Study Guide - NUCLEAR CHEMISTRY

Key Terms:Binding energy, chain reaction, decay series, electron capture, fission, fusion, half-life, isotopes, radioisotopes, mass defect, nucleon, nuclide, rate of decay, transmutation, transuranium elements, zone of stability

Nuclear Reactions and Symbols (you must know how to write, balance these, including the particles):

A. Types of Radioactive Decay:1. Alpha decay follows the form:

Where A is the parent isotope (the atom being broken apart) B is the daughter isotope or the isotope formed. When an element is broken down in alpha decay it looses two neutrons and two (2) protons. Alpha decay is is not very penetrating because the He atoms capture electrons before traveling very far. However it is very damaging because the alpha particles can knock atoms off of molecules.Alpha decay is the most common in elements with an atomic number greater than 83.

2. Beta negative decay follows the form:

The beta emission increases the atomic number by one (1) by adding one (1) proton. At the same time, one (1) neutron is lost so the mass of the daughter isotope is the same as the parent isotope. Beta negative decay is more penetrating than alpha decay because the particles are smaller, but less penetrating than gamma decay. Beta electrons can penetrate through about one (1) cm of flesh, thick aluminum sheet, etc. Beta decay is most common in elements with a high neutron to proton ratio.

3. Gamma decay follows the form:

In gamma emission, neither the atomic number or the mass number is changed. A very highly charged gamma ray is given off when the parent isotope falls into a lower energy state. Gamma radiation is the most penetrating of all. These photons can pass through the body and cause damage by ionizing all the molecules in their way. Concrete or thick lead will block gamma.

4. Positron emission (also called Beta positive decay) follows the form:

In this reaction a positron is emitted. A positron is exactly like an electron in mass and charge force except with a positive charge. It is formed when a proton breaks into a neutron with mass and no charge and this positron with no mass and the positive charge. Positron emission is most common in lighter elements with a low neutron to proton ratio.

5. Electron capture follows the form:

In this reaction a nucleus captures one (1) of its own atom's inner shell electrons which reduces the atomic number by one. This captured electron joins with a proton in the nucleus to form a neutron. Electron capture is common in larger elements with a low neutron to proton ratio.

Summary:Beta emission - a beta is produced (right side)Positron emission - a positron (positive electron is produced (right side)Alpha emission - a Helium ion is produced (right side)Gamma emission - energy is produced (right side)Electron capture - an electron is absorbed (left side)Neutron capture - an neutron is absorbed (left side)

B. Nuclear Transmutations: The change of one element into another. These occur when nuclei are struck by neutrons or other nuclei. These reactions are useful in creating new radioisotopes.

6. Fusion: combining two light nuclei to form a heavier, more stable nucleus.

7. Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers (occurs naturally with U-235)

8. Transformation/Transmutation: Change of one element into another:

01

92235

56142

3691

013n U Ba Kr n

1327

24

1530

01Al He P n

98249

818

106263

014Cf O X n

Half-Life

All radioactive elements disintegrate according to their specific half life. The half life of a radioactive substance is the time required for half of the initial number of nuclei to disintegrate. The decay rate expresses the speed at which a substance disintegrates. The following equation represents the relationship between the number of nuclei remaining, N, the number of nuclei initially present, NO, the rate of decay, k, and the amount of time, t.

The relationship between the half-life of a radioactive substance and k, the rate at which it decays can also be found.

By using these equations, it is possible to calculate how much of a nuclear substance will be left after a certain time and how much of a substance originally existed. A common example is isotopic dating in which the ages of archeological artifacts are d etermined by measuring the activity of the isotopes.

Applications of Radioisotopes (Optional – study only if you have time/interest) Radioisotopes have a number of important applications beyond the production of energy or weapons of mass destruction. 1.             Neutron Activation Analysis – neutron bombardment is used to determine trace amounts of substances. By looking at the radiation emitted by irradiated samples, measurements of concentrations of elements in the nanogram range are possible. 2.             Geological Dating – certain isotopes are used for dating a variety of materials, including rocks and human remains. 238U is especially useful for rocks, with a half life of 4.5 billion years. 14C is used for measuring material less than 50,000 years old.  3.             Tracers – complex chemical reactions can be followed using certain radioisotopes. Tracers are particularly useful in biochemistry and medicine, especially in toxicology. 131I is useful for studying thyroid conditions, 99Tc for bone disorders. These substances have very short half-lives. 4.             Oncology – cancer cells are more sensitive to ionizing radiation than normal cells. This fact is used in radiation therapy. Gamma radiation from 60Co and 137Cs are commonly used in a highly directed beam that exposes as little healthy tissue as possible. Variations include placing radioisotopes directly into cancerous tumors. 5.             Radiation Detection – before the development of Geiger counters scintillation counters, and film badges, nuclear scientists could not monitor their exposure to radiation. These devices are essential for safe use of radioisotopes.

particle What is it?

symbol charge mass relative penetrating

power

ExampleApplies to which

particles

alpha particles

helium nuclei

2He4

or 2a4+2 6.664

E-24 g1 92U238 => 90Th234 +

2He4 

Atomic Numbers > 83; the 2 p+ 2n0 loss

brings the atom diagonally back to the

belt of stability.

beta particles

high speed

electrons

-1eo or -

1Bo–1 9.11

E-28 g100 53I131 => 54Xe131 + -1eo 

Isotopes below the belt of stability (high

neutron : proton ratios). Causes a loss

of 1 neutron and a gain of 1 proton. 

When a B-particle is emitted, the at. no. increases by 1. A neutron is converted into a p+ and e-:        

on1 => 1p1 +  -1eo 

gamma Rays

high energy photons

ogo 0 0 10000   

Generally accompanies other radioactive radiation because it is the energy lost from other nucleon changes. Gamma radiation is

generally not shown in the nuclear equation.

positron emission

positron1eo

+1 9.11 E-28 g

 6C11 => 5B11 + 1eo

Isotopes above the belt of stability (low

neutron : proton ratios). Causes a loss of 1 proton and a gain

of 1 neutron. 

Causes the atomic number to decrease. It converts a proton to a neutron + positron

 1p1 => on1+ 1eo

electron capture

inner shell

electron-1eo 

–1 9.11 E-28 g

 37Rb81+ -1eo=> 36Kr81

Isotopes above the belt of stability (low

neutron : proton ratios). Causes a loss of 1 proton and a gain

of 1 neutron. 

The nucleus capture an inner shell electron; thereby converting a p+

to a no

1p1  + -1eo => on1