Atomic and Nuclear Particles

The effects that high-velocity atomic and nuclear particles or intense radiation have on the properties of an explosive are of practical interest. The question of whether such irradiation can cause initiation, and under what conditions, is also important. 

Primary explosives have been irradiated with electrons [14,105-107], neutrons [14,101], fission fragments [14,108,109], a-particles [100,110], X-rays [106], and 7-rays [111,112]. 

Bowden and Singh [14] used the electron beam of an electron microscope (75 kV, 200 nA) and found that lead and silver azide could be made to explode in the beam, but this was partly due to heating of the crystal. Fluxes of slow thermal neutrons up to 10 m and of fast (2 MeV) neutrons up to 10 m do 

Bowden [120] points out that the track widths in explosive crystals are greater than is usually found in inert materials, which indicates that some additional energy could have come from partial decomposition of the material. However, the heat liberated is not enough to produce explosion even when two tracks intersect. The probability of three or more tracks intersecting within 10 sec is small unless the fission-fragment density is high. 

Although the results indicate that initiation rarely occurs as a direct result of irradiation, two important points emerge from the work. The first is that the hot spot size of 10 -10 m suggested by Bowden and Yoffe and found to apply to 

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Ionising radiation means atomic and nuclear particles, i.e., gamma rays, electrons neutrons, etc. The intensity of ionising radiation at the earth s surface is not high enough to significantly affect mbbers and hence radiation exposure is only a consideration in connection with apphcations in nuclear plant and possibly where radiation is used to induce crosslinking or for sterilisation. 

Properties of Particles. From the research of the early part of the twentieth century, the existence of several types of particles was firmly estabhshed, and the properties were deterrnined. The particles that are involved in the decay of radioisotopes are given in Table 4. An additional type of conservation is that in all atomic and nuclear decays, the number of nucleons, ie, protons and neutrons, is conserved and the number of leptons, ie, electrons and neutrinos, is also conserved. 

Another consequence of the quantum theory of the atomic and nuclear systems is that no two protons, or two neutrons, can have exactly the same wave function. The practical appHcation of this rule is that only a specific number of particles can occupy any particular atomic or nuclear level. This prevents all of the electrons of the atom, or protons and neutrons in the nucleus, from deexciting to the single lowest state. 

QUANTUM NUMBER. A number assigned to one of the various quantities that describe a particle or state. Many different characteristics of atomic and nuclear systems, as well as of those entities that arc introduced as a part of particle physics, are described by means of quantum numbers. The quantum numbers arise from the mathematics of the eigenvalue problem and may be related to the number of nodes in the eigenfunction. Any state may be described by giving a sufficient set of compatible quantum numbers, In the customary formulations, each quantum number is either an integer (which may be positive, negative, or zero) or an odd half-integer. 

Matters are made up of small particles such as molecules and atoms. Thermodynamic laws have been postulated and inferred without looking into the micro-properties or microstates within the systems. A branch of thermodynamics has evolved, which tries to interpret thermodynamic properties based on the properties of micro constituent of the system. This branch is called the Statistical Thermodynamics. An offshoot is the Nuclear Thermodynamics , where matter is treated as another form of energy and role of atomic and subatomic particle forms are studied in determining thermodynamic properties. 

The emission of atomic and nuclear radiation obeys the rules of quantum theory. As a result of this, one can only talk about the probability that a reaction will take place or that a particle will be emitted. If one attempts to measure the number of particles emitted by a nuclear reaction, that number is not constant in time it has a statistical uncertainty because of the probabilistic nature of the phenomenon under study. 

This review is not presented from the historical point of view. Atomic and nuclear behavior and the theory and experiments backing it are discussed as we understand them today. Emphasis is given to the fact that the current picture of atoms, nuclei, and subatomic particles is only a model that represents our best current theoretical and experimental evidence. This model may change in the future if new evidence is obtained pointing to discrepancies between theory and experiment. 

For many nuclei, more than one mode of decay is positive. Users of radioisotopic sources need information about particles emitted, energies, and probabilities of emission. Many books on atomic and nuclear physics contain such information, and the most comprehensive collection of data on this subject can be found in the Table of Isotopes by Lederer and Shirley." Figure 3.12 shows an example of a complex decay scheme taken from that book. 

TABLE 11.2. Summary of atomic and nuclear properties associated with particle interactions (q.n. = quantum number). ... 

All science is based on a number of postulates. Quanmm mechanics has also elaborated a system of postulates that have been formulated to be as simple as possible and yet to be consistent with experimental results. Postulates are not supposed to be proved-their justification is efficiency. Quantum mechanics, the foundations of which date from 1925 and 1926, still represents the basic theory of phenomena within atoms and molecules. This is the domain of chemistry, biochemistry, and atomic and nuclear physics. Further progress (quantum electrodynamics, quantum field theory, and elementary particle theory) permitted deeper insights into the structure of the atomic nucleus but did not produce any fundamental revision of our understanding of atoms and molecules. Matter as described by non-relativistic quantum mechanics represents a system of electrons and nuclei, treated as pointlike particles with a definite mass and electric... 

Reactions of this type also release a lot of energy. Where does the energy come from Well, if you make very accurate measurement of the masses of all the atoms and subatomic particles you start with and all the atoms and subatomic particles you end up with, and then compare the two, you find that there s some ""missing mass. Matter disappears during the nuclear reaction. This loss of matter is called the mass defect The missing matter is converted into energy. 

The total stopping power for electrons is the sum of collision and radiative stopping powers, as described in O Chap. 6 in this Volume. These quantities have been tabulated in the ICRU Report 37 for electrons and positrons (ICRU 1989a). The total stopping power for protons, alpha particles (helium ions) and heavy ions is the sum of collision (atomic) and nuclear stopping powers, the latter being important only at low energies. 

Atomic and Nuclear Glasses. In the atomic and nuclear technology area, special glasses are used as particle detectors, dosimeters, x-ray imaging screens, and radiationabsorbing windows that shield against nuclear and x-radiation. 

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