P7 Flashcards

Question

Describe how to determine one and two half-lives of a sample of 1000 undecayed nuclei FROM A GRAPH

Answer 1

- first find 500 on the y-axis (where undecayed nuclei are shown), then trace it to the line horizontally, then vertically down to the x-axis to find the time - to find the second half-life, halve 500 to get 250 and repeat the process

Answer 2

- one half life of this isotope = 15 days - 45/15 = 3 [] so 3 half lives, meaning to half the initial count rate three times also - 200/2 = 100 - 100/2 = 50 - 50/2 = 25 count rate after 45 days = 25 counts/s

Answer 3

- radiotherapy for cancer treatment - medical imaging - tracers to monitor organ (function)

Answer 4

- patient is given small amount of radioactive isotope - isotope emits gamma radiation that is detected by monitors - for monitoring kidneys for example: [] patient given water with small amounts of radioactive iodine [] if kidney is healthy, reading goes up as the iodine enters the kidney, then down as it exits [] if kidney is blocked, reading doesn't go down after entering the kidney why: - radioactive substances used here like radioactive iodine have half lives that are long enough for the tests to be carried out, but short enough that they decay almost completely soon enough so that the patient is not harmed - radioactive substances used here emit gamma radiation which pass through all body tissues and can be detected by the detector and displayed on the monitor - radioactive substances used here decay into stable, harmless products

Answer 5

- patient injected with solution with gamma-emitting isotope [] half life should be long enough to take the image but short enough that it almost completely decays afterwards - solution absorbed by nearby organ - gamma camera detects gamma radiation through holes in thick lead grid in front of detector - detector signals used to build up image of the radiation in the organ and thus of the organ itself

Answer 6

- narrow beam of radiation from cobalt fired at tumours/cancer cells to destroy them [] however may harm surrounding tissue [] half life of 5 years - used due to penetrative power - radioactive implants [] sometimes also emit beta radiation [] come as small seeds/tiny rods [] permanent implants half half lives long enough that they irradiate and thus damage/kill tumours and that they decay shortly after doing so

Answer 7

- 50% = radon gas in air - 10% = CMBR - 11.5% = food + drink - 14% = ground - 14% = medical purposes - 0.2% = nuclear weaponry - 0.2% = air travel - 0.1% = nuclear reactors

Answer 8

the splitting of an atom's nucleus into 2+ smaller DAUGHTER nuclei ROUGHLY EQUAL IN SIZE - RELEASES ENERGY (in form of gamma radiation and kinetic energy of released neutrons and fragment nuclei) - RELEASES TWO OR THREE (fission) NEUTRONS

Answer 9

induced = when nuclear fission is induced via a neutron colliding with the nucleus and being absorbed - most commonly in reactors, when uranium-235 or plutonium-239 absorb neutrons spontaneous = when nuclear fission happens without a neutron striking the nucleus

Answer 10

- one nuclear fission releases other neutrons which can induce more nuclear fission in fissionable nuclei - causes CHAIN REACTION of nuclear fission - steady release of energy as such

Answer 11

controlled = nuclear reactor uncontrolled = nuclear bomb

Answer 12

- use water (at high pressure) in pipes through reactor core as a coolant and moderator [] slows down rate of reactions by slowing fission neutrons via collisions with water molecules and thus taking energy so can't trigger more fission - use control rods in reactor core which absorb surplus neutrons [] depth of rods adjusted to maintain steady reaction as necessary - thick concrete walls enclose reactor so gamma radiation doesn't escape

Answer 13

- when two smaller nuclei are forced near enough that they form one heavier nucleus - releases energy (nuclear radiation and kinetic energy of particles emitted and the new nucleus) - creates and emits some particles - only happens if nuclei used are LESS THAN OR EQUAL TO RELATIVE MASS OF 55 [] can happen above this, but energy must be supplied

Answer 14

gives particles increased kinetic energy and forces them closer together [] collide with more force, helping to overcome electrostatic repulsion due to both having like charges

Answer 15

- heated by using a large electric current through the plasma - plasma contained with a magnetic field around the edges of the reactor so they don't touch the walls and go cold

Answer 16

benefits: - uses heavy hydrogen as fuel, which is naturally abundant in seawater unlike the radioactive fuels for nuclear fission - reaction product, helium, is a harmless gas - releases a lot of energy, so could easily meet electricity and energy demands disadvantages: - hard to make them economical, as the energy used to sustain the magnetic field and heat the plasma via electric currents currently outweighs the profit of the energy released by the reaction - nuclear fusion reactors are still in early stages of development and could take years to become practical

Answer 17

sieverts/Sv - 1 Sv = 1000 mSv

Answer 18

- produce nuclear waste [] has to be stored safely underground for many many years so that the surrounding areas are not contaminated by radioactivity [] unused uranium and plutonium from the waste are chemically removed for future use - nuclear meltdowns like Fukushima and Chernobyl [] impact economy and health across the world pretty much - risk of radiation on human and environmental health - at the moment, have a relatively short operating life (20 years) with high construction and decommissioning costs

Answer 19

- longer operating lives (60 years instead of 20) - lower costs of commission and decommission - less effect on environment - more safety features [] eg. convection of outside air through cooling panels along reactor walls

P7 Flashcards

Radioactivity (44 cards)