Natalie Wong (F4 SC 3)


Radioactive isotopes

Food Irradiation

Food irradiation is a method of treating food in order to make it safer to eat and have a longer shelf life. This process is not very different from other treatments such as pesticide application, canning, freezing and drying. The end result is that the growth of disease-causing microorganisms or those that cause spoilage are slowed or are eliminated altogether. This makes food safer and also keeps it fresh longer. Food irradiated by exposing it to the gamma rays of a radioisotope -- one that is widely used is cobalt-60. The energy from the gamma ray passing through the food is enough to destroy many disease-causing bacteria as well as those that cause food to spoil, but is not strong enough to change the quality, flavor or texture of the food. It is important to keep in mind that the food never comes in contact with the radioisotope and is never at risk of becoming radioactive.
external image
external image


Agricultural Application

Radioactive isotopes are used in the agricultural industry as tracers in plants. Radioisotopes are added to fertilizers in small but known quantities. The uptake of the fertilizer can be measured by the researcher measuring how radioactive a plant has become. This technique is largely a research tool without practical application on farms. Examples of isotopes used for this purpose include phosphorous32 and nitrogen15.

Medicine

Many of us are aware of the wide use of radiation and radioisotopes in medicine particularly for diagnosis (identification) and therapy (treatment) of various medical conditions.

Diagnosis

external image
external image

Radioisotopes are an essential part of diagnostic treatment. In combination with imaging devices which register the gamma rays emitted from within. they can study the dynamic processes taking place in various parts of the body. The most widely used diagnostic radioisotope is technetium-99m*, with a half-life of six hours, and which gives the patient a very low radiation dose. Such isotopes are ideal for tracing many bodily processes with the minimum of discomfort for the patient. They are widely used to indicate tumours and to study the heart, lungs, liver, kidneys, blood circulation and volume, and bone structure.
external image
external image

A major use of radioisotopes for diagnosis is in radio-immuno-assays for biochemical analysis. They can be used to measure very low concentrations of hormones, enzymes, hepatitis virus, some drugs and a range of other substances in a sample of the patient's blood. The patient never comes in contact with the radioisotopes used in the diagnostic tests.

Treatment


external image
external image

Iodine-131 is commonly used to treat thyroid cancer, probably the most successful kind of cancer treatment, and also for non-malignant thyroid disorders. Iridium-192 wire implants are used especially in the head and breast to give precise doses of beta rays to limited areas, then removed. A new treatment uses samarium-153 complexed with organic phosphate to relieve the pain of secondary cancers lodged in bone.

Cheng Sheun Fang (F4SC1)

Radiotherapy is the treatment of disease with radiation. Doctors use radiotherapy most often to treat certain kinds of cancers. The method of radiotherapy familiar to most people is X-ray treatment. X-ray radiation, however, can only show dense materials such as bone. A better way of diagnosing internal disorders is through the use of radionuclides, or radioactive tracers (isotopes).

Radioactive Isotopes
Radioactive tracers that are introduced into the body by injection are called radiopharmaceuticals. According to the type of radionuclide, the tracer will collect in one or more areas of the body. Since the tracer emits radiation, it is easily tracked by a Geiger counter (a device that measures radioactive levels) or scanning device. Because the tracer sends out information for a long time, doctors can follow its path through the body and check to see if organs are working properly.

Radioactive trace elements are a favorite diagnostic tool because they can be used to target individual organs, like the kidney. The trace elements also give off less radiation than a standard x-ray, so they are generally safer to use.

Beta and Isotope Injection Therapy
Once a radiotherapy diagnosis has been made, the doctor has a choice of treatments. For cancers near the skin surface, a stream of beta particles is used to kill cancerous cells. For cancers in a body organ, an isotope such as radioactive iodine is injected into the patient. The doctor will leave the isotope in the body until it has killed the cancer cells. The tracer is then flushed from the body before it can do permanent damage.

Edith Quimby
The person most responsible for the use of nuclear medical procedures is Edith Quimby, an American radiologist. Quimby was the first researcher to accurately measure the amount of radiation necessary to allow body traces. She later determined the exact dosages needed to use radiation as a diagnostic tool.

Other Uses
In addition to diagnostic applications, radiotherapy is used to sterilize medical instruments. Because it can be applied at very low temperatures,
radiation can be used to sterilize plastic instruments that might be destroyed by steam. In addition, the radiation can reach all areas of an instrument, including small cervices, that traditional steam treatments often misses.


Sharifah Samira(F4 SC1)

Modern Uses of RadioIsotopes

Smoke Detectors and Americium-241

external image smk_det.gif
How many of us have smoke detectors in our house? Chances are that a great number of homes have had one or more of these devices installed as an early warning system in case of fire. What most consumers don't know is that many of these units contain a small amount of americium-241. By utilizing the radioactive properties of this material, smoke from a fire can be detected at a very early stage. This early warning capability has saved many lives. In fact, studies have shown that 80% of fire injuries and 80% of fire fatalities occur in homes without smoke detectors.

Archaeological Dating

Significant progress has been made in this field of study since the discovery of radioactivity and its properties. One application is carbon-14 dating. Recalling that all biologic organisms contain a given concentration of carbon-14, we can use this information to help solve questions about when the organism died. It works like this..when an organism dies it has a specific ratio by mass of carbon-14 to carbon-12 incorporated in the cells of it's body. (The same ratio as in the atmosphere.) At the moment of death, no new carbon-14 containing molecules are metabolized, therefore the ratio is at a maximum. After death, the carbon-14 to carbon-12 ratio begins to decrease because carbon-14 is decaying away at a constant and predictable rate. Remembering that the half-life of carbon-14 is 5700 years, then after 5700 years half as much carbon-14 remains within the organism.

Agricultural Applications - radioactive tracers

Radioisotopes can be used to help understand chemical and biological processes in plants. This is true for two reasons: 1)radioisotopes are chemically identical with other isotopes of the same element and will be substituted in chemical reactions and 2)radioactive forms of the element can be easily detected with a Geiger counter or other such device.
external image geiger_1.gif
Example:
A solution of phosphate, containing radioactive phosphorus-32, is injected into the root system of a plant. Since phosphorus-32 behaves indentically to that of phosphorus-31, the more common and non-radioactive form of the element, it is used by the plant in the same way. A Geiger counter is then used to detect the movement of the radioactive phosphorus-32 throughout the plant. This information helps scientists understand the detailed mechanism of how plants utilized phosphorus to grow and reproduce.

Alif Fitri (F4SC1)

There are two types of isotopes, namely the radioactive and non-radioactive isotopes.

Despite producing harmful radiations, radioactive isotopes have important uses such as:

  • Cobalt-60 is used in radioteraphy for cancer treatment.
  • Gamma rays of Cobalt-60 are used to destroy bacteria in food without affecting the quality.
  • Carbon-14 is used for carbon dating to estimate the age of fossils and artefacts.
  • Phosphate fertilisers that contain phosphorus-32 are used to study the metabolism of phosphorus in plants

Rachael Lee (F 4 Sc 1)

Uses of isotopes :
Chlorine-36 is used in the measurement of sources of chloride and determining the age of water up to about 2 million years old
Lead-210 is used to date layers of soil and sand deposited up to about 80 years ago
Magnesium-27 is used in the location of leaks in water pipes
Ytterbium-169 is used for brain scans
Uranium-235 is enriched as a fuel for most nuclear reactors

Properties of Particles
Name
Symbols
Identity
Relative Charge
Relative Mass
Penetrating Power
Interaction with Charged Plates
Hazards
alpha
external image alpha.gif, 42He
helium nucleus
2+
4
low - stopped by a sheet of paper
attracted to negative plate, deflected by positive plate
harmful if ingested
beta
external image beta.gif, 0-1e
electron
1-
1
2000
moderate - pass through paper and ½mm aluminium, stopped by ½mm lead
attracted to positive plate, deflected by negative plate
skin burns, harmful if ingested particularly iodine-131 in thyroid & strontium-90 in bones
gamma
external image gamma.gif
electromagnetic radiation
0
0
high - only stopped by several centimetres of lead or many centimetres of concrete
unaffected
most dangerous as these are the most penetrating, as a consequence, gamma rays can be used to sterilize materials & destroy bacteria in food

Uses of Radioisotopes
Isotope
Radiation Emitted
Half-life
Use
Carbon-14
beta
5730 years
radiometric dating:determination of age of carbon-containing artifacts up to about 70,000 years
also used as a biological tracer, for example, in studies of photosynthesis
Naturally occurring radioisotope
Chlorine-36


measurement of sources of chloride and determining the age of water up to about 2 million years old
Naturally occurring radioisotope
Lead-210


date layers of soil and sand deposited up to about 80 years ago
Naturally occurring radioisotope
Tritium


measure the age of 'young' groundwater up to about 30 years old
Naturally occurring radioisotope
Titriated water is used to study sewage and liquid wastes
Potassium/Argon


radiometric dating:100 000 to several billion years
Rubidium/Strontium


radiometric dating:millions of years
Uranium/Lead
U-238 alpha & gamma
4.5 x 109 years
radiometric dating:millions to billions of years
Oxygen-18


biological tracer, for example, in studies of photosynthesis
Sodium-24
beta, gamma
15 hours
location of leaks in water pipes, studies of body electrolytes
Isotope prepared in a nuclear reactor
Magnesium-27
beta, gamma
9.5 minutes
location of leaks in water pipes
Potassium-42
beta & alpha
22 hours
determination of exchanged potassium in blood flow
Isotope prepared in a nuclear reactor
Chromium-51
alpha
27.7 days
labelling of red blood cells & quantifying gastro-intestinal protein loss
Isotope prepared in a nuclear reactor
Iron-59
beta, gamma
46.3 days
in blood studies, when incorporated into steel it is used to determine the amount of friction in machinery
Cobalt-60
beta, gamma
5.3 years
cancer treatment as tumour cells tend to be more susceptible to radiation than other cells
Gallium-67
gamma
3.3 days
tumour-seeking agent
Isotope prepared in a cyclotron
Krypton-81
gamma
13 seconds
lung ventilation studies
Isotope prepared in a cyclotron
Technetium-99


Medical tracer used to locate brain tumours and problems with the lungs, thyroid, liver, spleen, kidney, gall bladder, skeleton, blood pool, bone marrow, salivary & lacrimal glands & heart blood pool & to detect infection
Isotope prepared in a nuclear reactor
Iodine-131
beta, gamma
8.1 days
Medical tracer to study & treat the thyroid gland & used in the diagnosis of adrenal medullary & for imaging suspected neural crest and other endocrine tumours
Isotope prepared in a nuclear reactor
Iodine-123


used in imaging to monitor thyroid function & detect adrenal dysfunction
Isotope prepared in a cyclotron
Ytterbium-169
gamma
3 days
brain scans
Isotope prepared in a nuclear reactor
Uranium-235
alpha, gamma
7.1 x 108 years
enriched as a fuel for most nuclear reactors
Plutonium-239
alpha, gamma
24 400 years
fuel for most "fast-breeder" nuclear reactors
Americium-241
alpha
432 years
domestic smoke alarms & neutron gauging
Americium-241 is a decay product of plutonium-241 formed in nuclear reactors.
Copper-64


studying genetic disease affecting copper metabolism
Isotope prepared in a nuclear reactor
Iridium-192


supplied as a wire for use as an internal radiotherapy device
Molybdenum-99


used as the 'parent' in a generator to produce technetium-99m, the most widely used radioisotope in nuclear medicine
Isotope prepared in a nuclear reactor
Phosphorus-32


treatment of excess red blood cells
Isotope prepared in a nuclear reactor
Samarium-153


used in the treatment of pain associated with bony metastases of primary tumours
Isotope prepared in a nuclear reactor
Yttrium-90


liver cancer therapy
Isotope prepared in a nuclear reactor
Thallium-201


locating damaged heart muscle
Isotope prepared in a cyclotron
Caesium-137


radiotracing to identify sources of soil erosion & depositing, also used in thickness gauging
Gold-198


trace factory waste causing ocean pollution and to trace sand movement in river beds and on ocean floors
Gadolinium


used in X-ray fluorescence
Zinc-65 & Manganese-54


used to predict the behaviour of heavy metals in effluents from mining waste water



Tan Sien Yi (F4Sc1)

Use in nuclear medicine

As radioisotopes can be tracked down with special machines as they pass through natural systems, this has been used to diagnose certain diseases.

In general, diagnostic tests of this type are done by injecting a radionuclide or radioisotope into the bloodstream intravenously (by a syringe or needle). This radioisotope acts like a tracer, spreading all around the body and through each organ as they function. The patient is then run through a special imaging device similar to the X-ray machine like the 'gamma camera' or 'positron emission tomography' (PET scanner).
A PET scanner
A PET scanner

The device images the patient's body and detects concentrations of the radioisotope around the body. Certain telltale signs or quirks that the radioisotope do in the body may give a diagnosis to doctors.
Diagram briefly explaining how the PET scan detects the radioisotope.
Diagram briefly explaining how the PET scan detects the radioisotope.

For example, the radioisotope Iodine-131 is used to diagnose problems in the thyroid gland. The thyroid gland normally absorbs all isotopes of iodine. Therefore, a PET scan on a healthy patient would show the injected Iodine-131 to be absorbed by it. However, if the thyroid gland is not functioning properly, the Iodine-131 will not appear to be absorbed, showing a 'cold spot' on the imagery. Based on the radio-accumulation of the tracer, this could be used to diagnose a thyroid gland-related disease, like cancer.

On the other hand, the radioisotope Technetium-99m, or Tc-99m for short, can be attached to certain pharmaceuticals to be transported to the bones. Any increased physiological function, such as due to a fracture in the bone, will usually mean increased concentration of the tracer. This will create a 'hot spot' on the PET scan due to the high radio-accumulation. This tracer can also be used to check cerebral blood flow in the brain, blood flow in the heart, and can even be used to label white blood cells to visualize sites of infection.

Osteosarcoma.gif
The accumulation of the Tc-99m radioisotope tracer shows a 'hot spot' indicating a cancer in the cheek bone (maxillary osteosarcoma) of this 17-year old girl.


Some rare medicinal procedures also require the radioisotope to be inhaled as a gas or aerosol instead of injections. These include the use of Xenon-133. When inhaled, the tracer can be used to image and assess the function of the lungs.


Adeline Kong (F4 Sc 1)


Uses of Radioisotopes
(Brief uses of various radioactive isotopes / Radioisotopes)

Isotope
Radiation Emitted
Half-life
Use
Carbon-14
beta
5730 years
radiometric dating:determination of age of carbon-containing artifacts up to about 70,000 years
also used as a biological tracer, for example, in studies of photosynthesis
Naturally occurring radioisotope
Chlorine-36


measurement of sources of chloride and determining the age of water up to about 2 million years old
Naturally occurring radioisotope
Lead-210


date layers of soil and sand deposited up to about 80 years ago
Naturally occurring radioisotope
Tritium


measure the age of 'young' groundwater up to about 30 years old
Naturally occurring radioisotope
Titriated water is used to study sewage and liquid wastes
Potassium/Argon


radiometric dating:100 000 to several billion years
Rubidium/Strontium


radiometric dating:millions of years
Uranium/Lead
U-238 alpha & gamma
4.5 x 109 years
radiometric dating:millions to billions of years
Oxygen-18


biological tracer, for example, in studies of photosynthesis
Sodium-24
beta, gamma
15 hours
location of leaks in water pipes, studies of body electrolytes
Isotope prepared in a nuclear reactor
Magnesium-27
beta, gamma
9.5 minutes
location of leaks in water pipes
Potassium-42
beta & alpha
22 hours
determination of exchanged potassium in blood flow
Isotope prepared in a nuclear reactor
Chromium-51
alpha
27.7 days
labelling of red blood cells & quantifying gastro-intestinal protein loss
Isotope prepared in a nuclear reactor
Iron-59
beta, gamma
46.3 days
in blood studies, when incorporated into steel it is used to determine the amount of friction in machinery
Cobalt-60
beta, gamma
5.3 years
cancer treatment as tumour cells tend to be more susceptible to radiation than other cells
Gallium-67
gamma
3.3 days
tumour-seeking agent
Isotope prepared in a cyclotron
Krypton-81
gamma
13 seconds
lung ventilation studies
Isotope prepared in a cyclotron
Technetium-99


Medical tracer used to locate brain tumours and problems with the lungs, thyroid, liver, spleen, kidney, gall bladder, skeleton, blood pool, bone marrow, salivary & lacrimal glands & heart blood pool & to detect infection
Isotope prepared in a nuclear reactor
Iodine-131
beta, gamma
8.1 days
Medical tracer to study & treat the thyroid gland & used in the diagnosis of adrenal medullary & for imaging suspected neural crest and other endocrine tumours
Isotope prepared in a nuclear reactor
Iodine-123


used in imaging to monitor thyroid function & detect adrenal dysfunction
Isotope prepared in a cyclotron
Ytterbium-169
gamma
3 days
brain scans
Isotope prepared in a nuclear reactor
Uranium-235
alpha, gamma
7.1 x 108 years
enriched as a fuel for most nuclear reactors
Plutonium-239
alpha, gamma
24 400 years
fuel for most "fast-breeder" nuclear reactors
Americium-241
alpha
432 years
domestic smoke alarms & neutron gauging
Americium-241 is a decay product of plutonium-241 formed in nuclear reactors.
Copper-64


studying genetic disease affecting copper metabolism
Isotope prepared in a nuclear reactor
Iridium-192


supplied as a wire for use as an internal radiotherapy device
Molybdenum-99


used as the 'parent' in a generator to produce technetium-99m, the most widely used radioisotope in nuclear medicine
Isotope prepared in a nuclear reactor
Phosphorus-32


treatment of excess red blood cells
Isotope prepared in a nuclear reactor
Samarium-153


used in the treatment of pain associated with bony metastases of primary tumours
Isotope prepared in a nuclear reactor
Yttrium-90


liver cancer therapy
Isotope prepared in a nuclear reactor
Thallium-201


locating damaged heart muscle
Isotope prepared in a cyclotron
Caesium-137


radiotracing to identify sources of soil erosion & depositing, also used in thickness gauging
Gold-198


trace factory waste causing ocean pollution and to trace sand movement in river beds and on ocean floors
Gadolinium


used in X-ray fluorescence
Zinc-65 & Manganese-54


used to predict the behaviour of heavy metals in effluents from mining waste water


Jennifer Kwong(F4Sc1)

The radioisotope most widely used in medicine is technetium-99m, employed in some 80% of all nuclear medicine procedures - 40,000 every day. It is an isotope of the artificially-produced element technetium and it has almost ideal characteristics for a nuclear medicine scan. These are:

> It has a half-life of six hours which is long enough to examine metabolic processes yet short enough to minimise the radiation dose to the patient.
> Technetium-99m decays by a process called "isomeric"; which emits gamma rays and low energy electrons. Since there is no high energy beta emission the radiation dose to the patient is low.
> The low energy gamma rays it emits easily escape the human body and are accurately detected by a gamma camera. Once again the radiation dose to the patient is minimised.
> The chemistry of technetium is so versatile it can form tracers by being incorporated into a range of biologically-active substances to ensure that it concentrates in the tissue or organ of interest.

Its logistics also favour its use. Technetium generators, a lead pot enclosing a glass tube containing the radioisotope, are supplied to hospitals from the nuclear reactor where the isotopes are made. They contain molybdenum-99, with a half-life of 66 hours, which progressively decays to technetium-99. The Tc-99 is washed out of the lead pot by saline solution when it is required. After two weeks or less the generator is returned for recharging.

A similar generator system is used to produce rubidium-82 for PET imaging from strontium-82 - which has a half-life of 25 days.

Myocardial Perfusion Imaging (MPI) uses thallium-201 chloride or technetium-99m and is important for detection and prognosis of coronary artery disease.

For PET imaging, the main radiopharmaceutical is Fluoro-deoxy glucose (FDG) incorporating F-18 - with a half-life of just under two hours, as a tracer. The FDG is readily incorporated into the cell without being broken down, and is a good indicator of cell metabolism.

In diagnostic medicine, there is a strong trend to using more cyclotron-produced isotopes such as F-18 as PET and CT/PET become more widely available. However, the procedure needs to be undertaken within two hours of a cyclotron.

Fan Sie Hwei (F4SC1)

EXTRA:
Radiocarbon dating
is a radiometric datingmethod that uses the naturally occurring isotope carbon-14 (14C) to determine the age of carbonaceous materials up to about 60,000 years.
Carbon has two stable, nonradioactive isotopes: carbon-12 (12C), and carbon-13 (13C). In addition, there are trace amounts of the unstable isotope carbon-14 (14C) on Earth. Carbon-14 has a half-life of 5730 years and would have long ago vanished from Earth were it not for the unremitting cosmic ray impacts on nitrogen in the Earth's atmosphere, which create more of the isotope. The neutrons resulting from the cosmic ray interactions participate in the following nuclear reaction on the atoms of nitrogen molecules (N2) in the atmospheric air:

n + mathrm{~^{14}_{7}N}rightarrowmathrm{~^{14}_{6}C}+ p
n + mathrm{~^{14}_{7}N}rightarrowmathrm{~^{14}_{6}C}+ p


The highest rate of carbon-14 production takes place at altitudes of 9 to 15 km (30,000 to 50,000 ft), and at high geomagnetic latitudes, but the carbon-14 spreads evenly throughout the atmosphere and reacts with oxygen to form carbon dioxide. Carbon dioxide also permeates the oceans, dissolving in the water. For approximate analysis it is assumed that the cosmic ray flux is constant over long periods of time; thus carbon-14 is produced at a constant rate and the proportion of radioactive to non-radioactive carbon is constant: ca. 1 part per trillion (600 billion atoms/mole). In 1958 Hessel de Vries showed that the concentration of carbon-14 in the atmosphere varies with time and locality. For the most accurate work, these variations are compensated by means of calibration curves. When these curves are used, their accuracy and shape are the factors that determine the accuracy and age obtained for a given sample.
Plants take up atmospheric carbon dioxide by photosynthesis, and are ingested by animals, so every living thing is constantly exchanging carbon-14 with its environment as long as it lives. Once it dies, however, this exchange stops, and the amount of carbon-14 gradually decreases through radioactive beta decay.

mathrm{~^{14}_{6}C}rightarrowmathrm{~^{14}_{7}N}+ e^- + bar{nu}_e
mathrm{~^{14}_{6}C}rightarrowmathrm{~^{14}_{7}N}+ e^- + bar{nu}_e


By emitting an electron and an anti-neutrino, carbon-14 is changed into stable (non-radioactive) nitrogen-14. This decay can be used to measure how long ago once-living material died. However, aquatic plants obtain some of their carbon from dissolved carbonates which are likely to be very old, and thus deficient in the carbon-14 isotope, so the method is less reliable for such materials as well as for samples derived from animals with such plants in their food chain.
Half-life
The half-life of a quantity whose value decreases with time is the interval required for the quantity to decay to half of its initial value. The concept originated in the study of radioactive decay which is subject to exponential decay but applies to all phenomena including those which are described by non-exponential decays.
The term half-life was coined in 1907, but it was always referred to as half-life period. It was not until the early 1950s that the word period was dropped from the name.


Yeoh Hsu Yin (F4 SC1)

Carbon Dating

external image cdate1.gif
Carbon dating is a variety of radioactive dating which is applicable only to matter which was once living and presumed to be in equilibrium with the atmosphere, taking in carbon dioxide from the air for photosynthesis.
Cosmic ray protons blast nuclei in the upper atmosphere, producing neutrons which in turn bombard nitrogen, the major constituent of the atmosphere . This neutron bombardment produces the radioactive isotope carbon-14. The radioactive carbon-14 combines with oxygen to form carbon dioxide and is incorporated into the cycle of living things.
The carbon-14 forms at a rate which appears to be constant, so that by measuring the radioactive emissions from once-living matter and comparing its activity with the equilibrium level of living things, a measurement of the time elapsed can be made.

external image cdate2.gif
Presuming the rate of production of carbon-14 to be constant, the activity of a sample can be directly compared to the equilibrium activity of living matter and the age calculated. Various tests of reliability have confirmed the value of carbon data, and many examples provide an interesting range of application.
Carbon-14 decays with a halflife of about 5730 years by the emission of an electron of energy 0.016 MeV. This changes the atomic number of the nucleus to 7, producing a nucleus of nitrogen-14. At equilibrium with the atmosphere, a gram of carbon shows an activity of about 15 decays per minute.
The low activity of the carbon-14 limits age determinations to the order of 50,000 years by counting techniques. That can be extended to perhaps 100,000 years by accelerator techniques for counting the carbon-14 concentration.
external image cdate3.gif


Celia Fernandez (F4 Sc1)


Food Irradiation
Food irradiation is a method of treating food in order to make it safer to eat and have a longer shelf life. This process is not very different from other treatments such as pesticide application, canning, freezing and drying. The end result is that the growth of disease-causing microorganismns or those that cause spoilage are slowed or are eliminated altogether. This makes food safer and also keeps it fresh longer.

Food irradiated by exposing it to the gamma rays of a radioisotope -- one that is widely used is cobalt-60. The energy from the gamma ray passing through the food is enough to destroy many disease-causing bacteria as well as those that cause food to spoil, but is not strong enough to change the quality, flavor or texture of the food. It is important to keep in mind that the food never comes in contact with the radioisotope and is never at risk of becoming radioactive.

external image fruit.gif

Applications and uses of stable isotopes
I. Tracing studies:

Nitrogen cycling: To investigate nitrogen cycling in crop plants, 15N-labelled fertilizer (urea, ammonium nitrate, and so on) either 2-5% enriched or 0.36% depleted in 15N is applied. Following the tracer yields data with which one can quantify the fate of the added fertilizer N as it passes into various partitions: the portion taken up by the plants, the portion remaining in the soil N pool, the portion lost by denitrification into the atmosphere, and the portion leached into runoff waters. Such data leads to recommendations for fertilization that yield the greatest benefit to food crops and the least possible pollution of drinking water by nitrate runoff. 15N levels in the soil and water can also be an indication of the origin of the N, pinpointing its source.
Physiological tracing: Medical researchers use 13C as a noninvasive alternative to 14C for analyzing metabolic processes. 13C-labeled compounds metabolize to 13CO2, which is detectable in the breath.


III. Archaeological investigations:
As mentioned, the characteristic isotope-ratio "signatures" of food species are passed on to consumers. Though there may be further fractionation during metabolic processing of food by the consumers, the mean delta13C values of the two main groups, C3 and C4, of primary producers can remain visible through many trophic levels to the top of the food chain. It is possible to determine the proportion of C3 and C4 plant species in the diet of herbivores and to make inferences about the prey species selected by carnivores. A remarkable application of this fact depends on the further observation that original North American plant communities were composed almost exclusively of C3 species (mean delta13C = -27o/oo), while maize (Zea mays) is a C4 plant with a delta13C value of -14o/oo. It has proven possible to determine the time of introduction of maize agriculture in the New World, and the rate at which it was adopted, by examining the delta13C values of skeletons and carbonized deposits in cooking pots. During the period A.D 1000-1200, the delta values of human collagen recovered from skeletal material changed from -21.4o/oo to -12o/oo as the isotope content of the diet was altered by the introduction of maize. This in turn can now be correlated with the great changes in population density and levels of civilization that resulted from the abandonment of the hunter-gatherer mode of life and the substitution of long-term agricultural settlements.

IV. Correction of carbon-14 dates:
Since carbon is strongly fractionated by biological processes, it is not possible to date ancient carbon-bearing material by the carbon-14 method without taking this fractionation into account. If biological samples selectively accumulate heavy C isotopes, this will make them appear spuriously young. It has been found that rates of 13C stable isotope fractionation are doubled for 14C. Stable isotope analysis gives an independent measure of fractionation such that if, for instance, a sample is 1.5% heavier in 13C than "modern standard carbon" through the effects of fractionation, then it will be 3% heavier in 14C than it would have been had fractionation not taken place. Since the average lifetime of a 14C atom is ~8000 years, a 3% increase in 14C content through fractionation will make it appear too young by 3% of 8000 years, or 240 years.

Fan Sie Hwei (F4 Sc 1)

In an element, some isotopes are stable while the rest are unstable isotopes. Unstable isotopes are radioactive isotopes.
Radioactive isotopes will undergo spontaneous decay to emit radioactive rays: alpha, beta and gamma. After radioactive decay, the proton number and nucleon number of the isotope may change.
There are many uses of radioisotopes, namely in the field of medicine, agriculture, industry, archeology, food preservation and electricity generation.

Agriculture
(a) Using the radioactive crabon-14 in carbon dioxide, the path of carbon during the photosyntheses process can be determined. The rate of absorption of phosphorous by the plant can be determined by adding radioactive phosphate ions to the ground.
(b) Male pests can be attracted into traps using female hormones (pheromone). The male pests are then exposed to gamma radiation which can cause genetic mutation to the gametes (sperms). The male pests are then released to be allowed to mate with the females. The offspring produced will have physical defects such as undeveloped digestive organs and wings. This will terminate the survival of the following generation.

Teh Su Yuin (F4 Sc 1)


Isotopes of plutonium

Plutonium (Pu) has no stable isotopes. A standard atomic mass cannot be given.

Decay modes
Twenty plutonium radioisotopes have been characterized. The most stable are Pu-244, with a half-life of 80.8 million years, Pu-242, with a half-life of 373,300 years, and Pu-239, with a half-life of 24,110 years. All of the remaining radioactive isotopes have half-lives that are less than 7,000 years. This element also has eight meta states, though none are very stable (all have half-lives less than one second).
The isotopes of plutonium range in atomic weight from 228.0387 u (Pu-228) to 247.074 u (Pu-247). The primary decay modes before the most stable isotope, Pu-244, are spontaneous fission and alpha emission; the primary mode after is beta emission. The primary decay products before Pu-244 are uranium and neptunium isotopes (neglecting the wide range of daughter nuclei created by fission processes), and the primary products after are americium isotopes.

Production and uses

A pellet of plutonium-238, glowing under its own light, used for radioisotope thermoelectric generators.
A pellet of plutonium-238, glowing under its own light, used for radioisotope thermoelectric generators.
external image magnify-clip.png A pellet of plutonium-238, glowing under its own light, used for radioisotope thermoelectric generators.
Pu-239, a fissile isotope which is the second most used nuclear fuel in nuclear reactors after U-235, and the most used fuel in the fission portion of nuclear weapons, is produced from U-238 by neutron capture followed by two beta decays.
Pu-240, Pu-241, Pu-242 are produced by further neutron capture. The odd-mass isotopes Pu-239 and Pu-241 have about a 3/4 chance of undergoing fission on capture of a thermal neutron and about a 1/4 chance of retaining the neutron and becoming the following isotope. The even-mass isotopes are not fissile and also have a lower overall probability (cross section) of neutron capture; therefore, they tend to accumulate in nuclear fuel used in a thermal reactor, the design of all nuclear power plants today. In plutonium that has been used a second time in thermal reactors in MOX fuel, Pu-240 may even be the most common isotope. All plutonium isotopes and other actinides, however, are fissionable with fast neutrons.
Pu-241 has a halflife of 14 years. While nuclear fuel is being used in a reactor, a Pu-241 nucleus is much more likely to fission or to capture a neutron than to decay. However, in spent nuclear fuel that is cooled for decades after use, much or most of the Pu-241 will beta decay to americium-241, one of the minor actinides and less fissionable.
Pu-243 has a halflife of only 5 hours, beta decaying to americium-243. Because Pu-243 has little opportunity to capture an additional neutron before decay, the nuclear fuel cycle does not produce long-lived Pu-244 in significant quantity.
Pu-238 is not normally produced in as large quantity by the nuclear fuel cycle, but some is produced from neptunium-237 by neutron capture (this reaction can also be used with purified neptunium to produce Pu-238 relatively free of other plutonium isotopes for use in radioisotope thermoelectric generators), by the (n,2n) reaction on Pu-239, or by alpha decay of curium-242 which is produced by neutron capture from Am-241.

Pu-240 as obstacle to nuclear weapons

Pu-240 undergoes spontaneous fission as a secondary decay mode at a small but significant rate. The presence of Pu-240 limits the plutonium's nuclear bomb potential because the neutron flux from spontaneous fission, initiates the chain reaction prematurely and reduces the bomb's power by exploding the core before full implosion is reached. Plutonium consisting of more than about 90% Pu-239 is called weapons-grade plutonium; plutonium from spent nuclear fuel from commercial power reactors generally contains at least 20% Pu-240 and is called reactor-grade plutonium. However, modern nuclear weapons use fusion boosting which mitigates the predetonation problem; if the pit can generate a nuclear weapon yield of even a fraction of a kiloton, which is enough to start deuterium-tritium fusion, the resulting burst of neutrons will fission enough plutonium to ensure a yield of tens of kilotons.
Pu-240 contamination is the reason plutonium weapons must use the implosion method. Theoretically, pure Pu-239 could be used in a gun-type nuclear weapon, but achieving this level of purity is prohibitively difficult. Pu-240 contamination has proven a mixed blessing to nuclear weapons design. While it created delays and headaches during the Manhattan Project because of the need to develop implosion technology, those very same difficulties are currently a barrier to nuclear proliferation. Implosion devices are also inherently more efficient and less prone toward accidental detonation than are gun-type weapons.

Table

nuclide
symbol
↓

Z(p)
↓

N(n)
↓

isotopic mass (u)
↓

half-life
↓

nuclear
spin
↓

representative
isotopic
composition
(mole fraction)
↓

range of natural
variation
(mole fraction)
↓

excitation energy
228Pu
94
134
228.03874(3)
1.1(+20-5) s
0+


229Pu
94
135
229.04015(6)
120(50) s
3/2+#


230Pu
94
136
230.039650(16)
1.70(17) min
0+


231Pu
94
137
231.041101(28)
8.6(5) min
3/2+#


232Pu
94
138
232.041187(19)
33.7(5) min
0+


233Pu
94
139
233.04300(5)
20.9(4) min
5/2+#


234Pu
94
140
234.043317(7)
8.8(1) h
0+


235Pu
94
141
235.045286(22)
25.3(5) min
(5/2+)


236Pu
94
142
236.0460580(24)
2.858(8) a
0+


237Pu
94
143
237.0484097(24)
45.2(1) d
7/2-


237m1Pu
145.544(10) keV
180(20) ms
1/2+


237m2Pu
2900(250) keV
1.1(1) µs



238Pu
94
144
238.0495599(20)
87.7(1) a
0+


239Pu
94
145
239.0521634(20)
24.11(3)E+3 a
1/2+


239m1Pu
391.584(3) keV
193(4) ns
7/2-


239m2Pu
3100(200) keV
7.5(10) µs
(5/2+)


240Pu
94
146
240.0538135(20)
6561(7) a
0+


241Pu
94
147
241.0568515(20)
14.290(6) a
5/2+


241m1Pu
161.6(1) keV
0.88(5) µs
1/2+


241m2Pu
2200(200) keV
21(3) µs



242Pu
94
148
242.0587426(20)
3.75(2)E+5 a
0+


243Pu
94
149
243.062003(3)
4.956(3) h
7/2+


243mPu
383.6(4) keV
330(30) ns
(1/2+)


244Pu
94
150
244.064204(5)
8.00(9)E+7 a
0+


245Pu
94
151
245.067747(15)
10.5(1) h
(9/2-)


246Pu
94
152
246.070205(16)
10.84(2) d
0+


247Pu
94
153
247.07407(32)#
2.27(23) d
1/2+#



Notes

  • Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
  • Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.



Amy Lee (F4SC1)


Natural Abundance Variations in Stable Isotopes and their Potential Uses in Animal Physiological Ecology
Chemical, biological, and physical processes lead to distinctive “isotopic signatures” in biological materials that allow tracing of the origins of organic substances. Isotopic variation has been extensively used by plant physiological ecologists and by paleontologists, and recently ecologists have adopted the use of stable isotopes to measure ecosystem patterns and processes. To date, animal physiological ecologists have made minimal use of naturally occurring stable isotopes as tracers. Here we provide a review of the current and potential uses of naturally occurring stable isotopes in animal physiological ecology. We outline the physical and biological processes that lead to variation in isotopic abundance in plants and animals. We summarize current uses in animal physiological ecology (diet reconstruction and animal movement patterns), and suggest areas of research where the use of stable isotopes can be fruitful (protein balance and turnover and the allocation of dietary nutrients). We argue that animal physiological ecologists can benefit from including the measurement of naturally occurring stable isotopes in their battery of techniques. We also argue that animal physiologists can make an important contribution to the emerging field of stable isotopes in biology by testing experimentally the plethora of assumptions upon which the techniques rely.