91Ó°ÊÓ

Alpha decay is a common type of nuclear decay, a process by which an unstable atomic nucleus loses energy by releasing energy in the form of alpha particles. An alpha particle is the same as a helium nucleus, comprising 2 protons and 2 neutrons. This means that whenever an atom undergoes alpha decay, its atomic number decreases by 2, and its mass number decreases by 4.

In our exercise, uranium-235 undergoes a series of alpha emissions. This is part of the transformation of heavy elements into more stable ones. As uranium emits an alpha particle:

• The original uranium isotope ( ^{235}_{92}U ) loses 4 from its mass number, reducing to the final mass number of 207 for lead.
• The atomic number is reduced by 2 after each emission.

This change is systematic, and in our case, it requires several alpha decays to transform uranium-235 into lead-207, involving 7 such decays in total.

Beta decay is another form of radioactive decay in which a neutron in the nucleus transforms into a proton and an electron. The electron, known as a beta particle, is emitted from the atom. Unlike alpha particles, beta particles are much lighter. Furthermore, beta decay increases the atomic number by 1 while the mass number remains unchanged.

During beta decay:

• One neutron is transformed into a proton and an electron.
• The newly formed electron (beta particle) is emitted from the nucleus.
• The atomic number of the element increases by 1, but the mass number remains constant.

In our scenario, uranium-235 to lead-207 conversion requires 4 beta emissions. This is essential to adjust the atomic number to coincide with that of lead (82) after accounting for the repeated decrease due to alpha decays.

Uranium-235 ( ^{235}_{92}U ) is a heavy and unstable isotope of uranium, commonly used in nuclear reactors and weapons due to its ability to sustain a nuclear chain reaction. This isotope contains 92 protons and 143 neutrons.

• Its instability makes it prone to emit radiation through different decay paths, including alpha and beta decay.
• Through these processes, uranium-235 eventually becomes a more stable element like lead-207.
• This decay series is part of a sequence known as a decay chain or radioactive decay series.

The decay of uranium-235 not only provides insights into nuclear physics but also has practical applications, such as in the energy sector and radiometric dating.

Lead-207 ( ^{207}_{82}Pb ) is a stable isotope of lead. It is the result of a long series of radioactive decays starting from heavier parent isotopes like uranium-235.

• Lead-207 is the endpoint of the decay process that began with uranium-235.
• As a final product, it is stable, meaning it no longer undergoes radioactive decay.
• This stable nature makes it useful in different scientific fields, such as geochronology.

Achieving lead-207 from uranium-235 involves multiple steps, as evidenced by the necessity for both alpha and beta decays. Each step brings the uranium nucleus closer to a more stable and less radioactive state.