Nuclear Radiation• nuclear reactions different from other reactions –

________________________________________

________________________________________

1

Nuclear Radiation• in 1895 German physicist Wilhelm Roentgen

discovered that invisible rays were emitted when electrons bombarded the surface of certain materials– named these emissions _________________________

• Marie & Pierre Curie isolated the 1st radioactive material – Marie Curie came up with word ‘radioactive’

– Curies won Nobel Prize in 1903 & Marie won another in 1911

2

Nuclear Radiation• recall from Chapter 4

– nucleus made up of protons and neutrons

– atomic # (_____) is the number of protons

– mass # (______) is the protons + neutrons

– ______________________ are atoms with the same atomic

number but different atomic masses (different # of neutrons)

– nuclides represented by

A = Mass #

Z = Atomic #

X = Element Symbol

3

Nuclear Radiation• example – carbon series of isotopes

carbon–12

carbon–13

carbon–14

4

Nuclear Radiation

• isotopes of atoms with unstable nuclei are called

_______________________

• these radioisotopes emit radiation to try & get a more stable atomic configuration

• while undergoing radioactive decay, atoms lose energy by emitting radiation

• three most common types of radiation are alpha (α), beta (β), & gamma (γ)

5

Nuclear Radiation

Table 24.2 – Pg. 861

6

Nuclear Radiation

Figure 24.2 – Pg. 862

7

Nuclear Radiation• alpha particles (α) have same composition as

helium atoms (2 protons & 2 neutrons) with a +2 charge ( )

Figure 24.3 – Pg. 862

24 He

8

Nuclear Radiation• beta particles (β or e–) are very fast moving

electrons with a –1 charge ( )– emitted when a neutron converts to a proton

10e

Figure 24.4 – Pg. 863

10e

9

Nuclear Radiation• gamma rays (γ) are high energy photons with no

mass or charge ( )– always accompanies other nuclear decays

00

92238U 2

4He + 90234Th + 20

0

10

Nuclear Radiation• x–rays are a form of high-energy electromagnetic

radiation

– not produced by radioactive sources

– emitted from certain materials in an excited state

11

Penetrating Power• the more energy content of the

radiation, the more damage it can cause

• different rays can penetrate different levels of the human body (α stopped by skin, β can penetrate 1cm, are highly penetrating)

12

Radioactive Decay• all decay (except gamma radiation) involves the

conversion of an element into another element

• ______________________________ – when an

atom’s atomic number is altered

• protons & neutrons also called ___________________

• nucleons held in the nucleus by the strong nuclear force

13

Radioactive Decay• ________________________________________

– acts on subatomic particles that are extremely close together & it overcomes the electrostatic repulsion among protons

Figure 24.6 – Pg. 865 14

Radioactive Decay• atoms undergo radioactive decay to gain stability

• types of decay – ___________________________

________________________________________

________________________________________

15

Radioactive Decay• beta decay decreases the # of neutrons in an atom by

converting it to a proton

• results in a new atom with no loss in the

_______________________ & gain of 1 in

_______________________

Figure 24.8a – Pg. 86716

Radioactive Decay• alpha decay decreases the # of neutrons & protons

• results in a new atom with a loss of 4 in the

_______________________ & loss of 2 in

_______________________

Figure 24.8b – Pg. 867

17

Radioactive Decay• _______________________ –

a decay process that involves the emission of a positron from the nucleus to reduce protons

• _______________________ – a particle with the same mass as an electron, but opposite charge

• results in a new atom with no loss in the _______________________ & loss of 1 in _______________________

10e or e+ or +

Figure 24.9a – Pg. 868

18

Radioactive Decay• _____________________ –

occurs when the nucleus of an atom draws in a surrounding electron & combines it with a proton to form a neutron

• results in a decrease in protons

• results in a new atom with no loss in the _____________________ & loss of 1 in _____________________

Figure 24.9b – Pg. 868 19

Radioactive Decay

Table 24.3 – Pg. 868

20

Radioactive Decay• nuclear reactions are expressed by a balanced

nuclear equation

• in nuclear equations mass numbers & charges are conserved – treat the arrow like an equal sign & make sure the mass

numbers & atomic numbers equal on both sides of the equation

21

Radioactive Decay• Examples: Write balanced nuclear equations for the

following processes1. carbon–11 produces a positron

2. bismuth–214 produces a β particle

3. neptunium–237 produces an α particle

4. Uranium-235 undergoes electron capture

5. silver–116 produces a β particle

6. bismuth–211 produces an α particle and 3 gamma rays

22

Radioactive Decay• Examples: carbon–11 produces a positron

611C

611C ? + ?

611C 1

0e + ?

611C 1

0e + ZAX

_____________________________

_____________________________

_____________________________

23

Radioactive Decay• Examples: bismuth–214 produces a β particle

83214 Bi

83214 Bi ? + ?

83214 Bi -1

0e + ?

83214 Bi -1

0e + ZAX

_____________________________

_____________________________

_____________________________

24

Radioactive Decay• Examples: neptunium–237 produces an α

particle

93237Np

93237Np ? + ?

93237Np 2

4He + ?

93237Np 2

4He + ZAX

_____________________________

_____________________________

_____________________________

25

Radioactive Decay• Examples: uranium–235 undergoes electron

capture U23592

? ? + U23592

? e+ U 01-

23592

26

X e+ U AZ

01-

23592

_____________________________

_____________________________

_____________________________

Radioactive Decay• Examples: silver–116 produces a β particle

47116 Ag

27

Radioactive Decay

83211Bi

28

• Examples: bismuth–211 produces an α particle and 3 gamma rays

Radioactive Decay Series• many times a radioactive nucleus can not create a

stable (nonradioactive) atom through a single decay

• ___________________________________________

– a series of nuclear reactions that begins with an

unstable nucleus & results in the formation of a stable

nucleus– most well known series is of uranium–238 to lead–206 (it

takes 14 different radioactive decay steps)

92238U 82

206Pb29

Radioactive Decay Series

Figure 24.10 – Pg. 87030

Radioactive Decay• Example: The first 4 steps of uranium–238 decaying into lead–206 are alpha, beta, beta, alpha. Write the nuclear equation for each

step.

1..

2..

3..

4..

31

Radioactive Decay Rates• to measure the speed (rate) of decays, scientists

use half–lives

• ____________________________ – the amount

of time required for ½ of a radioisotope to decay

into its products

32

Radioactive Decay Rates• every radioactive nuclide has a specific half-life

• from seconds to billions of years

• example: gold–198 (used for cancer treatment) has a half–life of 2.7 days– how much would remain of a 50g implant after 1

week?

33

50g 2.7 days 25g 2.7days 12.5g 2.7 days 6.25g

Radioactive Decay Rates• Example: the half–life of strontium–90 is 29 years; if you

had 10.0 g of strontium–90 today, 29 years from now you would have 5.0 g left

Table 24.4 – Pg. 871

34

Figure 24.11 – Pg. 871

35

Radioactive Decay Rates• each radioisotope has a specific half–life– range from seconds to billions of years

Table 24.5 – Pg. 871

36

Radioactive Decay RatesExample: Krypton-85 is used in indicator lights of

appliances. The half-life of krypton-85 is 11 years. How much of a 2.000 mg sample remains after 33 years?

• 1st look at what is known/unknown:– initial amount = 2.000 mg amount remaining = ? mg

– elapsed time (t) = 33 years

– half-life (T) = 11 years

• 2nd solve for unknown

37

Radioactive Decay Rates• 2nd solve for unknown (cont.)

– since there have been 3 half–lives, then divide initial amount by 2 three times

38

2.0 mg 2

1.0 mg

1.0 mg 2

0.5 mg

0.5 mg 2

Radioactive Decay RatesExample: The half-life of cobalt-57 is 270 days. How

much of a 5.000 mg sample will remain after 810 days?

39

Radioactive Decay Rates• since half-lives are constant, radioisotopes can be

used to determine the age of an object

• ________________________________________

– the process of determining the age of an object

by measuring the amount of certain isotopes– carbon-14 (half-life = 5730 years) dating used to

measure the age of artifacts that were once part of a living organism

– other radioisotopes like uranium-238 (half-life = 4.5x109 years) to date older objects

40

Nuclear Reactions• we’ve seen where one element can be converted

into another through spontaneous emission of radiation (transmutation)

• elements can also be forced to transmutate by bombarding them with high-energy alpha, beta, or gamma radiation

41

Nuclear Reactions• ________________________________________

– the process of striking nuclei with high-velocity charged particles– Rutherford did this in his experiment

– particle accelerators use electrostatic & magnetic fields to accelerate charged particles at high speeds

Figure 24.13– Pg. 875 42

Nuclear Reactions• ________________________________________

– the elements with atomic numbers 93 & higher (right after uranium)

• all these elements were produced by induced transmutation

• they are also radioactive

43

Nuclear Energy• to gain stability heavy nuclei can split into smaller

nuclei

• ________________________________________

– the splitting of nuclei into fragments– fission comes with a very large release of energy

– produces 26 million times as much energy as the an equal amount of natural gas

44

Nuclear Fission• nuclear power plants use fission to produce

electricity– by bombarding uranium-235 with neutrons

45

Nuclear Fission• each fission of uranium-235 releases 2 neutrons

• these 2 neutrons can then cause another fission reaction– which then produces 2 more neutrons

• this self–sustaining process is called a

________________________________________

• amount of energy released can increase rapidly– how atomic bombs work

46

Nuclear Fission

Figure 24.16– Pg. 879 47

Nuclear Fission

48

Nuclear Fission• if exactly one neutron causes another fission event

then the process is said to be critical

• to get to critical state, a specific mass of fissionable

material is used called the ____________________

Figure 24.17– Pg. 880 49

Nuclear Fission• fission can be used to produce energy

• controlled reactions can occur in reactors

• energy produced is used to heat water to make steam to run generators

50

Nuclear Fission

Figure 24.20– Pg. 881 51

Nuclear Fission• inside the reactor core,

neutrons are slowed down by a moderator and by _______________________ (made of substances that absorb neutrons – ex. Cd, B)

• nuclear reactors produce highly radioactive waste

52

Nuclear Energy• can combine lighter elements (mass #s < 60)

• ________________________________________

– the combining of atomic nuclei

• the sun is powered by fusion reactions

53

Nuclear Fusion• fusion seen as better than fission– products are not generally radioactive

– produces much more energy

– lighter elements are more abundant

• however fusion requires extremely high energy for reaction to go– also known as

_________________________________

– ex. fusion of hydrogen atoms needs 5,000,000 K (8,999,540 °F)

54

• 2 types of nuclear energy

1. ________________ – combining 2 light nuclei to form a heavier nucleus

1. ________________ – splitting a heavy nucleus into 2 nuclei with smaller mass #s

Country (in order of total nuclear

output)

% of Total Power Production

1. United States 20.22. France 75.23. Japan 28.94. Russia 17.85. Germany 26.16. South Korea 31.17. Ukraine 48.68. Canada 14.89. United Kingdom 17.910. China 1.9

55

Nuclear Detection• radiation with enough energy to ionize matter that

it collides with is called ionizing radiation

• ______________________________________

uses this to detect radiation

Figure 24.24– Pg. 885 56

Nuclear Detection• also detected by _______________________________– they detect bright flashes when ionizing radiation excites

electrons of atoms

Figure 24.25– Pg. 886 57

Medicinal Uses• radioactive nuclides used to study how healthy areas

of the human body are

• _____________________________ – radioactive

nuclides that can be introduced into organisms and

traced by monitoring their radioactivity

• used to detect diseases & monitor the effectiveness of a drug

58

Medicinal Uses• radiation can damage or destroy healthy cells• can also destroy unhealthy cells (cancer)

• radiation therapy also destroys healthy cells in the process of destroying cancerous cells (side effects)

59

Medicinal Uses

60

Nuclide Half-Life Area of the Body Studied

131I 8.1 days thyroid59Fe 45.1 days red blood cells

99Mo 67 hours metabolism32P 14.3 days eyes, liver, tumors

51Cr 27.8 days red blood cells87Sr 2.8 hours bones99Tc 6.0 hours heart, bones,

liver, lungs133Xe 5.3 days lungs24Na 14.8 hours circulatory system

RadiationTable 24.6 – Pg. 889

61

RadiationTable 24.7 – Pg. 889

62