Radiation Detectors and Carbon Dating Help
There are two types of equipment used to detect radiation, ionization counters and scintillation counters .
Ionization counters detect the production of ions in matter.
The Geiger counter, invented in 1928 and named after one of its two inventors, H. Geiger and E.W. Muller, counts particles emitted by radioactive nuclei in a non-reactive noble gas, like argon. Alpha and beta particles are detected this way.
Scintillation counters detect nuclear radiation from flashes of light made when radiation affects a sample.
A sample that emits flashes of light when struck by radiation is called a phosphor . Rutherford used zinc sulfide as a phosphor to detect alpha particles. Sodium iodide and thallium combined together are used to detect gamma radiation in the same way.
Isotopes are also used in the dating of ancient soils, plants, animals, and the tools of early peoples. The isotope of carbon 14 C, which has a half-life of 5,730 years, can be used to calculate the age of old things. Since the rate of radioactive decay is constant, observing the decay rate allows the calculation of years that have past in relation to the half-life.
Carbon dating of organic materials depends a lot on the preservation of the original sample. Most people agree that carbon dating is only accurate to between 30,000 and 50,000 years. Other radiometric methods that make use of uranium, lead, potassium, and argon can measure much longer time periods since they are not restricted to organic samples that were once alive. The oldest rocks tested on earth have been dated around four billion years old. This radioactive dating allowed scientists to measure the earth’s crust at near this age and meteorites at around 4.4 × 10 9 years.
Nuclear medicine is the specific focus of radiology that uses minute amounts of radioactive materials, or radiopharmaceuticals , to study organ function and structure. Nuclear medicine imaging is a combination of many different sciences, including chemistry, physics, mathematics, computer technology, and medicine.
Because X-rays travel through soft tissue, such as blood vessels, heart muscle, and intestines, contrast tracers are used in nuclear imaging. Nuclear imaging examines organ function and structure, whereas diagnostic radiology is based on the anatomy of bones and hard tissues.
A relatively new use for radioactive isotopes/radiopharmaceuticals is in the detection and treatment of cancer. This branch of radiology is often used to help diagnose and treat abnormalities very early in the stages of a disease, such as thyroid cancer. Since rapidly dividing cells like those present in cancer are more vulnerable to radiation than slow-growing normal cells, treatment using medical isotopes works well.
Radon-222, used initially, and now cobalt-60, are used as implants near a cancer or shot as a narrow beam to an inoperable brain cancer or used before surgery to shrink a tumor in lung or breast cancers.
A radioactive tracer is a very small amount of radioactive isotope added to a chemical, biological, or physical system in order to study the system. For example, radioactive barium ( 37 Ba) is used to diagnose unusual abdominal pain, gastroesophageal reflux, and gastric or duodenal ulcers or cancer. Thallium ( 201 Tl) is a radioactive tracer used to detect heart disease. This isotope binds with great enthusiasm to heart muscle that is well oxygenated. When a patient with heart trouble is tested, a scintillation counter detects the levels of radioactive thallium that have bonded to oxygen. When areas of the heart are not receiving oxygen, there is very little thallium binding and it is seen as a dark area.
Radioactively tagged enzymes, or proteins containing radioactive components, are used in the medical area of study called radioimmunology . Radioimmunology measures the levels of biological factors (proteins, enzymes) known to be changed by different diseases. Some of these medical isotopes used in medicine include phosphorus ( 32 P), iron ( 59 Fe), and iodine ( 131 I).
Radioactive elements are an important area of chemical study. New uses and methods of detection will increase this area of research as more and more nuclear sub-particles are discovered.
Practice problems for these concepts can be found at – Radiochemistry Practice Test
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