# 21.3 Radioactive decay  (Page 5/21)

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Because each nuclide has a specific number of nucleons, a particular balance of repulsion and attraction, and its own degree of stability, the half-lives of radioactive nuclides vary widely. For example: the half-life of ${}_{\phantom{\rule{0.5em}{0ex}}83}^{209}\text{Bi}$ is 1.9 $×$ 10 19 years; ${}_{\phantom{\rule{0.5em}{0ex}}94}^{239}\text{Ra}$ is 24,000 years; ${}_{\phantom{\rule{0.5em}{0ex}}86}^{222}\text{Rn}$ is 3.82 days; and element-111 (Rg for roentgenium) is 1.5 $×$ 10 –3 seconds. The half-lives of a number of radioactive isotopes important to medicine are shown in [link] , and others are listed in Appendix M .

Half-lives of Radioactive Isotopes Important to Medicine
Type The “m” in Tc-99m stands for “metastable,” indicating that this is an unstable, high-energy state of Tc-99. Metastable isotopes emit γ radiation to rid themselves of excess energy and become (more) stable. Decay Mode Half-Life Uses
F-18 β + decay 110. minutes PET scans
Co-60 β decay, γ decay 5.27 years cancer treatment
Tc-99m γ decay 8.01 hours scans of brain, lung, heart, bone
I-131 β decay 8.02 days thyroid scans and treatment
Tl-201 electron capture 73 hours heart and arteries scans; cardiac stress tests

Several radioisotopes have half-lives and other properties that make them useful for purposes of “dating” the origin of objects such as archaeological artifacts, formerly living organisms, or geological formations. This process is radiometric dating    and has been responsible for many breakthrough scientific discoveries about the geological history of the earth, the evolution of life, and the history of human civilization. We will explore some of the most common types of radioactive dating and how the particular isotopes work for each type.

The radioactivity of carbon-14 provides a method for dating objects that were a part of a living organism. This method of radiometric dating, which is also called radiocarbon dating    or carbon-14 dating, is accurate for dating carbon-containing substances that are up to about 30,000 years old, and can provide reasonably accurate dates up to a maximum of about 50,000 years old.

Naturally occurring carbon consists of three isotopes: ${}_{\phantom{\rule{0.5em}{0ex}}6}^{12}\text{C}\text{,}$ which constitutes about 99% of the carbon on earth; ${}_{\phantom{\rule{0.5em}{0ex}}6}^{13}\text{C}\text{,}$ about 1% of the total; and trace amounts of ${}_{\phantom{\rule{0.5em}{0ex}}6}^{14}\text{C}.$ Carbon-14 forms in the upper atmosphere by the reaction of nitrogen atoms with neutrons from cosmic rays in space:

${}_{\phantom{\rule{0.5em}{0ex}}7}^{14}\text{N}+{}_{0}^{1}\text{n}\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{}_{\phantom{\rule{0.5em}{0ex}}6}^{14}\text{C}+{}_{1}^{1}\text{H}$

All isotopes of carbon react with oxygen to produce CO 2 molecules. The ratio of ${}_{\phantom{\rule{0.5em}{0ex}}6}^{14}\text{C}{\text{O}}_{2}$ to ${}_{\phantom{\rule{0.5em}{0ex}}6}^{12}\text{C}{\text{O}}_{2}$ depends on the ratio of ${}_{\phantom{\rule{0.5em}{0ex}}6}^{14}\text{C}\text{O}$ to ${}_{\phantom{\rule{0.5em}{0ex}}6}^{12}\text{C}\text{O}$ in the atmosphere. The natural abundance of ${}_{\phantom{\rule{0.5em}{0ex}}6}^{14}\text{C}\text{O}$ in the atmosphere is approximately 1 part per trillion; until recently, this has generally been constant over time, as seen is gas samples found trapped in ice. The incorporation of ${}_{\phantom{\rule{0.5em}{0ex}}6}^{14}\text{C}{}_{\phantom{\rule{0.5em}{0ex}}6}^{14}\text{C}{\text{O}}_{2}$ and ${}_{\phantom{\rule{0.5em}{0ex}}6}^{12}\text{C}{\text{O}}_{2}$ into plants is a regular part of the photosynthesis process, which means that the ${}_{\phantom{\rule{0.5em}{0ex}}6}^{14}\text{C}\text{:}\phantom{\rule{0.2em}{0ex}}{}_{\phantom{\rule{0.5em}{0ex}}6}^{12}\text{C}$ ratio found in a living plant is the same as the ${}_{\phantom{\rule{0.5em}{0ex}}6}^{14}\text{C}\text{:}\phantom{\rule{0.2em}{0ex}}{}_{\phantom{\rule{0.5em}{0ex}}6}^{12}\text{C}$ ratio in the atmosphere. But when the plant dies, it no longer traps carbon through photosynthesis. Because ${}_{\phantom{\rule{0.5em}{0ex}}6}^{12}\text{C}$ is a stable isotope and does not undergo radioactive decay, its concentration in the plant does not change. However, carbon-14 decays by β emission with a half-life of 5730 years:

following processes: Solid phosphorus pentachloride decomposes to liquid phosphorus trichloride and chlorine gas b. Deep blue solid copper(II) sulfate pentahydrate is heated to drive off water vapor to form white solid copper(II) sulfate
How to know periodic table oftend
how to get atomic number of an element
how do you solve the examples in a much more explanatory way
Ogunleye
The reaction of aceto nitrile with propane in the presence of the acid
Explain this paragraph in short
What is solid state?
What is chemical reaction
Manish
transforming reactants to product(s)
Andre
process
Andre
Example of Lewis acid
Example of Lewis acid
Chidera
Chlorine
Anything with an empty orbital... the hydrogen ion is the most common example. BH3 is the typical example, but any metal in a coordination complex can be considered a Lewis acid.
Eszter
okay thanks
Jovial
aluminium and sulphur react to give aluminium sulfide.How many grams of Al are required to produce 100g of aluminium sulphide
aluminium and sulphur react to give aluminium sulphide how many grams of Al are required to produce 100g of aluminium sulphide?
Soni
aluminium and sulphur react to give aluminium sulphide how many grams of Al are required to produce 100g of aluminium sulphide?
Soni
2Al+3S=Al2S3
galina
m(Al)=100×27×2/150=36g
galina
150 comes from?
Soni
thank you very much
Soni
molar mass of Al2S3
galina
150.158
thiru
Why can't atom be created or destroyed
matter simply converts to pure energy
that's nice
Meshach
explain how to distinguish ethanol from a sample of ethanoic acid by chemical test
explain how ethanol can be distinguished from ethanoic acid by chemical test
Alice
Using a suitable experiment, describe how diffusion occurs in gases.
when the excited energy which are in gaseous state collides with another to liberate from one place to another
Meshach
what is electrolytes?
substance which splits into ions during melting or dissolving
galina
on passing electric current though electrode
Kv
State that use law of partial pressure in a gas jar containing a gas and water what is the total pressure composed of 272cm^3 of carbon (iv) oxide were collected over water at15°c and 782mmHg pressure. calculate the volume of the dry gas at stp(SVP of water at 15°c is 12mmHg)
was Dalton's second postulate"atoms of the same kind have have similar/same mass and size" Or " the one mentioned in B here?