25.1 - Nuclear Radiation

radiation - particles and rays emitted by radioactive matter

isotope - number of protons don’t equal neutrons

radioisotope - nuclei of unstable isotopes; gain stability by giving off large amounts of energy

nuclear reactions are not affected by temperature, pressure, or catalysts; they can’t be slowed down, sped up, or stopped

Becquerel

• 1852-1908

• French Chemist

• 1896 - accidental discovery

  • studying ability of uranium salts that had been exposed to sunlight to fog photographic film plates

  • there was a storm → no sunlight

  • left sample on plate

  • uranium still fogged plate

Marie and Pierre Curie

• 2 of Becquerel’s associates

• showed that rays emitted by uranium caused the plates to fog up

• helped discover radiation

the stability of a nucleus depends on the ratio of protons to neutrons and the overall size of the nucleus

an unstable nucleus releases energy by emitting radiation during the process of radioactive decay which are spontaneous and don’t require input of energy

TYPES OF RADIATION

Alpha

• 238/92 U → 234/90 Th + 4/2 He

• blocked by sheet of paper

• alpha particle - 2 protons, 2 neutrons, double positive charge

• atomic number decreases by 2 and atomic mass decreases by 4 after decay

Beta

• beta particle - electron resulting from the breaking apart of a neutron → breaks up into protons, which stay in nucleus, and electron, which is released

• 14/6 C → 14/7 N + 0/-1 e

• stopped by wood

• atomic number increases by 1 and the atomic mass stays the same after decay

Gamma

• gamma ray - high energy photon emitted by radioisotope

• 230/90 Th → 226/88 Ra + 4/2 He + y

• nuclei often emit gamma rays along with alpha and beta particles

• atomic number and mass are not altered dafter decay

• stopped by lead/concrete

25.2 - Nuclear Transformations

band of stability - a region on a graph where the number of neutrons vs the number of protons for stable nuclei

nuclear force - attractive force that acts between all nuclear particles that are extremely close together; EX: protons and neutrons in nucleus

neutron to proton ratio determine type of decay

positron - particle with mass of an electron but positive charge

atomic number > 83 → radioactive

unstable - either p>n or p<n

radioactive energy comes from a small quantity of mass

half life - time required for one half of sample to decay; every radioisotope has this

after each half life (t1/2), half of the existing radioactive atoms have decayed into atoms of a new element

transuranium elements - atomic number > 92

• don’t occur in nature

• radioactive

• transmutate

• synthesized in nuclear reactors and accelerators

transmutation - conversion of an atom of one element to another; can occur through radioactive decay or when particles bombard the nucleus of an atom

25.3 - Fission and Fusion of Atomic Nuclei

fission - splitting nuclei into smaller fragments

• used only with U-235 and Pu-239

• struck with slow moving neutrons → more neutrons released → strike other nuclei → chain reaction (some of the neutrons produced react with other fissionable atoms, producing more neutrons which react with fissionable atoms)

• tremendous amounts of energy (= to 20 000 tons of TNT)

• controlled fission reactions produce useful energy in nuclear reactor (heat → steam → turbines → electricity)

neutron moderation - slows down neutrons so reactor fuel captures them to continue chain reaction; H2O or C based (form of graphite)

neutron absorption - reduces number of slow moving neutrons before they hit fissionable matter; use control rods which are made up of cadmium

nuclear waste - water cools spent rods and acts as radiation shield to reduce radiation levels

fusion - nuclei combine to produce nucleus of greater mass; more energy than fission; energy released by sun — needs high temperatures

25.4 - Radiation in your Life

ionizing radiation - radiation emitted by radioisotopes; enough energy to knock electrons off some atoms of the bombarded substance to produce ions

Geiger counters, scintillation counters, and film badges are used to detect radiation

neutron activation analysis - procedure used to detect trace amounts of elements in samples