Question

Detecting Material Flaws Flaws in welded metal parts of airplanes can be identified by placing the isotope iridium-192 on one side of the weld and photographic film on the other side to detect gamma rays that pass through. How does the gamma ray emission affect the atomic number and mass number of the iridium?

Short answer

In conclusion, the gamma ray emission from iridium-192 does not affect the atomic number (Z) and mass number (A) of the isotope. The atomic number remains 77, and the mass number remains 192. The main purpose of using iridium-192 in detecting material flaws is to utilize the emitted gamma rays to penetrate the metal and create an image on the photographic film on the other side, revealing any defects in the weld.

Step-by-step solution

Understand Gamma Decay

Gamma decay is a type of radioactive decay in which an unstable nucleus releases a gamma photon (high-energy electromagnetic radiation) without changing the number of protons or neutrons in the nucleus. This process typically occurs after another type of decay (such as alpha or beta decay) has taken place and the nucleus is left in an excited state. In gamma decay, the nucleus transitions from an excited state to a lower-energy state, emitting a gamma photon in the process.

Analyze Iridium Isotope

For the isotope iridium-192, the atomic number (Z) is 77, which denotes the number of protons in the nucleus, and the mass number (A) is 192, which is the sum of protons and neutrons together. The given isotope has 77 protons and 115 neutrons (192 - 77 = 115).

Determine Change in Atomic Number and Mass Number Due to Gamma Ray Emission

Since gamma decay does not involve any changes in the number of protons or neutrons in the nucleus, the emission of gamma rays from an iridium-192 nucleus will not affect its atomic number or mass number. To summarize: - Atomic number (Z) before gamma emission: 77 - Atomic number (Z) after gamma emission: 77 - Mass number (A) before gamma emission: 192 - Mass number (A) after gamma emission: 192 In conclusion, the gamma ray emission from iridium-192 does not affect the atomic number and mass number of the isotope. The main purpose of using iridium-192 in detecting material flaws is to utilize the emitted gamma rays to penetrate the metal and create an image on the photographic film on the other side, revealing any defects in the weld.

Key concepts

Understanding Radioactive Decay

Radioactive decay is a natural and spontaneous process by which an unstable atomic nucleus loses energy to reach a more stable state. It is driven by the quantum mechanics governing the particles within an atom's nucleus. During this process, the nucleus emits radiation in the form of particles or electromagnetic waves. There are main types of radioactive decay: alpha, beta, and gamma decay.

In alpha decay, the nucleus emits a helium nucleus (two protons and two neutrons), causing a decrease in both atomic and mass numbers. In beta decay, a neutron is transformed into a proton (or vice versa), and a beta particle is emitted, altering the element's atomic number but not its mass number. Unlike alpha and beta decay, gamma decay involves the release of electromagnetic radiation, known as gamma rays, without any change in the atomic structure of the element. This is because the nucleus releases excess energy to transition from an excited state to a lower energy state without altering the number of protons or neutrons.

Demystifying the Atomic Number

The atomic number, often symbolized as Z, is a fundamental property of elements that tells us the number of protons in the nucleus of an atom. This number is crucial as it defines the element itself; no two different elements can have the same atomic number. Since protons are positively charged, the atomic number also indicates the amount of positive charge in the nucleus. Consequently, it determines the chemical properties of an element and its place in the periodic table.

Interestingly, all atoms of the same element share the same atomic number, but they can have different masses due to varying numbers of neutrons. These different versions are known as isotopes. Since gamma decay has no impact on the number of protons, the atomic number remains unchanged after emitting gamma radiation. This can be exemplified by studying the gamma decay of isotopes such as iridium-192.

Mass Number: A Measure of Nucleus Content

The mass number, denoted as A, represents the total number of protons and neutrons in an atom's nucleus. It provides us with information about the mass and size of the nucleus. While the number of protons (atomic number) assigns the identity of an element, it's the number of neutrons that can vary to produce isotopes. Different isotopes of an element have different mass numbers, but the same atomic number.

When gamma decay occurs, the nucleus emits only a gamma photon, which has no rest mass and thus doesn't affect the nucleus's combined count of protons and neutrons. Therefore, the mass number remains constant during gamma decay. Diving into practical applications like the use of iridium-192 for flaw detection, we can confidently say that while gamma rays do notable work in non-destructive testing, they do not alter the mass number of the isotope in question.

Exploring Iridium-192

Iridium-192 is an isotope of iridium with an atomic number of 77 and a mass number of 192, implying it has 77 protons and 115 neutrons in its nucleus. It is commonly used in industrial radiography to inspect metals for internal defects, thanks to its high-energy gamma-ray emissions. These gamma rays can deeply penetrate materials and expose hidden flaws on a photographic film placed on the opposite side of a material being tested, like the welded metal parts of airplanes.

Iridium-192 undergoes gamma decay after it has experienced other forms of radioactive decay and is left in an excited state. A noteworthy aspect of iridium-192's gamma decay is that it involves only the emission of energy and no change in either atomic or mass numbers. This property is critical, as it means that following a gamma emission, the radionuclide remains iridium-192, and thus the reliability of the material inspection does not degrade due to the decay process.