Topic 7: Atomic/Nuclear Physics.

Topic 7: Atomic/Nuclear Physics. • Structure & properties of the nucleus • Binding energy & nuclear forces • Radioactivity & Decay • Alpha • Beta • Gamma • Half-life • Radiocarbon dating • Applications

Natural Radioactivity: • Elements > At. No. 83, Bi, are radioactive. • Too many protons and • neutrons in the nucleus. • Stable Unstable • Binding Energy can’t hold nucleons together. • Isotopes of elements may be unstable. • All will naturally emit particles and energy to become more stable.

Radioactive Decay

Types of Nuclear Radiation • ALPHA (a) PARTICLE is identical to helium nucleus. ( 2 protons and 2 neutrons), mass number of 4 and atomic number of 2. • BETA (b) PARTICLE is a high-energy electron. It has a negative charge and mass number of 0. ∙ • GAMMA (g) RAYS are high-energy radiation, like X-rays. They contain no mass or charge, only energy. λ = 10-10 to 10-14 m

The Discovery of Radioactivity ALPHA BETA GAMMA Henri Becquerel (1852-1908) Mysterious rock

Radioactivity: Historical Overview 1896: Becquerelaccidentally discovered that a mysterious rock emitted invisible radiation onto a photographic plate. 1898: Marie and Pierre Curie discovered polonium (Z=84) and radium (Z = 88), two new radioactive elements. The Nobel Prize in Physics 1903 "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel" "in recognition of the extraordinary services he has rendered by his discovery of spontaneous radioactivity" Pierre Curie France Marie Curie France Antoine Henri Becquerel France

Radioactivity(How to separate radiation.)

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.

Radioactivity

Radiation Exposure: • BACKGROUND RADIATION is the radiation that is in the environment. • Background radiation can come from food, building materials, cosmic rays, etc. • The air molecules in the Earth’s atmosphere block out some cosmic rays.

The HALF-LIFE of a radioisotope is the • amount of time it takes for half of the sample to decay. • A DECAY CURVE is a graph of the decay • of a radioisotope (amount vs. time). • Rate of decay equation. Using the activity constant, λ, in decays/s, we have: • N = Noe-λt

Note: Chart displays average values of half-life for common isotopes.

Further, if we define activity, A, as A =N A = Noe-t A =Aoe-t which means that the activity decreases exponentially with time also. , for C14 = 3.83x10-12 /s (5370 yr half-life) N13 = 1.16x10-6 /s (10 min. half-life)

Half Life So far we have:N = Noe-tand A = N A = Aoe-t T½ = ln(2) /  or T½ = .693 /  A = Ao2-n We can : • find T½if we wait for N (or A) to decrease by half. • find  by measuring N and A. Know either  or T½ , we can find the other.

Note: Chart displays average values of half-life for common isotopes.

Chart based on individual isotopes, with average half-life estimates.

1. An isotope has the same value of a. mass number b. neutron number c. atomic number d. nucleon number e. nucleon number and neutron number 2. The isotope, tritium, has a half-life of 12 years. Assume we have 10 kg of the substance. How much tritium will be left after 48 years? a. .20 kg b. 1.8 kg c. .63 kg d. 1.7 kg e. 1.7 kg 3. Radioactive nuclei can decay spontaneously by emitting the following particles: a. helium nuclei, high-speed electrons, photons b. electrons, neutrons, molecules c. helium nuclei, electrons, cyclotrons d. electrons, carbons, photons e. quarks and gamma Quick Quiz

Nuclear Forces I.

Nuclear Forces II. Nucleons close together. More Binding Energy per Nucleon. Nucleons far apart. Less Binding Energy per Nucleon.

Binding energy & nuclear forces • average binding energy per nucleon = total energy / A Most stable is Iron, Fe . It has the greatest Binding Energy per Nucleon.

Quick Quiz 4. The smallest particle of any chemical element that can exist by itself and yet retain the qualities that distinguish it as that element is: A. an electron B. a proton C. a neutron D. an atom E. a molecule 5. The mass of an electron: A. is almost the same as that of a neutron B. is negative C. equals that of a proton D. is zero if the electron is at rest E. is much less than that of a proton 6. The mass of a neutron in amu’s: A. exactly equals that of an electron B. exactly equals that of a proton C. is a little more than that of a proton D. is exactly that of a proton plus an electron E. is as yet unmeasured

FISSION is splitting a big atom into two smaller atoms by bombarding with neutrons. 235U + n 92Kr + 142Ba + 3n + 200 MeV Energy, E = (Δm)c 2 , is released and starts a CHAIN REACTION.

Chain Reaction: Uranium 235 is struck with a neutron. Splits into Krypton and Barium and releases 3 more neutrons.

Nuclear Power: 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 with a half-life of thousands of years • Breeder Reactors can produce Plutonium or

In a flash,what a nuclear explosioncan do to a building. . . .

Quick Quiz 7. The atomic number of an element is: A. the whole number nearest to its mass B. the number of protons in its nucleus C. the total number of protons and neutrons in its nucleus D. the number of neutrons in its nucleus E. its order of discovery on the Periodic Table 8. Iron has atomic number 26. Naturally mined iron contains isotopes of mass numbers 54, 56, 57, and 58. Which of the following statements is FALSE? A. Every atom of iron has 26 protons B. Some iron atoms have 30 neutrons C. Some iron atoms have 54 neutrons D. Iron is most stable 9. A femtometer is: A. larger than 10−9 m B. 10−9 m C. 10−12 m D. 10−15 m E. 10−18 m

Steam generator Meltdown shield A Nuclear Reactor Used to Boil Water for a Steam Turbine (

US Nuclear Power Plants 15% of power in US from nuclear

World Nuclear Power Plants

10. The half-life of a radioactive substance is: A. half the time it takes for the entire substance to decay B. usually about 50 years C. the time for radium to change into lead D. calculated from E = mc2 E. the time for half the substance to decay 11. The half-life of radium is about 1600 years. If a rock initially contains 1000 g of radium, the amount left after 6400 years will be about: A. 938 g B. 63 g C. 31 g D. 16 g E. less than 16 g 12. Radioactive 90Sr has a half-life of 30 years. What percent of a sample of 90Sr will remain after 60 years? A. 0% B. 25% C. 50% D. 75% E. 14% Quick Quiz

What Happened at Chernobl. 1. Steam Explosion. 2. Partial Meltdown. 3. Containment held.

FISSION: a Neutron collideswith a 235U nucleus to form an excited state that decays into two smaller nuclei (plus neutrons) plus ENERGY! • Equation is: 235U + n 92Kr + 142Ba + 3n + 200 MeV 235U will not fission without being “kicked” by neutron. Process also works with 252Cf.

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 100,000,000C • Problem to reach and maintain this temp • Good source of future energy – lots of H in ocean • Waste products decay much faster than fission

NUCLEAR FUSION : Joining atoms. 1H2 + 1H3 2He4 + 0n1 + 17.59 MeV

5 Particle detectors: • Photographic Film. • Scintillation Screen.

3. Geiger-Muller Tube. 4. Cloud Chamber. 5. Bubble Chamber.

The Linear Accelerator was invented by John Cockcroft and E. T. S. Walton at the Cavendish Laboratory, Cambridge, England, in the late 1920s

The Nobel Prize in Physics 1939 Awarded to E.O. Lawrence, Univ. of California, Berkeley "for the invention and development of the Cyclotron and for results obtained with it, especially with regard to artificial radioactive elements"

The “Marie Curie’s” of Today Women In Physics • Her work involved slowing down light to 17m/s in an ultra-cold gas. • Did 7 months at CERN, the European Laboratory for Particle Physics near Geneva. • From Netherlands, now teaches at Harvard. • “After I discovered quantum physics, I've been hooked ever since.I would rather do physics than go to the movies.” Lene Vestergaard

Women In Physics • Born in Hong Kong • “Reading the biography of Marie Curie inspired me so much that I decided to devote my life to physics.” • Graduated from Vassar summa cum laude and Phi Beta Kappa, and then earned her Ph.D. from Harvard. • Working at MIT, she was a member of the team that discovered a new particle known as J/psi, or the charm quark. • She played a key role in the discovery of the gluon, the “particle that holds quarks together to form protons and neutrons.” Sau Lan Wu

Women In Physics • She was the 1st tenured woman in physics at Princeton; the 1st tenured woman theorist in Physics at Harvard & MIT. • She's the most cited theoretical physicist in the world in the last five years. • Research in theoretical high energy physics. • “I really like that my work is getting more people interested in Physics.” Lisa Randall

Finding the Age of Rocks • You need a radioactive decay that has a longer half-life than 14C (5700 yrs.). • Potassium-Argon • 40K decays to 40Ar with a 1200 Myr half-life. • Uranium-Lead • 235U to 207Pb with 700 Myr half-life. • But, only works with volcanic layers. • So, the ages of fossils are interpolated from ages of volcanic layers above and below them.

Note: Chart display average value of distance and depth.

Known Elementary Particles u d

Fundamental Particles:The Building Blocks of Matter Proton-Neutron Collision Showing Fundamental Particles

Nuclear Physics and Particle Physics Study: • smallest known building blocks of the universe • interactions between them and … Quark

… and their large effects …

and affect us all. • History: alchemy, atomic weapons • Astronomy: sunlight, “metals”, cosmology • Medicine: PET, MRI, chemotherapy • Household: smoke detectors, radon • Nanotechnology: the study of the very small • Archaeology & Earth Sciences: dating

Matter atom Matter quarks electron Nucleus neutron proton 2 types: Up and Down

Topic 7: Atomic/Nuclear Physics.