Atomic Structure

the radius of the nucleus is less than 1/10,000 of the radius of the whole atom.

energy levels that are further from the nucleus are at a higher energy than those which are closer to the nucleus.

if an atom absorbs electromagnetic radiation an electron can move from a lower energy level to a higher energy level. The atom then emits electromagnetic radiation and the electron returns back to the lower energy level.

1) Everything was made of atoms and they could not be divided.

2) Electrons were discovered in the atom. (are not tiny spheres and do have internal structures)

3) Plum pudding model (ball of positive charge with electrons embedded into it)

***Alpha scattering experiment took place (used gold because it could be hammered into the very thin layer). Fired alpha particles at the foil. Most passed through clearly, but some were deflected and some were reflected.

4) Atoms must be mainly empty space, as the alpha particles went straight through. The centre of the atom must be positive as the alpha particles were deflected. The mass of the atom must be concentrated in the centre as the alpha particles bounced straight back. (nuclear Model)

5) Electrons orbit the nucleus at specific distances (orbits/shells)

6) The positive charge in the nucleus is due to positive protons.

7) Neutrons were discovered in the nucleus.

some isotopes have an unstable nucleus. to become stable it must give out radiation. (radioactive decay)

radioactive decay is totally random.

the activity is the ate at which a source of unstable nuclei decay. activity is measured in becquerel (Bq)

1Bq = 1 decay per second.

geiger muller tube used to measure the activity of a radioactive source. count rate is the number of decays recorded each second by the detector.

Alpha = Helium atom.

Beta = High-speed electron emitted from the nucleus. (neutron changes into a proton and an electron.)

Gamma rays = Electromagnetic radiation from the nucleus.

Neutron

when radiation collides with atoms, that can cause the atoms to lose electrons and form ions.

Alpha particles =

• are large
• can travel for 5cm before colliding with an air particle.
• stopped by a single sheet of paper.
• very strongly ionising (can form a lot of ions) and are dangerous if inhaled or swallowed.

Beta particles = 

• can travel for 15cm in the air before colliding with an air particle.
• stopped by a few mm of aluminium.
• Quite strongly ionising (can form a few ions), can penetrate the skin.

Gamma radiation = 

• travels several metres before it is stopped in air.
• stopped by a few cms of lead.
• Weakly ionising (forming very few ions), can pass into and out of the body easily.

The half-life of a radioactive isotope is the time for the number of nuclei of the isotope in a sample to halve.

the half-life is also the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.

1000 = 20 minutes

500 = 20minutes

250 = 20 minutes

125 = 20 minutes

1) Radioactive rocks (granite)

2) Cosmic rays (very high energy particles which travel through space and crash into the Earth's atmosphere). (supernova)

3) Fall out from nuclear weapons testing (releases radioactive isotopes into the atmosphere.)

4) Nuclear accidents from nuclear power plants.

your exposure is affected by your location and occupation (job)

the dose of radiation is measured in sieverts (Sv)

Ionising radiation can increase the risk of cancer in humans

irradiation is exposing an object to nuclear radiation (sterilising medical equipment)

to sterilise a needle -

• put the needle into a plastic wrapper to stop bacteria from entering.
• place it in a lead shield with a radioactive isotope above.
• allow the gamma radiation to irradiate the object
• this will sterilise the object.

when irradiating an object, it will not become radioactive, this is because it comes in contact with the radiation, but not the radioactive isotope itself.

alpha radiation can be stopped by wearing gloves. beta and gamma radiation can be stopped by wearing a lead apron and staying behind lead walls and glass. monitoring radiation can also help with protecting yourself.

contamination is when unwanted radioactive isotopes end up on other materials. This is hazardous as the radioactive atoms decay and emits ionising radiation. 

They are good as tracers, to see internal organs, to see if they are working normally.

to check the function of the thyroid gland, the patient drinks a solution of radioactive iodine. Radioactive iodine will emit gamma rays that will pass out of the bod and be detected. If the scan shows that the gland has absorbed too much or too little iodine, then it can be used to diagnose the patient's problems.

bone scans can be used to visualise damage done by arthritis or to detect tumours. 

• They must emit radiation that can pass out of the body and can be detected.
• The tracer must not be strongly ionising to minimise damage to body tissues.
• the tracer must not decay into another radioactive isotope.
• the tracer must have a short half-life so it is not present in the body for a long time.

Scientists discovered that some cancers can be destroyed using ionising radiation. this is called radiotherapy. This is when gamma rays pass into the patient's body and destroy tumour cells. However, healthy tissue may also be damaged. Radioactive rods can also be inserted into the body to treat some cancers including prostate. This means that the radiation is targetted to a tumour very precisely, so there is less healthy tissue damage.

in some elements, the nucleus is large and unstable.

in nuclear fission, the nucleus of these elements split. However, the nucleus needs to first absorb a neutron. This triggers the nucleus to undergo fission. When the nucleus splits it forms two smaller nuclei of roughly equal size (daughter nuclei). it also emits two or three neutrons plus gamma radiation.

Energy is released during the fission reaction and all of the products have kinetic energy. The neutrons can then be absorbed by more Uranium nuclei and trigger more fission reactions. This is called a chain reaction.

Controlled chain reactions take place in nuclear reactors, this generates electricity.

The explosion caused by a nuclear weapon is caused by an uncontrolled fission chain reaction.

In fusion, two light nuclei are joined to form a heavier nucleus. Some of the mass of the nuclei can be converted into energy, which is released as radiation. this process occurs as stars release energy. This is not a chain reaction. High temp, high pressure to overcome the repel of the nucleus.

alpha can damage DNA if it gets into our body.

smoke detectors - 

• two metal plates
• radioactive element releases alpha radiation
• air particles between the metal plates
• when the alpha com into contact with the air particles, it makes the air particles become charged ions.
• These ions then move to the oppositely charged metal plates. this causes a small current between the plates.
• smoke particles attach to the ions and stop them from moving, this will reduce the current flowing between the plates and sets off the smoke alarm.

why use alpha for this?

• it is the most ionising
• alpha radiation is easily stopped, this means no alpha radiation passes out of the smoke detector.

• one side of aluminium is a detector and the other side is beta radiation.
• if rollers are too far apart and the aluminium is thick the beta radiation will not be detected by the detector.
• the detectors tell the rollers to move closer together to make the aluminium thinner.
• if the rollers go too close, they will be too thin and the detector will detect too much beta radiation.
• the detector tells the rollers to move further apart to make the aluminium thicker.

why use beta?

• alpha would be stopped straight away and would not work.
• gamma would pass straight through no matter what the thickness was and it would not be able to detect a small change in thickness like beta radiation would.

medical tracers - 

• radioactive dye is absorbed by a tumour.
• the dye emits gamma radiation
• gamma radiation passes out of the body and can be detected on a scanner.

why use gamma?

• alpha would be stopped by the body tissue and would not be detected by a scanner.

treating cancers - 

• gamma radiation is absorbed by cancer cells, this kills it.

why use gamma?

• alpha and beta would not be able to penetrate the body.