CHEM 1406 Concept Review: Nuclear Chemistry

Back to Chemistry 1406 Concept Reviews

Radioisotope: An isotope that is unstable enough to manifest radioactivity, which means that it will undergo spontaneous nuclear decay over time.

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: $LaTeX: ^x_yA\:\longrightarrow\:^{x-4}_{y-2}B\:+\:^4_2\alpha$ $^x_yA\:\longrightarrow\:^{x-4}_{y-2}B\:+\:^4_2\alpha$

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

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

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: $LaTeX: ^x_yA^{\ast}\:\longrightarrow\:^x_yA\:+\:^0_0\gamma$ $^x_yA^{\ast}\:\longrightarrow\:^x_yA\:+\:^0_0\gamma$

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: $LaTeX: ^x_yA\:\longrightarrow\:^x_{y-1}B\:+\:^0_1e$ $^x_yA\:\longrightarrow\:^x_{y-1}B\:+\:^0_1e$

Bombardment Reactions

Bombardment reactions are reactions where one nucleus (or particle) is accelerated at high speeds and slammed into another nucleus. These reactions can sometimes lead to a larger atom being formed from two smaller ones. Bombardment reactions are used to carry out transmutations.

Transmutations: The transformation of one element into another by bombarding a stable nucleus with high speed particles such as alpha particles, protons, neutrons, or small nuclei.

Particles Found in Nuclear Reactions

Particle	Symbol	Mass Number	Charge	Degree of penetration
Neutron	$^1_0n$	1	0	Can be very high
Proton	$^1_1p$	1	1+	Moderate
Alpha particle	$LaTeX: ^4_2\alpha\:\:or\:\:^4_2He$ $^4_2\alpha\:\:or\:\:^4_2He$	4	2+	Low
Beta Particle	$LaTeX: ^{\:0}_{-1}\beta\:\:or\:\:^{\:0}_{-1}e$ $^{\:0}_{-1}\beta\:\:or\:\:^{\:0}_{-1}e$	0	1-	Moderate
Positron	$^0_1e$	0	1+	Moderate
Gamma Ray	$LaTeX: ^0_0\gamma$ $^0_0\gamma$	0	0	Very High

Balancing Nuclear Equations

In a nuclear equation, the sum of the mass numbers on the reactant side must equal the sum of the mass numbers on the product side. Likewise, the sum of the atomic numbers (or charges) on the reactant side must equal the sum of the atomic numbers (or charges) on the product side. For example, in the following equation:

$LaTeX: ^{24}_{11}Na\:+\:^4_2\alpha\:\longrightarrow\:^1_1H\:+\:^x_y?$ $^{24}_{11}Na\:+\:^4_2\alpha\:\longrightarrow\:^1_1H\:+\:^x_y?$

The unknown element (?) can be found by solving the following 2 equations, one for the top number (mass) and one for the bottom (charge).

$24+4=1+x$ and $11+2=1+y$

Solving these equations gives you $x=27$ and $y=12$ , which means the unknown element is $LaTeX: ^{27}_{12}Mg$ $^{27}_{12}Mg$ .

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. For example, if the half-life of iodine-131 is 8 days, and you have a 10 gram sample. After 8 days, only 5 grams of the sample will still be iodine-131. The rest will have decayed and broken down 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)

An alternative way of viewing the decay curve would be as follows:

$LaTeX: 100\:g\:bismuth\:\:\longrightarrow\:\:50\:g\:bismuth\:\:\longrightarrow\:\:25\:g\:bismuth\:\:\longrightarrow\:\:12.5\:g\:bismuth...$ $100\:g\:bismuth\:\:\longrightarrow\:\:50\:g\:bismuth\:\:\longrightarrow\:\:25\:g\:bismuth\:\:\longrightarrow\:\:12.5\:g\:bismuth...$

where each arrow represents 1 half-life. In this case, the half-life for bismuth is 5 days. Therefore, to go from 100 g bismuth to 12.5 g bismuth would take $LaTeX: 3\cdot5\:\:or\:\:15$ $3\cdot5\:\:or\:\:15$ days.

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 known environmental issues.
	Raw material is not easily available and is expensive.		Raw material is cheap and easily available
	Produces tremendous amounts of energy.		Produces tremendous amounts of energy.