Active target technology development for nuclear astrophysics

核天体物理学是核物理的众多应用之一，也是最令人兴奋的应用之一。它试图解释我们周围的所有元素，空气中的氧气，血液中的铁，计算机芯片中的硅，都是从哪里来的。它们是在哪里形成的，是如何形成的？最重要的是，核天体物理学试图了解核反应如何影响所有恒星的生死。如此微小的物体是如何影响像恒星这样的大质量物体的呢？大多数恒星通过燃烧稳定的元素来获得能量，比如我们熟悉的碳和氧，经过很长一段时间。能量是由核反应产生的，将一种元素转化为另一种元素。然而，并不是所有类型的碳都是一样的。不同的类型具有不同数量的中子(但质子数量相同)，因此被称为同位素。一种元素的某些同位素是不稳定的或具有放射性的，经过一段时间后会变化或衰变成不同的元素。在一些非常热的恒星中，核反应发生得如此之快，以至于不稳定的同位素在有时间衰变之前就会与其他同位素发生反应。通常，这些炽热的恒星会在壮观的恒星烟花表演中爆炸，比如新星和超新星。因此，为了理解这些正在爆炸的恒星，我们需要能够研究起作用的不稳定同位素的核反应。天文学家可以通过观察它们发出的光线来研究这些正在爆炸的恒星。通过这种光，他们可以知道在爆炸中产生了哪些元素，这为核物理学家提供了关于哪些核反应可能是重要的信息。然后，科学家可以将这些观测结果与计算机模型的预测进行比较，看看我们是否了解这些正在爆炸的恒星是如何工作的。这些模型需要关于核反应产生和销毁这些不稳定同位素的速度的信息，这就是核物理学的用武之地。在过去的几年里，技术的进步使科学家能够加速这些短暂的不稳定同位素，以便它们可以用于研究这些反应。已经建立了实验室来为研究提供这种不稳定光束，并且正在开发能够产生更多种类和更高强度的不稳定光束的新实验室。其中一个这样的实验室位于加拿大温哥华的TRIUMF，名为ISAC。拟议的研究将开发新的探测器技术，该技术将使用ISAC提供的不稳定光束。该项目将探索使用GEM(气体电子倍增器)放大探测器中这些不稳定同位素在氦上的核反应产物产生的非常微弱的信号。宝石将需要在低压下可靠地工作，并能够在较长时间内一致地放大探测器上的信号。为了以非常低的概率研究反应，探测器还需要能够从大量的背景噪音中识别出感兴趣的反应，我们将开发一些巧妙的硬件和软件技巧来做到这一点。一旦投入使用，主动目标探测器将被用于研究几个反应，这些反应对我们理解这些正在爆炸的恒星至关重要，因此将有助于解释所有元素是在哪里产生的。

Nuclear astrophysics is one of the many applications of nuclear physics and arguably one of the most exciting. It tries to explain where all the elements around us, the oxygen in the air, the iron in our blood, the silicon in computer chips, come from. Where and how were they formed? On top of this, nuclear astrophysics tries to understand how nuclear reactions affect the life and death of all stars. How do such tiny things influence such massive objects as stars? Most stars get their energy by burning stable elements, such as the carbon and oxygen we are familiar with, over long periods of time. The energy is produced by nuclear reactions, turning one element into another. However, not all types of carbon, for example, are the same. Different types have different numbers of neutrons (but the same number of protons) and are called isotopes. Some isotopes of an element are unstable or radioactive and will change or decay into a different element, after a certain amount of time. In some stars which are very hot, the nuclear reactions happen so quickly that unstable isotopes will react with other isotopes before they have time to decay. Often, these hot stars will explode in spectacular displays of stellar fireworks, such as novae and supernovae. So to understand these exploding stars we need to be able to study the nuclear reactions with unstable isotopes that play a role. Astronomers can study these exploding stars by looking at the light that shines from them. From this light, they can tell what elements were produced in the explosion and this gives nuclear physicists information on which nuclear reactions could be important. Scientists can then compare these observations with the predictions of computer models to see if we understand how these exploding stars work. These models need information on how quickly these unstable isotopes are created and destroyed by nuclear reactions and that is where the nuclear physics comes in. In the last few years, advances in technology have allowed scientists to accelerate these short-lived unstable isotopes so that they can be used to study these reactions. Laboratories have been built to provide such unstable beams for studies and new laboratories are being developed that can produce more variety of unstable beams and higher intensities. One such laboratory is at TRIUMF in Vancouver, in Canada and is called ISAC. The proposed research will develop new detector technology that will use the unstable beams available at ISAC. The project will explore the use of GEMs (Gas Electron Multipliers) to amplify the very weak signals produced in the detector by the products of the nuclear reactions of these unstable isotopes on helium. The GEMs will need to operate reliably at low pressures and be able to amplify the signal consistently across the detector for an extended period of time. In order to study reactions with a very low probability, the detector will also need to be able to identify the reactions of interest from the large amount of background noise and we will develop some clever hardware and software tricks to do this.Once operational, the active target detector will be used to study several reactions which are key to our understanding of these exploding stars and so will help to explain where all the elements are created.