module 4

Question 1

What did John Dalton Dalton and Democritus agree on?

Answer 1

matter was made up of tiny spheres (atoms) that couldn’t be broken up, be Dalton thought each element was made from different types of atoms.

Question 2

What did J.J. Thomson discover?

Answer 2

electrons, these could be removed from charge. Dalton’s theory wasn’t quite right. Thomson suggested atoms were spheres of positive charge with tiny negative electrons stuck in them-plum pudding model

Question 3

What did Rutherford discover?

Answer 3

he fired alpha particles at thin gold foil-alpha scattering experiment. From plum pudding model expected them all to go through sheet or slightly deflected. Most went through some more deflected more than expected, few deflected back the way they came. Plum pudding model proved wrong.

Question 4

How did Rutherford’s experiment change the shape of the atom?

Answer 4

due to some alpha particles coming back scientist knew most mass of atom was concentrated in centre in tiny nucleus. Nucleus had positive charge since repelled positive alpha particles. Because nearly all went through most of atom was empty space-first nuclear atom

Question 5

How did the atom look after Rutherford?

Answer 5

positively charged nucleus surrounded by cloud of negative electrons.

Question 6

What did Niels Bohr discover?

Answer 6

electrons orbiting nucleus do it in certain distances called energy levels. His theoretical calculations agreed with experimental data. After Bohr further experiments found protons subatomic particle to make the nucleus positively charged.

Question 7

What did James Chadwick discover?

Answer 7

proved existence of proton explained imbalance between atomic and mass numbers.

Question 8

What does the current model of an atom look like?

Answer 8

the nucleus’ radius is 10,000 times smaller than the atom. radius of atom is 1*10 to the power of -10 m. if electrons gain energy by absorbing EM radiation have to move to higher energy level far from nucleus (oppsite with other way round).

Question 9

What is the atomic number?

Answer 9

number of protons.

Question 10

What is an isotope?

Answer 10

an atom with different number of neutrons, all elements have different isotopes usually 1 or 2 stable ones. unstable decay and try to become stable by emitting radiation=radioactive decay. spit out 1 or more types of ionising radiation form nucleus, also release neutrons when decay. ionising radiation=radiation that knocks off electron-positive charged.

Question 11

What is ionising power?

Answer 11

of radiation source is how easily it can knock off electrons.

Question 12

How do alpha particles work?

Answer 12

emitted from nucleus. 2 protons and 2 neutrons. Don’t penetrate far into materials stopped quickly. Can only travel a few CMs in air can be absorbed by paper. Large-most ionising. Used in smoke detectors. ionises air particles causes current to flow. Smoke-binds to ions, current stops and alarm sounds.

Question 13

How do beta particles work?

Answer 13

fast moving electron. moderately ionising, penetrate moderately far into materials before colliding-range=few Meters. absorb by aluminium (5 mm thick). Per beta particle neutron turns to proton in nucleus. Used to test thickness of sheets of metals.

Question 14

How do gamma rays/EM waves work?

Answer 14

electromagnetic radiation released by nucleus, penetrate far, have long range. weak at ionising tend to pass through than collide, eventually hit and do damage. Absorbed by thick sheets of lead or meters of concrete.

Question 15

What are nuclear equations?

Answer 15

showing radioactive decay by using element symbols written: atom before decay=atom after decay+radiation emitted. Total mass and atomic numbers must be equal on both sides.

Question 16

What is alpha decay?

Answer 16

atomic number reduces by 2 and mass number reduces by 4. proton is positive neutron is neutral so charge decreases. equation wirtten as helium nucleus top:4 bottom:2 He

Question 17

When are gamma rays sometimes emitted?

Answer 17

When a nucleus decays by alpha or beta decay.

Question 18

What is beta decay?

Answer 18

protons increase by 1-increase positive charge by 1. Nucleus lost electron but gained proton so no mass changes.

Question 19

How does gamma decay work?

Answer 19

Gamma rays are a way of getting rid of excess energy from a nucleus. There is no change of the atomic mass or atomic number of an atom.

Question 20

What is a radioactive substance and how do you measure radiation?

Answer 20

A substance that gives out radiation from nuclei of their atoms. Measured with Geiger-Muller tube and counter, records count-rate, number of radiation counts reaching per second.

Question 21

What is radioactive decay?

Answer 21

Random. Can’t predict which nucleus in sample will decay next, or when 1 will decay. Can find out time takes for amount of radiation emqitted by source to halve, known as half-life. Can be used to make predictions about radioactive sources, though decays are random. Half-life can be used to find rate which source decays-activity. Activity is measured in becquerels, Bq

Question 22

What happens when a nucleus decays to become a stable nucleus?

Answer 22

Activity as a whole will decrease (older sources emit less radiation). For some isotopes it takes a few hours before nearly a unstable nuclei have decayed, others last millions of years.

Question 23

What is the problem with trying to measure radioactivity?

Answer 23

Activity never reaches zero, this is why we have to use idea of half-life to measure how quickly activity drops off.

Question 24

What is the half life?

Answer 24

Time taken for number of radioactive nuclei in an isotope to halve. Also time taken for activity, and so count-rate to halve. Short half-life means activity falls quickly, because nuclei are very unstable and rapidly decay. Sources with short half-life are dangerous because of high amount of radiation they emit at start, but quickly become safe.

Question 25

What is a long half-life?

Answer 25

Activity falls more slowly because most of nuclei don’t decay for long time, source just sits there, releasing small amounts of radiation for long time. This can be dangerous because nearby areas are exposed to radiation for years or millions of years.

Question 26

How do you plot half-life?

Answer 26

Activity against time. Found from graph by finding time interval on bottom axis corresponding to halving of activity on vertical axis.

Question 27

What is background radiation?

Answer 27

Low-level radiation around all the time.

Question 28

Where does the meaurments and subtraction of background radiation come from?

Answer 28

Radioactivity of naturally ocuring unstable isotopes all around us. Radiation from space called cosmic rays, mostly from sun, earth’s atmosphere protects us. Human activity: fallout, nuclear explosions, nuclear waste-only represents tiny proportion of radiation.

Question 29

What does the radiation dose tell you?

Answer 29

Risk of harm of body tissue due to exposure to radiation. Measured in sieverts (Sv). Dose from background radiation is small, so millisieverts often used (1Sv=1000 mSv). Your radiation dose varies depending on where live, what job.

Question 30

What is irradiation, and how is it prevented?

Answer 30

Objects near radioactive source are irradiated by it-exposed to it. Irradating something doesn’t make it radioactive. Keeping sources in lead-lined boxes, standing behind barriers, or being in different room and using remote-controlled arms reduce effects or irradiation.

Question 31

What is contamination?

Answer 31

If unwanted radiactive atoms get onto or into object, object is said to be contaminated. Contaminating atoms might then decay, releasing radiation-could cause harm. Contamination especially dangerous because radioactive particles get inside your body.

Question 32

How is contamination prevented?

Answer 32

Gloves and tongs should be used when handling sources, to avoid particles getting stuck in skin or under nails. Some workers wear protective suits to stop breathing in particles.

Question 33

How are beta and gamma rays harmful outside the body?

Answer 33

Can penetrate body and get to delicate organs. Alpha less dangerous-can’t penetrate skin, easily blocked by samll air gap. High levels of irradiation from all sources are dangeous, especially from beta and gamma.

Question 34

How are alpha particles dangerous inside the body?

Answer 34

Do damage in very iocalised areas. So contamination rather than irradiation, majour concern when working with alpha sources. Beta less damaging inside body, radiation absorbed over wider areas, some passes out body. Gamma least dangerous inside body, mostly pass straight out, lowest ionising power.

Question 35

What are the risks of using radiation?

Answer 35

Can enter living cells and ionise atoms/molecules. Can lead to tissue damage. Lower doses cause minor damage without killing cells. Can give rise to mutant cells-divide uncontrollably-cancer. Higher doses kills cells-raidation sickness if lot of cells get blatted at once.

Question 36

How are gamma sources useful?

Answer 36

Certain raioactive isotopes injected, progress around body, can be followed using an external detector. Computer converts reading to a display showing where strongest reading is coming from.

Question 37

How is iodine useful in radiation?

Answer 37

Iodine-123 absorbed by thyroid gland like normal iodine-127, but gives out radiation-can be detected to indicate whether thuroid gland is taking in iodine as should.

Question 38

How are isotopes useful in radiation in the body?

Answer 38

Isotopes taken into the body-usually gamma (never alpha), radiation passes out of body withou causing much ionisation. Have short half-life, so radioactivity inside patient quickly disappears.

Question 39

What is radiotherapy?

Answer 39

High doses of ionising radiation kills all living cells, can treat cancer. Gamma rays directed carefully, at just right dosage to kill cancer cells and not damagind normal cells. Radiation-emmiting implants also be put next to or inside tumors. Some damage inevitably done to normal cells-sickness.

Question 40

How do you weigh up the risks and benefits of radiation?

Answer 40

traces can be used to diagnose life-threatinig conditions, risk of cancer from 1 of tracer is small. Prolonged exposure to radiation pose risk in future, cause side effects. Many people with cancer have radiotherapy. Preceived risk-how risky a person thinks something is. Not same as actual risk of procedure and percieved risk can vary from person to person.

Question 41

What is nuclear fission?

Answer 41

Type of nuclear reaction, releases energy from large unstable atoms, by splitting them into smaller atoms.

Question 42

What are the steps involved in nuclear fission?

Answer 42

Spontaneous fission rarely happens. Nucleus absorbs neutron before splits. When splits 2 lighter elements roughly same size form. 2/3 neutrons also released when atom splits. If any slow enough moving neutrons-absorbed by other nucleus, cna cause more fission-chain reaction. Energy not transferred to kinetic energy stores of products is carried away by gamma rays. Energy carried by gamma rays an in kinetic energy stores of remaining free neutrons and other decay products used to heat water making steam-turn turbines and generators. Energy produced by fission controlled by changing how quickly chain reaction can occur-using control rods-lowered and raised in nuclear reactor. They abosrb neutrons.

Question 43

What can an uncontrolled chain reaction cause?

Answer 43

Lots of energy being released as explosion-nuclear weapons.

Question 44

What is nuclear fusion?

Answer 44

2 light nuclei collide at high speed and fuse, creates larger heavier nucleus.

Question 45

What do heavier nucleus produced in fusion have?

Answer 45

Not as much weight as 2 separate light nuclei had. Some mass converted to energy-released as radiation. Fusion releases a lot of energy

Question 46

Why can’t we use fusion at the moment?

Answer 46

Temperatures and pressures needed are too high that fusion reactors are really hard and expensive to build.