# 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:

An atom or group of atoms bearing anelectrical charge such as the sodium and chlorine atoms in a salt solution.
Hello guys! Answer me questions nah
it's a list that shows the chemical element arranged according to their properties.
what is the chemical equation for ideal gas?
what's Boyle and gas law?
what's the meaning of this℃ in atomic table
wat are ions
Sinyene
What is periodic table
How to mix chemical
why the elements of group 7 are called Noble gases
they aren't. group 8 is the noble gasses. they are snobs that don't mix with others like nobles, they have full valence shells so they don't form bonds with other elements easily. nobles don't mingle with the common folk...
Jessica
the group 7elements are not the noble gases . according to modern periodic group 18 are called noble gases elements because their valence shell are completely field so that they can't gain or loss electron so they are not able to involve in any chemical reaction.
Leena
Group 7 element they are not noble gases they halogen and halogen mean salt formers
SIRAJO
what is chemistry
chemistry is the branch of science which deal with the composition of matter
SHEDRACK
discuss the orbital stracture of the following methane,ethane,ethylene,acetylene
Why phosphurs in solid state have one atom but in gas state have four atoms
Are nuclear reactions both exothermic reactions and endothermic reactions or what?
to what volume must 8.32 NaOH be diluted to its analytical concentration 0.20 M
weight in mg 1.76 mole of I
Sheriza
the types of hydrocarbons
u are mad go and open textbook
Emmanuel
hahahahahahahahahahahahaha
Jessica
aliphatic and aromatic hydrocarbons
Osakue
stupid boy Emmanuel
Ohanaka
saturated and unsaturated
Leena
aromatic hydrocarbon aliphatic hydrocarbon
SIRAJO
I don't use to see the messages
Hhhhhh
SIRAJO
how can you determine the electronegativity of a compound or in molecules
when u move from left to right in a periodic table the negativity increases
reeza
Are you trying to say that the elctronegativity increases down the group and decreases across the period?
Ohanaka
yes and also increases across the period
reeza
for instance when you look at one group of elements in a periodic table electronegativity decreases when you go across the table electronegativity increases. hydrogen is more electronegative than sodium, potassium of that group. oxygen is more electronegative than carbon.
reeza
i hope we all know that organic compounds have carbon as their back bone
OK,Thank you so much for the answer. I am happy now
can I ask you a question now
Osakue
yes
hanna
what is the oxidation number of nitrogen, oxygen and sulphur
Osakue
5, -2 & -2
hanna
What is periodic table
SIRAJO
What is an atom?
is a smallest particle of a chemical element that can exist
Osakue
Osakue
it is a substance that cannot be broken down into simpler units by any chemical reaction
An atom is the smallest part of an element dat can take part in chemical reaction.
Idris
an atom is the smallest part of an element that can take part in a chemical reaction nd still retain it chemical properties
Precious
Is the smallest particles of an element that take part in chemical reaction without been change
John