Chemistry LESSON 3 - Nuclear Radiation

Lesson Objectives:


  • Students learn the history of the discovery of radiation and nuclear chemistry.
  • Students learn about alpha, beta, and gamma radiation (most common forms of radiation): their similarities and differences and their effect on the atoms that produce them as well as their relative energies and damage potential.
  • Students learn the concept of half-life and how to calculate the amount of a radioactive isotope remaining given half-life information.
  • Students learn that half-life is isotope specific, that most naturally-occurring isotopes are not radioactive, and how radioactivity is measured.
  • Students are introduced to the concept that the nucleus is held together by strong nuclear forces.
  • Students complete specific activity calculations and are first introduced to the unit conversion method.
  • Students are introduced to the Big Bang theory and how it relates to nuclear fusion and fission reactions and the creation of the majority of the elements.
  • Students are asked to investigate a science-based societal issue

About radiation: Who discovered it? And how? Radiation is invisible, right?

Yes, radiation is invisible, and that certainly made it hard to discover, but not impossible. In 1896, a French scientist named Henri Becquerel (pronounced "beck-er-L") was working with a mineral called pitchblende. He didn't know it at the time, but pitchblende is radioactive. One day Becquerel accidentally placed a key between one of his pitchblende samples and a piece of photographic film.

What's "photographic film"?

Ah, yes. Photographs and film. Hmmm...
In the 19th century folks discovered that light, just a ray of light, could cause chemical reactions in a silver solution. It's really a very interesting reaction, but I don't want to get into it now. Suffice it to say that photographic films are coated with chemicals which can detect light. It is like a chemical version of an eye, OK?

OK.

Anyway, Becquerel later used that plate, and when he developed it he discovered an image of the key on it!

Weird!

Really weird. Becquerel had no explanation for that image. Finally he decided that some invisible particles or light rays from the pitchblende penetrated the photographic container and caused the plate to be exposed. The key had blocked some of the "light", so a shadow of the key was made.

So Becquerel discovered radiation by accident?

Aye, but Becquerel was smart enough to figure out what was going on. His discovery led the way to many important inventions, and increased our knowledge of many things - from the universe to atoms.

Is beta decay the only kind of radiation? And is tritium the only radioactive substance?

No, there are two other forms of radiation and many different types of radioactive substances beside tritium.

What other forms of radiation are there?

Beta radiation is just one kind of radiation. The other two are called alpha and gamma radiation. We wonít encounter them until we start to study other, heavier elements. Besides, they are more in the area of physics than chemistry.

But what are these alphas and gammas? They sound like ancient Greek letters.

Thatís where the names come from. Of course the Greeks had no idea about radiation. Radiation wasnít discovered until the 20th century. As it was discovered, the three types were named after those three Greek letters. They were named based upon their ability to pass through matter.

Like a ghost?

Sort of. (But remember, thereís no such thing as a ghost!)
Alpha particles are very weak and cannot pass through a piece of paper. Even your skin can block them.
Beta particles are a bit stronger. They can pass through skin and some can even go through a book!

What are these particles anyway?

Actually we have discussed them already.
Alpha particles are actually fast moving 4He, with no electrons. So alpha particles have a positive charge from the two protons.

A +2 charge?

Yes, exactly. Beta particles are fast-moving electrons. So they have a charge of -1.

That's what is spit out of tritium when it decays.

Right, and that is why we call it beta decay. In beta decay a high speed electron is spit out of the nucleus. In alpha decay a high speed helium nucleus is spit out. Many different elements have isotopes which produce alpha and beta radiation - spitting out alpha particles (4He-2) or beta particles (e-).

And what about the gamma radiation?

Gamma rays are extremely powerful and it takes very thick bricks to stop them. Gamma isnít a particle at all. It is a high-energy ray of light.

Let me see if I got this straight. There are only three kinds of radiation and they are named by how well they pass through a substance.

Yes. Now it is your turn to tell me the three types of radiation.

Alpha particles are the weakest and are just helium atoms stripped of their electrons, so they have a positive charge (+2) because of the two protons on each particle.
Beta particles are more powerful and are just electrons, so they each have a single negative charge (-1).
And gamma rays are not particles at all -- just very powerful rays of light which can pass through lots of things.

Very good!

How often do these radioactive substances decay?

They do it all the time. Nothing can stop radioactive decay, not even freezing temperatures. The rate of decay is not affected by the chemical or physical state of the sample.

No, no. I mean, how long does it take to get rid of all the radioactivity?

Oh, well that depends on the particular radioisotope. That brings us to the subject of half-life.

Half life! I thought life was all or nothing. You can't have a half life.

No, YOU can't have a half life, and neither can I, but a radioisotope can have a half-life (notice the hyphen). The rate at which a radioactive sample decays, its half-life, depends on the specific radioisotope.
Take tritium (3H) as an example. It has a half-life of about 12 years.

And that means...?

That means, half of a sample of tritium will have decayed after 12 years. So if you start with 1,000 atoms of tritium, in twelve years you would have only 500 atoms of tritium left. And you would have 500 atoms of something else. Can you tell me what those 500 atoms of something else would be?

I suppose they are the left over helium atoms (3He) produced by the decay of tritium.

You "suppose" very well. After 12 years, half of the tritium would have been transmuted to helium-3.

And what about the other 500 tritiums?

Well, they are tritium and they will do what tritium always does, beta-decay into helium-3. So in 12 more years half of those 500 tritium atoms will have decayed into more helium-3.

Leaving only 250 tritiums.

Yes, exactly. After a total of 24 years those 1,000 tritium atoms would have decayed into 750 helium-3 atoms, with only 250 of the original tritium atoms left. That's because 24 years is TWO half-lives for tritium. After each half-life, only half the original radioisotope remains, and that's why we call it "half-life". It's the time it takes half of the radioisotope to decay.
Now tell me how much tritium there would be in each successive 12 year interval. Start with 1,024 tritium atoms.


OK. In 12 years you would have half of 1,024 (or 512) tritium decays, producing 512 helium-3 atoms, and leaving 512 tritiums to continue decaying.
In another 12 years half of those 512 tritiums would have decayed away, leaving only 256 tritiums.
Another 12 years (36 years from when we started) would leave only 128 atoms of tritium.
Then another half-life goes by, so 12 years later you have only 64 tritiums. Then 32, then 16, then 8, then 4, then 2, and then just 1 tritium left. I suppose that decays in 12 years, too.

Another good supposition. But the funny thing about radioactive decay is that it is all a matter of probability. With 1,024 tritium atoms, you can be confident that about 512 will have decayed after 12 years. Just like you would be confident that if you flipped a coin 1,024 times it would come up heads about 512 times. But if you only had one coin flip, it might come up heads or tails. One or the other, but you don't know which. That's the problem with probabilities. They can trick you up sometimes. Especially when you are thinking about just one event. Like one coin flip or one tritium decay.

Sounds complicated.

Well, frankly, some folks understand the problems with probability immediately and others don't. The important thing to understand is that you don't really work with one, or even 1,000, atoms at any one time. You work with billions! So it doesn't really matter about the small numbers problem and the probabilities.

So, you're wasting my time.

No! I'm teaching you both the theory and the practice of alchemy. A good alchemist knows both.

OK. OK
There are other radioisotopes beside tritium, right?

Yes, and they each have their own half-life. That is, each radioisotope decays at its own rate.

Which cannot be changed. Not even by freezing it. Right?

That's right. You have been paying attention, haven't you? Let's consider another radioisotope.
Carbon-14 (14C) has a half-life of almost 6000 years (5770 years to be exact). Tell me, if I waited 12,000 years, how much of the original carbon-14 would remain?

That's easy. Half!
No wait. Half of half. Because it has gone through two half-lives (12,000 years = 2 X 6,000 years). So it would have only a quarter of its original radioactive substance left.

Yes. I'm glad you caught your error there. In fact we can write down a series of ever smaller fractions to represent the half-life decays. All radioisotopes decay by half during each half-life. So after each half life we have half of what we started with.
Use 1 to represent the "fraction" of radioisotope we start with (actually the 1 means ALL the atoms are the radioisotope). Then we get a series of fractions like this: 1, 1/2, 1/4, 1/8, 1/16, 1/32,........

And it goes on forever!

Yes, or very close to forever. By doubling the number under the fraction line (the denominator) we are halving the entire number. See?

I think I get it. Give me another radioisotope.

OK. Potassium-40 has a half-life of 1.3 billion years.

What? That's ridiculous!

No, that's a fact. Some radioisotopes are very patient. Others are not, and they have half-lives measured in fractions of a second. It all depends on which radioisotope you are dealing with. So, if I had a rock with only 1/8 as much potassium-40 as it had when it was made (from molten lava), how old is that rock?

Huh?

Oh, you can do this Arthur. All I'm doing is turning the problem around. If the rock has only 1/8 as much potassium-40 as it started with, how many half-lives have gone by.

Oh, I see. Well, just a half-life back in time it would have had 1/4 of its radioactivity. And a half-life before that it had half (1/2) its radioactivity. And a half-life before that it had all its radioactive potassium-40.
Let's see, that means it went through, one half life (to get to 1/2), then a second half-life (to get to 1/4) and a third half-life to get to 1/8. So that rock sat through three half-lives.

Yes. So, how old is it then?

Ah, three half-lives at 1.3 billion years each half-life is 3.9 billion years. (3 X 1.3 billion years = 3.9 billion years)

That's right! The rock is 3.9 billions years old. Get it?

Yeah. I get it. Just figure out how many half-lives have gone by and multiply that by the length of one half-life to figure out how long it has been decaying. But how radioactive is a rock?

That depends on the rock. Some are very radioactive and some are not very radioactive at all. We measure radioactivity using a 20th century device called a Geiger counter (pronounced "Guy-ger" counter).

Named after some guy named Geiger, I assume.

Aye! A Geiger counter counts the number of particles given off by a radioactive substance. The exact way it does that is best left for a physics class. However, we all express the amount of radioactivity in a substance by the number of disintegrations it has each second.

Do we call each unit of disintegration a "Geiger"?

No (but that's a good guess).
Becquerel's discovery with pitchblende got the attention of a French husband and wife team, called the Curies. They built on his work and found two new radioactive elements, polonium (Po) and radium (Ra). We named the unit of radiation after them. I'll spare you the details. But they studied huge amounts of radioactive decay. One gram of the radioisotope they studied, radium-226 (226Ra), produces 37 billion disintegrations per second. We now call that much radioactivity a Curie (abbreviated "Ci").
One Curie (Ci) equals 37 billion disintegrations per second (abbreviated "37 bdps").

Wow! That's a lot of radioactivity.

Yes it is! We express it as Curies per gram (of rock, or gas, etc.) That brings us to our last radioactive word. Specific activity is the number of Curies per gram.

So, a one-gram rock which gives off 37 billion disintegrations each second has a specific activity of one. As a matter of fact, one gram of pure radium-226 (whatever that is) has a specific activity of one, by definition!

Yes. Very good. And if you had a one-gram rock which gave 18 and a half (18.5) billion disintegrations per second...

... it would have a specific activity of one-half.

Correct. Now suppose you had a 100-gram rock which gave off 370 billion disintegrations per second (370 bdps). What would be its specific activity?

Ah, that's a harder one. But I can do it!
That 100-gram rock has 100 grams (obviously) producing 370 billion disintegrations per second.

But we express specific activity in "Curies per gram", not "Curies per 100 grams".

I know. I know!
So only one gram of that rock would be producing 3.7 billion disintegrations per second. (I just divided 370 bdps by 100 grams to get the number of disintegrations produced by just one gram of the rock).
So one gram of that rock produces only 1/10 of a Curie (3.7 bdps divided by a full Curie, which is 37 bdps, equals 1/10 of a Curie).
So that rock has a specific activity of 1/10 (or 0.1).

Yes, but 1/10 of what? What are the units of specific activity?

Oh, Curies per gram! So I suppose I should say that the rock has a specific activity of 0.1 Curies per gram.

Yes. You're absolutely right! You sound like a real scientist when you say it that way.
It's always a good idea to think of the units you are dealing with whenever you are working on a scientific math problem. It makes what you are talking about clearer.

It's easy to get lost in this kind of thinking. I lose track of where I am in the math, sometimes.

We all do! The trick is to work your math slowly and orderly. Each person goes about their math work in a different way. But as long as it is clear to them (and correct) then that is fine.

How do YOU do YOUR math work? With that "calculator" from the 20th century?

Well, yes and no. Calculators help, especially with complex numbers. But calculators are worthless if you don't know what you are doing. That's why it is good to write things down in an orderly manner, and be particularly careful with your units. Be sure you haven't forgotten an important step.

OK. But how DO you do your math work?

I lay out the problem as a series of steps, and see if it makes sense. Then I do the calculations. I'll use the previous problem as an example. (This is MY way of doing the same problem. That's not to say that you did it wrong because you did it differently.)
First I ask myself, "What do I have?" ("What do I know?") and "What do I want?" ("What do I want to know?").

You "have" a 100 gram rock producing 370 billion disintegrations per second. And you "want" the specific activity.

That's right. The next step is to recognize the connection between what I "want" and what I "have". In this problem it is the units of specific activity that makes the connection.

How's that?

Well the units of specific activity are "Curies per gram". Right?

Right.

And a Curie is 37 billion disintegrations per second. Another way of saying that is, 1 Curie EQUALS 37 billion disintegrations per second.

Yeah, I'm with you so far. (I think.)

Good. Now I line the units up in order to go from what I have to what I want.
The rock is 100 grams and produces 370 billion disintegrations per second.
I'm going to write that as "370 bdps/100 grams".

That's 3.7 bdps per gram!

Yes it is, but let's not move too quickly. Let's also remember the units we want to have at the end of it all. We want the answer to be in Curies per gram, because that's what specific activity is! So we must "convert" disintegrations per second into Curies.
Conversions are a very important part of science math problems. Some people panic when they see "conversion problems". They really don't need to panic. Besides, the panic just makes things worse! If they think about the units involved in any conversion, it all goes very smoothly and clearly.

How do you mean?

Well, one Curie equals 37 bdps. I'm going to write that as "37 bdps = 1 Curie". If you have been following my thinking you can now line up my "thoughts" into a single math statement. Try it.

OK (but I'm not sure what you are trying to do).
37 billion disintegrations per second = 1 Curie (37 bdps = 1 Curie)
Specific activity is expressed as Curies per gram (Curie/gram)
and the rock is 100 grams producing 370 bdps.

Very good. Now line them up in such as way as to get rid of the numbers and units I don't need while keeping the ones I want.

How can you get rid of the units you don't need?

By converting them. I do that by remembering that any number divided by itself is 1. Also I remember that any number multiplied by one is unchanged. Those two rules are the most important rules in mathematics!

Yeah, even I know that anything divided by itself is one! And multiplying by one is a useless exercise!

Not useless. Useful! You'll see why in a moment. Now, have you thought that 37 billion disintegrations divided by a second equals one?

One what?!

37 billion disintegrations divided by one second equals one. One Curie! Remember?

Ah, yeah. So what?

So, one equals 1 Curie divided by 37 billion disintegrations per second.
That's written as "1 = 1 Curie/37 bdps".

I see. All you've done is move it around to make the one equal to something related to the problem. To the conversion that is.

Yes. Exactly. Now, let's get back to the problem.
That 100 gram rock produces 370 billion disintegrations per second.
And, "1 = 1 Curie/37 billion disintegrations per second".
Now, what would happen if I multiplied the 370 billion disintegrations per second in that 100 gram rock, by 1?

Just multiplying by one does nothing. It is unchanged.

Yes you are right. It "does nothing" and it is unchanged. But we can do something and change the number if, instead of multiplying by one, we multiple by "1 Curie/37 bdps". When we do that we are just multiplying by one because "1 = 1 Curie/37 billion disintegrations per second". That's the same as 1, but it allows us to convert our problem into the units we want.

But multiplying by "1 = 1 Curie/37 billion disintegrations per second" is just dividing by 37 billion.

That's right. Now let's write this all out as an "equation".
370 bdps/100 grams (that's the rock)
multiplied by
1 Curie/37 bdps.

That's 370 bdps/100grams times 1Curie/37bdps or another way of saying it is
(370bdps/100grams) X (1Curie/37bdps)

Yes. And now you have your answer!

No, I don't! Where?

Let's write it as a proper math expression. It will make it more obvious.

The Rock
370 bdps
----------------
100 grams


times
x

The Conversion
1 Curie
---------------
37 bdps


equals
=

The Answer (almost)
10 Curies
----------
100 grams


or
=

The Answer (finally)
0.1 Specific activity
(Curies/gram)


Notice that the bdps above and below the fraction line "cancel each other out".

Yeah, because you can slide the numbers left and right along the fraction.
So really you could have written that equation as 370 bdps/37bdps = 10.

Yes you could have. And the bdps disappears because you are dividing something by itself (bdps/bdps =1). That leaves you with just a clean "10".

And the part "Curies/100grams" that's still there? What about it?

Oh, yes. We divide that 10 from above, by the 100 grams of rock to give 0.1 Curies/gram. And that is our answer. The specific activity is 0.1 Curies/gram.

It looks like a long way to go for a simple answer.

Well, it is a disciplined way to do the problem, and it works for me! It lets me keep track of the units and lays it all out in a clear manner.

Must I do the math your way?

No. If you have a way that works for you and you are happy with it, then stick with it. However, I've found that by lining up all the information, and juggling the math around to reflect what I am trying to get at, I arrive at the right answer every time.
And speaking of time, I think it is time to end this lesson. Any final questions about atoms?

Yeah. Where did atoms come from? How were they made?

Oh, goodness! You do like to tackle the big questions don't you?
The universe and everything in it started many billions of years ago in a Big Bang!

An explosion?

Yes, but not your typical explosion. It was an explosion from nothing that created everything.

What?! Sounds like magic - or nonsense.

Yes, it does. It isn't quite magic, but it is about as close as science gets to magic! And I assure you it isn't nonsense either. I don't want to get into the details of exactly how this Big Bang came about. It's a very specialized subject, and I'm not sure I fully understand it myself! Suffice it to say that out of this huge explosion came all the protons, neutrons and electrons which make atoms.

All kinds of atoms were created by the Big Bang?

No, just the smallest and simplest elements were made directly from the Big Bang. The vast majority of atoms created were just hydrogen and helium, with all their various isotopes. That's why they are so common.

The "air of the universe".

Yes. But there was also a trace of the next heavier elements: lithium, beryllium, and boron.

Oh, new elements! What's their atomic number? And their abbreviations? Are they difficult to learn?

It's very simple really. These next three elements were the ones to have more protons (and neutrons and electrons).
Lithium has 3 protons and is abbreviated (Li).
Beryllium has an atomic number of 4 and is abbreviated (Be)
And boron has 5 protons and is written as simply (B)


How many neutrons does each have?

Well lithium usually has 4 neutrons.

So it has an atomic mass of 7. Usually.

Yes. Most lithium, but not all lithium, has 4 neutrons, which along with the 3 protons (which define it as lithium) give it an atomic mass of 7 Daltons. However, some lithium has only 3 neutrons.
But, see here, I don't want you to try to memorize ALL the various isotopes. It's good to know the isotopes of hydrogen and a few special isotopes. But it will be a waste of your time to memorize them all. You can always look up their atomic mass later, if you need to. No alchemist goes far without his "Handbook of Chemistry". Recall, it is the number of PROTONS that really matter.

Yeah, yeah, I know. So, from this Big Bang came the first 5 elements?

Yes, that's right. Also, some were made in a process called "nuclear synthesis", which means the creation of nuclei.

How? With what?

With the starting material of the Big Bang - the hydrogen and helium mostly. And the "how" was (and still is) "nuclear fusion"

OK. Now you're just giving me names without meaning. What's nuclear fusion?

As the name implies, nuclear fusion is a reaction in which the nucleus of one atom fuses with the nucleus of another.

I see. And by adding together two atoms, you add together all the protons that were in them. So you build heavier elements using the light ones.

Yes, exactly. In the process you also make an awful lot of energy -- lots of gamma rays!

Sounds dangerous. And this still goes on? Inside stars?

Yes indeed. The main nuclear fusion reaction is the fusing together of two hydrogen atoms to get helium. The leftover energy powers the sun, and most of the other stars in the universe too.

But there was already helium from the original Big Bang.

Yes, and the universe is making more helium as it powers the sun and stars. But I see you are getting anxious to learn how the heavier elements were formed.

Probably from more nuclear fusions, using heavier elements than hydrogen.

That's right. As a star grows old it uses up its hydrogen. Eventually there is nothing but helium in the star. Then the star shrinks and starts to slam the heliums together...

... creating atoms with 4 protons. Beryllium!
But, hey, there was beryllium created in the Big Bang too.

Yes, but I haven't finished my story. Two berylliums can get slammed together to make an element with 8 protons, oxygen. Oxygen makes up about 20% of our atmosphere.

You mean the air we breath was made inside a star?

Yep, and so were most of the atoms in your body. The carbon atoms, with 6 protons are the result of fusing other smaller atoms.

Like by fusing two lithium atoms (atomic number 3) or a helium and a beryllium (atomic numbers 2 and 4). Either way you get 6 protons.

Right. The exact nuclear reactions are not important for us to go into. But, as you can see, it is simply a matter of slamming atoms together, fusing their nuclei, and getting new elements. There are also a lot of unstable nuclei formed and they rapidly decay into more stable forms, giving off all three forms of radiation as they rearrange their new nuclei.

Nuclear fusion is another form of transmutation!

Yes, it is. These nuclear fusions go on all the time inside stars all over the universe. Eventually they end up with atoms containing 26 protons (and a bunch of neutrons). We call that element iron.

So iron is the heaviest element.

No. Iron is the heaviest element created within stars. After a big star has "burned" all its nuclear fuel and run out of options, it undergoes a final big squeeze and then explodes!

The star explodes?!

Yes. We call it a "nova". During this tremendous explosion, more atoms are slammed together, and elements heavier than iron are formed. Like cobalt, mercury, and gold!

Wow! When will our sun explode?

Don't worry. This star will not die for billions of more years.

Hey, does this mean that all this "stuff", all these atoms in me are from explosions? From Big Bangs and novas?

That's right. The iron in your blade and in your blood was once at the center of a star, billions of years ago. So was the air we breath and the water we drink.

We are made of star stuff!

You said it. I think that is really amazing, don't you?

Yeah, it sure is!

Why not take a break and think about that? After you've had a rest we'll go into the most important part of alchemy and atoms.


Grading for this lesson:

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Assignment for Lesson 3

Do the test below. If you get 3 or fewer wrong, it will be assumed that you understand the lesson, and you can go on immediately to the next lesson.

If you get more than 3 wrong, you will be asked to resubmit the wrong answers and show your work. The teacher will then look at your work and give you advice on what you are doing wrong.



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1. Which of these atoms is NOT an isotope of the others?


A4He
B234U
C235U
D238U
E236U
Fnone of the above

 

2. Which of the following is NOT a type of radiation?


AAlpha particles
BTransmutation
CGamma Rays
DBeta Particles
EAll of the above are types of radiation
FNone of the above are types of radiation

 

3. What is an alpha particle and what is its charge?


AAn alpha particle is a powerful beam of light and has a neutral charge.
BAn alpha particle is a powerful beam of light and has a charge of -1.
CAn alpha particle is an electron, so it has a charge of +1.
DAn alpha particle is an electron, so it has a charge of -1.
EAn alpha particle is a helium nucleus and has a charge of +1.
FAn alpha particle is a helium nucleus and has a charge of +2.

 

4. What is a beta particle and what is its charge?


AA beta particle is a powerful beam of light and has a neutral charge.
BA beta particle is a powerful beam of light and has a charge of -1.
CA beta particle is an electron, so it has a charge of +1.
DA beta particle is an electron, so it has a charge of -1.
EA beta particle is a helium nucleus and has a charge of +1.
FA beta particle is a helium nucleus and has a charge of +2.

 

5. What is a gamma ray and what is its charge?


AA gamma ray is a powerful beam of light and has a neutral charge.
BA gamma ray is a powerful beam of light and has a charge of -1.
CA gamma ray is an electron, so it has a charge of +1.
DA gamma ray is an electron, so it has a charge of -1.
EA gamma ray is a helium nucleus and has a charge of +1.
FA gamma ray is a helium nucleus and has a charge of +2.

 

6. How many electrons does an alpha particle have?


A5
B2
C0
D3
E1
F4

 

7. What types of radiation are involved in transmutation?


Aalpha
Balpha & beta
Cbeta
Dbeta & gamma
Egamma
Falpha & gamma

 

8. Where did nitrogen (atomic number 7) come from?


AIt was created inside a star billions of years ago.
BIt is created when oxygen goes through alpha decay.
CIt is created when we breathe.
DIt is created by gamma rays.
EAll of the above
FNone of the above

 

9. Radioisotope "X" has an atomic mass of 224 and decays into another element with an atomic mass of 220. How would you protect yourself from the particle emitted in the decay of radioisotope X?


Aby standing as close to it as possible
Bno particle would be emitted
Csomething as heavy and thick as lead is required
Da piece of paper would do
Ethere is no way to protect yourself
Fnone of the above

 

10. What is the difference between the carbon in your body and the carbon in a distant star?


AThe carbon in a star is heavier.
BThe carbon in a star is older.
CThe carbon in a star is lighter.
DNothing except distance
ESomething but we don't know what
FNone of the above

 

11. What is half-life?


A37 billion disintegrations per second.
BThe temperature at which half the atoms in an element break down.
Cone disintegration per second
DThe temperature at which my car has used up half its oil.
EThe length of time required for half the amount of a radioisotope to decay.
F the number of Curies per gram of a substance (Ci/gram)

 

12. I started with 100 atoms of M but an hour later I had only 50 Ms and 50 Ns that seemed to appear out of nowhere! And an hour after that, I had 25 Ms and 75 Ns. What is the half-life of M?


Athree-quarters of an hour
Bhalf an hour
Ctwo-hours
Done-hour
Eone and a half hours
Fnone of the above

 

13.Assume you have 4 grams of radioactive water and it is producing 148 billion beta particles per second. (Wow, now that is "hot water"!) What is the specific activity of that water?

[Hint : remember to use Curies per gram as your units of measurement.]

A296 (Curies / gram)
B148 billion (Curies / gram)
C38.5 billion (Curies / gram)
D4 (Curies / gram)
E1 (Curies / gram)
F0 (Curies / gram)

 

14. What is the main type of nuclear fusion that happens in stars?


AThe main nuclear fusion reaction is the fusing together of two hydrogen atoms to get helium.
BThe main nuclear fusion reaction is the fusing together of two helium atoms to get beryllium.
CThe main nuclear fusion reaction is the fusing together of two beryllium atoms to get oxygen.
DWe don't know what happens in stars.
EThere is no main nuclear fission in stars.
FNone of the above

 

15. How does alpha decay change an atom?


AIt lowers the atom's atomic number.
BIt causes the atom to lose two protons.
CIt lowers the atom's atomic mass.
DIt causes the atom to lose one or two neutrons.
EIt transmutes the atom into a different element.
FAll of the above

 

16. What kind(s) of radiation do stars give off?


Aalpha & beta
Bbeta & gamma
Calpha & gamma
Dalpha, beta & gamma
Ealpha only
Fgamma only

 

17.How are elements heavier than iron formed?


AIn stars.
BIn stars bigger than our sun.
CIn stars hotter than our sun.
DOnly during the big bang, which is why elements like gold are so rare.
EIt requires a nova or other tremendous explosion.
FWe don't know how such heavy elements form.

 
In the 20th century humans learned how to slam tritium atoms together, causing nuclear fusion, the same process that occurs in the sun. The energy is released so quickly that this nuclear reaction is referred to as a bomb - a hydrogen bomb! Each H-bomb is designed to carry a specific amount of tritium in order to produce a specific amount of fusion (when detonated). However, because of tritiumís beta decay, all H-bombs must be dismantled at regular intervals and fresh tritium added. Recall NOTHING, not even the military, can stop the constant decay of radioisotopes!

18. Consider an H-bomb which requires a minimum of 1 kilogram of tritium for a "proper" detonation. What is the minimum amount of tritium which must be packed into this bomb for it to work (able to be detonated) for 12 years? (Recall that tritium has a half-life of 12 years.)


A2 kg
B5 kg
C3 kg
D4 kg
E0.5 kg
F1 kg

 

19. Consider an H-bomb which requires a minimum of 1 kilogram of tritium for a "proper" detonation. What is the minimum amount of tritium which must be packed into this bomb for it to work (able to be detonated) for 24 years? (Recall that tritium has a half-life of 12 years.)


A2 kg
B4 kg
C7 kg
D3 kg
E5 kg
F8 kg

 

20. Consider an H-bomb which requires a minimum of 1 kilogram of tritium for a "proper" detonation. What is the minimum amount of tritium which must be packed into this bomb for it to work (able to be detonated) for 36 years? (Recall that tritium has a half-life of 12 years.)


A3 kg
B4 kg
C5 kg
D6 kg
E7 kg
F8 kg


 

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