Radioactive tracers
Introduction
Transportation, whether in plants or animals is the key to the efficient assimilation of the nutrients that the
organisms synthesise, get from their environment or digest. The study of these processes helps us in many
ways.
The study of transport mechanisms in plants helps us to understand the uptake of the various types of
substances and their passage through the plants. This has helped a great deal in developing fungicides,
pesticides, growth regulators, etc. and how they should be administered to the plants.
In animals too the study of transport has helped us in diagnosing disease and in developing new and more
effective drugs and treatments.
Taken from: http://www.tutorvista.com/content/science/science-ii/transportation/introduction.php
An important technique used to study transport in both animals and plants, used in a multitude of applications,
is the use of radioactive tracers.
Radioactive isotopes
Isotopes are atoms of the same elements which contain the same number of protons but different number of
neutrons (eg. Carbon-12 has 6 neutrons, while Carbon-14 has 8 neutrons). Radioactive isotopes are isotopes
which are unstable (that is, their nucleus does not hold together well and therefore breaks down, making the
compound radioactive) and undergoes radioactive decay while emitting heat and radiation.
Taken from: http://scienceray.com/philosophy-of-science/radioactive-substances-and-its-uses/
You may have heard of Carbon dating?
Carbon dioxide in the air contains a small amount of the natural
radioactive carbon -14. Plants absorb carbon -14 during the process
of photosynthesis and transfer it to animals through the food chain.
When plants and animals die, the supply of carbon -14 stops and
the carbon -14 content in deed plants and animals will decrease due
to radioactive decay. Archaeologists can estimate the edge of an
artifact through a method known as carbon dating. Through this
method, the percentage of carbon -14 remaining in an ancient
artifact is determined to estimate its age.
There are many practical applications to the use of radioactivity/radiation. Radioactive isotopes (aka radioisotopes) are used to study living organisms, to diagnose and treat diseases, to sterilize medical instruments
and food, to produce energy for heat and electric power, and to monitor various steps in all types of industrial
processes.
Tracers
Tracers are a common application of radio-isotopes. A tracer is a radioactive isotope of an element whose
pathway through which a chemical reaction can be followed. Tracers are commonly used in the medical field
and in the study of plants and animals.
Taken from: http://www.ndt-ed.org/EducationResources/HighSchool/Radiography/usesradioactivity.htm
Using isotopes as tracers
Radioactive isotopes have many useful applications in a wide variety of situations, for example, they can be
used within a plant or animal to follow the movement of certain chemicals. In medicine, they have many uses,
such as imaging, being used as tracers to identify abnormal bodily processes, testing of new drugs and
conducting research into cures for disease.
Phosphorus uptake by plants
Plants take up phosphorus-containing compounds from the soil through their roots. By adding a small amount
of radioactive phosphorus-32 to fertiliser and then measuring the rate at which radioactivity appears in the
leaves, it is possible to calculate the rate of uptake of phosphorus from the soil. The information gathered could
help plant biologists to identify plant types that can absorb phosphorus quickly. These plants may give better
yields resulting in more food or fibre at less expense.
Carbon-14 was used by Melvin Calvin (after whom the Calvin cycle is named) to map the path of carbon in
photosynthesis and for which he won the Nobel Prize in 1961. It is useful as a radioactive tracer in plants as
carbon is taken in by the plant in the form of carbon dioxide and is then incorporated into the carbon containing
compound, glucose, and other carbohydrates (eg. starch).
Pesticide levels
To measure pesticide levels, a pesticide can be tagged with a radioisotope such as chlorine-36, and this is
applied to a field of test plants. Over a period of time, radioactivity measurements are made. Estimates can
then be made about how much accumulates in the soil, how much is taken up by the plant and how much is
carried off in run-off surface water.
Medical tracers
Radioactive isotopes and radioactively labelled molecules are used as tracers to identify abnormal bodily
processes. This is possible because some elements tend to concentrate (in compound form) in certain parts of
the body – iodine in the thyroid, phosphorus in the bones and potassium in the muscles. When a patient is
injected with a compound doped with a radioactive element, a special camera can take pictures of the internal
workings of the organ. Analysis of these pictures by a specialist doctor allows a diagnosis to be made.
The thyroid gland, situated in the neck, produces a hormone called thyroxine, which regulates the rate of
oxygen use by cells and the generation of body heat. Within each molecule of thyroxine, there are 4 iodine
atoms. If a patient is made to drink a solution of sodium iodide that has been doped with radioactive iodine131, most of it will end up in the thyroid gland. A special camera can capture the radiation emitted by the
iodine-131, and an image of the gland can be constructed. An assessment can then be made about the shape,
size and functioning of the gland.
Positron emission tomography (PET)
A positron emission tomography (PET) scan
measures important body functions, such as blood
flow, oxygen use and glucose use. The
information gathered helps doctors find out how
well organs and tissues are functioning.
Radionuclides used in PET scanning are isotopes
with short half–lives, such as carbon-11 (~20
min), nitrogen-13 (~10 min), oxygen-15 (~2 min)
and fluorine-18 (~110 min). These radionuclides
are added into compounds normally used by the
body such as glucose (or variations of glucose),
water or ammonia. Such labelled compounds are
known as radiotracers. In some situations, the
patient is required to breath oxygen gas labelled with oxygen-15.
The radionuclides used in PET decay
by a process called positron emission.
A positron is the antimatter version of
the electron. When a positron meets
an electron, an annihilation event
occurs, resulting in the production of
two gamma rays. The two emitted
gamma rays travel in opposite
directions.
PET scanner
The scanning instrument picks up the
location of these gamma rays and,
with the aid of a powerful computer, generates a map of where these events are occurring. By combining the
PET scan with a CT scan, a more complete picture of how well an organ is functioning can be made.
Positron emission tomography (PET) is different to other medical imaging techniques because it requires
patients to be injected with a radioactive substance. The images a PET scanner produces shows where in the
body the radioactive substance has been transported. This means a PET image is a picture of what is happening
metabolically in the body compared to other medical imaging techniques that show the structure or parts of the
body.
Due to the short half-lives of most radioisotopes, the radiotracers must be produced using a cyclotron (a type of
particle accelerator) and radiochemistry laboratory that are close to the PET imaging facility. The half-life of
fluorine-18 is long enough such that fluorine-18 labelled radiotracers can be manufactured commercially at an
off-site location.
Taken from: http://www.sciencelearn.org.nz/Contexts/Just-Elemental/Looking-Closer/Using-isotopes-as-tracers
In radiotherapy (also called radiation therapy), gamma radiation emitted by cobalt -60 is used in the treatment
of cancer. The radiation will destroy cancerous cells and shrink tumors. Radioactive tracers are used to check
the function of body organs: a) Iodine -131 or strontium -89 is injected into a patient’s body or taken orally to
detect damage to the thyroid gland b) Sodium -24 is injected into blood vessels to detect to clotting of blood
during a head injury c) Barium -138 or iodine -131 are injected into a patient’s body to detect brain tumors.
Taken from: http://scienceray.com/philosophy-of-science/radioactive-substances-and-its-uses/
Phosphorus-32 can also be used to detect and treat cancers as it has been found that cancer cells accumulate
more phosphorus than normal cells.
Further reading on radio-isotopes as tracers, below…
Sci-Tech Encyclopedia: Radioactive tracer
A radioactive isotope which, when injected into a chemically similar substance or artificially attached to a
biological or physical system, can be traced by radiation detection devices. Many problems in biology and
medicine not amenable to other approaches can be solved by the use of these tracers. See also Radioactivity;
Radioactivity and radiation applications; Radioisotope; Radioisotope (biology).
The simplest radioactive tracer studies consist of the tagging of a biological entity with a radioactive isotope
(radioisotope). The entity is then tracked by following the radiation from the isotope. The operation becomes
more complex when a large number of biological particles are labeled, for example, in the tagging of red blood
cells or bacteria. When the labeled substance is injected into an animal, it is impossible to follow the individual
labeled particles, but their average movement can be tracked by observations of the radiation. Finally, a
radioisotope of a particular element can be used to tag that element. Phosphorus-32 can be introduced into the
soil where a plant is growing, and the amount of phosphorus absorbed and its distribution throughout the plant
can be studied.
In most biological tracer experiments, the radio-isotope is introduced into the system and its radiation
subsequently measured with Geiger-Müller counters or scintillation detectors. Extremely soft (low-intensity)
radiations can be detected by the use of photographic film. See also Geiger-Müller counter; Scintillation counter.
In medical applications, a radioactive atom can be attached to a molecule or more complex substance, which
can then be used to examine a chemical reaction in a test tube, or it can be administered to a patient by
ingestion or injection and subsequently be incorporated into a biochemical process. The radioactive emissions
from the radioactive atom can be used to track (trace) the behavior of the labeled molecule or substance in
biological processes by means of medical imaging, utilizing techniques such as positron emission tomography
(PET) or single-photon-emission computed tomography (SPECT). See also Medical imaging.
The branch of medicine that uses radioactive tracers in the care of patients is called nuclear medicine.
Radiotracers of practically every element can be produced in nuclear reactors or cyclotrons. Radioactive tracers
are used as part of the diagnostic process. Three radionuclides—carbon-14, tritium (hydrogen-3), and
phosphorus-32—remain the backbone of modern biomedical sciences. See also Nuclear medicine.
Taken from: http://www.answers.com/topic/radioactive-tracer
Radioactive tracers are substances that contain a radioactive atom to allow easier detection and measurement.
(Radioactivity is the property possessed by some elements of spontaneously emitting energy in the form of
particles or waves by disintegration of their atomic nuclei.) For example, it is possible to make a molecule of
water in which one of the two hydrogen atoms is a radioactive tritium (hydrogen-3) atom. This molecule
behaves in almost the same way as a normal molecule of water. The main difference between the tracer
molecule containing tritium and the normal molecule is that the tracer molecule continually gives off radiation
that can be detected with a Geiger counter or some other type of radiation detection instrument.
One application for the tracer molecule described above would be to monitor plant growth by watering plants
with it. The plants would take up the water and use it in leaves, roots, stems, flowers, and other parts in the
same way it does with normal water. In this case, however, it would be possible to find out how fast the water
moves into any one part of the plant. One would simply pass a Geiger counter over the plant at regular
intervals and see where the water has gone.
Industry and research. Radioactive tracers have applications in medicine, industry, agriculture, research, and
many other fields of science and technology. For example, a number of different oil companies may take turns
using the same pipeline to ship their products from the oil fields to their refineries. How do companies A, B, and
C all know when their oil is passing through the pipeline? One way to solve that problem is to add a radioactive
tracer to the oil. Each company would be assigned a different tracer. A technician at the receiving end of the
pipeline can use a Geiger counter to make note of changes in radiation observed in the incoming oil. Such a
change would indicate that oil for a different company was being received.
Another application of tracers might be in scientific research on plant nutrition. Suppose that a scientist wants
to find out how plants use some nutrient such as phosphorus. The scientist could feed a group of plants
fertilizer that contains radioactive phosphorus. As the plant grows, the location of the phosphorus could be
detected by use of a Geiger counter. Another way to trace the movement of the phosphorus would be to place
a piece of photographic film against the plant. Radiation from the phosphorus tracer would expose the film, in
effect taking its own picture of its role in plant growth.
Medical applications. Some of the most interesting and valuable applications of radioactive tracers have been
in the field of medicine. For example, when a person ingests (takes into the body) the element iodine, that
element goes largely to the thyroid gland located at the base of the throat. There the iodine is used in the
production of various hormones (chemical messengers) that control essential body functions such as the rate of
metabolism (energy production and use).
Suppose that a physician suspects that a person's thyroid gland is not functioning properly. To investigate that
possibility, the patient can be given a glass of water containing sodium iodide (similar to sodium chloride, or
table salt). The iodine in the sodium iodide is radioactive. As the patient's body takes up the sodium iodide, the
path of the compound through the body can be traced by means of a Geiger counter or some other detection
device. The physician can determine whether the rate and location of uptake is normal or abnormal and, from
that information, can diagnose any problems with the patient's thyroid gland.
Taken from: http://www.scienceclarified.com/Qu-Ro/Radioactive-Tracers.html