The world's second nuclear explosion was achieved with uranium-235. This isotope is unstable and fissions when struck by a neutron. It is, however, found in natural uranium at a concentration of only 0.7 percent. To be useful in nuclear weapons, the concentration must be increased.
Introduction. Influenza, or flu, is a caused by a virus infecting the respiratory system, meaning your nose, throat, bronchial tubes, and lungs. Flu symptoms are usually more severe than those of the common cold and are more likely to affect other parts of your body.
Influenza (Flu) What You Need to know What is influenza? Influenza (also called the âfluâ) is a contagious respiratory illness caused by influenza viruses that infect the nose, throat and lungs. It can cause mild to severe illness and, at times, can lead to death. The best way to prevent the flu is by getting a flu vaccine each year. Signs and symptoms of flu People who have the flu often have some or all of these signs and symptoms: