1. Nuclear Stability and Decay
What determines the type of decay a radioisotope undergoes?
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2. Interpret Data
The stability of a nucleus depends on the ratio of neutrons to protons.
The region of the graph in which these points are located is called the band of stability.
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3. Interpret Data
The stability of a nucleus depends on the ratio of neutrons to protons.
For elements of low atomic number (below about 20), this ratio is about 1.
Above atomic number 20, stable nuclei have more neutrons than protons.
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4. Nuclear Stability and Decay
A nucleus may be unstable and undergo spontaneous decay for different reasons.
The neutron-to-proton ratio in a radioisotope determines the type of decay that occurs.
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5. Nuclear Stability and Decay
Some nuclei are unstable because they have too many neutrons relative to the number of protons.
When one of these nuclei decays, a neutron emits a beta particle (fast-moving electron) from the nucleus.
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6. Nuclear Stability and Decay
Some nuclei are unstable because they have too many neutrons relative to the number of protons.
When one of these nuclei decays, a neutron emits a beta particle (fast-moving electron) from the nucleus.
A neutron that emits an electron becomes a proton. n 1
p + e –1
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7. Nuclear Stability and Decay
Some nuclei are unstable because they have too many neutrons relative to the number of protons.
When one of these nuclei decays, a neutron emits a beta particle (fast-moving electron) from the nucleus.
A neutron that emits an electron becomes a proton. n 1
p + e –1
This process is known as beta emission.
It increases the number of protons while decreasing the number of neutrons.
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8. Nuclear Stability and Decay
Radioisotopes that undergo beta emission include the following. Cu 66 29
Zn + 30 e –1 C 14 6
N + 7 e –1
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9. Nuclear Stability and Decay
Other nuclei are unstable because they have too few neutrons relative to the number of protons.
These nuclei increase their stability by converting a proton to a neutron.
An electron is captured by the nucleus during electron capture. Co 59 27
Ni e 28 –1 Cl 37 17
Ar e 18 –1
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10. Nuclear Stability and Decay
A positron is a particle with the mass of an electron but a positive charge.
Its symbol is e.
During positron emission, a proton changes to a neutron, just as in electron capture. +1 B 8 5
Be + 4 e +1 O 15 8
N + 7 e +1
When a proton is converted to a neutron, the atomic number decreases by 1 and the number of neutrons increases by 1.
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11. Nuclear Stability and Decay
Nuclei that have an atomic number greater than 82 are radioactive.
These nuclei have both too many neutrons and too many protons to be stable.
Therefore, they undergo radioactive decay.
Most of them emit alpha particles.
Alpha emission increases the neutron-to-proton ratio, which tends to increase the stability of the nucleus.
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12. Nuclear Stability and Decay
In alpha emission, the mass number decreases by four and the atomic number decreases by two. Ra
226 88
Rn He
222 86 4 2 Th
232 90
Ra He
228 88 4 2
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13. Nuclear Stability and Decay
Conservation of mass is in chemical reactions.
Mass is not conserved during nuclear reactions.
Small quantity of mass is converted into energy released during radioactive decay.
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14. During nuclear decay, if the atomic number decreases by one but the mass number is unchanged, the radiation emitted is
A. a positron.
B. an alpha particle.
C. a beta particle.
D. a proton.
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15. During nuclear decay, if the atomic number decreases by one but the mass number is unchanged, the radiation emitted is
A. a positron.
B. an alpha particle.
C. a beta particle.
D. a proton.
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