{y-2}B\:+\:^{\:\:0}_{-1}\beta$

 

Gamma Decay:  Radioactive decay that often accompanies other radioactive decays which occurs as a result of an unstable high energy nucleus (sometimes referred to as a metastable nucleus) collapsing into a more stable state.  The extra energy is released as an extraordinarily high energy photon called a “gamma ray”.

General formula for isolated Gamma Decay:  $^x_yA^{\ast}\:\longrightarrow\:^x_yA\:+\:^0_0\gamma$

 

Positron Emission:  Radioactive decay that occurs as a result of a proton in the nucleus being converted into a neutron.  The particle released is effectively a high energy positively charged electron called a “positron.”

General formula for Positron Emission:  $^x_yA\:\longrightarrow\:^x_{y-1}B\:+\:^0_1e$

 

Electron Capture:  The nuclear reaction that occurs as a result of an electron from the cloud surrounding the nucleus falling into or “being captured” by the nucleus.  A positively charged proton becomes “neutralized” by the negatively charged electron, effectively converting it into a neutron.

General formula for Electron Capture:  $_y^xA+^{\:\:\:0}_{-1}e\:\left(orbital\:electron\right)\longrightarrow^{\:\:\:\:x}_{y-1}B$

 

 

Particles Found in Nuclear Reactions

Particle	Symbol		Particle	Symbol
Neutron	$^1_0n$		Alpha particle	$^4_2\alpha\:\:\:\:or\:\:\:\:^4_2He$
Proton	$^1_1p\:\:\:or\:\:\:^1_1H$		Beta Particle	$^{\:\:0}_{-1}\beta\:\:\:\:or\:\:\:\:^{\:\:0}_{-1}e$
Electron	$^{\:\:0}_{-1}e$		Positron	$^0_1e$

 

 

Nuclear transmutations:  Forced nuclear reactions achieved by bombarding (striking) a nucleus with a neutron or another nucleus.  These reactions are also sometimes referred to as “bombardment reactions.”

 

Condensed Notation for Bombardment Reactons

As a nuclear reaction equation, the above would be expressed as follows:

$^{14}_{\:7}N+^4_2He\longrightarrow^{17}_{\:8}O+^1_1H$

 

 

Measuring Radiation

Curies (Ci):  a unit of activity, equal to the number of disintegrations per second that occur in 1 gram of radium

Becquerel (Bq): the SI unit for radiation activity which is equal to 1 disintegration per second.

Rad:  a unit that measures the amount of radiation absorbed by a gram of material such as body tissue

Gray (Gy):  the SI unit for absorbed dose, which is defined as the joules of energy absorbed by 1 kg of tissue.

Radiation Equivalent in Humans (rem):  measures the biological effects of different kinds of radiation.

 

 

Half-Life of a Radioisotope

Half-life:  the time necessary for one half of a radioactive sample to decay. 

Example: The half-life of iodine-131 is 8 days, and you start with 10 grams.  After 8 days, only 5 grams of the sample will still be iodine-131.  The rest will have decayed into other particles and/or elements.

 

Decay Curve:  A diagram which shows the decay of an isotope for each half-life.  An example is below:

 

Decay Curve for Bismuth (Half-life = 5 days)

 

 

Mass-Energy Conversion

When nuclear reactions occur, a small amount of mass is destroyed and converted into energy.  Albert Einstein discovered that the relationship between the mass destroyed and the energy produced is as follows:

$E=\Delta mc^2$

Where “E” is the energy released, “m” is the mass destroyed or “mass defect”, and c is the speed of light.

 

 

Fission vs. Fusion

Nuclear Fission	Nuclear Fusion
A heavy nucleus breaks up to form two or more smaller nuclei.	Two light nuclei combine to form a heavier nucleus.
It involves a chain reaction.	Chain reaction is not involved.
The heavy nucleus is bombarded with neutrons.	Light nuclei are heated to extremely high temperatures.
We have proper mechanisms to control fission reaction for generating electricity.	Proper mechanisms to control and sustain fusion reaction are still being developed.
Disposal of nuclear waste is a major environmental problem.  (Long-lived radioactive isotopes)	No real radioactive waste to dispose of.  No environmental issues.
Produces tremendous amounts of energy.	Produces tremendous amounts of energy.