物理代写|核物理代写nuclear physics代考|PHYS585

物理代写|核物理代写nuclear physics代考|The p-p Cycle

The temperature in the core of the Sun is $1.5 \times 10^7 \mathrm{~K}$. The Sun consists mainly (91\%) of hydrogen, and the main source of the Sun’s energy comes from the fusion chain in which 4 protons are converted into a nucleus of ${ }_2^4 \mathrm{He}$ in a three-stage process.
\begin{aligned} &2 \times\left(p+p \rightarrow d+e^{+}+v\right)[2 \times 1.42 \mathrm{MeV}] \ &2 \times\left(d+p \rightarrow{ }_2^3 \mathrm{He}\right)[2 \times 5.49 \mathrm{MeV}] \ &{ }_2^3 \mathrm{He}+{ }_2^3 \mathrm{He} \rightarrow{ }_2^4 \mathrm{He}+p+p+\gamma[12.89 \mathrm{MeV}] \end{aligned}
We see that the total energy released in this process is $26.71 \mathrm{MeV}$.
Other fusion and $\beta$-decay processes are possible. For example, the ${ }_2^3 \mathrm{He}$ produced at stage 2 of (10.33) could fuse with a pre-existing nucleus of ${ }_2^4 \mathrm{He}$ in the reaction
$${ }_2^3 \mathrm{He}+{ }_2^4 \mathrm{He} \rightarrow{ }_4^7 \mathrm{Be}+\gamma .$$
The ${ }_7^4 \mathrm{Be}$ converts into ${ }_3^7 \mathrm{Li}$ by electron capture. The ${ }_3^7 \mathrm{Li}$ then fuses with another proton to produce a final state consisting of two nuclei of ${ }_2^4 \mathrm{He}$. The full fusion scheme is shown in Fig. $10.3$ and is called the “p-p cycle”, although it is actually a fusion chain rather than a cycle. We note that neutrinos are produced in some stages of this cycle. These are known as “solar neutrinos” and are the main source of the huge flux the neutrinos reaching the Earth $\left(7 \times 10^{14} \mathrm{~m}^{-2} \mathrm{~s}^{-1}\right)$.

物理代写|核物理代写nuclear physics代考|Fusion Reactors

For over 60 years, scientists and engineers have been trying to harness nuclear fusion reactions in order to provide a controlled fusion reactor, which can be used to supply energy, in analogy with fission reactors. Such reactors would have huge advantages:

• The fuel would be mainly seawater. Seawater has $1.5 \times 10^{-4}$ deuterons for each normal hydrogen atom. This must be increased to around $20 \%$ in order to be used in a fusion reactor. There are three different ways of enhancing the concentration of heavy water $\left(\mathrm{D}_2 \mathrm{O}\right)$.
• Electrolysis: Hydrogen is ionized more easily than deuterium so that during the process of electrolysis more hydrogen nuclei than deuterons drift to the cathode, leaving a solution with enhanced deuterium.
• Distillation: The boiling point of heavy water is slightly higher than that of ordinary water, so that with careful distillation the ordinary water can be boiled off.
• Chemical Separation: The chemical potential of deuterium in a compound differs from that of hydrogen. The difference depends on the compound and the temperature. This can be used to exchange deuterium between one compound and another. The method that is most commonly used is the “Girdler sulphide process” in which hydrogen sulphide $\left(\mathrm{H}_2 \mathrm{~S}\right)$ is passed through water which is kept in hot and cold tanks. As the hydrogen sulphide mixes with water in the hot tank, deuterons from the water replace the hydrogen atoms in the hydrogen sulphide, thereby depleting the heavy water concentration, whereas in the cold tank deuterons from the hydrogen sulphide replace the hydrogen atoms in the water, thereby enriching the heavy water concentration.

These enrichment processes are not expensive, and there would be sufficient supply for millions of years.

• The process produces very little radioactive waste, although some radioactive nuclides are generated as a result of the interactions of the neutrinos produced in the fusion process with the walls of the reactor.
• There is no carbon emission.

物理代写|核物理代写核物理代考| p-p循环

. The p-p Cycle . The p-p Cycle

\begin{aligned} &2 \times\left(p+p \rightarrow d+e^{+}+v\right)[2 \times 1.42 \mathrm{MeV}] \ &2 \times\left(d+p \rightarrow{ }_2^3 \mathrm{He}\right)[2 \times 5.49 \mathrm{MeV}] \ &{ }_2^3 \mathrm{He}+{ }_2^3 \mathrm{He} \rightarrow{ }_2^4 \mathrm{He}+p+p+\gamma[12.89 \mathrm{MeV}] \end{aligned}

$${ }_2^3 \mathrm{He}+{ }_2^4 \mathrm{He} \rightarrow{ }_4^7 \mathrm{Be}+\gamma .$$

物理代写|核物理代写核物理代考|核聚变反应堆

60多年来，科学家和工程师们一直试图利用核聚变反应，以提供一个可控的核聚变反应堆，它可以用来提供能源，类似于裂变反应堆。这样的反应器将有巨大的优势:

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