Particle Nature of The Nucleus -All nuclei have mass that is multiple of specific number. -t.f. nucleus made of smaller particles: protons, neutrons = nucleons.

Mass or Nucleon Number Nucleons live in nucleus -protons and neutrons. Mass number (A) is equal to the total all neutrons and protons in the nucleus. If p+ and no = atomic weight 1, the mass number gives the atomic weight in amu - u. Notation A - Mass number A X Z - atomic proton# Z

Isotopes Most elements have a few different isotopes. Isotopes of the same substance have equal proton numbers, but different numbers of neutrons. For the same element, the Z number must always be the same but the A number may vary. Electron configuration determines chemical properties. Different isotopes of the same element behave the same way chemically.

Nuclides Nuclide is a distinct type of atom or isotope with specific number of p+ and no. Ex: C-14. Nuclides are defined by many different aspects, such as half life, mode of decay, percent abundance, and so on. Isotopes are sets of nuclides having the same number of p+, but different number of no - . Each individual isotope is a separate nuclide. Isotopes of a given element generally have similar chemical properties.

Calculations of nucleons: For a given isotope: protons (Z) + neutrons = mass number (A) Its easy to find the number of no in isotope. A – Z is total neutrons. 1. Find the number of no in 37 Cl 17

Atomic Mass Unit a unit u, of mass used to express atomic and molecular weights, equal to one-twelfth of the mass of an atom of carbon-12. It is equal to approximately 1.66 x 10-27 kg.

Isotopes 2: Which of the following gives the correct number of electrons, protons and neutrons in the neutral atom 6529Cu? SOLUTION: A = 65, Z = 29, so N = A – Z = 65 – 29 = 36. Since it is neutral, the number of electrons equals the number of protons = Z = 29.

Isotopes 3. Ag-102, Ag-103 and Ag-104 are all isotopes of the element silver. Which one of the following is a true statement about the nuclei of these isotopes? A. All have the same mass. B. All have the same number of nucleons. C. All have the same number of neutrons. D. All have the same number of protons. SOLUTION: Isotopes of an element have different masses and nucleon totals. Isotopes of an element have the same number of protons, and by extension, electrons. This is why their chemical properties are identical.

Mass Spectrometer Sorts differently massed nuclei using E and B fields. E field accelerates atoms, strips e- so only have charge on nucleus. B field causes curved motion of varying radii depending on charge and mass.

Derive equations Knowing the pd of the E field, find the velocity of a charged nucleus of mass m. Knowing the B strength, predict the radius of curvature of a nucleus mass, m and velocity v.

Mass Spectrometer Fc = FB mv2/r = qvB mv/r = qB m = qBr/v Isotopes The mass spectrometer, strips the atom of electrons & accelerates nucleus through a pd into a magnetic field. H nuclei had 3 different masses: The charge of the hydrogen nucleus is e, scientists postulated the a neutral particle: the neutron, which had mass without charge. Fc = FB mv2/r = qvB mv/r = qB m = qBr/v

4: Track X shows the deflection of a singly-charged carbon-12 ion in the deflection chamber of a mass spectrometer. Which path best shows the deflection of a singly- charged C-14 ion? Assume both ions travel at the same speed. SOLUTION: Since carbon-14 is heavier, it will have a bigger radius than carbon-12. Since its mass is NOT twice the mass of carbon-12, it will NOT have twice the radius.

Strong Nuclear Force A nucleus is ~10-15 m in diameter. The Coulomb repulsion between protons is enormous. Most nuclei do NOT spew out their protons, there is a force that acts within the nucleus to overcome the Coulomb force. The strong nuclear force holds nucleons together. The more nucleons, the more nuclear force. Heating metals or shining EM radiation can strip e- from atom. Cannot pull apart nucleus with so little energy.

Radioactive Decay process occuring when nucleus cannot hold together Nucleus emits particles and/or energy 1896 Antoine Becquerel discovered that certain U salts emitted rays that could penetrate dark paper to expose a photographic plate. Called penetrating rays radiation.

Two types of Decay Artificial/Induced Natural Spontaneous Unstable Nucleus Bombard Nucleus with a particle.

Particles Emitted From Nucleus include: Alpha Beta Positron Gamma Neutrino Antineutrino Photon

Spontaneous Radioactive Decay is random process – cannot predict whether individual nucleus will change. The type of decay & rate of decays do not depend on pressure, temperature, chemical bonds.

Alpha Particles Rays a rays are helium nuclei, (2p+ and 2no), that are emitted from nucleus. They are positively charged since e- missing. When nucleus is too large, it may emit alpha particle.

Alpha Decay of Americium-241 to Neptunium-237 He nucleus Daughter Parent

a particles are easily stopped by skin or thin sheet of paper a particles are easily stopped by skin or thin sheet of paper. Likely to knock e- from orbits if they hit them. a loses all its KE at once when it’s stopped. Charge = +2e. Mass = 4 units. Energy is KE = ½ mv2.

Alpha a Decay Alpha a have KE ~5 MeV

Beta b Particles electrons emitted from nucleus. More penetrating than alpha because they are smaller. Think of b as a no that emits e-, becomes a p+.

Less capable of ionizing (knocking out e-) Need a few mm of Al to stop them. Charge = -1 or -e. mass = e considered massless in mass # calcs. KE = ½ mv2. v can be sig portion of c.

Positron Decay like beta decay but p+ loses b+ (positive electron )becomes a neutron:

Gamma g Radiation Highly penetrating. Can pass thru human body, concrete, lead. Similar to x-rays & light, but from the nucleus with shorter l. Gamma ray emission is when an excited nucleus de-excites to lower (more stable) state in the nucleus. In diagrams, a gamma ray is represented by this: In equations = g.

Gamma rays are EM waves. They have: Lowest ionizing power. No charge Gamma rays are EM waves. They have: Lowest ionizing power. No charge. No mass. Energy described by E = hf. Travel with vel of light in vacuum. No maximum stopping range.

Neutrinos are particles that are emitted with beta and positron decay Neutrinos are particles that are emitted with beta and positron decay. No charge. Almost no mass. They do not interact with matter.

How could we distinguish the different types of radiation How could we distinguish the different types of radiation? What could we observe?

Nuclear Physics 8: Properties of Becquerel Rays 9 min. https://www.youtube.com/watch?v=INF9y154EZA Read Homer Section 7.1 Kerr Nuclear Problems.

Nuclear Decay Equations

Products of Decay When a parent nucleus decays, a daughter product, is produced, a new element could be produced. We can identify products by balancing mass and atomic numbers. 34

1. U – 232 decays by alpha emission 1. U – 232 decays by alpha emission. Write the nuclear equation and determine the daughter of the decay.

alpha 232 4 A U He + X 92 2 Z X will have 4 less nucleons than U-232. X will have 2 less protons than U-232.

Daughter will be: 228 X 90 Look up on periodic table element with 90 p+ (Thorium). Answer is: 228 Th 90 37

Positron/Beta Decay During beta decay a beta, b- (e-) or a positron b+ (+e) is emitted from the nucleus. When an e- (b-) emitted a no changes to a p+, the atomic number increases by 1. When an e+ (b+) emitted a p+ changes to a no, the atomic number decreases by 1.

A neutrino v or antineutrino v is also emitted in positron or beta decay. b+ decay emits neutrino v. b- decay emits an antineutrino v.

Positron Decay like beta decay but: neutrino Proton no + b+ + n A positron particle b+ is the antimatter e-. 90 Ru b+ + ___ + __. 44 +1 90 Ru b+ + 90 Tc + n. 44 +1 43

3. C-14 undergoes beta decay 3. C-14 undergoes beta decay. Write the decay equation and identify the daughter.

14 0 A C e + X + v. 6 -1 Z A beta particle/e- has atomic number –1 and is considered massless.

Balance – make right side add up to left side. 14 0 A C e + X + v. 6 -1 Z A will be 14. Z will be ??

4. Radium-226 decays by alpha emission 4. Radium-226 decays by alpha emission. Write the decay equation and identify the daughter.

226 Ra X + 4He 88 2 Mass X = 226 – 4 = 222. Atomic number Z 88 – 2 = 86. 222 Rn 86 226 Ra + 4He 88 2

5. Sulfur 35 emits b- particles when it decays 5. Sulfur 35 emits b- particles when it decays. Write the decay equation and identify the daughter.

35 S 0 e + A X + v. 16 -1 Z Atomic number X is 17 since neutron went to proton, so daughter is: 35 17Cl.

6. Complete the equation: 23 Mg b+ + __ __ + __. 12 +1 __ 23 Mg b+ + 23Na+ n. 12 +1 11

Gamma g radiation Often emitted in another type of decay.

Spontaneous Random Decay & Half life Radioactive decay is random & not affected by outside factors. There is no way of knowing whether a particular nucleus will decay.

Changing temperature or pressure does not change chances of a decay, a chemical rx does not alter its activity.

The more stable the nucleus, the less likely that it will decay. Nuclear Stability The more stable the nucleus, the less likely that it will decay.

We can only know the chances of a decay happening in a sample.

Rate of Decay is proportional to number (N) of atoms in the sample Rate of Decay is proportional to number (N) of atoms in the sample. If large number of atoms, the number decaying would be larger. Radioactive decay is an exponential process. The number, N, of parent atoms decreases exponentially over time so do the number of decays/ unit time.

As number of parent atoms decreases, the rate in units per second decreases exponentially. The daughter product grows as a mirror image.

Half Life t1/2 defined as: time it takes for half of original parent in a sample to decay, or time for original mass to be halved, or time for activity to be halved.

Activity in counts/sec (Bq) easier to measure Activity in counts/sec (Bq) easier to measure. It’s the decay rate of the sample.

What is the half life of this sample?

Ex 1: The half life of Quinnium is 4 days Ex 1: The half life of Quinnium is 4 days. If we start with 160 g of pure Quinnium , how much will be left after 12 days?

Exact multiple of half lives: 160 g 80 g 40 g 20 g 4 days 8 days 12 days 3 half lives have passed

Measure the activity using ionizing properties (Geiger Counter) Youtube Geiger Muller Tube.5 min. https://www.youtube.com/watch?v=bcjMOr-qiwA

Short Lived Nuclei – read it off

Half life Questions M01/430/S(2)pg 17 . M02/430/S(2) 16 M05/4/PHYSI/SP2/ENG/TZ2/XX+ 10 –

Background Radiation Other sources of radiation (rocks, soil, building materials etc.) are all around us. To read sample first get a background count and subtract it. Youtube Geiger Muller Tube.5 min. https://www.youtube.com/watch?v=bcjMOr-qiwA

Nuclear Stability Electrostatic repulsion in the positively charged nucleus makes it want to decay. The strong nuclear force holds the nucleus together. More p+ , more repulsion. More nucleons = more strong force.

The extra neutrons increase the strong force & help shield against electric repulsion.

Proton/Neutron Ratio As more p+ in nucleus, more no needed for stability. There is an ideal p+ to no ratio for each element for stable nucleus . Heavier elements require more no.

Nuclides above the band are too large -decay by a Nuclides above the band are too large -decay by a. To the left b- decay occurs. Nuclides below the band have too few no, positron decay occurs. A p+ becomes a no.

Summery: Natural Decay occurs spontaneously Summery: Natural Decay occurs spontaneously. a decay reduces the mass # by 4 and the atomic # by 2. b- decay does not affect the mass #, but increases daughter's the atomic # by 1. b+ decay does not affect the mass #, but decreases the daughter's atomic # by 1. g decay affects neither the atomic nor the mass # but returns excited nucleus to ground state.

Properties of Becquerel Rays 9 min http://www.youtube.com/watch?v=INF9y154EZAhttp://www.youtube.com/watch?v=I7WTQD2xYtQ

9. Energy From Reactions 10 min 8.1 Natural transmutations and half lives 10 min http://www.youtube.com/watch?v=I7WTQD2xYtQ 9. Energy From Reactions 10 min http://www.youtube.com/watch?v=-YMgacsJyD0&playnext=1&list=PL0191606751B22A12&feature=results_main

Velocity Selector Crossed E and B fields Felc = Fmag Eq = qvB v = E/B

Detectors Count How many land at each point.

Read Hamper 7.4 and 7.5 ForHwk. Hamper pg 162 15-17, pg 163 #18 – 19, 20 and pg 166 #21,22, pg

Rd Hamper 7.4 Do 15-17 pg 162 and finish #2 pg 167

Read Hamper 7.2 and the Mass Do Hwk Nuclear Structure Homework Read Hamper 7.2 & 7.3 w reading.