Types of Radioactivity

Soon after Becquerel s discovery, a young graduate student named Marie Sklodowska Curie (1867-1934) (one of the first women in France to pursue doctoral work) decided to study uranic rays for her doctoral thesis. Her first task was to determine whether any other substances besides uranium (the heaviest known element at the time) emitted these rays. In her search. Curie discovered two new elements, both of which also emitted uranic rays. Curie named one of her newly discovered elements polonium, after her home country of Poland. The other element she named radium, because of its high level of radioactivity. Radium is so radioactive that it gently glows in the dark and emits significant amounts of heat. Since it was clear that these rays were not unique to uranium. Curie changed the name of uranic rays to radioactivity. In 1903, Curie and her husband, Pierre Curie, as well as Becquerel were all awarded the Nobel Prize in physics for the discovery of radioactivity. In 1911, Curie received a second Nobel Prize, this time in chemistry, for her discovery of the two new elements. 

In order to understand these different types of radioactivity, we must briefly review the notation for symbolizing isotopes from Section 2.6. Recall that we can represent any isotope with the following notation  

96 is nwmI ciriiB ii hMsr sf Maris Carie ai6 her csitrihitieis to ear aaArstoaiag ef laMeaetnitjr. 

Since A represents the sum of the number of protons and neutrons, and since Z represents the number of protons, the number of neutrons in the nucleus (N) is A — Z. 

A Radium, discovered by Marie Curie, is so radioactive that it glows visibly and emits heat. 

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There are other less common types of radioactive decay. Positron emission results in a decrease by one unit in the atomic number K capture involves the incorporation of one of the extranuclear electrons into the nucleus, the atomic number is again decreased by one unit. 

The most important types of radioactive particles are alpha particles, beta particles, gamma rays, and X-rays. An alpha particle, which is symbolized as a, is equivalent to a helium nucleus, fHe. Thus, emission of an alpha particle results in a new isotope whose atomic number and atomic mass number are, respectively, 2 and 4 less than that for the unstable parent isotope. 

Activities and existing and projected volumes of all types of radioactive waste are Hsted in Reference 7. 

The geologic aspects of waste disposal (24—26), proceedings of an annual conference on high level waste management (27), and one from an annual conference on all types of radioactive waste (28) are available. An alternative to burial is to store the spent fuel against a long-term future energy demand. Uranium and plutonium contained in the fuel would be readily extracted as needed. 

Anyone working with different types of radioactive material should know the conditions when various materials may be present. The following provides some additional guidance as to where radioactive materials may be present ... 

Usually atoms resulting from nuclear fission arc radioactive. There are also radioactive atoms produced from neutron capture by both U and U. Both types of radioactive atoms remain in the nuclear fuel. It is these radioactive atoms that comprise the nuclear wastes that require disposal in an environmentally acceptable manner. 

There are three common ways by which nuclei can approach the region of stability (1) loss of alpha particles (a-decay) (2) loss of beta particles (/3-decay) (3) capture of an orbital electron. We have already encountered the first type of radioactivity, a-decay, in equation (/0). Emission of a helium nucleus, or alpha particle, is a common form of radioactivity among nuclei with charge greater than 82, since it provides a mechanism by which these nuclei can be converted to new nuclei of lower charge and mass which lie in the belt of stability. The actinides, in particular, are very likely to decay in this way. 

This type of radioactivity, /3-decay, is found in both the light and heavy elements. 

The origin of the rays was initially a mystery, because the existence of the atomic nucleus was unknown at the time. However, in 1898, Ernest Rutherford took the first step to discover their origin when he identified three different types of radioactivity by observing the effect of electric fields on radioactive emissions (Fig. 17.4). Rutherford called the three types a (alpha), (3 (beta), and y (gamma) radiation. 

Beta Particle—An electron that is emitted from the nucleus of an atom during one type of radioactive transformation. A beta particle has a mass and charge equal in magnitude to that of the electron. The charge may be either +1 or -1. Beta particles with +1 charges are called positrons (symbolized (3+), and beta particles with -1 charges are called negatrons (symbolized (3 ). 

The common type of radioactive emission that does not consist of matter is the gamma ray. 

We can observe three common types of radioactive decay in nature. We can occasionally observe others. 

Gamma emission is the release of high-energy, short-wavelength photons, which are similar to x-rays. The representation of this radiation is y. Gamma emission commonly accompanies most other types of radioactive decay, but we normally do not show it in the balanced nuclear equation since it has neither appreciable mass nor charge. 

This section summarizes the key events that led the United States to be the first country to successfully develop the atomic bomb. It also discusses the world s current nuclear weapons arsenal and details the uses of other types of radioactive materials as terrorist weapons. 

The other types of radioactive materials cited in this section (medical industry and food industry sources) produce significantly lower activity levels than fuel from a nuclear power plant. However, these sources of radioactive materials may be appealing to terrorists because they are far more accessible. Thousands of hospitals, medical treatment facilities, and food industry plants scattered across the U.S. are protected by relatively low levels of security. 

Three common types of radioactive decay are observed in nature, and two others are occasionally observed. 

Gamma emission, in which high-energy electromagnetic radiation is emitted from the nucleus. This commonly accompanies the other types of radioactive decay. It is due to the conversion of a small amount of matter into energy. 

In usual practice, two types of radioactive counters are mainly employed depending on the type of radioactive substance used, namely ... 

So, now (1913) one has a set of rules which characterize the daughter atom in terms of a knowledge of the parent element and the type of radioactive decay. The rules work they give rise to the concept of isotopes elements which correspond to different atomic weights but which are chemically identical. However, the rules are purely empirical no explanation exists for the rules as the matter now stands. Something is still missing in this story. 

Radioactive Waste Disposal. There are two principal types of radioactive materials produced in the operation of nuclear generating stations. Over 99% of the radioactivity produced is... 

A great deal was learned from the atomic bomb survivors. The US military dropped the first atomic bomb on Hiroshima, Japan on 6 August 1945 and a second on Nagasaki, Japan, three days later. The bombs used two different types of radioactive material, 235U in the first bomb and 239Pu in the second. It is estimated that... 

Here are the missing particles and the types of radioactive decay ... 

Consider the nuclei 15C, 15N, and 150. Which of these nuclei is stable What types of radioactive decay would the other two undergo Calculate the binding energy difference between 15N and 150. Assuming this difference comes from the Coulomb term in the semiempirical binding energy equation, calculate the nuclear radius. 

Radioactive decay is what chemists refer to as a first-order reaction that is, the rate of radioactive decay is proportional to the number of each type of radioactive nuclei present in a given sample. So, if we double the number of a given type of radioactive nuclei in a sample, we double the number of particles emitted by the sample per unit time.2 This relation may be expressed as follows ... 

Electron emission (ft -) A type of radioactive decay, where a neutron in the nucleus of an unstable atom converts into a proton and releases an electron and an antineutrino (compare with electron capture and positron emission). 

Neutron emission A type of radioactive decay, where a neutron is ejected from the nucleus of a decaying atom. 

Positron emission (fi+) A type of radioactive decay where a proton converts into a neutron, positron, and neutrino (compare with electron emission). 

Now, let us analyze each type of radioactive decay individually. 

Alpha particles are positively charged with a mass of 4 amu (atomic mass units, 1amu=1/12th.of carbon atom). They are, then, the nuclei of Helium atoms. These particles are the slowest moving and the most massive of the three types of radioactivity. As such, they have the least penetrating ability through matter. A sheet of paper will stop their movement. 

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