3 ms·

Because heavier elements have higher binding energies than iron.

jjk166 5y ago
It's the binding energy per nucleon that matters. The nuclei you're producing needs to have a higher binding energy than the nuclei you're fusing do on their own. There is nothing you can fuse with iron, or any heavier nucleus, that will produce a stable element with greater binding energy than its components. Nickel-62 is actually the most stable nucleus, with the most binding energy per nucleon, but stellar nucleosynthesis ends with Nickel-56 which decays into Iron-56, which has the lowest mass per nucleon. All nuclei heavier than Nickel-62 are produced endothermically.
- Gauge_Irrahphe 5y ago
  You are confusing nucleon (neutron or proton) with nuclide or nucleus. You still get extra energy from fusing a nucleon with nickel-62
  - jjk166 5y ago
    No, I'm not. Nuclei fuse. A proton is just a hydrogen-1 nucleus, and neutron capture isn't fusion.
    - Gauge_Irrahphe 5y ago
      OK, Which weighs more? A nickel-62 nucleus and a proton, or a copper-63 nucleus?
      - jjk166 5y ago
        You don't get a copper-63 nucleus if you hit a nickel-62 nucleus with a proton, you get a copper-61 nucleus and two neutrons in the reaction: 62Ni(p,2n)61Cu Copper-63 has spin of 3/2 while nickel-62 has a spin of 0, so you can't simply add a proton (whose spin is 1/2), you need at least 3 fermions to participate in the reaction. The Copper-61 and two neutrons of course have a higher mass than the Nickel-62 and the proton.
        Gauge_Irrahphe 5y ago
        That doesn't make any sense, the difference between nickel-62 and copper-63 is one extra proton. It's also bullshit, since the differences in spin get equalized by neutrinos.
        Gauge_Irrahphe 5y ago
        Also note that this closely corresponds to what we see: A star would be expected to burn by fusing hydrogen into heavier nuclei, which shed helium as alpha particles once they get too heavy, eventually ending up with mostly lead and helium. Which either undergoes a fission event which fissions the heavy metals into iron, or stays the way it is, a white dwarf. No need for "exotic" physics. And it also explains the persistent failure of fusion energy, as it tries to build upon nonexistent mechanisms made up to confuse people trying to build nuclear weapons.
        jjk166 5y ago
        Okay, a lot to unpack here. > That doesn't make any sense, the difference between nickel-62 and copper-63 is one extra proton. It's also bullshit, since the differences in spin get equalized by neutrinos. First, nuclei are not simply the sum of their protons and neutrons. They have structure. While copper-63 happens to have 1 more proton than Nickel-62, in its stable, lowest-energy form it also has 2 neutrons that are in a different configuration. This is why it's spin is not simply the sum of Nickel-62's spin and a proton's spin. Spin needs to be preserved. Producing neutrinos to carry off spin would violate conservation of lepton number. You need to create a lepton pair, which is exactly how Nickel-63, produced by neutron capture, is able to beta decay into Copper-63. > Also note that this closely corresponds to what we see: A star would be expected to burn by fusing hydrogen into heavier nuclei, which shed helium as alpha particles once they get too heavy, eventually ending up with mostly lead and helium. This is not what we see. Stars burn hydrogen by two different methods into helium via the pp process and the CNO cycle. Carbon is formed in the triple-alpha process where three alpha particles fuse. Heavier elements are formed along the alpha ladder by adding alpha particles, a process that stops at iron-56. There are some other side processes like Carbon, Oxygen, Neon, and Silicon burning which also end at iron-56. Heavier elements like lead are not produced during the star's lifetime, but rather during events like supernovae and neutron star collisions by neutron capture in the s and r processes. > No need for "exotic" physics. And it also explains the persistent failure of fusion energy Fusion reactors fail because of plasma instabilities which have nothing to do with nuclear reactions. > as it tries to build upon nonexistent mechanisms made up to confuse people trying to build nuclear weapons. Basic principles like conservation of spin are not exotic physics nor are they a conspiracy. If the American government did sabotage fusion research to preserve nuclear secrets, why don't any of those powers who discovered those nuclear secrets anyways like Russia or North Korea have working fusion reactors? Please take the time to read up on nuclear physics, it's a fascinating topic and very enlightening about why many things in the universe are the way they are.

It's the binding energy per nucleon that matters. The nuclei you're producing needs to have a higher binding energy than the nuclei you're fusing do on their own. There is nothing you can fuse with iron, or any heavier nucleus, that will produce a stable element with greater binding energy than its components. Nickel-62 is actually the most stable nucleus, with the most binding energy per nucleon, but stellar nucleosynthesis ends with Nickel-56 which decays into Iron-56, which has the lowest mass per nucleon. All nuclei heavier than Nickel-62 are produced endothermically.

Gauge_Irrahphe 5y ago
You are confusing nucleon (neutron or proton) with nuclide or nucleus. You still get extra energy from fusing a nucleon with nickel-62
- jjk166 5y ago
  No, I'm not. Nuclei fuse. A proton is just a hydrogen-1 nucleus, and neutron capture isn't fusion.
  - Gauge_Irrahphe 5y ago
    OK, Which weighs more? A nickel-62 nucleus and a proton, or a copper-63 nucleus?
    - jjk166 5y ago
      You don't get a copper-63 nucleus if you hit a nickel-62 nucleus with a proton, you get a copper-61 nucleus and two neutrons in the reaction: 62Ni(p,2n)61Cu Copper-63 has spin of 3/2 while nickel-62 has a spin of 0, so you can't simply add a proton (whose spin is 1/2), you need at least 3 fermions to participate in the reaction. The Copper-61 and two neutrons of course have a higher mass than the Nickel-62 and the proton.
      - Gauge_Irrahphe 5y ago
        That doesn't make any sense, the difference between nickel-62 and copper-63 is one extra proton. It's also bullshit, since the differences in spin get equalized by neutrinos.
      - Gauge_Irrahphe 5y ago
        Also note that this closely corresponds to what we see: A star would be expected to burn by fusing hydrogen into heavier nuclei, which shed helium as alpha particles once they get too heavy, eventually ending up with mostly lead and helium. Which either undergoes a fission event which fissions the heavy metals into iron, or stays the way it is, a white dwarf. No need for "exotic" physics. And it also explains the persistent failure of fusion energy, as it tries to build upon nonexistent mechanisms made up to confuse people trying to build nuclear weapons.
        jjk166 5y ago
        Okay, a lot to unpack here. > That doesn't make any sense, the difference between nickel-62 and copper-63 is one extra proton. It's also bullshit, since the differences in spin get equalized by neutrinos. First, nuclei are not simply the sum of their protons and neutrons. They have structure. While copper-63 happens to have 1 more proton than Nickel-62, in its stable, lowest-energy form it also has 2 neutrons that are in a different configuration. This is why it's spin is not simply the sum of Nickel-62's spin and a proton's spin. Spin needs to be preserved. Producing neutrinos to carry off spin would violate conservation of lepton number. You need to create a lepton pair, which is exactly how Nickel-63, produced by neutron capture, is able to beta decay into Copper-63. > Also note that this closely corresponds to what we see: A star would be expected to burn by fusing hydrogen into heavier nuclei, which shed helium as alpha particles once they get too heavy, eventually ending up with mostly lead and helium. This is not what we see. Stars burn hydrogen by two different methods into helium via the pp process and the CNO cycle. Carbon is formed in the triple-alpha process where three alpha particles fuse. Heavier elements are formed along the alpha ladder by adding alpha particles, a process that stops at iron-56. There are some other side processes like Carbon, Oxygen, Neon, and Silicon burning which also end at iron-56. Heavier elements like lead are not produced during the star's lifetime, but rather during events like supernovae and neutron star collisions by neutron capture in the s and r processes. > No need for "exotic" physics. And it also explains the persistent failure of fusion energy Fusion reactors fail because of plasma instabilities which have nothing to do with nuclear reactions. > as it tries to build upon nonexistent mechanisms made up to confuse people trying to build nuclear weapons. Basic principles like conservation of spin are not exotic physics nor are they a conspiracy. If the American government did sabotage fusion research to preserve nuclear secrets, why don't any of those powers who discovered those nuclear secrets anyways like Russia or North Korea have working fusion reactors? Please take the time to read up on nuclear physics, it's a fascinating topic and very enlightening about why many things in the universe are the way they are.