In 2010, a team of scientists from Russia and the United States reported creation of the first atom of element 117, which is named tennessine, and whose symbol is Ts. The synthesis involved the collision of a target of 24997Bk with accelerated ions of an isotope which we will denote Q. The product atom, which we will call Z, immediately releases neutrons and forms 294117Ts: 24997Bk + Q → Z → 294117Ts + 3 10n (b) Isotope Q is unusual in that it is very long-lived (its half-life is on the order of 1019 yr) in spite of having an unfavorable neutron-to-proton ratio (Figure 21.1). Can you propose a reason for its unusual stability?
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Step 1: Understand the concept of nuclear stability. The stability of a nucleus is determined by the balance between protons and neutrons. A stable nucleus has a neutron-to-proton ratio close to 1:1 for light elements (Z<20) and 1.5:1 for heavy elements (Z>20).
Step 2: Consider the neutron-to-proton ratio. The isotope Q is said to have an unfavorable neutron-to-proton ratio, which typically means it has either too many or too few neutrons compared to protons. This would usually make the nucleus unstable.
Step 3: Reflect on the half-life of the isotope. Despite the unfavorable ratio, isotope Q has a very long half-life, which indicates it is quite stable. This is unusual and suggests there must be another factor contributing to its stability.
Step 4: Consider the concept of 'magic numbers' in nuclear physics. These are specific numbers of protons or neutrons in a nucleus that result in increased stability. These numbers are 2, 8, 20, 28, 50, 82, and 126 for both protons and neutrons.
Step 5: Propose a reason for the unusual stability. It's possible that isotope Q has a 'magic number' of protons or neutrons, which could explain its stability despite the unfavorable neutron-to-proton ratio.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Isotopes and Stability
Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons. The stability of an isotope is influenced by its neutron-to-proton ratio; typically, a ratio close to 1:1 is considered stable. However, some isotopes can exhibit unusual stability despite having unfavorable ratios due to factors such as nuclear shell effects or the presence of magic numbers of nucleons, which can lead to increased binding energy.
Half-life is the time required for half of the atoms in a radioactive sample to decay. It is a crucial concept in nuclear chemistry, as it provides insight into the stability and longevity of isotopes. A long half-life, such as that of isotope Q, suggests that the isotope undergoes decay processes very slowly, which can be attributed to its unique nuclear structure or energy levels that resist decay.
Nuclear reactions involve the transformation of atomic nuclei through processes such as fusion, fission, or radioactive decay. In the context of the question, the collision of 24997Bk with isotope Q leads to the formation of tennessine (294117Ts) and the release of neutrons. Understanding the mechanics of these reactions, including energy considerations and conservation laws, is essential for analyzing the stability and behavior of the resulting isotopes.
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