21.5 Detection of radioactivity
Summary
TLDRIn this educational video, Mr. Donny explores the detection of radioactivity, introducing viewers to the methods like photographic film, Geiger counters, and scintillation counters. He explains how these tools work to detect radioactive emissions and discusses the use of radiotracers in various applications, including scientific research and medical diagnostics. The video also addresses the misconception about the age of water molecules and their continuous transformation in nature.
Takeaways
- 🔬 The discovery of radioactivity was initially attributed to Henri Becquerel, who observed that uranium emitted particles without the need for external energy sources like sunlight.
- 📷 Photographic film was used to detect emissions from radioactive materials, revealing radioactivity even in the absence of expected conditions like sunlight.
- 🌐 Radioactivity can be detected through the ionization of gases, as demonstrated by the Geiger counter, which uses a high voltage source to create an electrical current when radiation ionizes an inert gas.
- 💡 Scintillation counters use a phosphor material that emits light when struck by radiation, which then triggers an electron emission through the photoelectric effect, creating a detectable electrical signal.
- 🔋 The photomultiplier tube in scintillation counters amplifies the signal from a single emitted electron, making it easier to detect and measure.
- 🌿 Radiotracers are radioactive elements used to trace chemical processes, such as determining the source of oxygen in photosynthesis by using oxygen-18.
- 🦕 The script challenges the common notion that the water we drink is the same water from the time of the dinosaurs, arguing that water molecules are constantly being broken down and reformed.
- ⚕️ Medical applications of radiotracers include tracking the path of elements in the body, such as iodine-131, which is essential for thyroid function and metabolism.
- 🧬 Radiotracers can be used to study chemical reactions and biological processes, providing insights into how elements are transformed and utilized within organisms.
- 🔍 The script provides a basic introduction to the detection of radioactivity and the use of radiotracers, with links for further information on the history and technical details.
- 📚 The educational content is aimed at explaining the fundamental concepts of radioactivity detection and the practical applications of radiotracers in various fields.
Q & A
How was radioactivity first discovered?
-Radioactivity was first discovered by Henri Becquerel while studying uranium. He noticed that uranium could make things fluoresce and initially thought this was due to sunlight. However, during a cloudy day, he found that photographic film was still exposed to an image of the rock, indicating that the rock emitted particles on its own, not because of sunlight.
What is the function of a Geiger counter in detecting radioactivity?
-A Geiger counter detects radioactivity by using a high voltage source to create an electric current when a radioactive particle enters the tube filled with inert gas, causing the gas to ionize. This ionization leads to a movement of charged particles towards the electrodes, completing the circuit and generating an electrical current that can be detected and counted.
How does a scintillation counter work to detect radioactivity?
-A scintillation counter works by using a phosphor or other material that emits light when struck by radiation. The emitted light's photons then hit a photo cathode, causing electrons to be emitted through the photoelectric effect. These electrons are multiplied by a photomultiplier tube, creating a signal that can be detected and measured.
What are radiotracers and how are they used in scientific research?
-Radiotracers are radioactive elements or atoms used to trace processes in various systems. They can be used to determine the origin of elements in chemical reactions, such as in photosynthesis, by labeling specific atoms and tracking their radioactivity to see where they end up in the process.
How can radiotracers help in understanding the source of oxygen in photosynthesis?
-Radiotracers, such as oxygen-18, can be used to label water molecules in photosynthesis. By supplying plants with water containing oxygen-18 and then analyzing the radioactivity of the resulting oxygen and glucose, scientists can determine that the oxygen in O2 comes from the water molecule.
What is the rant about the water we drink being the same as during the time of dinosaurs?
-The rant challenges the idea that the water we drink today is the same as the water that existed during the time of dinosaurs. It argues that water molecules are constantly being broken down and reformed through processes like photosynthesis and cellular respiration, so it's not accurate to say that the exact same water molecules exist today.
What medical application of radiotracers was mentioned in the script?
-The script mentioned the use of iodine-131 as a radiotracer in medical applications. It is used to follow the path of iodine in the body, particularly in the thyroid gland, which requires iodine to produce thyroid hormones that regulate metabolism.
What is the role of the inert gas in a Geiger counter?
-The inert gas, such as argon, in a Geiger counter is used to create an environment that does not conduct electricity until a radioactive particle enters the tube. The ionization of the inert gas by the radioactive particle allows for the movement of charged particles, which then generates an electrical current that can be detected.
What is the photoelectric effect and how is it used in scintillation counters?
-The photoelectric effect is a phenomenon where light hitting a surface causes an electron to be emitted. In scintillation counters, this effect is used to convert the light emitted by the scintillator when struck by radiation into an electrical signal by causing electrons to be emitted from the photo cathode.
What is the purpose of a photomultiplier tube in a scintillation counter?
-A photomultiplier tube in a scintillation counter is used to amplify the signal created by the photoelectric effect. It turns one emitted electron into many more, making the signal strong enough to be easily detected and measured by the counter.
What are some of the other applications of radiotracers mentioned in the script?
-The script mentions stable isotope probing with carbon-13 as an application of radiotracers, which can be used to track where carbon ends up in various systems. Additionally, it discusses the use of radiotracers in medical diagnostics to monitor the activity of elements in the body.
Outlines
🔬 Discovering Radioactivity and Detection Methods
This paragraph introduces the topic of radioactivity detection, starting with the historical discovery by Henri Becquerel who observed uranium's fluorescence and its ability to make objects fluoresce. He initially believed this was due to the sun's energy absorption and re-emission but later found that uranium emitted particles on its own, even without sunlight. This discovery was made using photographic paper to detect emissions, which led to the understanding that these emissions were not X-rays but charged particles. The paragraph then explains the working principle of a Geiger counter, which detects radiation by ionizing an inert gas within a tube, creating an electrical current that can be measured and counted. The Geiger counter's design includes a high voltage source, electrodes, and a thin window for radiation to enter, resulting in a clicking sound that indicates radiation detection.
🌟 Scintillation Counters and Radiotracer Applications
The second paragraph delves into scintillation counters, which use a phosphor material that emits light when struck by radiation. This emitted light, upon hitting a photo cathode, triggers the photoelectric effect, causing electrons to be emitted. These electrons are then multiplied by a photomultiplier tube, creating a signal that can be detected and measured. The paragraph also discusses the use of radiotracers in scientific research, such as tracing the origin of oxygen in photosynthesis using oxygen-18, a radioactive isotope. Radiotracers can be used to follow the path of elements in various processes, with a specific mention of iodine-131's role in thyroid function and its medical applications. The speaker also addresses a common misconception about the water cycle, arguing that the water we drink is not the same water from the time of the dinosaurs due to the constant breakdown and formation of new water molecules.
📋 Summary of Radioactivity Detection and Radiotracers
The final paragraph serves as a summary of the methods for detecting radioactivity, mentioning photographic film, Geiger counters, and scintillation counters. It also touches upon the concept of radiotracers, which were discussed in the previous paragraph. The speaker expresses hope that the information was helpful and invites further questions, promising to provide links for those interested in more detailed information.
Mindmap
Keywords
💡Radioactivity
💡Geiger Counter
💡Scintillation Counter
💡Radiotracers
💡Ionization
💡Photomultiplier Tube
💡Photoelectric Effect
💡Isotopes
💡Iodine-131
💡Henri Becquerel
💡Photosynthesis
Highlights
Introduction to the detection of radioactivity and the uses of radiotracers.
Henry Becker's discovery of radioactivity through uranium fluorescence and photographic paper.
Becker's realization that uranium emits particles on its own, not due to sunlight.
The concept of radiation and the differentiation from X-rays based on charge.
Explanation of how a Geiger counter works using high voltage and inert gas to detect radiation.
The process of ionization in a Geiger counter creating an electrical current from radioactive emissions.
Scintillation counters' use of phosphor materials to emit light upon radiation impact.
Photoelectric effect in scintillation counters leading to electron emission and signal multiplication.
Application of radiotracers in tracing chemical reactions, such as photosynthesis.
Use of oxygen-18 in tracing the source of oxygen in photosynthesis.
Debunking the myth that water we drink is the same as during the time of dinosaurs.
Medical applications of radiotracers, such as iodine-131 in thyroid function.
Importance of thyroid hormones in controlling body metabolism and the effects of imbalances.
Summary of methods for detecting radioactivity: photographic film, Geiger counters, and scintillation counters.
Discussion on the practical applications and innovative uses of radiotracers.
Invitation for further exploration and questions on the topic of radioactivity detection and radiotracers.
Transcripts
how's it goin ladies and gentlemen mr.
Donny here again this time take a look
at 21.5 stuff detection of radioactivity
our objectives are to explain the
different ways in which radioactivity
can be detected as well as the uses for
radiotracers all right so big question
is how can we detect radioactivity how
do we even know it's there
all right so this is going to be a very
basic video just kind of introducing
some of there's like fantastic stories
of how this was all discovered I'm not
going to go in a great detail with that
but I'll provide links to that
information
first how was it first discovered well
Henry Becker L was studying uranium and
he noticed that it would fluoresce and
it can make things fluoresce and the he
thought that maybe the Sun is hitting
the rock in the rocks absorbing that
energy and then remitting it later and
that's what he was testing until one day
oh well how was he testing it he was
using photographic paper to detect the
emission of what he thought were x-rays
from the rock but on a cloudy day you
know you had this Sun and he was like
alright cool but it was a cloudy day so
there wasn't enough sunlight and he
thought he ruined his experiment you
know he had the rock sitting on top of
the photographic paper but it was cloudy
out so he was like well we're not going
to get any fluorescence we're not going
to get this uranium rock to emit any
particles but on a hunch he decided to
develop the photographic film anyway and
he noticed that it was exposed to add
the image of the rock on it even though
there was no sunlight to give it energy
and excited in the first place so the
rock itself must be emitting particles
on its own not because of the sunlight
but from its you know it's old whatever
got going on with it
so radiation discovered it was very
teary who coined the phrase radiation
and they later figured out that it
wasn't x-rays because the particles that
were coming out for charge all right so
what happens is sometimes another way to
detect it is that when you have
radioactivity and you have radioactive
particles being shot off they can
collide with other atoms other nuclei
and cause them to I
which is helpful because if we have
charges then we can do stuff with those
charges like detect them with electrical
currents so this is how the Geiger
counter works so the Geiger counter
basically works as such it has a high
voltage source so it's got some power
it's got an amplifier in counter and so
from the high voltage source we have two
electrodes we got a positive electrode
and the outside of this tube is a
negative electrode so in this tube we
have a screen in the front which is
really thin and it allows things to pass
through it into the tube which is
important and the rest of the tube is
you know usually like metal and doesn't
let stuff through but in this window if
there's a radioactive sample outside it
can emit radiation and it can pass
through that window so this is what
happens first the radiation enters that
thin window and into the tube right so
we have so a radioactive emission coming
into the tube which is filled with an
inert gas like argon argon is a noble
gas it's not very reactive it's not
going to conduct electricity so right
now we have a broken circuit here so
it's not connecting it's broken until
the radiation comes in to the tube and
then it causes the inert gas to ionize
it can kick off an electron or something
it causes you know the argon gas to
become ionized and now that we have
charged particles and we have these
electrodes that are charged we'll get
some migration of those charged
particles so the charged particles
migrate towards the anode and towards
the cathode so you get the negative
going towards positive terminal and we
get that positive argon moving towards
the negative terminal now what does
happen is a movement of charge and the
movement of charge is an electrical
current so we just completed the circuit
and we got a charge we were able to
detect a current so the current is
detected by the amplifier encountered
and it's counted so this can also be
detected by a speaker given the clicking
sound so that's why in you know if you
know Geiger counters at all
person comes mine is probably going that
click I could click like like from the
radioactive samples so you can hook it
up to a speaker and make a sound that
way and then the counter opponent so you
can count how often you're getting that
radiation into the tube all right
there's also these things called
scintillation counters which I think are
pretty neat so the big idea is that a
scintillator has a phosphor or some
other material that will emit light when
radiation strikes it so we have the same
kind of idea we got some you know atoms
inside here and then when radiation
comes in it'll hit with those atoms and
those atoms will give off light right so
that light is being emitted which is
pretty cool so if some piece radioactive
particle comes in boom causes light to
be emitted now when that light is
emitted the photons of that light strike
a photo cathode which is right here
which is then going to emit an electron
to the photoelectric effect which
deserves its own video in its entirety
basically it's light hits a surface and
it causes an electron to be shot out so
that's what's happening here so the
light hits the photo cathode and it
causes an electron to be shot out now
the photomultiplier tube is pretty much
going to turn this one electron being
emitted into a bunch of electrons which
can then be detected more easily at the
end by the detector right so that's why
we call it a multiplier tube it's
causing that signal to get multiplied
again I'm not going to go into how it
does that because that deserves its own
video in and of itself that's the big
idea scintillation counters the
radioactivity causes light to be emitted
and that light we can use to make an
electrical current that we can measure
and count all right so yeah so other
clever applications we can do things
with these radioactive particles we can
use radiotracers which is pretty much
just using radioactive elements and
atoms to trace how things are going on
so let's say we had this chemical
reaction yeah photosynthesis we got
carbon dioxide and water give enough
sugar and oxygen
well the question is does the o2 come
from the co2 or from the h2o because
they both have co2 or I'm sorry they
both have oxygen or you know is it a
little bit of both how do we even know
well here's the clutter application you
can make water using oxygen 18 so we can
make all these waters using oxygen 18
instead of 16 so oxygen 18 is
radioactive so now you can go alright
well where did this oxygen 18 end up and
you can detect its radioactivity so you
supply that water to the plant you let
the plant go through photosynthesis and
then you just then you just separate the
o2 from the c6h12o6 from the glucose and
you see what's radioactive and it turns
out that it's the o2 the o2 is
radioactive so that tells us that the
oxygen in o2 came from the water
molecule which is pretty cool so you can
do other things like that you can do
there's stable isotope probing with
carbon 13 where you can see where the
carbon ends up in systems but I got I
got a rant alright I have to rant and
yes it has to do with dinosaurs so every
time I hear this did you know that water
we drink is the same water that was
around during the dinosaurs it's all
just a big cycle I always get a little
bitter and it's stupid but it it irks me
so let's think about this yes I
understand the water cycle it's you know
starts in the oceans evaporates
condenses into clouds and comes down as
rain people drink it and then they
excrete it and it gets cycled through
and all the excitement but is it really
the same water molecules really is it
because let's think about it we have
photosynthesis which is using water and
it's breaking it apart right where did
the water go huh where does the water go
it's not over here it's not water
anymore it's part of the glucose and
it's you know made into oxygen it's no
longer a water molecule but then we get
cellular respiration where we have you
know that glucose and other oxygen
molecules reacting to give us more co2
and h2o new h2o so is it really the same
h2o if you rearrange the atoms is it the
same and
my opinion it's not it's not so we're
always breaking down water molecules and
making new ones all the time so is it
really same water dinosaurs not all of
it probably some of it is but not all of
it uh yeah you know the example of
things that shouldn't bother me would do
all right anyway
other applications there's medical
applications of these radiotracers you
can follow a path of elements in the
body
a big one is iodine at 131 and your
thyroid your thyroid needs iodine 131 to
work effectively it needs that so it can
make these thyroid hormones and the
thyroid hormones control your metabolism
in your body if you don't have enough
activity of your thyroid you get
hypothyroidism your body kind of slows
down you have a loss of appetite you put
on weight and your body is pretty much
just you know it's metabolism and slow
down which is if you have
hyperthyroidism you're like constantly
hungry and you can't put on way you have
weight loss and you're just always
eating because your metabolism is too
high so yeah I thought that was pretty
neat it's applications so to summarize
what can you say about the following
what can you say about how radioactivity
can be detected
you know photographic film a Geiger
counter scintillation counters what can
you tell me about those and what can you
say about radiotracers okay so I hope
you found that helpful I'll see you in
class and I'll put links to things in
more detail if you're curious you can
check out those ones bring questions get
back
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