Chapter 4 Physics POWERPOINT

Atomic Structure
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Terms in this set (23)
Atomic Structure
Isotopes: Same number of protons, different numbers of neutrons
What makes Nucleus Stable?
1. An atom stays together because opposite charges attract. The positively charged proton and the negatively charged electrons are attracted to each other. It is weaker with distance, but is fairly long‐range.
2. Why does the nucleus stay together? The protons have like charge and repel each other, yet they remain in close proximity.
3. Protons and neutrons (but not electrons) feel an attractive nuclear force. But it is very short range. Protons have to be quite close to each other (as in a nucleus) in order for the nuclear attraction to be stronger than the electromagnetic repulsion.
4. Larger nuclei need more neutrons (to provide more
attraction) in order for the nucleus to be stable
Notation
A over Z >>> X to the side
A = mass number
Z = atomic number
X = chemical symbol
A = Mass number = number of nucleons = protons + neutrons
Z = Atomic number = number of proton
Image: Notation
Notation Examples
(235 over 92 >>> U) = Uranium 235. It has 92 protons, and 235‐92=143 neutrons. It makes up about 0.72% of all natural Uranium
(238 over 92 >>> U) = Uranium 238. It has 92 protons, and 238 ‐ 92=146 neutrons. It makes up about 99% of all natural Uranium
Periodic Table
Chemical Elements: Chemical behavior depends on the number of protons
Recall: Isotopes have the same number of protons, but a different number of neutrons
Clarifying "radiation" Electromagnetic Spectrum
Red (4x10^-7) to purple (7x10^-7) (LEFT TO RIGHT)
10^2 radio waves
1
10^-2 microwave
10^-4 Infrared
(VISABLE LIGHT)
10^-8 ultraviolet
10^-10 X-rays
10^-12 gamma rays
Nuclear Radiation
- A result of nuclear process; not thermal
- "Ionizing Radiation" high energy, so called because it can knock electrons out of an atom, creating an ion
- Alpha, beta, and gamma decay
(less common are position emission, electron capture, spontaneous fission
Gamma Decay
Gamma particle = fancy y
It is a photon whose energy corresponds to the gamma regime of the spectrum
Alpha Decay
- Alpha decay is often followed by gamma decay
- Alpha particle = fancy a
It is 2 protons and 2 neutrons, Or, the same as a helium nucleus
(Example: Plutonium 238)
Beta Decay
Basically, a neutron "explodes" into a proton + electron. It is also often followed by gamma decay.
(Example: Carbon 14)
Beta particle = fancy B
B- is an electron
B+ is a positron
Summary- Gamma decay or gamma emission. Nucleus emits a gamma photon. The nucleus has less energy afterwards, but hasn't changed type. • Alpha decay or alpha emission. Nucleus emits an. alpha particle (or, Helium 4 nucleus). It changes type. What's left is a different element. • Beta decay or beta emission. A neutron explodes into a proton and an electron. The nucleus left behind has changed typeMeasuring Radiation: R.E.A.D"R"adioactivity: rate of ionizing radiation release by a material. Units: Becquerel(Bq) = decayspersecond OR Curie (Ci) "E"xposure: the amount of radiation traveling through the air. It actually is in terms of how much ionization it would produce in 1 kg of air (STP, humidity). Units: Coulombs/kg (C/kg) OR Roentgen (R) (1/4000)C/kg "A"bsorbed dose: the amount of radiation that is absorbed by an object or person; i.e., the amount of energy absorbed per kilogram. Units: Gray (Gy) = Joule/kg (J/kg) OR "radiation absorbed dose" (rad) = 0.01 Gy "D"ose Equivalent: a combination of absorbed dose and the resulting medical effects. Units: rem (from "roentgen equivalent man") = dose in rads that will cause the same biological damage as 1 rad of x‐rays or gamma‐rays OR Sievert (Sv) = 100 rem.R.E.A.D. Radioactivity, Exposure, Absorbed Dose, Dose Equivalent (Alpha, beta, gamma)Dose Equivalent: Absorbed dose and damageSafety - External Exposure- Gamma is the most dangerous, because it penetrates well; thick shielding is necessary to stop gamma particles - Beta is less dangerous because it does not penetrate as well. A layer of clothing can stop beta particles. - Alpha is least dangerous. It does not penetrate the layer of dead skin.Safety - Internal Exposure- Alpha is most dangerous because it is all absorbed into living tissue - Beta is somewhat less dangerous because not all of it is absorbed into living tissue - Gamma is least dangerous because it is least likely to be absorbedTwo Ways Radiation Can Harm YouRadiation illness • Cell damage • High doses • Quickly noticeable Radiation‐induced cancer • DNA damage • Any dose • Long term consequenceRadiation Illness (radiation sickness, radiation poisoning, acute radiation syndrome)• Due to cell damage • A threshold of about 100 rem ~ 1 Gray • Major power plant malfunction; nuclear warfare • Data is limited • Affects are not proportional to exposure; • i.e., twice as much exposure doesn't mean you get twice as sickRadiation Induced Cancer- DNA damage •Linear No‐Threshold Hypothesis (LNT) • Cumulative exposure • Disputed at low exposures • Threshold model—low doses are harmless • Hormesis model—low doses are beneficial • LNT is used by theNuclear Regulatory CommissionNuclear Decay and Half-LifeHalf life: The time it takes half of the radioactive isotopes in a sample to decay.Nuclear Decay and Half-Life (continued)- Carbon dating (fossils) • 14C has a half life of 5700 years • Limit is about 50,000 years, or about 9 half‐lives. • Accuracy between 25 and 200 years. • Potassium/argon dating (rocks) • 40K has a half life of 1.25×10 9 years • It can date as far back as the age of the earth, 4.5×10 9 years • Accuracy is within 100,000 yearsFission and Fusion- Fission: A large nucleus breaks apart into two smaller nuclei (and a few other things) • Fusion: Small nuclei combine to form a larger nucleus. Attractive for power productionFusion- Interplay between the repulsive electromagnetic force and the attractive nuclear force - In order to have enough kinetic energyto overcome the electromagnetic barrier, the proton must be at about 10 million kelvinFusion Updates- Tokamaks • None have produced more energy than was put in. • Fusion record set in 2016—70 seconds by the Korean Superconducting Tokamak Advanced Research reactor •ITER—international, largest project. Started in 2013, finish 2025. Designed for 500 MW output for 20 minutes, 50 MW input. Almost all other projects are in support of ITER. - Lockheed Martin Compact Fusion Reactor (CFR) • Announced 2014 with 5 year projection • They are still working on it, but it's getting bigger