Notes

Physics Study Notes by Bill Cosby (scroll to the bottom for most definitions)

-continuous spectra
-emission spectra : excite an element and diffract the ray, then use a prism or diffraction grating to identify the lines
-absorption spectra: pass a ray of light through an element, then diffract the ray, then use a prism or diffraction grating to identify the missing lines which are its unique identity
-quantized: electrons can only occupy given energy levels

- Fundamental Forces:

Strong force: over a short distance + very powerful
Weak force: over a short distance + very weak
Electromagnetic Force: involve charged matter + attractive or repulsive + infinite range + relatively strong
Gravitational Force: only attractive + infinite range + relatively weak

For a stable atom: electromagnetic force has to cancel out with the gravitational force

more neutrons -> stronger electromagnetic force which is repulsive and splits the atom in order to regain stability

Alpha -> Beta -> Gamma Radiation

Alpha: short range + heaviest + slowest moving + strongest ionizing ability + can be stopped with a paper (lowest penetration)

Beta: medium range + medium mass + medium speed + medium ionizing ability + can be stopped with a few mm of aluminium (medium penetration)

Gamma: longest range + smallest mass + speed of light + weakest ionizing ability + can be stopped with 10 cm of lead (highest penetration)


Nuclear Equations:

Alpha: mass number -> 4
atomic number -> 2
extra atom? : N/A

Beta: mass number -> 0
atomic number -> -1
extra atom? : anti neutrino

Positron: mass number -> 0
atomic number -> +1
extra atom? : neutrino

Gamma: no mass
no proton
atom stays the same




- Background Radiation:

1 (Bq) = 1 decay per second

Measured using Geigar Counter : Detects the number of ionizations taking place inside the GM tube

Radiation of substance = measured radiation - background radiation

OUR RADIATION COMES FROM:
1. Medicine
2. Nuclear Industry
3. Cosmic Rays (outer space)
4. Food/drinking water
5. Radon
6. Building and Soil


Radioactive decay is a random process and is NOT affected by external conditions. We only know the chances of decay happening in a period of time

Radioactive decay is an exponential process


- Half Life

Definition: The time taken for half the number of the nuclides present to decay

Activity: Rate of decay of a particular sample

Decay constant: The probability of the decay of a nucleus per unit time





How do I measure half-life experimentally?

If it is short then:
1. readings can be taken of activity vs time
2. Make a graph using the points you plotted.
3. The decay constant is the gradient of the curve (draw a tangent line)

If it is long then:

1.Calculate the number of nuclei present (N)
2. Use dN/dt = -(lambda)N (lambda is the decay constant)



- Nuclear Reactions:

Artificial Transmutations: We can make nuclear reactions happen by bombarding a nucleus with a nucleon, an alpha particle or another small nucleus.

- Units:

1 MeV/c2 = 1.79 x 10-30 kg

1 kg = 9 * 10^16 Joules

1 eV = 1.6 * 10^-19 Joules

1 MeV = 1.6 * 10^-13 Joules

1 u of mass = 931.5 MeV

1 MeV * c^-2 = MeV





- Unified Mass Units:

Atomic Mass Unit: One twelfth the mass of a carbon-12 atom



- Mass Defect and Binding Energy ( E = mc^2)

Mass Defect: the difference between the mass of a nucleus and the masses of its component nucleons


Binding Energy: The minimum energy required to completely separate the nucleus of its nucleons
OR
The energy released when a nucleus is assembled


- Fission and Fusion

Fission: A nuclear reaction whereby large nuclei are induced to break up into smaller nuclei and release energy in the process. (used in nuclear reactors and bombs)

^ this causes a chain reaction: when the original neutron causing the reaction has resulted in the production of three neutrons


Fusion: A nuclear reaction where small nuclei are induced to join together into larger nuclei and release energy in the process. (this reaction fuels the sun)


- Binding Energy per Nucleon

Whenever a nuclear reaction releases energy, the products of the reaction are in a lower energy state than the reactants. The mass loss is converted to energy.

If the element is BEFORE Iron-56 then it will do FUSION to gain binding energy
If the element is AFTER Iron-56 then it will do FISSION to gain binding energy (see page 76)





























Definitions: (this section will be a compilation of SOME the definitions previously mentioned, read the full summary to get a better understanding)




Half Life: The time taken for half the number of the nuclides present to decay

Activity: Rate of decay of a particular sample

Decay constant: The probability of the decay of a nucleus per unit time

Artificial Transmutations: We can make nuclear reactions happen by bombarding a nucleus with a nucleon, an alpha particle or another small nucleus.

Atomic Mass Unit: One twelfth the mass of a carbon-12 atom



- Mass Defect and Binding Energy ( E = mc^2)

Mass Defect: the difference between the mass of a nucleus and the masses of its component nucleons


Binding Energy: The minimum energy required to completely separate the nucleus of its nucleons
OR
The energy released when a nucleus is assembled


Fission: A nuclear reaction whereby large nuclei are induced to break up into smaller nuclei and release energy in the process. (used in nuclear reactors and bombs)



Fusion: A nuclear reaction where small nuclei are induced to join together into larger nuclei and release energy in the process. (this reaction fuels the sun)