Science Chem One Research

1. DEFINITION OF RADIOISOTOPE AND NUCLEAR RADIATION. ACCESSED 11 FEBRUARY 2009 http://www.medterms.com/script/main/art.asp?articlekey=5188 Last review: 18th November 2003 MedicineNet

Definition of Radioisotope Radioisotope: A

version of a chemical element that has an unstable nucleus and emits radiation during its decay to a stable form. Radioisotopes have important uses in medical diagnosis, treatment, and research. A radioisotope is so-named because it is a radioactive isotope, an isotope being an alternate version of a chemical element that has a different atomic mass. http://www.virtualmedicalcentre.com/Medical_Dictionary.asp?termid=1249&title=Radioisotope Last review: Virtual Medical Centre

Radioisotope Radioisotope: a form of a chemical element which undergoes spontaneous nuclear disintegration, emitting radiation.

ACCESSED 12 FEBRUARY 2009 http://www.ausetute.com.au/halflife.html Last review: Aus-e-tute

Half-Life

Key Concepts •

The half-life of a radioisotope is the time required for half the atoms in a given sample to undergo radioactive, or nuclear, decay.

•

Half-life is given the symbol t½

•

Different radioisotopes have different halflives.

•

The amount of radioactive isotope remaining can be calculated: Nt = No x (0.5)number of half-lives Where: Nt = amount of radioisotope remaining No = original amount of radioisotope number of half-lives = time ÷ half-life

Examples Consider strontium-90 which has a half-life of approximately 28 years. •

Initially, at time t=0, the sample is 100% strontium-90

•

After 28 years, only half the original amount of strontium will remain: ½ x 100% = 50%

•

After another 28 years, only half of this amount of strontium-90 will remain: ½ x 50% = 25%

•

After another 28 years, only half of this amount of strontium will remain:

% Number Time % StrontiumStrontiumof Half- (years 90 that has 90 lives ) decayed remaining

0

0

100

0

1

28

50

50

2

56

25

75

3

84

12.5

87.5

4

112

6.25

93.75

5

140

3.125

96.875

6

168

1.5625

98.4375

http://www.biomed.curtin.edu.au/resources/Radweb/sld020.htm Last Reviewed: Biomed HALF LIFE OF RADIOISOTOPES

http://www.remm.nlm.gov/halflife.htm Last Reviewed: July 11 2008 US Department of Health and Medical Services, Radiation Event Medical Management

Decay Rate/Half-Life of Radioisotopes - Illustrations

(from the Uranium Information Center, Melbourne,

Australia, www.uic.com.au/ral.htm):

http://www.nrc.gov/reading-rm/basicref/teachers/05.pdf United States Nuclear Regulatory Commision

The rate of nuclear decay is measured in terms of HALF LIVES. The half life of any radioactive material is the length of time necessary for one half of the atoms of that material to decay to some other material. During each half life, one half of the atoms which started that half life period will decay. Half lives range from millionths of a second for highly radioactive fission products to billions of years for long-lived materials (such as naturally occurring uranium). No matter how long or short the half life is, after seven half lives have passed, there is less than 1 percent of the initial activity remaining. Radiation emitted by radioactive material can produce IONIZATIONS and, therefore, is called IONIZING RADIATION. Ionization is the process of stripping, knocking off, or otherwise removing electrons from their orbital paths, creating “free” electrons and leaving charged nuclei. The negatively charged electrons and positively charged nuclei may interact with other materials to produce chemical or electrostatic changes in the material where the interactions occur. If chemical changes occur in the cells of our bodies, some cellular damage may result. The biological effects of radiation exposure are discussed in Chapter 6.

The REM is based on the biological damage caused by ionization in human body tissue. It is a term for dose equivalence and equals the biological damage that would be caused by one RAD of dose. The REM accounts for the fact that not all types of radiation are equally effective in producing biological change or damage. That is, the damage from one rad deposited by beta radiation is less than that caused by one rad of alpha radiation. The REM is numerically equal to the dose in RADs multiplied by a QUALITY FACTOR, which accounts for the difference in the amount of biological damage caused by the different types of radiation.

United States Nuclear Regulatory Commision http://www.nrc.gov/reading-rm/basic-ref/glossary/halflife.html February 14 2007

Half-life

The time in which one half of the atoms of a particular radioactive substance disintegrate into another nuclea Measured half-lives vary from millionths of a second to billions of years. Also called physical or radiological life. http://www.nrc.gov/reading-rm/basic-ref/glossary/ionization.html

Ionization

The process of adding one or more electrons to, or removing one or more electrons from, atoms or molecules creating ions. High temperatures, electrical discharges, or nuclear radiations can cause ionization. http://www.nrc.gov/reading-rm/basic-ref/glossary/ion.html

Ion (1) An atom that has too many or too few electrons, causing it to have an electrical charge, and therefore, be chemically active. (2) An electron that is not associated (in orbit) with a nucleus. http://www.nrc.gov/reading-rm/basic-ref/glossary/isotope.html

Isotope

Any two or more forms of an element having identical or very closely related chemical properties and the sam atomic number but different atomic weights or mass numbers.

http://www.ead.anl.gov/pub/doc/rdd.pdf Argonne Medical Laboratory, NVS August 2005 As a general rule of thumb, 7 to 10 half-lives can indicate how long an isotope could be expected to remain radioactive. (Less than 1% of the original amount remains after seven half-lives.)

----HEALTH & INDUSTRY The RAD (Radiation Absorbed Dose) is a measure of the absorbed dose (energy deposited) in a material. One RAD is the deposition of one hundred ergs of energy in one gram of any material (NRC Regulations use per gram of body tissue) due to the ionization from any type of radiation. One erg of energy is equal

to about one ten billionth of a BTU, or about one ten millionth of a watt.

http://www.ead.anl.gov/pub/doc/rdd.pdf Argonne Medical Laboratory, NVS August 2005 Radionuclides are used in a variety of industry, medicine, and scientific research applications, as illustrated by the examples below. Many of these are in sealed sources, used in civil engineering (in flow gauges and to test soil moisture and material thickness/integrity for construction), in petroleum engineering (in well logging for oil exploration), in the airline industry (in fuel gauges and to check welds and structural integrity), in medicine (cancer treatment, pacemakers, and diagnostics), in homes (smoke detectors), and to make electricity (in radiothermal

generators or RTGs, that generate power in remote areas ranging from lighthouses to outer space).

Three of the nine isotopes considered candidates for an RDD are strong gamma-ray emitters: Cs-137 (from Ba-137m), Co-60, and Ir-192. These three could pose an external hazard to individuals who handle them (e.g., potential terrorists) if their protective shielding was removed or not used. In fact, it is precisely their gamma radiation that makes these three isotopes valuable for commercial and medical applications. Gamma emitters are used to sterilize food and equipment, irradiate tumors, nondestructively evaluate

high-integrity welds and castings (industrial radiography), and in industrial gauges.

As background on potential health effects, evidence linking radiation exposure to observable biological effects has only been found at relatively high doses, i.e., acute doses exceeding 25 rads (see below). (For context, natural background radiation translates to an average annual dose of about 0.3 rem, which is far below the threshold for acute effects and corresponds to a lifetime risk of about 1 in 100.) On average, about half of all cancers that can be induced by radiation are fatal; this ranges from about 10% for thyroid cancer to essentially 100% for liver cancer. An RDD would most likely result in relatively small radiation exposures, which overall might not substantially differ from an annual background dose. But in the unlikely event someone was highly exposed, chelation therapy (to enhance excretion) and other medical interventions could be pursued, including to limit internal

deposition.

Illustrative Case Study: 1987 Radiological Accident in Goiania, Brazil In September 1987, a hospital in Goiania, Brazil, moved to a new location and left its radiation cancer therapy unit behind. Found by scrap metal hunters, it was dismantled and the cesium chloride source containing 1,400 Ci of cesium-137 was removed. Pieces were distributed to family and friends, and several who were intrigued by the glow spread it across their skin. Eleven days later, alert hospital staff recognized symptoms of acute radiation syndrome in a number of victims. The ensuing panic caused more than 112,000 people – 10% of the population – to request radiation surveys to determine whether they had been exposed. At a makeshift facility in the city’s Olympic Stadium, 250 people were found to be contaminated. 28 had sustained radiationinduced skin injuries (burns), while 50 had ingested cesium, so for them the internal deposition translated to an increased risk of cancer over their lifetime. Tragically, 2 men, 1 woman, and 1 child died from acute radiation exposure to the very high levels of gamma radiation from the breached source. In addition to the human toll, contamination had been tracked over roughly 40 city blocks. Of the 85 homes found to be significantly contaminated, 41 were evacuated and 7 were demolished. It was also discovered that through routine travels, within that short time people had crosscontaminated houses nearly 100 miles away. Cleanup generated 3,500 m3 radioactive waste at a cost of $20 million. The impacts of this incident continued beyond the health and physical damage to profound

psychological effects including fear and depression for a large fraction of the city’s inhabitants. Further, frightened by the specter of radioactive contamination, neighboring provinces isolated Goiania and boycotted its products. The price of their manufactured goods dropped 40% and stayed low for more than a month. Tourism, a primary industry, collapsed and recent population gains were reversed by business regression. Total economic losses were estimated at hundreds of millions of dollars. A key lesson learned from this incident is the importance of enhancing the broader understanding of radiation. This fact sheet is intended to help support that objective. (For additional information see: International Atomic Energy Agency (IAEA), 1988, The Radiological Accident in Goiania, Vienna, Austria.)

>>http://www.northland.cc.mn.us/biology/ Biology1111/Bioreadings/radioisotopes.ht m http://www.worldnuclear.org/info/inf05.html