Page 1 12/25/2015 SCE 4350: Nuclear Science Nuclear Science Major Points of the Lesson: The Nucleus –Nucleons (A) = Protons (Z) + Neutrons (N) –Number

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04/21/23 SCE 4350: Nuclear Science

Nuclear ScienceMajor Points of the Lesson:• The Nucleus

– Nucleons (A) = Protons (Z) + Neutrons (N)

– Number of protons & neutrons in nucleus is limited.

• Radioactivity is the result of nuclear decay via emission of “radiation” (α or β particles, rays, etc.) producing a more stable element.

• Half-Life (2n exponential decay)

• Isotopes - 3000 known nuclei, but only 266 stable ones!

– medical applications

• Natural radioactivity > At. No. 83

• Fusion (Joining) v. Fission (Splitting) of Atoms

– both release energy.

Page 204/21/23 SCE 4350: Nuclear Science

Nucleus: Particle Composition

• Z protons + N neutrons = A nucleons

With a 1 →10 fm diam., f = “femto” = 10-15

• 1920: Ernest Rutherford

– Bombarded gold (Au) foil with Alpha particles

– Most of atom is empty space with massive +charged nucleus.

• 1932: James Chadwick discovered neutron (bombarded Be with α).

• Isotope: same Z (# protons), different N (# neutrons).

– 15O and 16O … or … 12C and 14C … or … 238U and 235U …


Today, we know

Particle Charge Mass (amu)

Proton +1 1.007276

Neutron 0 1.008665

Electron –1 .0005486

Alpha (α) particle is identical to helium nucleus. It has 2 protons and 2 neutrons, mass number of 4 and atomic number of 2.

Beta (β) particle is a high-energy electron. It has a negative charge and mass number of 0.

Gamma (γ) rays are high-energy radiation, like X-rays. They contain no mass or charge, only energy. Wavelength, λ = 10-10 to 10-15 m.


Nuclear Shielding:1.Thick paper stops Alpha.2.A sheet of Aluminum can stop Beta.3.A slab of Lead stops Gamma.


Antoine Henri Becquerel

1/2 of the prize (France)

The Nobel Prize in Physics 1903

"in recognition of the extraordinary services he has rendered by his discovery of spontaneous radioactivity"

"in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel"

Pierre Curie France 1/4 of the prize

Marie Curie France 1/4 of the prize

Contributors to the Study of Nuclear Physics


Radioactive Decay Examples

= +


Alpha Emitters

Note: An Alpha particle has the same structure as a Helium nucleus.


Beta Emitters

Note: During Beta Decay, a Neutron spontaneously changes to a Proton.


Producing Radioactive Isotopes:

TRANSMUTATION is the process of changing one element into another (can be via bombardment OR emission of radiation).

This can be natural or artificial.

A stable atom can be bombarded with fast-moving particles, protons, or neutrons.

A radioactive isotope is called aRADIOISOTOPE.


A stable atom can be bombarded with fast-moving particles.


Radiation Exposure:

BACKGROUND RADIATION is theradiation that is in the environment.

Background radiation can come from food, building materials, cosmic rays, etc.

The air molecules in the atmosphere block out some cosmic rays.


Note: Chart displays average values of doses from common sources.

a basements of buildings


Radioactivity Exposure


Half-Life:The HALF-LIFE of a radioisotope is theamount of time it takes for half of the sample to decay.

A DECAY CURVE is a graph of the decayof a radioisotope (amount vs. time).

Some radioisotopes have long half-lives. For other radioisotopes, the half-life can be short.


Note: Chart displays average values of half-life for an isotope.

A = Ao2-n

Ao = original amount

A = final amount

n = number of half-lives

Page 1604/21/23 SCE 4350: Nuclear ScienceChart based on individual isotopes, with average half-life estimates.

Radio-Isotopes Used in Medicine


Fission and Fusion:FISSION is splitting a big atom into twosmaller atoms by bombarding with neutrons.

Energy is released according to Einstein’s equation: E = mc2. E is energy, m is mass, c is speed of light.

The fission process can continue until all of the available “big atoms” are gone. This is a CHAIN REACTION.



A Nuclear Fission Reaction.+ 200 MeV

Unstable More Unstable



Chain

Reaction:

A Chain Reaction

Uranium 235, struck with a neutron, and split into Krypton and Barium


FUSION is the combining of two small atoms into one bigger atom with release of energy.

More energy is released than fission.

Occurs continuously in the sun and stars

Requires temperature of 100,000,000C

Problem to reach and maintain this tempGood source of future energy – lots of H in oceanWaste products decay much faster than fission


NUCLEAR FUSION : Joining atoms.

1H2 + 1H3 2He4 + 0n1 + 17.59 MeV


Nuclear Power:This is a fission reaction. Mass of uranium is kept small and CONTROL RODS absorb neutrons to prevent chain reaction.

Problems are:•Public perception•Security•Hazardous radioactive waste that hashalf-life of thousands of years

*storage 2150 ft underground in NM10% of power in US from nuclear power

Page 2504/21/23 SCE 4350: Nuclear Science(A Nuclear Reactor Used to Boil Water for a Steam Turbine


A Nuclear Reactor Used to Generate Electricity


Nuclear Accident: Chernobl.

1. Steam Explosion.

3. Containment held.

2. Partial Meltdown.


Particle detectors:

1. Photographic Film.

2. Scintillation Screen.

3. Gieger-Muller Tube.

4. Cloud Chamber.

5. Bubble Chamber.


Thank you for your attention.

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Page 1 12/25/2015 SCE 4350: Nuclear Science Nuclear Science Major Points of the Lesson: The Nucleus –Nucleons (A) = Protons (Z) + Neutrons (N) –Number