Nuclear Half Life: Intro and Explanation
Summary
TLDRThis video explains the concept of nuclear half-life, focusing on how it determines the time it takes for half of a radioactive element to decay into another element. Using thorium-234 as an example, the video illustrates how it decays into protactinium through beta decay, with its half-life being 24 days. The video also highlights different half-lives for various elements, such as uranium-238 with a half-life of 4.5 billion years and polonium-218 with a half-life of just three minutes, demonstrating the wide range of nuclear decay times.
Takeaways
- ⚛️ Nuclear half-life is the time it takes for half of a radioactive substance to decay.
- 🔄 In a nuclear process, the number of protons and neutrons in an atom's nucleus changes.
- 💡 An example is thorium-234 undergoing beta decay, where a neutron turns into a proton, transforming thorium into protactinium.
- 📉 The half-life of thorium-234 is 24 days, meaning every 24 days, half of the thorium decays into protactinium.
- 🧪 After 24 days, 80 grams of thorium becomes 40 grams, then 20 grams after another 24 days, and so on.
- ⏳ The half-life process continues, reducing the amount of thorium by half with each cycle, but it doesn't disappear—it changes into another element.
- 📊 Half-life is represented as T1/2, and different elements have different half-lives based on their decay process.
- 🌍 Uranium-238, for example, has a half-life of 4.5 billion years, taking that long for half of it to decay.
- ⏱️ Polonium-218, on the other hand, has a very short half-life of only three minutes, decaying rapidly into lead.
- 🧮 The key concept is that half-life is the time needed for half of a sample to decay into something else.
Q & A
What is nuclear half-life?
-Nuclear half-life is the time it takes for half of a radioactive substance to undergo a nuclear process, where the number of protons and neutrons in the nucleus changes.
What happens during beta decay?
-During beta decay, a neutron in the atom's nucleus turns into a proton, increasing the number of protons in the nucleus and changing the element.
What is the significance of the number of protons in an atom?
-The number of protons in an atom determines what element the atom is. A change in the number of protons results in the atom becoming a different element.
In the example given, what element does thorium-234 decay into?
-Thorium-234 decays into protactinium-234 after undergoing beta decay, where one neutron turns into a proton.
What is the half-life of thorium-234?
-The half-life of thorium-234 is 24 days, meaning it takes 24 days for half of the thorium sample to decay into protactinium-234.
How does the amount of thorium change after each half-life?
-After each half-life, the amount of thorium decreases by half. For example, after the first 24 days, 80 grams becomes 40 grams, then 20 grams after another 24 days, and so on.
How can nuclear half-life be represented in equations?
-Nuclear half-life is often represented with the notation T½, indicating the time it takes for half of a sample to decay.
Do all radioactive elements have the same half-life?
-No, different radioactive elements have different half-lives. For example, uranium-238 has a half-life of 4.5 billion years, while polonium-218 has a half-life of just 3 minutes.
What happens to uranium-238 during its decay process?
-Uranium-238 undergoes alpha decay, turning into thorium-234. This process has a half-life of 4.5 billion years.
Why is it important to understand nuclear half-life?
-Understanding nuclear half-life is important because it helps scientists predict how long it takes for radioactive materials to decay, which has applications in fields like nuclear energy, medicine, and environmental studies.
Outlines
🔬 Understanding Nuclear Half-Life
This paragraph introduces the concept of nuclear half-life, explaining that it describes the time it takes for nuclear processes, where the number of protons and neutrons in an atom's nucleus changes, to occur. The example given is the beta decay of thorium-234, where a neutron turns into a proton, transforming the element into protactinium. The explanation continues with a practical example, showing how thorium decays over time, reducing by half every 24 days until most of the sample has changed into protactinium. The key takeaway is that half-life refers to the time required for half of a material to undergo decay, and it's often denoted as T 1/2.
⏳ Half-Life Variation Across Elements
This paragraph expands on the concept of half-life by discussing how different nuclear processes have vastly different half-lives. For example, uranium-238 has a half-life of 4.5 billion years, while polonium-218 has a much shorter half-life of only three minutes. The example illustrates how, in a laboratory setting, half of a polonium-218 sample could decay in the time it takes for a brief break. The paragraph emphasizes that the half-life varies significantly depending on the element and decay process, providing contrasting examples to show the diversity in time scales for nuclear reactions.
Mindmap
Keywords
💡Nuclear half-life
💡Nuclear process
💡Beta decay
💡Thorium-234
💡Proactinium-234
💡Decay process
💡Uranium-238
💡Alpha decay
💡Polonium-218
💡Graph of decay
Highlights
Nuclear half-life tells us how long it takes for nuclear processes to occur.
A nuclear process involves a change in the number of protons and neutrons in an atom's nucleus.
An example of a nuclear process is thorium-234 undergoing beta decay, where one of its neutrons turns into a proton.
When thorium-234 undergoes beta decay, it changes into protactinium-234 due to the increase in protons.
The half-life of thorium-234 is 24 days, meaning it takes 24 days for half of a thorium sample to decay into protactinium.
After each half-life, the remaining thorium is reduced by half: from 80 grams to 40 grams, from 40 to 20 grams, and from 20 to 10 grams.
Half-life refers to the time it takes for half of a sample of a radioactive element to decay into another element.
A graph of thorium's decay over time shows exponential reduction in the amount of thorium, with each bar representing a half-life period.
Half-lives vary greatly between elements: uranium-238 has a half-life of 4.5 billion years, while polonium-218 has a half-life of just 3 minutes.
Polonium-218's short half-life means that half of its sample would decay in 3 minutes, making it challenging to study without immediate observation.
For uranium-238, it would take 4.5 billion years for half of a sample to decay into thorium-234.
The time between each stage in a decay process differs based on the half-life of the element involved.
Half-life is crucial for understanding the time required for radioactive decay and is represented by the symbol T₁/₂.
The concept of nuclear half-life applies to different radioactive elements, each with its own distinct half-life duration.
Half-life calculations help predict the amount of time required for a specific amount of a radioactive element to decay.
Transcripts
we're going to talk about nuclear
half-life and then we're going to do
some practice math problems on this
stuff so nuclear half-life tells us how
long it takes for nuclear processes to
occur so a nuclear process is one where
the number of protons and neutrons in an
atom's nucleus where the number of those
protons and neutrons change here is an
example of a nuclear process so here we
have thorium 234 and it is undergoing
beta decay which means that one of its
neutrons turns into a proton so it
originally had 90 protons and then it
gets 91 protons but here's the thing
the number of protons and Adam has
determines what kind of an element it is
so when thorium which had 90 protons
ends up getting 91 protons it changes
into a different element what used to be
an atom of thorium now turns into an
atom of P a proact inium okay so this is
a decay process for thorium turning into
proact inium now we said nuclear
half-life tells us about how how long it
takes for these sort of processes to
occur how long does it take for this to
happen for thorium to turn into proact
inium well let's talk about this let's
say we start with 80 grams of thorium
if 24 days go by at the end of those 24
days I'm going to be left with 40 grams
of thorium the other forty grams of
thorium have turned in a pro acting okay
so I'm only left with 40 now after
another 24 days there's only 20 grams of
thorium left and after another 24 days
there's only 10 grams of thorium left
all the rest has turned into proact
inium so here's the thing every 24 days
the amount of thorium that we have
gets cut in half because the other half
becomes proact inium so we'd say that
for this process for this reaction the
half-life is 24 days so half-life is the
time that it takes for 1/2 of a certain
amount of thorium to decay to turn into
proact inium to disappear okay so 24
days to go from 80 to 40 the amount we
have gets cut in half 24 days to go from
40 to 20 cut in half again 24 days to go
from 20 to 10 gets cut in half again and
remember it's not I'm saying
disappearing but it's not that it
disappears it's that it's just not
thorium anymore it's becoming proactive
but so when I say disappear that's what
I mean I sometimes I think it's easier
to think about that okay so anyway we
say that half-life the time required for
half of a sample to decay and we often
abbreviate half-life with lowercase T
with this 1/2 so I can write here that
the T 1/2 for this is 24 days ok maybe
you're more of a visual person so let's
look at a quick graph of what's going on
here okay let's imagine that this is a
graph of thorium turning into pro acting
here's the amount of thorium that we
start with and then after one half-life
we have half of it and then after
another half-life we have half of this
and then after another half-life we have
half of this and so on ok now if this is
showing a story I'm going to proact
inium each of these bars would be
separated by 24 days that would be the
amount of time between them now all
nuclear reactions all these different
decay processes have different
half-lives ok for different amounts of
time for example and oh and I should say
that
these amounts of time vary widely so for
example uranium-238 here undergoes alpha
decay to make thorium-234 and the
half-life for this reaction is 4.5
billion years which means that it would
take 4.5 billion years for half of a
sample of uranium 238 to turn into
foreign okay but then on the other hand
polonium 218 undergoes alpha decay to
make lead to 14 and the half-life of
this process is only three minutes so
that means that if you were in the lab
studying polonium 218 and you had to get
up and like run to the bathroom for
three minutes by the time you came back
half of the polonium you had in your
sample would have disappeared it would
have turned into lead okay so if this
were a graph for uranium's decay instead
of thorium the difference between each
one of these bars would be 4.5 billion
years would be the amount of time
between each half-life and if this were
polonium it would be three minutes to go
from here to here and three minutes to
go from here to here so that is
half-life the time required for half of
a sample to decay to turn into something
else - as I keep saying to disappear
okay so that's a background on half-life
now let's do some calculations for
half-life
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