nucleon: anything you find in the nucleus, includes protons and neutrons

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Page 1: Nucleon: anything you find in the nucleus, includes protons and neutrons
Page 2: Nucleon: anything you find in the nucleus, includes protons and neutrons

Nucleon: anything you find in the nucleus, includes protons and neutrons

Page 3: Nucleon: anything you find in the nucleus, includes protons and neutrons

Number of protons determines element

Symbol: p+

Positive charge: +eMass = mp = 1.6726e-27 kgNumber of protons in nucleus =

atomic number, symbol = Z

Page 4: Nucleon: anything you find in the nucleus, includes protons and neutrons

Symbol is n0

No chargeMass = mn = 1.6749e-27 kgNumber of neutrons in nucleus =

neutron number, symbol NTotal number of nucleons (protons +

neutrons) in a nucleus is call the atomic mass number, symbol A

A = Z + N

Page 5: Nucleon: anything you find in the nucleus, includes protons and neutrons

Atoms of the same element can have different number of neutrons in the nucleus (even though same number of protons), called ISOTOPES

Isotopes react almost identically when compared to each other, but in physics we’re concerned with different isotopes

Masses on periodic table are weighted averages based on natural abundances

Page 6: Nucleon: anything you find in the nucleus, includes protons and neutrons

Ex, since most carbon is carbon-12, the number is pretty close to 12

Page 7: Nucleon: anything you find in the nucleus, includes protons and neutrons

The number of neutrons strongly affects the stability of the nucleus

In unstable isotopes, the number of neutrons partly determines the rate at which the nucleus decays and releases radiation

Page 8: Nucleon: anything you find in the nucleus, includes protons and neutrons

Masses of atoms are sometimes given in atomic mass units (amu), which has the unit “u”

Not an SI unit, but measuring small things in kg can seem silly, so it’s common

Based on neutral carbon-12 atom, 12.000000u

1 u = 1/12 the mass of carbon-12 1 u = 1.660539e-27 kg

Page 9: Nucleon: anything you find in the nucleus, includes protons and neutrons

Since the strong nuclear force holds nucleons together, energy must be added to separate them… this is binding energy

Separated nucleons have more energy

Nucleons bound in nucleus haven’t had energy added yet, so they have more energy

Page 10: Nucleon: anything you find in the nucleus, includes protons and neutrons

Since separated nucleons have more energy, they must have more mass (energy is directly related to mass)

Nucleons bound in the nucleus have less energy and therefore less mass

Page 11: Nucleon: anything you find in the nucleus, includes protons and neutrons

Mass defect = difference between the mass of the nucleus and its individual nucleons

Directly related to the binding energy added to break apart the nucleus

Page 12: Nucleon: anything you find in the nucleus, includes protons and neutrons

1896: leaves uranium in a drawer with a photographic plate and accidentally identifies another part of the electromagnetic spectrum

Page 13: Nucleon: anything you find in the nucleus, includes protons and neutrons

Isolated two other radioactive elements: polonium and radium

Put them under different stresses, but the elements always emitted radiation, so concluded radioactivity comes from deep within the atom (i.e., the nucleus)

Page 14: Nucleon: anything you find in the nucleus, includes protons and neutrons

Results from the decay of an unstable nucleus

Decay happens because it results in a more stable nucleus

Page 15: Nucleon: anything you find in the nucleus, includes protons and neutrons

Ernest Rutherford found 3 distinct forms of radiation & divided based on ability to pass through material and deflection in magnetic field Alpha (α): could barely pass through a single

sheet of paper. Deflected as a positive particle in a magnetic field.

Beta (β): can pass through about 3mm of aluminum. Deflected as a negative particle in a magnetic field. *

Gamma (γ): can pass through several centimeters of LEAD! Not deflected in a magnetic field.

Page 16: Nucleon: anything you find in the nucleus, includes protons and neutrons

Alpha radiation is a Helium atom, but we call it an alpha particle since it comes from radiation With protons and neutrons leaving

the nucleus it gets smaller, often more stable

Alpha particle: charge +2e, since no electrons

Use conservation of nucleons to write-out decay

Page 17: Nucleon: anything you find in the nucleus, includes protons and neutrons

Total mass of the daughter nucleus plus the alpha particle is less than the mass of the original nucleus Missing mass was turned into energy : E =

mc2

Works with our understanding of conservation of mass and energy being interchangeable

Energy found mostly in kinetic energy of alpha particle and daughter nucleus moving away from one another

Page 18: Nucleon: anything you find in the nucleus, includes protons and neutrons

A neutron falls apart and becomes a proton and an electron Leaving electron is the beta particle

That’s why a neutrons mass is a little bigger than a protons

Page 19: Nucleon: anything you find in the nucleus, includes protons and neutrons

Particles emitted are opposite from beta negative decay Positive positron, sometimes called an

anti electron (antimatter version of an electron)

Same mass as an electron, but positive charge

Page 20: Nucleon: anything you find in the nucleus, includes protons and neutrons

Emits a form of EMR, not a particle =>much harder to stop (it’s pretty high-up in frequency of the EM spectrum)

Happens most often after alpha and beta decay

Nucleus has been through a lot and needs to release excess energy

Since it’s a release of energy A and Z stay the same

Page 21: Nucleon: anything you find in the nucleus, includes protons and neutrons

Half life of an element: the time it will take half of the parent atoms to transmutate into something else Through alpha or beta decays, or

another process Total number of atoms stays constant Based on statistics

Page 22: Nucleon: anything you find in the nucleus, includes protons and neutrons

The half life of C-14 is 5730 years. Explain what you would expect to happen over a long period of time.

Page 23: Nucleon: anything you find in the nucleus, includes protons and neutrons
Page 24: Nucleon: anything you find in the nucleus, includes protons and neutrons

Activity measures the number of nuclei that decay per second Measured in Becquerels (Bq) =

decays/second. Geiger counter clicking in movies

measures the activity of the sample. As time passes, the number of nuclei

available decrease and sample activity does too

Page 25: Nucleon: anything you find in the nucleus, includes protons and neutrons
Page 26: Nucleon: anything you find in the nucleus, includes protons and neutrons

You have 75 g of lead-212. If it has a half life of 10.6 hours, determine how long it will take until only 9.3 g remains.

Page 27: Nucleon: anything you find in the nucleus, includes protons and neutrons

What do you think of when I say nuclear energy?

Page 28: Nucleon: anything you find in the nucleus, includes protons and neutrons

There are 2 types of nuclear reactions that release energy Fission Fusion

Page 29: Nucleon: anything you find in the nucleus, includes protons and neutrons

The process of causing a large nucleus (A > 120) to split into multiple smaller nuclei, releasing energy in the process. Can start when large nuclei absorbs a

neutron, causing it to become unstable to the point that it falls apart

Reaction that we use in nuclear power plants and early nuclear weapon

Pretty easy and cheap energy Lots of nuclear waste stored for a long time

Page 30: Nucleon: anything you find in the nucleus, includes protons and neutrons

The process of causing small nuclei to stick together into a larger nucleus, in the process releasing energy. Process that drives our sun and all other

suns We can duplicate in a lab, but use more

energy than we get out Left over products are safe, so lots of

research goes into trying to develop fusion reactors

Page 31: Nucleon: anything you find in the nucleus, includes protons and neutrons

The most typical fuel used in a fission reactor is uranium-235. 1939: 4 German scientists discovered that

uranium-235 would become very unstable if it gained an extra neutron, forming uranium-236.

Uranium-236 is so unstable that a fraction of a second later it will split to form two smaller atoms, and in the process release energy.

Page 32: Nucleon: anything you find in the nucleus, includes protons and neutrons

If one neutron gives rise to another reaction, the self sustaining reaction that results is called critical. Each reaction leads to one reaction afterwards. This is a “chain reaction”.

If 2+ neutrons give rise to more reactions, the increasing rate of reactions is called supercritical. Each reaction leads to multiple reactions afterwards. Generations of reactions increase exponentially

Page 33: Nucleon: anything you find in the nucleus, includes protons and neutrons

There are a few situations when we want this to happen... Nuclear bomb, since we want one reaction

we kick off to result in a cascade of exponentially more and more reactions within a split second

When a nuclear power plant is first being started up▪ Then stepped down to a critical reaction.▪ If the nuclear reactor is melting down then

supercritical reactions are BAD

Page 34: Nucleon: anything you find in the nucleus, includes protons and neutrons

You need subcritical reactions Less than a neutron gives rise to other

reactions

Page 35: Nucleon: anything you find in the nucleus, includes protons and neutrons

Reactors use control rods to control the rate of the reaction. Made from elements such as boron and

cadmium, control rods are very good at absorbing neutrons.

If a reaction is going supercritical, drop the control rods further into the core to absorb extra neutrons and the reaction slows.

If the reaction is going subcritical, pull the control rods out further, which lets more neutrons react and get more reactions going again.

Page 36: Nucleon: anything you find in the nucleus, includes protons and neutrons