21.5 Detection of radioactivity

Summary

In 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

00:00

🔬 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.

05:01

🌟 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.

10:02

📋 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.

Keywords

💡Radioactivity

Radioactivity refers to the process by which an unstable atomic nucleus loses energy by emitting radiation. In the video, radioactivity is the central theme, with the script discussing how it was first discovered by Henri Becquerel when he observed uranium causing photographic plates to fluoresce without the need for sunlight. Radioactivity is essential for the detection methods and applications of radiotracers described in the video.

💡Geiger Counter

A Geiger counter is a device used to detect and measure ionizing radiation. The script explains its working principle, which involves a high voltage source creating an electric field within a tube filled with inert gas. When radiation enters, it ionizes the gas, creating charged particles that produce a current, which is then detected and counted, often producing an audible 'click' sound for each instance of radiation detected.

💡Scintillation Counter

Scintillation counters are radiation detection devices that work by using a scintillator material that emits light when struck by radiation. The script describes how this light is then converted into an electrical signal by a photomultiplier tube, which amplifies the signal for easier detection. This method is particularly interesting as it translates invisible radiation into visible light, making it easier to observe and measure.

💡Radiotracers

Radiotracers are radioactive isotopes used to trace the path of substances within a system. The video script provides an example of using oxygen-18, a radioactive isotope, to determine the source of oxygen in photosynthesis. Radiotracers are valuable in various fields, including medical diagnostics and environmental studies, for tracking the movement and transformation of elements.

💡Ionization

Ionization is the process by which an atom or molecule gains or loses electrons, resulting in the formation of ions. In the context of the video, ionization is crucial for the operation of both Geiger counters and scintillation counters, as it creates charged particles that can be detected and measured as evidence of radiation.

💡Photomultiplier Tube

A photomultiplier tube is a type of photodetector that amplifies the current produced by the photoelectric effect. The script explains its use in scintillation counters, where it multiplies the electrons emitted by the photo cathode upon being struck by light, resulting in a stronger signal that can be more easily measured.

💡Photoelectric Effect

The photoelectric effect is the phenomenon where light striking a material ejects electrons from it. The script mentions this in relation to the operation of scintillation counters, where the emitted light from the scintillator causes the photomultiplier tube to emit electrons, initiating the detection process.

💡Isotopes

Isotopes are atoms of the same element that have different numbers of neutrons, resulting in different atomic masses but similar chemical properties. The video script discusses stable isotopes like carbon-13 and radioactive isotopes like iodine-131, which are used in applications such as stable isotope probing and medical diagnostics.

💡Iodine-131

Iodine-131 is a radioactive isotope of iodine that is used in medical applications, particularly for diagnosing and treating thyroid disorders. The script explains its importance in the thyroid gland's function, as it is necessary for the production of thyroid hormones that regulate metabolism.

💡Henri Becquerel

Henri Becquerel was a French physicist who is credited with the discovery of radioactivity. The script recounts his accidental discovery when he observed uranium salts causing photographic plates to fluoresce, leading to the realization that radiation was being emitted from the uranium itself, independent of external energy sources like sunlight.

💡Photosynthesis

Photosynthesis is the process by which plants convert carbon dioxide and water into glucose and oxygen using solar energy. The video script uses photosynthesis as an example to illustrate the use of radiotracers, specifically oxygen-18, to trace the origin of the oxygen produced, demonstrating that it comes from water molecules.

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