Cấu trúc nguyên tử của hầu hết các yếu tố có chứa một hạt nhân ổn định. Trong điều kiện bình thường, những yếu tố này vẫn không thay đổi vô thời hạn. Họ không phải là phóng xạ. Nguyên tố phóng xạ, tương phản, chứa một hạt nhân là không ổn định. Các hạt nhân không ổn định thực sự là một trạng thái kích thích mà không thể được duy trì vô thời hạn, phải thư giãn, hoặc phân rã, một cấu hình ổn định hơn. Decay xảy ra một cách tự nhiên và biến đổi hạt nhân. | Chapter 2 What is Radioactivity Radioactive Elements The atomic structure of most elements contains a nucleus that is stable. Under normal conditions these elements remain unchanged indefinitely. They are not radioactive. Radioactive elements in contrast contain a nucleus that is unstable. The unstable nucleus is actually in an excited state that can not be sustained indefinitely it must relax or decay to a more stable configuration. Decay occurs spontaneously and transforms the nucleus from a high energy configuration to one that is lower in energy. This can only happen if the nucleus gives off energy. The energy emitted by the relaxing nucleus is radiation. All radioactive elements have unstable nuclei that is what makes them radioactive. The Nature of Radiation The energy emitted by an unstable nucleus comes packaged in very specific forms. In the years that followed the discovery of radioactivity determining the kind of radiation emitted from radioactive compounds was of great interest. It was found that these radiations consisted of three types called alpha a beta P and gamma y radiations after the first three letters in the Greek alphabet see Figure . The nuclear emission transforms the element into either a new element or a different isotope see page 10 of the same element. A given radioactive nucleus does this just once. The process is called a decay or a disintegration. 2003 Taylor Francis 8 Radiation and Health Figure . A radioactive atom possesses an unstable nucleus. This means that radioactive atoms will emit radiation sooner or later and convert into a more stable state. The types of radiation that may be emitted are called alpha a beta P and gamma y radiation. The evidence for the three types of radiation comes from an experiment in which the radiation from radioactive compounds was passed through a magnetic field. y-rays passed through the field without disturbance whereas the two other types were deflected from a straight line. Because it .
