Section 30-1 & 30-2 Structure & properties of the nucleus Binding energy & Nuclear Forces

The Structure of the Nucleus

Structure of the Nucleus Every atom has a nucleus, a tiny but massive center.Every atom has a nucleus, a tiny but massive center. The nucleus is made up of particles called nucleons.The nucleus is made up of particles called nucleons. There is the proton, which is positively charged, and theThere is the proton, which is positively charged, and the Neutrons, which are neutrally charged. Different atoms are have different numbers of protons and neutrons.Different atoms are have different numbers of protons and neutrons. These different types of nuclei are referred to as nuclides.These different types of nuclei are referred to as nuclides.

The number of protons in a nucleus is called the atomic number. The total number of nucleons, protons + neutrons, is called the atomic mass number. The atomic number is referred to as “Z” and the atomic mass number is referred to as “A”. The neutron number is the number of neutrons and is referred to as “N”.

Isotopes are nuclei that have the same number of protons but different numbers of neutrons. Isotopes of the same atom are related. Nuclear masses are measured using atomic mass units. The notation for an atomic mass unit is “u”.

The total mass of a stable nucleus is always less than the sum of the masses of it’s constituent protons and neutrons. The lost mass goes into a form of energy, such as radiation or kinetic energy. The difference in mass (or energy) is called the TOTAL BINDING ENERGY. To find the average binding energy per nucleon one must divide the total binding energy by A (the atomic mass number).

Section 30-3 & 30-4 Radioactivity and alpha decay

Radioactivity Radiation is electromagnetic waves that carry energy!!! First discovered by Henri Becquerel though his studies of phosphorescence. Marie and Pierre Curie isolated the unknown elements polonium and radium. Rutherford classified the three types of rays-alpha, beta, and gamma.

Alpha Decay Alpha decay occurs when the strong nuclear force is unable to hold the nuclei together. When alpha decay occurs, a new element is formed. This process called transmutation. The original element is called the parent nucleus, and the resulting element is called the daughter nucleus.

Alpha Decay cont… The mass of the parent nucleus is greater then the mass of the daughter nucleus and an alpha particle. This difference in mass is a result of the kinetic energy that leaves with the alpha particles. The total energy released is called the disintegration energy, or Q value.

Alpha Decay example This is an example of alpha decay. N is the parent, and the 2 nd N is the daughter. A and Z are the atomic number and the atomic mass number.

Smoke Detectors Smoke detectors work in two ways. 1. One way uses an infrared light source and a detector that measures the attenuation of light when smoke particles are present. 2. The other way is based on ionization of air by radioactive decay. Radiation ionizes the air and provides an electric current. When smoke is present, the current is decreased. The detector measures this drop, and makes noise.

Section 30-5 Beta Decay

Beta Decay is a result of the Weak Force. In Beta Decay an electron and neutrino are created from the nucleus of an unstable isotope, transmuting it to a different element. In the nucleus, one of the neutrons turns into a proton. Such as Hydrogen3 turning into Helium3. The neutrino carries off energy and momentum that are required to maintain conservation laws Beta Decay

There are three different kinds of Beta Decay:  - and  + Decay and Electron Capture In a  - decay an electron and an antineutrino are emitted. In a  + decay a positron and a neutrino are emitted. In an electron capture the nucleus absorbs its own electron, which causes a proton to become a neutron and a neutrino is emitted. 30-5

Electron Capture 30-5

Section 30-6 Gamma decay

Gamma Decay When a nucleus is in an excited state known as an isomer or metastable state, it must release energy to become stable. It does this by emitting a high-energy gamma ray. Excited nucleons can also release this energy by way of internal conversion where the nucleus interacts with an electron and emits an X-ray. Brought to you by Brent, Jake, & Katie

Section 30-7 Conservation of Nucleon #

In any decay reaction, all conservation laws are observed, including conservation of the nucleon number. According to this law, the total number of nucleons (A) must remain constant in any process, though they may change into different types (i.e. protons to neutrons). Brought to you by Brent, Jake & Katie Alpha decay: A Z N A-4 Z-2 N’ He 30-7

Section 30-8 Half-life and Rate of Decay By Rick, Luke, Khalil

Nuclei do not decay all at once but rather one by one over a period of time. The half-life of an isotope is the amount of time it takes for half the original amount of the isotope to decay. We cannot predict exactly when one given nucleus will decay. Radioactive decay law N = N 0 e - t Where N = # of nuclei present N 0 = # of nuclei at t = 0 = decay constant The half-lives of known radioactive isotopes vary from about s to s. The half-life bears an inverse relationship to the decay constant. T 1/2 = / The greater  is, the more radioactive that isotope is said to be. Good night.

Section 30-9 Calculations involving Decay and Half-Life By Dylan and Aaron A+ Students

Calculations Involving Decay Rates and Half-Life The Isotope 14 6 C has a half-life of 5730 years. If at some time a sample contains 1.00 x carbon-14 nuclei, what is the activity of the sample? First we calculate the decay constant λ and obtain, λ = = = 3.83 x s -1, T 1/2 (5730)(3.156 x s/yr) ΔN = λN = (3.83 x s -1 )(1.00 x ) = 3.83 x decays/s. ΔT

A sample of radioactive stuff Again A lab has a 1.49μg of pure 13 7 N, Which has a half-life of 10.0 min (600s). (a) How many nuclei are present initially? (b) What is the activity initially? (c) What is the activity after 1.00 h? (d) After approximately how long will the activity drop to less than one per second? (a) Since the atomic mass is 13.0, then 13.0g will contain 6.02 x nuclei (Avogadro’s number). Since we have only 1.49 x g, the number of nuclei, N 0, that we have initially is given by the ratio. N 0 = 6.02 x 10 23, 1.49 x g 13.0 g So N 0 = 6.90 x nuclei. (b) λ = = 1.16 x s -1, then at t= 0 600s (ΔN) = λ N 0 = (1.16 x s -1 )(6.90 x ) = 8.00 x decays/s (ΔT) 0

Section Decay Series

Usually when one radioactive isotope decays it will decay into another radioactive isotope, causing a series of decays. These series of decay are what produce many of the elements found in nature that otherwise would have decayed long ago. Check out the cool chart on the right which shows the decay of 238 U.

Section Radioactive dating

HEY. WE’RE MEGAN, OWEN AND MATTHEW BLAIR ROPER. WE’RE GONNA TEACH Y’ALL ABOUT THE WIDE WONDERFUL WORLD OF CHAPTER 30, SECTION 11. ALSO KNOWN AS RADIOACTIVE DATING.

HERE IS THE SKINNY: Radioactive dating is the technique used to determine the age of ancient materials. The most common form, Carbon dating, is a comparison of Carbon 14 to Carbon 12 in matter. Carbon 14 is used to date once living things. All life forms absorb Carbon 14 while alive, but when they die, the Carbon 14 begins to decay, so from the ratio of C14 to C12, they can figure out the accurate age, this sentence has too many commas. Carbon dating is effective for up to 60,000 years. After that one must use Uranium 238 to Radioactively date. Everyone is lame, but us.

MATH. WOOOOOOOOOOOOOOOOOOO! A formula to calculate how old a sample is by carbon-14 dating is: t = [ ln (N f /N o ) / (-0.693) ] x t 1/2

So, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be: t = [ ln (0.10) / (-0.693) ] x 5,700 years t = [ (-2.303) / ( ) ] x 5,700 years t = [ ] x 5,700 years t = 18,940 years old This section of the Presentation has been brought to you by Howstuffworks and by Viewers like You

Section Tunneling

30-12: Stability and Tunneling Radioactive decay occurs only when the mass of the parent nucleus is greater than the sum of the masses of the daughter nucleus and all particles emitted. U238 can decay to Th234 because the mass of U238 is greater than the mass of Th234 plus the mass of the  particle. Systems tend to go in the direction that reduces their internal/potential energy. In radioactive decay, such as the example above, the potential energy is greater than the energy of the  particle. If the  particle were governed by classical physics, it couldn’t escape the nucleus. However, it could escape if there were an input of energy equal to the height of the barrier. But nuclei decay spontaneously without any input of energy. So how does the  particle pass the barrier? The particle passes through the barrier through a process called tunneling. In classical physics, this would violate the conservation of energy, however, the uncertainty principle tells us that energy conservation can be violated by an amount energy (change in energy) for a length of time (change in time) given by: (Change in Energy)(Change in Time) = h / 2  This is the result of the wave-particle duality. Quantum mechanics allows conservation of energy to be violated for brief periods of time; that may be long enough for an  particle to tunnel through the barrier. The change in energy represents the energy difference between the average barrier height and the particle’s energy. The change of time represents the time to pass through the barrier. The higher and wider the barrier the less time the particle has to tunnel, and the less likely it is to do so. In conclusion: The height and width of the barrier controls the rate of decay and the half-life of an isotope!!!

Section Detection of radiation

Detecting RADIOACTIVITY!!! Geiger Counter A Geiger counter is a metal case filled with a certain type of gas. Inside the metal case is a positively charged wire with just under the voltage required to ionize the gas within the container. When a charged particle enters through a thin glass panel at one end of the counter, it ionizes the particles of gas within the chamber. These particles are attracted towards the positively charged wire. As they accelerate towards the wire, they ionize additional particles. As the particles strike the wire, they create a voltage pulse which is amplified and sent to an electric counter. These pulses can also be sent to a loudspeaker, which causes each pulse to be heard as a “click” sound.

Other methods of detecting radiation! Scintillation counter- When the radiation particles hit the phosphorus inside this counter, they gives the phosphorus energy. When the phosphorus goes back to a ground state it gives off light. There is another tube inside, that turns the light into an electrical current. Semiconductor detector- consists of a reverse-biased p-n junction diode. When a particle passes through the junction, it can excite electrons through the conduction band, leaving holes in the valence band. The freed charges make a short electrical pulse. Photographic emulsion- Particles travel through film causing a chemical change in the emulsion. When this is developed it reveals the part of the particle. Cloud chamber- Super cooled gas inside a chamber condenses on any ionized particles. Showing their path and their time. Bubble chamber- A superheated liquid is held next to its boiling point. As a charged particle passes through the liquid the bubbles form around the ions produced by the particles. Wire chamber- 2 parallel wires are placed between planes of wires. The ones in between the two wires have extremely high voltage. The ions produced in the gas between the wires become an avalanche and create a high voltage current that creates a visible flash.