PSC 4010

Nuclear Technology: A matter of Energy

PSC 4010: Chapter 4Goals:

_ SWBAT classify examples of changes in matter (physical, chemical, nuclear)

_SWBAT distinguish between different nuclear reactions (radioactivity, fission, fusion)

_SWBAT compare the nature, speed, electric charge and penetrating power of alpha and beta particles, as well as gamma rays (and X rays). Also, to know how each can affect matter

_SWBAT calculate the decay time for an isotope given its half-life

_SWBAT identify the radioactive element involved, the type of radiation emitted and the new element formed for a given decay process

_ SWBAT understand the relationships between energy released in a nuclear reaction, mass defect, and stability of resulting isotope

PSC 4010: Chapter 4

Changes in matter can be: (Table on page 2.37) Physical (appearance) Chemical (electrons in last shell) Nuclear (nucleus)

PSC 4010: Chapter 4

Physical changes (p. 4.3 – 4.7):

Superficial change Needs little amount of energy DOES NOT change nature of

element or compound DOES NOT affect the properties

of element or compound Changes state of matter

PSC 4010: Chapter 4

Physical changes:

Sublimation

Condensation

Fusion

Evaporation

Deposition

Solidification

PSC 4010: Chapter 4Chemical changes (p. 4.8 – 4.12):

More profound change Needs more energy Involves electrons in last shell NEW SUBSTANCES are formed Evidences of chemical change:_change of color_gas release_formation of precipitate_change of temperature

PSC 4010: Chapter 4

Chemical changes:

PC

PC

C

P

PSC 4010: Chapter 4

Chemical changes:

Ionization: when an atom gains or loses one or more electrons

PSC 4010: Chapter 4

PSC 4010: Chapter 4

Nuclear changes (p. 4.13 – 4.16):

Most profound change Needs much more energy Involves particles in nucleus! An element is changed into

another ALL involve emission of

radiation (which can be harmless, dangerous, or lethal)

PSC 4010: Chapter 4

Radioactivity (natural): (p. 4.17 – 4.37)

spontaneous nuclear change nucleus of a very large and unstable isotope

disintegrates into a lighter and more stable element emits radiation in the form of particles (alpha and

beta) and in the form of energy (gamma rays)

PSC 4010: Chapter 4Radioactivity emissions:(Table 4.2 on page 4.21)

Alpha particles Beta particles Gamma rays

2 protons, 2 neutrons (He nuclei)

Electrons Wave

Positively charged Negatively charged No charge (highest energy)

Deflect toward negative pole in an electric field

Deflect toward positive pole in an electric field

No deflection

Not too penetrating More penetrating Most penetrating

Stopped with paper sheet Stopped with 2.5 cm thick wood

Stopped with 1 m thick concrete or lead block

PSC 4010: Chapter 4

PSC 4010: Chapter 4Radiation in an electric field:(Figure 4.7 on page 4.20)

PSC 4010: Chapter 4Nature of radiations (waves) (p. 4.23 – 4.25):

_Gamma rays are electromagnetic waves (like light), and therefore they behave as if they have no mass, they are just radiation (energy)

_Gamma and X-rays have highest frequencies, and energies of the whole electromagnetic spectrum. Therefore they are called IONIZING RADIATIONS

_Our eyes only see the colors contained in the narrow visible part of said spectrum

PSC 4010: Chapter 4

Nucleus

Gamma rays

Electrons

Gamma rays

Beta rays

Alpha rays

++

++

PSC 4010: Chapter 4Nature of radiations (particles) (p. 4.25 – 4.27):

_Alpha and Beta particles have a mass (particles)

_Alpha particles are very heavy compared to Beta particles, and both more than Gamma rays (massless)

_Alpha and Beta particles can physically remove electrons from atoms. Therefore they are also considered IONIZING RADIATIONS

PSC 4010: Chapter 4

Nuclear changes:

Gamma rays

Chemical change

Because X-rays can also ionize matter

PSC 4010: Chapter 4Uranium-238 decay chain (p. 4.27 – 4.32):

_Transmutation: Process by which an unstable radioactive element transforms into a more stable one

_During each step of the transmutation Alpha, Beta and Gamma rays (or neutrons) are emitted

_During the transmutation there is CONSERVATION OF MASS (number of protons and neutrons is the same before and after transmutation)

PSC 4010: Chapter 4Uranium-238 decay chain (p. 4.27 – 4.32):

Transmutation of an Alpha particle Emission of alpha particles (2 protons, 2 neutrons) Mass number decreases by four (2 protons + 2 neutrons) Atomic number decreases by two (2 protons)

Ex:

PSC 4010: Chapter 4Uranium-238 decay chain (p. 4.27 – 4.32):

Transmutation of an Beta particle Emission of beta particles (1 electron) Mass number DOES NOT change Atomic number increases by one (1 neutron is converted into 1 proton)

Ex:

PSC 4010: Chapter 4

Nuclear changes:

Decreases by two (2)

Increases by one (1)

Gamma rays do not affect the mass of the atom

PSC 4010: Chapter 4

Beta decay

Increases by one (1)

Increases by one (1). One neutrons transforms into one proton

Atomic mass remains the same

Mass number remains the same

PSC 4010: Chapter 4

PSC 4010: Chapter 4Half-life of radioactive isotopes(p. 4.32 – 4.37):

_Half-life of radioactive isotopes: Time it takes to lose half of its mass

Ex: Iodine-131 has a half-life of 8 days. Therefore, if you have 40kg, _after 8 days you end up with 20kg_after 8 more days (16) you end up with 10kg_after 8 more days (24) days you end up with 5kg_after 8 more days (32) you end up with 2.5kg_after 8 more days (40) s you end up with 1.25kg_after 8 more days (48) you end up with 0.625kg_and so on until it is completely transformed

_The longer the half-life, the lower the emissive radiation (and vice versa)_U-238 has a half-life of 4.5 billion years!

PSC 4010: Chapter 4

PSC 4010: Chapter 4

4.5 X 109 years

109 years4.5 9.0 13.5

PSC 4010: Chapter 4

1.8 X 10-3 s

8 days

10-3 s

days

1.8 3.6 5.4

8 16 24

PSC 4010: Chapter 4

Nuclear changes:

125 g

31.25 g

PSC 4010: Chapter 4Transmuting matter(p. 4.38 – 4.40):

_Natural transmutations are natural radioactivity, or spontaneous transformation of unstable elements (Rutherford demonstration)

_Artificial transmutations are forced transmutations produced in a laboratory or man-made environment (NOT spontaneous)Ex: Cobalt-60 and Iodine-131 are artificially made radioactive isotopes widely used in medicine

PSC 4010: Chapter 4Nuclear Fission(p. 4.40 – 4.44):

_Fission: to break into smaller parts_Nuclear Fission: Atoms nuclei broken into smaller atoms (bombarding nuclei with particles, usually neutrons) _Nucleus split as a result of fission, produces LOTS of radiation emission and Large amounts of energy released_These nuclear fission reactions can sometimes be considered chain reactions, as they produced more neutrons that will in turn split more nuclei of the same element_Chain reactions can be used to produced electricity for millions of people or just used to produce BOMBS

PSC 4010: Chapter 4Nuclear Fusion(p. 4.44 – 4.45):

_Nuclear Fusion: Opposite to fission, two smaller elements combine to produce a bigger and heavier one

_Nuclei fusing together produces EVEN MORE energy that Fission (3 to 3.5 times for same amount of fuel)

_Nuclear Fusion is how the Sun creates its energy!

_Nuclear Fusion is feasible for light elements (H or He) but nearly impossible for heavier elements since these reactions require temperature values of MILLIONS degrees, and extremely high pressure.

_Because of the extreme experimental conditions, nuclear fusion is also known as Thermonuclear reactions

PSC 4010: Chapter 4

Nuclear changes:

Nuclear Fission is splitting a bigger atom into two lighter ones

Nuclear Fusion is combining two lighter atoms into a bigger one

PSC 4010: Chapter 4Energy involved in nuclear changes (E = mc2)(p. 4.46 – 4.49):

Nuclear forces are extremely powerful, BUT can only work at small distances. That is why bigger nuclei are unstable.

Chemical change produces high amounts of energyNuclear Fission produces ONE MILLION times the amount of energy of a chemical reaction with the same amount of fuelNuclear Fusion produces up to THREE MILLION times the amount of energy of a chemical reaction with the same amount of fuel

PSC 4010: Chapter 4Mass defect(p. 4.47 – 4.49):

Mass defect is the difference between the mass of the protons and neutrons by separate, and the mass of the resulting nucleus. The difference of mass is converted to Energy

The greater the mass defect, the greater the amount of energy released!

Every nuclear reaction involves the generation of a new nuclei as elements transmute into others. This means that at each step of a decay chain, energy is released as a consequence of mass defect

PSC 4010: Chapter 4

Practice Exercises for Chapter 3:

Page 4.53 – 4.60 – Ex 4.45 – 4.69