Radioactive Decay


unstable isotopes

Quote that must be paraphrased

The turning point in the battle between theoretical physicists and empirical geologists and biologists occurred in 1896. In the course of an experiment designed to study x‑rays discovered the previous year by Wilhelm Röntgen, Henri Becquerel stored some uranium-covered plates in a desk drawer next to photographic plates wrapped in dark paper. Because it was cloudy in Paris for a couple of days, Becquerel was not able to "energize'' his photographic plates by exposing them to sunlight as he had intended. On developing the photographic plates, he found to his surprise strong images of his uranium crystals. He had discovered natural radioactivity, due to nuclear transformations of uranium. The significance of Becquerel's discovery became apparent in 1903, when Pierre Curie and his young assistant, Albert Laborde, announced that radium salts constantly release heat. The most extraordinary aspect of this new discovery was that radium radiated heat without cooling down to the temperature of its surroundings. The radiation from radium revealed a previously unknown source of energy. William Wilson and George Darwin almost immediately proposed that radioactivity might be the source of the sun's radiated energy.

Historical quote

These experiments show that the uranium radiation is complex, and that there are present at least two distinct types of radiation — one that is very readily absorbed, which will be termed for convenience the α radiation, and the other of a more penetrative character, which will be termed the β radiation.

Paths of α, β, and γ radiation in a magnetic field [slide]. Alpha particles deflect upward in this field obeying the right hand rule of a positively charged particle. Beta particles deflect the opposite way indicating negative charge. Gamma particles are unaffected by the field and so must carry no charge. In addition, the radius of curvature of the α particles is larger than that of the β particles. This shows that the alphas are more massive than the betas.

alpha decay

Alpha particles cannot penetrate a piece of paper or even the thin layer of dead skin that coats us all. They will quickly find and join with two electrons to become an atom of helium before they can do much harm. Alpha particles are most dangerous, however, when inhaled. The inside of our lungs are moist and sticky and not as well coated with expendable cells as our exteriors are. Were a bit of alpha emitting debris to find its way into our lungs, chances are pretty good that it would stick there long enough to emit an energetic and massive nuclear projectile into our tissues, ionizing and dissociating molecules along the way. Such activities are one source of lung cancer. Workers who handle plutonium (a significant alpha emitter) are well aware of this hazard and take great care to keep it outside of their bodies at all times.

beta decay

Also called beta minus decay.

Quote that must be paraphrased

The existence of neutrinos was first proposed by Wolfgang Pauli in a 1930 letter to his physics colleagues as a "desperate way out" of the apparent non-conservation of energy in certain radioactive decays (called beta decays) in which electrons were emitted. According to Pauli's hypothesis, which he put forward very hesitantly, neutrinos are elusive particles which escape with the missing energy in beta decays. The mathematical theory of beta decay was formulated by Enrico Fermi in 1934 in a paper which was rejected by the journal Nature because "it contained speculations too remote from reality to be of interest to the reader. Neutrinos from a nuclear reactor were first detected by Clyde Cowan and Fred Reines in 1956.

Not quite a quote. Enrico Fermi named the neutrino.

È un neutrone? (Is it a neutron?)

No, è un neutrino. (No, it's a neutrino.)

The name neutrino is a play on words in Italian. The Italian word for neutron (neutrone) is what linguists call an augmentative; that is, it indicates bigness or intensity. Some other augmentative words in Italian that readers might recognize are …

Change he suffix "-one" to "-ino" and you have a diminutive; that is, something small, cute, and innocuous. A small, cute, innocuous neutrone would be a neutrino in Italian and so it is in English now too. Some other diminutive words in Italian that readers might recognize are…

electron capture


electron capture