In beta-positive decay, a proton converts into a neutron and a positron.  The neutron is retained by the nucleus, keeping the atomic mass constant while decreasing the atomic number and thus changing the type of element.  The beta particle emitted is called a positron.  According to the conservation laws, beta-positive decay can be represented by the equation below.

Note: the parent atom has Z electrons to be electrically neutral, when the proton changes into a neutron and positron there is Z -1 electrons in the daughter nucleus.  An electron is released to drift away but this is not shown in the equation.  This will affect the mass defect equations you will learn about later.




Quantity

Symbol

SI Unit

X - parent element

X

--

Y- daughter element

Y

--

- beta particle (positron)

β

- neutrino

v

--

 












Beta-positive Decay for Nickel-56

The the beta-positive decay equation for nickel-56 is as follows:

 

The Neutrino and Antineutrino

The neutrino and antineutrino are a matter-antimatter pair.  The existence of an antineutrino was hypothesized when the kinetic energy of a beta particle following beta decay was lower than expected.  Because of the low kinetic energy scientists predicted that some other particle was carrying this energy away before the particle could be detected.  The prediction was later proven to be true.

 

Gamma Decay (γ)

Often the alpha and beta decay processes leave the daughter nucleus in an excited state with the nucleons spread apart.  Similar to that of an electron in an energy level, the nucleons will rearrange to form a more stable ground state and releases very high frequency gamma radiation as a result.

According to the EMR spectrum, gamma radiation has extremely high energy, which corresponds to a high frequency and a short wavelength.  Gamma radiation has no mass or charge, therefore producing no changes in the atomic number or atomic mass of the nucleus.  Also, there is no transmutation with the emission of gamma radiation.  Gamma rays are represented by the symbol ( γ ).

The nucleus may be left in an excited state after alpha or beta decay.  In the nuclear equation, this excited state is represented with an asterisk (*).  The nucleus then experiences gamma decay to return to a ground state.


Read
Read pages 806 and 807 for an example of a gamma decay chain and equation as well as a radioactive decay series.

      

Decay Series

Many of the daughter nuclei produced by alpha and beta decay are still unstable and, as such, will undergo further transmutation.  In such cases a decay series is used to illustrate the successive decays until a stable nucleus is produced. In most decay series, each "dot" (see page 807 of the text) represents a new nucleus.  Both alpha and beta decay form part of each series as the parent material undergoes successive decay in both forms until a stable nucleus is reached.

 

The Direction of Alpha and Beta Decay in the Diagram

First, focus on why alpha (red arrow) and beta (blue arrow) decay are drawn in the direction shown.  Recall that alpha decay (the release of a nucleus) involves a decrease in atomic mass number (by four) and a decrease in protons (by two).  On the chart, therefore, you need to move down four and left two to get to the new mass number and atomic number.  Also notice that the horizontal axis increases by one atomic number and the vertical axis increases by four atomic mass numbers per line.  

Beta decay results in no change to the atomic mass number, so there is no movement up or down on the graph.  Beta decay, however, does result in an increase in the atomic number, so there is a movement of one unit to the right.  When you have two horizontal blue arrows following each other they represent two beta decays in succession. 


Try This
Using the decay series on page 807 of the text, write the nuclear decay equations that represent the transmutation of protactinium-234 to radium-226 (from the radium decay series).  When ready, review the solution below.

Try This Solution:  Using Figure 16.11 on page 807, find the "dot" for protactinium-234 and note the chemical symbol and atomic number, .  Repeat for the daughter element,  (uranium-234 in).  Write the nuclear equation using the concepts of conservation of charge and nucleons as you balance each side. To do this you may have to add an alpha particle and/or beta particle.  If the decay is beta, remember to add the antineutrino.

Continue to follow the decay chain until all of the equations have been written.