physics m5 nature of radioactive decay

XNature of Nature of Radioactive Decay Radioactive Decay

Physics Module 5 Unit 7 Lesson 18 & 19

INTRODUCTION 2

OBJECTIVES 1

OBJECTIVES 2

Nature of Radioactive Decay

Half Life

QUIZ

INTRODUCTION 1

XIntroduction 1: Nature of Radioactive decay

Flip a ten and a twenty dollar coin two times and then answer the following questions:

1. Half or 50%

2. No

QUESTIONS1.What is the chance of getting a tail on any flip?2.Does the number of tails directly proportional to the number of flips?3.What is the meaning of random?4.Do you think the flipping of coins is a random movement?

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3. Random means not expected or unpredictable. It is anything that is, has no pattern.

4. Yes

Click here to check your answers.

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Introduction 2: Half Life Read the scenario below and then answer the questions that follow:

A farmer has a herd of 1024 goats. He noticed that half of his remaining herd of goats was stolen each week over a two month period.

1.Would he have any goat left at the end of the two months?

2.What number of goats remained each week of the two months?

Number of Goats Remaining

Number of Weeks

1024 0512 1256 2128 364 432 516 68 74 8

Ans 1: YesAns 2: The table shows the result:


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Introduction 2: Half Life Cont.3. What would affect the number of goats remaining at the end each

week?

4. Does the pattern at which the goats were stolen from the farmer remind you of radioactive decay?

5. Would the graph of the number of goat remaining vs. week number be similar to that of a radioactive decay curve?

Ans 3: The number of goats which died by natural cause or those sold or killed for the family.

Ans 4: Yes Ans 5: Yes


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Objectives Part 1 As a result of this lesson, the student will be able to:

1.define nuclear notation in own words.

2.accurately represent the nuclear reactions of alpha, beta, and gamma radiations in the standard form.

3.predict the types of nuclear radiations that will occur in certain nuclear reactions in the standard form.

4.outline an activity to demonstrate the random nature of radioactive decay.

5.state the differences between natural and artificial radioactivity.

6.explain that decay process is independent of the conditions external to the nucleus.

7.actively participate in discussions.

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Objectives Part 2 As a result of this lesson, the student will be able to:

1.define the term half life in your own words.

2.conduct a simple experiment on half life of a substance.

3.list the half lives of some radioactive materials.

4.determine the half life of a radioactive substance from a graph of mass of radioactive substance against time.

5.draw the graph of a mass of radioactive isotopes against time for a radioactive substance.

6.solve simple worded problems involving half lives.

7.respect the views of their peers.

8.work cooperatively in groups.

9.contribute meaningfully to open discussion.

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Nature of Radioactive decay Standard nuclear notation shows the chemical symbol, the mass number and the atomic number of the radioactive element.

Where A = mass or nucleon number Z = charge or atomic number X is the chemical symbol and N = neutron number are related (A = Z + N).

For example:

XAZ

C126

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Alpha Particles The characteristics of alpha radiation are :1.The symbol of alpha is .2.It occurs when the nucleus is too large.3.An alpha particle is emitted, reducing the size of the nucleus.

4.The daughter nucleus has an atomic number 2 less and an atomic mass 4 less than the parent nucleus.

Example :

4 4

2 2

A A

Z ZX Y He

241 237 4

95 93 2Am Np He.

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Beta Radiation The characteristics of Beta radiation are :

1.The symbol of beta is .

2.It occurs when the nucleus has too many neutrons relative to protons.

3.A beta particle is emitted, a neutron changes into a proton and emits an electron.

4.The daughter nucleus has an atomic number 1 more and an atomic mass the same as the parent nucleus.

For example:

0

1 1

A A

Z ZX Y e

14 0 14

6 1 7C .e N

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Gamma Radiation The characteristics of gamma radiation are :

1.The symbol of gamma is .

2.It occurs when a nucleus has excess energy.

3.A gamma ray is emitted is emitted from the nucleus.

4.The parent and daughter nuclides are the same. For example:

99 99

43 43Tc Tc .

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Radioactive Decay Chart

Source 1: http://www.ccnr.org/decay_U238.html

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http://www.ccnr.org/decay_U238.html

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Half Life Activity Questions

1.What is the relationship between the mass of radioactive material and half life?2.What fraction does the mass of substance decay each half life?

Re

M a s so fa c t i v e

m a t e r i a l

Half life

m

1t

2m

16m

3t2t

4m

No of Half life

Fraction of Mass of Substance remaining

0 1

1 ½

2 ¼

3 ₈¹̷

Answer 1: the mass of the substance is inversely proportional to the half of the substance.Answer 2: ½


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Half Life The “half-life” (h) is the time taken for half the mass or atoms of a radioactive substance to decay.

Example: Suppose a radioactive substance has 1,000 atoms or a mass of 40g and an half-life of 1 hour, how many atoms or mass of that substance would be left after:

1 hour (one life time)?

2 hours (two life times)?3 hours (three life times)?

4 hours (four lifetimes)?

500 20 (50%)250 10 (25%)

Time mass

remaining% of atomsremaining

#atomsremaining

62.5 2.5 (6.25%)125 5 (12.5%)

SOLUTION

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The grid figure represents a quantity of 92U239. Each time you click, one half-life goes by. Try it! 92U239– gray 82Pb206 - red

As we begin notice that no time has gone by and that 100% of the material is 92U239

Halflives

% 92U239 %82Pb206 Ratio of

92U239 to

82Pb206

0 100% 0% no ratio

Age = 0 half lives (233000x 0 = 0 yrs)

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CLICK


Halflives

% 92U239 %82Pb20

6

Ratio of

92U239 to

82Pb206

0 100% 0% no ratio

1 50% 50% 1:1


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CLICK


Halflives

% 92U239 %82Pb20

6

Ratio of

92U239 to

82Pb206

0 100% 0% no ratio

1 50% 50% 1:1

2 25% 75% 1:3


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CLICK


Halflives

% 92U239 %82Pb20

6

Ratio of

92U239 to

82Pb206

0 100% 0% no ratio

1 50% 50% 1:1

2 25% 75% 1:3

3 12.5% 87.5% 1:7


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92U239– gray 82Pb206 - red Question: How can you find the age of asample without knowing howmuch 92U239 was in it to begin with? Solution: Use the ratio to determine how many half lives have gone by since the sample formed.

In the example above, the ratio is 1:3.If the sample has a ratio of 1:3 that means it is 2 half lives old. If the half life of 92U239 is 233000 years then the sample is 2 x 233000 or 233000 years old.

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Activity

Remember, 1:1 ratio = 1 half life 1:3 ratio = 2 half lives 1:7 ratio = 3 half lives

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Animation: Radioisotope decay Click the play button to start animation

Screenshot taken from http://faculty.coloradomtn.edu/gcornwall/Starr%20Concepts%20Animations%20and%20videos/chapter16/videos_animations/half_life.html

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http://faculty.coloradomtn.edu/gcornwall/Starr%20Concepts%20Animations%20and%20videos/chapter16/videos_animations/half_life.html

XThe Half-Lives of Radioactive Materials

Taken from http://www.atral.com/U2381.html

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http://www.atral.com/U2381.html

XA Sample Calculation of Half Life

Question: The half-life of Plutonium -239 is 24110 years. If the original mass of Plutonium -239 is 120 g, how much remains after 96440 years?

Solution: First, find the number of half-life's.

# Half-lifes =

4

120 120 7.52 16

g

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120 ===> 60 ===> 30===> 15===> 7.5g Mass1 2 3 4 half lives

96440 years24110 years

= 4

OR

Now divide the gram sample in 1/2 four times.

Therefore the mass of Plutonium -239 after 96440 years is:

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QUIZ

Are you ready to test yourself? 1.There are seven multiple choice items that you are required to do. 2.For each item, click on the letter of the correct response and then click the button ‘NEXT QUESTION’ to continue.3.Click the BEGIN QUIZ button below to start the quiz.

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BEGIN QUIZ!

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QUIZ: Question 1 Given the nuclear reaction : , what name of radiation emit as ‘X’

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A. Alpha

B. Gamma

C. X-ray

D. Beta

FEEDBACKFEEDBACK

234 234

91 92Pa U .X

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Quiz: Feedback to Question 1Given the nuclear reaction : , what name of radiation emit as ‘X’

24NEXT QUESTIONNEXT QUESTION

The daughter nucleus of 234Pa91 has an atomic number 1 more and an atomic mass the same as the parent nucleus, hence the radiation has be beta.

234 234

91 92Pa U .X

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QUIZ: Question 2 Given the nuclear reaction: , what name of radiation emits as ‘Y’?

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A. Beta

D. X-ray

C. Gamma

B. Alpha

FEEDBACKFEEDBACK

212 208

84 82Po Pb .Y

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Quiz: Feedback to Question 2 Given the nuclear reaction : , what name of radiation emit as ‘Y’?


The daughter nucleus has an atomic number 2 less and an atomic mass 4 less than the parent nucleus and the looks like:

Hence Y is alpha radiation.

212 208

84 82Po Pb .Y

4 4

2 2

A A

Z ZX Y He

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QUIZ: Question 3 The graph on the right shows the half life decay of a radioactive material. What is the half life of the substance?

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A. 20 days

D. 24 days

B. 16 days

C. 8 days

FEEDBACKFEEDBACK

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Quiz: Feedback to Question 3 The graph on the right shows the half life decay of a radioactive material. What is the half life of the substance?


Half life is the taken for a radioactive material to decay by half of its mass. Since the original mass of the substance is 40 and the time taken for its original mass to decay 20g is 8 days, them half life of the substance 8 days.

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Quiz: Question 4 Use the graph to determine the mass of the radioactive substance after 40 days.

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A. 2.5 g

D. 0.75g

C. 4.0 g

B. 1.25 g

FEEDBACKFEEDBACK

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Quiz: Feedback to Question 4 Use the graph to determine the mass of the radioactive substance after40 days.


40# 40 58

tan 4040 1.2552

daysof half lives after days isdays

Hence mass of subs ce after days

g

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QUIZ: Question 5 A Physics institution requests 2 g of bismuth-214, which has a half life of 20 min. How many grams of bismuth-214 must be prepared if the travel time is 3 h?

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B. 512g

D. 224g

C. 18g

A. 1024 g

FEEDBACKFEEDBACK

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Quiz: Feedback to Question 5 A Physics institution requests 2 g of bismuth-214, which has a half life of 20 min. How many grams of bismuth-214 must be prepared if the travel time is 3 h?

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Since

hence there are 9 half lives.

The set up is as follows:

END OF QUIZ END OF QUIZ

9

9

1( )2

1( ) 222 2 1024

i fn

i

i

m Initial amount m

m g

m g g

3 60 min# 3 920 min

sof half lives after hours iss

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End of Quiz You have reached the end of the quiz. If you wish to review this lesson, go to the first slide. If you have finished viewing the lesson, click the Close (X) button.

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physics m5 nature of radioactive decay

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