Nuclear Physics

Describe the structure of an atom

An atom is a positively charged nucleus surrounded by negatively charged electrons.

Where is the majority of the mass in an atom

the Nucleus

Describe the model of Dalton 1803

Every particle of a substance eg water or hydrogen are identical. These particles have different masses and combine and rearrange themselves in chemical reactions

Simplified: Atoms are the smallest building block

All atoms of the same element are the same

Why was Daltons model introduced

Due to evidence from chemical reactions

Describe Tomsons model of an atom 1904

The model regarded the atom as a positively charged sphere through ehich the negatively charged electrons were distributed in sufffiecienet numbers to make the atom electrically neurtal

Simplified:

Positive atom

Negative electrons can be removed

Explains +/- ions

Why was Thomsons model (plum pudding model) introduced

As they discovered the electron

Describe Rutherford's model of the atom 1911

He said that there was a small dense positive nucleus. And most of the atom is empty space

Why was Rutherfords model of the atom introduced

Due to the Alpha-scattering experiment

Descibed Bohr's modele of the atom 1913

Atoms have a small, positively charged central nucleus and electrons orbiting in at specific fixed distances from the nucleus.

Why was Bohrs model introduced

to excplain emission spectra

Describe the Alpha scattering experiment

Conducted by Geiger and Marsden-->Alpha particles were fired at a gold foil, and it was expected that they would all go though the foil or only be partially deflected, instead some were deflected more than expected, and some bounced completely back. This showed that there was a concentrated positive charge in the center of atoms

What what can be interpreted from the alpha acattering experiment

1. There is a nucleus containing all the positive charge and most of the mass of the atom

2. The nucleus is very small and most of the atom is empty space

What is the size of a Hydrogen atom

10^-10m across

But molecules can be much bigger up to about 10nm

What is an element

All atoms of a partiular element have the name number of protons

Isotope

An isotope of an element has the same number of protons but different number of neutrons. These behave chemically in the same way as each other since they have the same number of electrons but some isotopes may be radioactive

Ion

An atom that has become charged by either gaining or losing an electron

Proton number

the number of protons in the nucleus

Nucleon number

The number of protons and neutrons in the nucleus

Why are some materials Radioactive

In some isotopes the combination of neutrons and protons makes the nucleus unstable

Some occur naturally other anre amn-made

The atom ecats to become more stable by emitting gamma radiation and Kinetic energy

This not achemical change it takes place inside the nucleus of an atom, it is not affected by any physical or chemical changes

What would you use to detect radiation

A Geiger counter

What are the 4 types of radiation

Alpha

Beta

Gamma

Neutron

What is alpha decay

It occurs in nuclides that are too heavy

The heavy nuclide will emit 2 protons and 2 neutrons or 4/2 He

What is Beta Decay

Happens in nuclides hat have too namy neutrons, one of those neutrons turns into a proton and an electron

What is Gamma decay

Occurs when the nucleus has too much energy. Nothing changes but the substance has less energy

What is neutron emmision

If a nuclei has Too many neutrons atoms can decay by shedding a neutron

Is Radioactive decay random and why

Random: Radioactive decay is random because we can never tell which nucleus will decay.

What does the term activity mean

IS the rate (Emissions per second) at which radiation is emitted from a radioactive material

Measured in Becquerel (Bq)

What does the term Half-Life mean

Is the time taken for the activity of a sample to drop by half

The shorter the Half-Life the greater the activity, but the sample decays away Much quicker

How to find the Half-Life fron an activity-time graph

How to calculate the net decline after a given number of half-lives

What are the properties of alpha radiation

Type of particle

Ionising power

Range in air

Material that shield

It is a helium-4 particle

With a high ionizing power

And a very small range in air--> 2-4 cm

Can be stoped by Paper

What are the properties of beta radiation

Type of particle

Ionising power

Range in air

Material that shield

Fast electron

-1 charge

Medium ionising power

30-50cm range in air

Stopped by 3mm of aluminium

What are the properties of gamma radiation

Type of particle

Ionising power

Range in air

Material that shield

It is the highest frequency EM wave with 0 charge

Low ionising power

Very large/infinite range in air

Stopped by 3-5cm of lead

what is Irradiation

Irradiation happens when a person or object is exposed to readiation emmited by radioactive materal

Irradiation stops as soon as the source is removed or shielded

What is contamination?

When the radioactive source itself enters your body or gets on your skin

Risks of Contamination and Irradiation in different types of radiation

What are the main sources of background radiation

Radon gas roughly 50%

Rocks

Cosmic rays

Foods

WHat does being exposed to radiation lead to

The ionisation of living cells. This can damage DNA which leads to cell death,mutation and possibly cancer

What are some saftey precautions when using radioactive materials

Shield sources e.g. lead lined boxes

Use tongs

Wear gloves and aprons

How can Radiation be measured

In mSv

Why is no dose of radiation safe

As a single ionisation could ause cancer however the risk is significantly lower

What is nuclear Fission

Is the process of splitting one large nuclei into two maller nuclei, energy is released in the form of KE and gamma radiation

What is nuclear Fusion

Is the proces of fusing two small nuclei to form one large nuclei, energy is released in the form of KE and Gamma radiation

Chain reactions in nuclear Fission

- only one extra neutron is required to induce a uranium-235 nucleus to split by fission

- during the fission, it produces two or three neutrons which move away at high speed

- each of these new neutrons can start another fission reaction, which again creates further excess neutrons

this is a chain reaction

Why is nuclear fusion hard

As it takes a lot of energy to bring the nuclei very close together.

And the temperature must be over 100 million degrees Celcius

Benefits of Pusion power stations

Lots of hydrogen fuel available in water

Produces helium which is safe

Lots of energy is released from each fusion event

Problems with Fusion power stations

very hard to give Hydrogen nuclei enough enrgy to voercome electrostatic repulsive forces

Need temperatures of over 100 million degrees

It is hard to contron and sustain reaction

Explain Nuclear power stations using fission

Where does some of the mass go in nuclear fusion

to energy

What are some uses of nuclear radiation

AS medical tracers

gamma emitters are used as alpha and beta would not escape the body to be detected they would be absorbed and cause damage

Radioactive dating

We use radioactive decaysd to date fossils and rocks

TO control thickness of a substance eg metal foil

IF the foil got too thick the count would go down and if it was too thin the count would go up helping monitoring the thickness of materials

Beta radiation is used as alpha would be completely blocked by the foil and gamma would pass right through

Sterilization

Food and medical equipment can be sterilized by irradiating them with nuclear radiation

Gamma rays are used as the ionize microbes leading to their death, Alpha or Beta would not penetrate the container of the food so Gamma radiation is used