Chemistry
Home > Chemistry > Core > Production of materials > Production of materials: 5. Nuclear materials
9.2 Production of materials: 5. Nuclear materials
| Syllabus reference (October 2002 version) | ||
|---|---|---|
|
5. Nuclear chemistry provides a range of materials
|
Students learn to:
|
Students: |
Extract from Chemistry Stage 6 Syllabus (Amended October
2002). © Board of Studies, NSW.
[edit: 25Jun08]
Prior learning: Preliminary module 8.2.3.
Background: Atoms contain protons and
neutrons in a nucleus surrounded by electrons in energy level
shells. Isotopes of an element are atoms of that element
containing the same number of protons but different numbers
of neutrons.
If the nucleus of an atom contains excess energy the nucleus
is unstable and can emit radiation. The radiation emitted is
characteristic of the nucleus. The emitted radiation can be
used in many ways in industry and medicine.
distinguish between stable and radioactive isotopes and describe the conditions under which a nucleus is unstable
- An isotope of an element, E, is
represented by AEZ,
where
A represents the mass number (the number of protons + neutrons)
Z represents the atomic number (the number of protons).
- Isotopes of the same element have the same atomic
number (Z).
- Only 279 of about 2000 known isotopes are stable. In a
stable isotope nucleus, the protons and neutrons are in a
low energy level and are unable to emit radioactivity.
- Radioactive isotopes are unstable. They emit radiation
as they spontaneously release energy. This is called
radioactive decay. An unstable isotope can be
called a radioisotope, an abbreviation of the term
radioactive isotope.
- The time for the radioactivity level from a given
amount of radioactive isotope to be halved is called its
half-life. Each radioactive isotope has a characteristic
half-life.
-
Radioactive isotopes can emit three types of radiation:
Radiation Symbol Type alpha 
4He2 particle beta 
0e-1 particle gamma 
high frequency electromagnetic radiation
describe how commercial radioisotopes are produced
-
The following example is only one of many possible
results of nuclear fission.
- When the uranium nucleus breaks up into two nuclei,
many different possible isotopes can form.
- Differences in chemical properties of the elements
produced can be used to chemically separate the different
radioisotopes. Any U-235 that has not undergone fission can
be separated and recycled into new fuel rods.
- The high-speed neutrons emitted can be used to bombard atoms of various elements to produce useful neutron rich isotopes.
describe how transuranic elements are produced
Background
Transuranic elements are elements with an atomic number above that of uranium with atomic number Z= 92.
Twenty-two transuranic elements have been made. The claim to production of element 118 has been withdrawn by the originating laboratory as no other laboratory anywhere in the world has been able to replicate this production.
Only three of the transuranic elements, those with atomic numbers 93, 94 and 95, have been produced in nuclear reactors.
- When U-238 is bombarded with neutrons it can be
converted to U-239 that undergoes beta decays to produce
neptunium and plutonium.
- Pu-239 is changed to americium by neutron bombardment.
-
Americium-241 is used in most house smoke alarms.
Note how mass (shown by the upper superscript numbers) is conserved and how charge (shown by the lower subscript numbers) is conserved.
For example:
Always check that a nuclear equation is balanced in the two ways shown in the equation above.
Transuranic elements from atomic number 96 and up are all made by accelerating a small nucleus (such as He, B or C) in a charged particle accelerator to collide with a heavy nucleus (often of a previously made transuranic element) target.
identify instruments and processes that can be used to detect radiation
Background
High energy radiation that causes ionisation of atoms is called ionising radiation and is potentially harmful to living things.
- Most radioactive emissions are ionising radiation and
are usually detected by a Geiger-Muller tube connected to a
counter. The Geiger-Muller tube contains gas that ionises
and produces a small pulse of electricity each time it is
ionised by radiation. The counter counts the number of
pulses.
- Low energy radiation that is too weak to ionise atoms is called non-ionising radiation and can be detected by a scintillation counter. Scientists investigating reactions in living things often prefer to use non-ionising radioisotopes because ionisation could cause unwanted chemical changes in living things. The non-ionising radiation emitted transfers energy to a solvent molecule and then to a fluorescent molecule that emits light. A photomultiplier produces an amplified electrical pulse from the light. A counter counts the pulses.
process information from secondary sources to describe recent discoveries of elements
- The nineteen transuranic elements with the atomic numbers above 95 (Z between 96 and 116, leaving out undiscovered 113 and 115) require high-energy particle accelerators to be produced. Use an Internet search engine and recent references to find out how particle accelerators are used to discover new transuranic elements. To process the sources you find, assess their reliability by comparing the information provided. Look for consistency of information.
use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine
-
Gather information to complete a table like the one
following on how gamma sources, such as Cobalt-60 (Co-60)
and Technetium-99m (Tc-99m), are used in industries and
medicine and use available evidence to
analyse the benefits and problems associated with the use
of radioactive isotopes. Note that the alternative to
gamma sources, X-rays, are not as penetrating and require
high voltage equipment that uses a lot of electrical
energy. However, the more expensive X-ray equipment is
more easily disposed of and does need to be locked away
in secure locations like potentially harmful gamma ray
sources.
Gamma source Use Benefits Problems Co-60 for checking defects in metal wings
Tc-99m for imaging an internal organ
identify one use of a named radioisotope:
- in industry
- in medicine
In industry
- Cobalt-60 (Co-60) is used in a process called industrial radiography, to inspect metal parts and welds for defects.
In medicine
- Technetium-99m (Tc-99m) is used in a wide range of medical applications, such as pinpointing brain tumours.
describe the way in which the above named radioisotopes are used and explain their use in terms of their chemical properties
In industry
- Cobalt-60 is used in industrial radiography to inspect
metal parts and welds for defects. Beams of radiation are
directed at the object to be checked from a sealed source
of Co-60. Radiographic film on the opposite side of the
source is exposed when it is struck by radiation passing
through the objects being tested. More radiation will pass
through if there are cracks, breaks, or other flaws in the
metal parts and will be recorded on the film. By studying
the film, structural problems can be detected.
- Co-60 is used because it is an emitter of gamma rays which will penetrate metal parts. Co-60 has a half-life of 5.3 years and can be used in a chemically inert form held inside a sealed container. This enables the equipment to have a long lifetime and not require regular maintenance.
In medicine
- Technetium-99m (Tc-99m) is used in over half of the
current nuclear medicine procedures, such as pinpointing
brain tumours. Tc-99m can be changed to a number of
oxidation states. This enables production of a wide range
of biologically active chemicals. The Tc-99m is attached to
a biological molecule that concentrates in the organ to be
investigated.
-
Tc-99m is used because:
- it has a very short half-life of 6 hours
- it emits low energy gamma radiation that minimises damage to tissues but can still be detected in a person's body by a gamma ray sensitive camera
- it is quickly eliminated from the body
- technetium is reasonably reactive; it can be reacted to form a compound with chemical properties that leads to concentration in the organ of interest such as the heart, liver, lungs or thyroid.
|