Atomic disintegration

Since the half-life is independent of the number of radioactive atoms, it remains constant throughout the decay process. Thus, 50% of the radioactive atoms disintegrate in one half-life, 75% in two half-lives, and 87.5% in three half-lives. 

The decay of radiocarbon (see Fig. 61) into nitrogen-14 proceeds at a constant rate, and its half-life is 5730 + 40 years (see Textbox 14). This means that in any material containing carbon, some radiocarbon atoms disintegrate before 5730 years have elapsed and others later after 5730 + 40 years have elapsed, however, only half of the original atoms of the carbon-14... 

Equation (1.29) suggests that there is a definite probability of any particular atom disintegrating at a given moment and this is proportional to the number of atoms present at that moment. 

Average-life period i of any radioactive atom is the length of time, which can exist before the atom disintegrates and can be calculated as follows. 

The number of atoms disintegrating in the interval between t and t + dt is equal to dn. Since dt is very small, dn may be taken as number of atom disintegrating at time t. The period of average life t is obtained by multiplying every possible life period t from zero to infinity, by the number of atoms dn and then dividing the product by the total number of atoms n0 present at the beginning of the time. Thus,... 

Laboratory at the University of Munich. At the Radium Institute in Vienna he made the first accurate determination of the atomic weight of radium. His work on radioactive elements strikingly confirmed the hypothesis of atomic disintegration proposed by Rutherford and Soddy. 

ATOMIC DISINTEGRATION. The name sometimes given to radioactive decay of an atomic nucleus and occasionally to the breakup of a compound nucleus formed during a nuclear reaction. See also Radioactivity. 

The activity of a radioactive sample is quoted in Becquerels (named after the discoverer of natural radioactivity) and it varies from one element to another. One atomic disintegration per second is called one Becquerel (Bq). A further unit often used is the Curie (Ci), which is the activity produced by 1 g of radium 226 and is equal to 3.7 x 1010 disintegrations per second. 

When the nucleus of a radioactive atom disintegrates, it emits various particles and so changes its own composition. When an alpha particle is lost then a new element is formed, which is two places to the left in the periodic table. When a beta particle is lost then a new element is formed which is one place to the right in the periodic table. Therefore, by a series of losses of alpha and beta particles, the element progressively changes. This is called decay , and the pattern it follows until a stable nuclear arrangement is reached (usually when the element lead is formed) is called the decay series (see Chapter 12). 

Second, when the exposure to intense light ends (the person goes indoors), the Cu2+ ions migrate to the surface of the silver chloride crystal, where they accept electrons from silver atoms as the tiny crystal of silver atoms disintegrates ... 

An increased precision in the location of atoms in the crystal lattice has shown that some irregularity in their position is very common. This in turn has led to an understanding of the way in which a crystal grows and of the changes brought about in a crystal lattice when it is bombarded by particles from without or suffers atomic disintegration within. It will be seen below that these may be matters of very practical concern. 

The nuclei of unstable atoms disintegrate or decay spontaneously, emitting alpha or beta particles and gamma radiation. Types of atoms that undergo this process are called radioactive isotopes. A decaying reactant isotope is referred to as a parent atom, and the atom produced is a daughter atom. In this ChemLab, heads-up pennies represent individual parent atoms of the fictitious element pennium, and tails-up pennies represent the daughter atoms of the decay. You will study the decay characteristics of pennium and will determine its half-life, which is the time required for one-half of the atoms to decay. 

In 1903, Ramsay and Soddy 0 announced the discovery of the fact that helium was a product of the atomic disintegration of radium, one gram of which produces about 0.45 cubic millimeter of helium per day. Later it was found that other radioactive substances also yield helium and that the charged helium atom is the alpha particle. 

The fundamental law of radioactive transformation (v. Schweidler, 1905) states that the number of atoms disintegrating per unit time (—(INIdt) is proportional to the number of atoms (N) present at the moment ... 

C1877 -1956) gave a theory of atomic disintegration among radioactive substances resulting in the formation of new substances. This was verified and established by 1909. 

The curie is a measure of the amoimt of radioactivity in a radioactive source. The curie is independent of the nature of the radiation (alpha, beta, or gamma) and its effect on biological tissue. A curie is defined as the amoimt of radioactive material that produces 3.7 X 10 atomic disintegrations per second. 

The atom is now known to consist of three primary particles protons, neutrons, and electrons, which make up the atoms of all matter. A series of experimental facts established the validity of the model. Radioactivity played an important part. Marie Curie suggested, in 1899, that when atoms disintegrate, they contradict Dalton s idea that atoms are indivisible. There must then be something smaller than the atom (subatomic particles) of which atoms were composed. 

Feussner, C. G. Bedreag, A. Sommerfeld, and N. Collins. Evidence of atomic disintegration by bombardment with a-rays was observed by H. Pettersson and... 

Symbol A The average number of atoms disintegrating per unit time in a radioactive substance. 

Although we have said that trihum is unstable, the chances of any one particular tritium atom disintegrating over a period of, say, 1 h would be very low. Relative stabilities of various isotopes are expressed in terms of their half-lives. This refers to the time it would take for exactly 50% of the material to undergo radioactive decay. In the case of trihum the hgure is approximately 12 years. 

The number of atomic disintegrations that occm in a radioactive material per second is called its ... 

Activity. The rate at which atomic disintegrations are taking place in a sample of material. Measured in the SI unit the becquerel (q.v.). Formerly measured in curies (q.v.). 

Henri Becquerel (1852-1908) discovered natural radioactivity in natural uranium and radium ores in 1896 (Section 13.1). In 1898, Marie Sklodowska Curie (1867-1934)—a student of Becquerel—and her husband Pierre discovered two radioactive elements, radium and polonium. In 1899, Marie Curie suggested that atoms of radioactive substances disintegrate when they emit these unusual rays. She named this phenomenon radioactivity. A given radioactive element gives off exactly the same type of radioactive particles or rays regardless of whether it is found in its pure state or combined with other elements. About 25 elements exist only in radioactive forms. Marie Curie s suggestion that atoms disintegrate contradicted Dalton s idea that atoms are indivisible. 

The rate of atomic disintegration (units Becquerel or Curie). 

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