10 - Radioactivity & Nuclear Processes

radioactive nucleus

a nucleus that undergoes spontaneous changes and emits energy in the form of radiation

radioactive decay

a process in which an unstable nucleus changes energy states and in the process emits radiation

alpha particle

the particle that makes up alpha rays

• identical to the helium nucleus and composed of two protons and two neutrons

beta particle

the particle that makes up beta rays

• identical to an electron but produced in the nucleus when a neutron is changed into a proton and an electron

gamma ray

a high-energy ray that is like an X-ray, but with a higher energy

radioisotope

an isotope of an element that emits nuclear radiation

daughter nucleus

the new nucleusproduced when unstable nuclei undergo radioactive decay

positron

a positively charged electron

electron capsule

a mode of decay for some unstable nuclei in which an electron from outside the nucleus is drawn into the nucleus, where it combines with a proton to form a neutron

half-life

the time required for one-half the unstable nuclei in a sample to undergo radioactive decay

free radical

an electron-deficient particle that is very reactive

acute radiation syndrome

the condition associated with and following short-term exposure to intense radiation

inverse square law of radiation

a mathematical way of saying that the intensity of radiation is inversely proportional to the square of the distance from the source of the radiation

physical unit of radiation

a radiation measurement unit indicating the activity of the source of the radiation; for example, the number of nuclear decays per minute

biological unit of radiation

a radiation measurement unit indicating the damage caused by radiation in living tissue

curie

a physical unit of radiation measurement corresponding to 3.7 × 10¹⁰ nuclear disintegrations per second

becquerel

a physical unit of radiation measurement corresponding to one nuclear disintegration per second

roentgen

a biological unit of radiation measurement used with X-rays and gamma rays

• the quantity of radiation that generates 2.1 × 10⁹ ion pairs per 1 cm³ of dry air or 1.8 × 10¹² ion pairs per 1 g of tissue

rad

a biological unit of radiation measurement corresponding to the transfer of 1 × 10^-2 J or 2.4 × 10^-3 cal of energy to 1 kg of tissue

gray

a biological unit of radiation measurement corresponding to the transfer of 1 J of energy to 1 kg of tissue

rem

a biological unit of radiation measurement corresponding to the health effect produced by 1 roentgen of gamma or X-rays, regardless of the type of radiation involved

scintillation counter

a radiation-detection device operating on the principle that phosphors give off light when struck by radiation

Geiger-Muller tube

a radiation-detection device operating on the principle that ions form when radiation passes through a tube filled with low-pressure gas

tracer

a radioisotope used medically because its progress through the body or localization in specific organs can be followed

hot spot

a tissue in which a radioactive tracer concentrates

cold spot

a tissue from which a radioactive tracer is excluded or rejected

radioactive dating

a process for determining the age of artifacts and rocks, based on the amount and half-life of radioisotopes contained in the object

moderator

a material capable of slowing down neutrons that pass through it

cyclotron

a cyclic particle accelerator that works by changing electrical polarities as charged particles cross a gap

linear accelerator

a particle accelerator that works by changing electrical polarities as charged particles cross gaps between segments of a long tube

transuranium elements

the elements with atomic numbers greater than that of uranium

nuclear fission

a process in which large nuclei split into smaller, approximately equal-sized nuclei when bombarded by neutrons

chain reaction

a nuclear reaction in which the products of one reaction cause a repeat of the reaction to take place

expanding chain reaction

a reaction in which the products of one reaction cause more than one more reaction to occur

critical reaction

a constant-rate chain reaction

supercritical reaction

a branching chain reaction

critical mass

the minimum amount of fissionable material needed to sustain a critical chain reaction at a constant rate

supercritical mass

the minimum amount of fissionable material that must be present to cause a branching chain reaction to occur

breeder reaction

a nuclear reaction in which isotopes that will not undergo spontaneous fission are changed into isotopes that will

thermonuclear reaction

a nuclear fusion reaction that requires a very high temperature to start

nuclear fusion

a process in which small nuclei combine or fuse to form larger nuclei