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Cake day: August 4th, 2023
  • kiwifruit@lemmy.worldtoHistory Memes@lemmy.world•Hannibal meeting Scipio in Syria (circa 193 BCE, colourized)English
    11·
    2 months ago

    Livy in Ab Urbe Condita writes of a legendary meeting between these two great and influential men at the court of Antiochus III and a conversation that followed

    “When Africanus (Scipo) asked who, in Hannibal’s opinion, was the greatest general, Hannibal named Alexander, the king of the Macedonians because with a small force he has routed armies innumerable and because he has traversed the most distant regions, even to see which transcended human hopes. To the next request, as to whom he would rank second, Hannibal selected Pyrrhus, saying that he had been the first to teach the art of castrametation, besides no one had chosen his ground or placed his troops more discriminatingly; he possessed also the art of winning men over to him, so that the Italian people preferred the lordship of a foreign king to that of the Roman people, so long the master in that land. When he continued, asking whom Hannibal considered third, he named himself without hesitation”

    Livy Ab Urbe Condita Book 35 Chapter 14

  • kiwifruit@lemmy.worldtoAsk Science@lemmy.world•How does Uranium decay work? (A lot of questions)English
    1·
    6 months ago

    I’m not a scientist, but do teach science.

    Uranium decay is a fascinating process with a lot going on. When Sagan talks about a stream of helium nuclei, he is referring to alpha particles. These are helium four nuclei, which means they contain two protons and two neutrons. They are emitted from the nucleus of a uranium atom during radioactive decay.

    The missing electrons are an interesting part of this. When an atom of uranium ejects an alpha particle, it loses two protons, but its electrons remain for a moment, making the new atom highly ionized. Over time, the uranium ion will stabilize as it interacts with other atoms. The ejected alpha particle, which is just a bare helium nucleus, will also eventually capture two free electrons from the environment and become a neutral helium atom.

    Uranium does not completely break apart into helium nuclei. Instead, it undergoes a slow process where each atom decays step by step. When uranium 238 undergoes alpha decay, it does not vanish but transforms into thorium 234. Thorium is also radioactive and will continue decaying through a long chain of transformations, eventually becoming lead, which is stable. So uranium is not simply breaking into helium, it is gradually changing into different elements.

    Half-life plays an important role in this process. The half-life of uranium 238 is about 4.5 billion years, meaning that if you started with a pure chunk of uranium, after that time only half of it would still be uranium. The other half would have decayed into different elements. But it is not just turning into helium. While each decay event emits a helium nucleus, the uranium itself is transforming into new elements along the way. Over long periods, the uranium will be replaced with a mixture of lead and other decay products, while the helium gas may escape into the environment.

    The danger of alpha radiation comes from how it interacts with living tissue. Alpha particles are highly ionizing, which means they can cause severe damage at a cellular level. However, they do not penetrate very far. A sheet of paper or even human skin can block them. The real risk comes from inhaling or ingesting radioactive materials. If uranium dust or other alpha-emitting particles enter the body, they can directly damage DNA, increasing the risk of cancer and other health problems. That is why uranium and similar materials are dangerous if they are inhaled or ingested but not as much of a threat when they are simply sitting in solid form.

    Uranium decay is a gradual process where atoms lose helium nuclei one by one, transforming into different elements over time. Half-life describes how long this process takes, with only a fraction of the uranium decaying in a given time period. Alpha radiation is dangerous inside the body but does not travel far outside of it.

    1. Uranium-238 - Wikipedia:https://en.wikipedia.org/wiki/Uranium-238

    2. Uranium Decay Series - ScienceDirect Topics:https://www.sciencedirect.com/topics/chemistry/uranium-decay-series

    3. The Timeline of Radioactive Decay for Uranium-238 - IET:https://www.theiet.org/media/8813/radioactive-decay-rate-of-uranium-238.pdf

    4. Decay Chain - Wikipedia:https://en.wikipedia.org/wiki/Decay_chain