Alpha decay generally occurs in atoms that have massive nuclei with a ratio of too many protons to neutrons. One way to deal with this instability within the nucleus is to release protons and neutrons in the form of an alpha particle. An alpha particle contains two protons and two neutrons and has a positive charge. Alpha decay can bring the number of protons and neutrons into a more stable configuration by decreasing the size of the nucleus. It is important to note that since the number of protons in the nucleus specify the element of an atom, once the nucleus releases the alpha particle, the element identification of the atom changes. For instance, the 92 proton uranium is listed as atomic number 92 on the Periodic Table. Once the nucleus of an atom of uranium releases two protons the element undergoes a process called transmutation and turns into the element thorium with an atomic number 90. Thorium is significant because it may be a viable alternative to using uranium for nuclear energy. This will be discussed more in a later segment of Nuclear 101.
Technically, since the alpha particle has two protons it is an atom of helium without electrons. Atomically speaking, alpha particles are relatively large and slow particles. A piece of paper and even the outer layers of skin are generally sufficient to stop alpha particles which are generally not considered harmful unless ingested.
Another way that a nucleus with too many neutrons or protons can stabilize itself is through beta radiation. Beta decay occurs when a proton transforms into a neutron or vice-versa depending upon which action would provide the most stable nucleus. The process of beta decay can occur in two forms, beta minus or beta plus decay. During beta minus decay, a neutron decays into a proton, an electron, and an antineutrino. During beta plus decay, a proton decays into a neutron, a positron, and a neutrino.
In the process of beta minus decay, a neutrally charged neutron splits into a positively charged proton, a negatively charged electron, and a neutrally charged antineutrino. The nucleus retains the new proton but emits the new electron and antineutrino. In the process of beta plus decay, a positively charged proton splits into a neutrally charged neutron, a positively charged positron, and a neutrally charged neutrino. The nucleus retains the new neutron but emits the new positron and neutrino. In beta decay, the emitted electron or positron is called a beta particle.
Beta particles are smaller and faster than alpha particles. Beta radiation is capable of penetrating human skin and can cause radiation damage such as skin burns and radiation sickness. It can be stopped by substances such as a board of aluminum several millimeters thick. Since this process involves the gain or loss of a proton in the nucleus, when the nucleus undergoes beta decay the atom undergoes transmutation and changes into a new element. That new element would be the number of protons now present within the nucleus.
To give one example of how beta decay works in regards to uranium and nuclear weapons production, if uranium-239 (atomic number 92) undergoes beta minus decay its nucleus gains a proton and transmutes into the element neptunium-239 (atomic number 93). Through beta minus decay neptunium-239 gains a proton and transmutes into a plutonium-239 (atomic number 94) that can be used to manufacture nuclear weapons.
How Stuff Works
Jefferson Lab Science Education
Lawrence Berkeley Laboratory
US Nuclear Regulatory Commission
University of Tennessee
**I have no formal training in nuclear physics and will gladly accept any and all feedback and will update this series accordingly with accepted corrections.