Determination of Key Nuclear Reaction Rates Governing 44Ti Production in Core Collapse Supernovae

牙齿和骨骼中的钙从何而来？遥远星系中的相同物质如何被用来理解宇宙中最大的爆炸？你可能会惊讶地知道！数十亿年前，一颗比我们的太阳稍大一点的星星，在一次爆炸中结束了自己的生命，爆炸的威力如此之大，以至于它的亮度一度相当于银河系中所有其他恒星的亮度总和。在那次被称为超新星的爆炸中，许多组成我们的元素都将被创造出来。当这种物质膨胀和冷却时，它将形成尘埃，在太空中扩散。从这些尘埃中，地球，太阳和太阳系的其他部分形成了。正如诺贝尔奖获得者威廉·福勒所说，“我们所有人都是真正的星尘”。其中一种元素是金属钛，其中一种被称为钛-44的元素通过一种称为放射性β衰变的自然过程转化为钙。当我们今天向太空望去时，我们偶尔会看到超新星发生在其他星系，有时甚至是我们自己的星系（我们所知道的最后一次发生在1667年）。绕地球运行的卫星可以非常详细地观察这些。他们希望看到的一件事是钛-44变成钙。他们可以看到这一点，因为当这种转变发生时，会发射出非常高能的光粒子，称为伽马射线，使其即使在遥远的距离上也可见。此外，我们可以计算出有多少伽马射线被发射出来，我们可以用它来测试我们认为是什么导致了恒星的爆炸。即使是我们最好的模型，在世界上最强大的计算机上运行，在模拟这些事件时仍然有很大的困难，因此像这样的测试或当前的巨大需求。为了使这些模拟足够准确，我们还需要知道一些最重要的事情，就是所谓的核反应速率。就像钙

Where does the calcium in your teeth and your bones come from? How can the same material in far off galaxies be used to understand the biggest explosions in the Universe? You might be surprised to know! Billions of years ago a star, a bit larger than our Sun, ended its life in an explosion so powerful it would have briefly been as bright as all the other stars in our Galaxy put together. In that explosion, known as a supernova, many of the elements that we are made of will have been created. As this material expanded and cooled it will have formed into dust, spreading out through space. From this dust, the Earth, the Sun and all the rest of our solar system has formed. As the Nobel laureate William Fowler said, 'All of us are truly and literally a little bit of stardust'. One of the elements created is the metal titanium, and a certain type of this, known as titanium-44, changes into calcium through a natural process called radioactive beta decay. As we look out into space today, we can occasionally see supernovae occurring in other Galaxies, or sometimes even our own (the last one that we know of occurred in 1667). Satellites orbiting the Earth can look at these in great detail. One of the things they hope to see is titanium-44 changing into calcium. They can see this because when this transition occurs very energetic particles of light, called gamma-rays, are emitted, making it visible even over the vast distances involved. Moreover, we can work out how many gamma rays were emitted, and we can use that as a test of computer models of what we think is happening to make the stars explode in the first place. Even our best models, running on some of the world's most powerful computers, still have great difficulty in simulating these events, and so tests such as this or of great current need. Some of the most important things we yet need to know to make these simulations sufficiently accurate, are what are known as nuclear reaction rates. Just as the calcium is