Poly(allyl diglycol carbonate) (PADC) is a plastic commonly used in the manufacture of eyeglass lenses alongside the material PMMA ( polymethyl methacrylate ). The monomer is allyl diglycol carbonate (ADC). The term CR-39 technically refers to the ADC monomer, but is more commonly used to refer to the finished plastic.
44-735: The abbreviation stands for "Columbia Resin #39", which was the 39th formula of a thermosetting plastic developed by the Columbia Resins project in 1940. The first commercial use of CR-39 monomer (ADC) was to help create glass-reinforced plastic fuel tanks for the B-17 bomber aircraft in World War II, reducing the weight and increasing the range of the bomber. After the war, the Armorlite Lens Company in California
88-450: A medical physicist . In radiation therapy, three-dimensional dose distributions are often evaluated using a technique known as gel dosimetry . Environmental Dosimetry is used where it is likely that the environment will generate a significant radiation dose. An example of this is radon monitoring. The largest single source of radiation exposure to the general public is naturally occurring radon gas, which comprises approximately 55% of
132-436: A biological material is fixed against CR-39 and kept frozen for a timescale of months to years in an environment that is shielded as much as possible from possible radiological contaminants. Before etching, photographs are taken of the biological sample with the affixed CR-39 detector, with care taken to ensure that prescribed location marks on the detector are noted. After the etching process, automated or manual 'scanning' of
176-416: A certain biological effect varies between different types of radiation, such as photons , neutrons or alpha particles . This is taken into account by the equivalent dose (H), which is defined as the mean dose to organ T by radiation type R ( D T,R ), multiplied by a weighting factor W R . This designed to take into account the biological effectiveness (RBE) of the radiation type, For instance, for
220-401: A dose can be inferred from readings taken by fixed instrumentation in an area in which the person concerned has been working. This would generally only be used if personal dosimetry had not been issued, or a personal dosimeter has been damaged or lost. Such calculations would take a pessimistic view of the likely received dose. Internal dosimetry is used to evaluate the committed dose due to
264-631: A personal dosimeter is worn on a position on the body representative of its exposure, assuming whole-body exposure, the value of Personal Dose Equivalent Hp(10), is sufficient to estimate an effective dose value suitable for radiological protection. Personal Dose Equivalent is a radiation quantity specifically designed to be used for radiation measurements by personal dosimeters. Dosimeters are known as "legal dosimeters" if they have been approved for use in recording personnel dose for regulatory purposes. In cases of non-uniform irradiation such personal dosimeters may not be representative of certain specific areas of
308-411: A source of radiation will give a dose which is dependent on many factors, such as the activity, duration of exposure, energy of the radiation emitted, distance from the source and amount of shielding. The worldwide average background dose for a human being is about 3.5 mSv per year [1] , mostly from cosmic radiation and natural isotopes in the earth. The largest single source of radiation exposure to
352-401: A variety of monitoring, bio-assay or radiation imaging techniques, whilst external dosimetry is based on measurements with a dosimeter , or inferred from measurements made by other radiological protection instruments . Radiation dosimetry is extensively used for radiation protection; routinely applied to monitor occupational radiation workers, where irradiation is expected, or where radiation
396-399: A water bath or a forced air oven. Benzoyl peroxide (BPO) is an alternative organic peroxide that may be used to polymerize ADC. Pure benzoyl peroxide is crystalline and less volatile than diisopropyl peroxydicarbonate. Using BPO results in a polymer that has a higher yellowness index, and the peroxide takes longer to dissolve into ADC at room temperature than IPP. CR-39 is transparent in
440-538: Is 10–20 joules per kilogram. A 1 cm piece of graphite weighing 2 grams would therefore absorb around 20–40 mJ. With a specific heat capacity of around 700 J·kg ·K , this equates to a temperature rise of just 20 mK. Dosimeters in radiotherapy ( linear particle accelerator in external beam therapy) are routinely calibrated using ionization chambers or diode technology or gel dosimeters. The following table shows radiation quantities in SI and non-SI units. Although
484-439: Is averaged over the whole organ; equivalent dose is rarely suitable for evaluation of acute radiation effects or tumour dose in radiotherapy. In the case of estimation of stochastic effects, assuming a linear dose response , this averaging out should make no difference as the total energy imparted remains the same. Effective dose is the central dose quantity for radiological protection used to specify exposure limits to ensure that
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#1732798594933528-420: Is credited with manufacturing the first CR-39 eyeglass lenses in 1947. CR-39 plastic has an index of refraction of 1.498 and an Abbe number of 58. CR-39 is now a trade-marked product of PPG Industries . An alternative use includes a purified version that is used to measure ionising radiation such as alpha particles and neutrons . Although CR-39 is a type of polycarbonate, it should not be confused with
572-411: Is exceeded. A good deal of information can be made immediately available to the wearer of the recorded dose and current dose rate via a local display. They can be used as the main stand-alone dosimeter, or as a supplement to other devices. EPD's are particularly useful for real-time monitoring of dose where a high dose rate is expected which will time-limit the wearer's exposure. In certain circumstances,
616-401: Is exposed to a known amount of radiation (derived from the primary standard) and a factor is issued to convert the instrument's reading to that dose. The user may then use their secondary standard to derive calibration factors for other instruments they use, which then become tertiary standards, or field instruments. The NPL operates a graphite-calorimeter for absolute photon dosimetry. Graphite
660-417: Is not used to assess acute radiation effects. Radiation dose refers to the amount of energy deposited in matter and/or biological effects of radiation, and should not be confused with the unit of radioactive activity ( becquerel , Bq) of the source of radiation, or the strength of the radiation field (fluence). The article on the sievert gives an overview of dose types and how they are calculated. Exposure to
704-399: Is often reported in rads and dose equivalent in rems . By definition, 1 Gy = 100 rad and 1 Sv = 100 rem. The fundamental quantity is the absorbed dose ( D ), which is defined as the mean energy imparted [by ionising radiation] (dE) per unit mass (dm) of material (D = dE/dm) The SI unit of absorbed dose is the gray (Gy) defined as one joule per kilogram. Absorbed dose, as a point measurement,
748-443: Is suitable for describing localised (i.e. partial organ) exposures such as tumour dose in radiotherapy. It may be used to estimate stochastic risk provided the amount and type of tissue involved is stated. Localised diagnostic dose levels are typically in the 0–50 mGy range. At a dose of 1 milligray (mGy) of photon radiation, each cell nucleus is crossed by an average of 1 liberated electron track. The absorbed dose required to produce
792-401: Is to simply average out a localised dose over the whole body. The problem of this approach is that the stochastic risk of cancer induction varies from one tissue to another. The effective dose E is designed to account for this variation by the application of specific weighting factors for each tissue ( W T ). Effective dose provides the equivalent whole body dose that gives the same risk as
836-495: Is unexpected, such as in the contained aftermath of the Three Mile Island , Chernobyl or Fukushima radiological release incidents. The public dose take-up is measured and calculated from a variety of indicators such as ambient measurements of gamma radiation, radioactive particulate monitoring, and the measurement of levels of radioactive contamination . Other significant radiation dosimetry areas are medical, where
880-424: Is used instead of water as its specific heat capacity is one-sixth that of water and therefore the temperature increase in graphite is 6 times higher than the equivalent in water and measurements are more accurate. Significant problems exist in insulating the graphite from the surrounding environment in order to measure the tiny temperature changes. A lethal dose of radiation to a human is approximately 10–20 Gy. This
924-528: The International Commission on Radiation Units and Measurements (ICRU) have published recommendations and data which are used to calculate these. There are a number of different measures of radiation dose, including absorbed dose ( D ) measured in: Each measure is often simply described as ‘dose’, which can lead to confusion. Non- SI units are still used, particularly in the USA, where dose
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#1732798594933968-502: The National Physical Laboratory, UK (NPL) provide calibration factors for ionization chambers and other measurement devices to convert from the instrument's readout to absorbed dose. The standards laboratories operates as a primary standard , which is normally calibrated by absolute calorimetry (the warming of substances when they absorb energy). A user sends their secondary standard to the laboratory, where it
1012-507: The visible spectrum and is almost completely opaque in the ultraviolet range. It has high abrasion resistance , in fact the highest abrasion/scratch resistance of any uncoated optical plastic. CR-39 is about half the weight of glass with an index of refraction only slightly lower than that of crown glass , and its high Abbe number yields low chromatic aberration , altogether making it an advantageous material for eyeglasses and sunglasses . A wide range of colors can be achieved by dyeing of
1056-477: The CR-39 is used to physically locate the ionising radiation recorded, which can then be mapped to the position of the radionuclide within the biological sample. There is no other non-destructive method for accurately identifying the location of trace quantities of radionuclides in biological samples at such low emission levels. Columbia-Southern Chemical Corporation Columbia-Southern Chemical Corporation
1100-596: The United States, along with Beauharnois , Quebec in Canada. Dosimetry Radiation dosimetry in the fields of health physics and radiation protection is the measurement, calculation and assessment of the ionizing radiation dose absorbed by an object, usually the human body. This applies both internally, due to ingested or inhaled radioactive substances, or externally due to irradiation by sources of radiation. Internal dosimetry assessment relies on
1144-480: The annual background dose. It is estimated that radon is responsible for 10% of lung cancers in the United States. Radon is a radioactive gas generated by the decay of uranium, which is present in varying amounts in the Earth's crust. Certain geographic areas, due to the underlying geology, continually generate radon which permeates its way to the Earth's surface. In some cases the dose can be significant in buildings where
1188-399: The body, where additional dosimeters are used in the area of concern. A number of electronic devices known as Electronic Personal Dosimeters (EPDs) have come into general use using semiconductor detection and programmable processor technology. These are worn as badges but can give an indication of instantaneous dose rate and an audible and visual alarm if a dose rate or a total integrated dose
1232-462: The concentration of radiation damage allows the chemical agent to attack the polymer more rapidly than it does in the bulk, revealing the paths of the charged particle ion tracks . The resulting etched plastic therefore contains a permanent record of not only the location of the radiation on the plastic but also gives spectroscopic information about the source. Principally used for the detection of alpha -emitting radionuclides (especially radon gas),
1276-412: The data to help identify opportunities to reduce unnecessary dose in medical situations. To enable consideration of stochastic health risk, calculations are performed to convert the physical quantity absorbed dose into equivalent and effective doses, the details of which depend on the radiation type and biological context. For applications in radiation protection and dosimetry assessment the (ICRP) and
1320-460: The dose received. Traditionally, these were lockets fastened to the external clothing of the monitored person, which contained photographic film known as film badge dosimeters . These have been largely replaced with other devices such as Thermoluminescent dosimetry (TLD), optically stimulated luminescence (OSL), or Fluorescent Nuclear Tract Detector (FNTD) badges. The International Committee on Radiation Protection (ICRP) guidance states that if
1364-419: The gas can accumulate. A number of specialised dosimetry techniques are used to evaluate the dose that a building's occupants may receive. Records of legal dosimetry results are usually kept for a set period of time, depending upon the legal requirements of the nation in which they are used. Medical radiation exposure monitoring is the practice of collecting dose information from radiology equipment and using
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1408-416: The general public is naturally occurring radon gas, which comprises approximately 55% of the annual background dose. It is estimated that radon is responsible for 10% of lung cancers in the United States. Because the human body is approximately 70% water and has an overall density close to 1 g/cm , dose measurement is usually calculated and calibrated as dose to water. National standards laboratories such as
1452-477: The general term " polycarbonate ", a tough homopolymer usually made from bisphenol A . CR-39 is made by polymerization of ADC in presence of diisopropyl peroxydicarbonate (IPP) initiator . The presence of the allyl groups allows the polymer to form cross-links ; thus, it is a thermoset resin. The polymerization schedule of ADC monomers using IPP is generally 20 hours long with a maximum temperature of 95 °C. The elevated temperatures can be supplied using
1496-443: The intake of radionuclides into the human body. Medical dosimetry is the calculation of absorbed dose and optimization of dose delivery in radiation therapy . It is often performed by a professional health physicist with specialized training in that field. In order to plan the delivery of radiation therapy, the radiation produced by the sources is usually characterized with percentage depth dose curves and dose profiles measured by
1540-504: The localised exposure. It is defined as the sum of equivalent doses to each organ ( H T ), each multiplied by its respective tissue weighting factor ( W T ). Weighting factors are calculated by the International Commission for Radiological Protection (ICRP), based on the risk of cancer induction for each organ and adjusted for associated lethality, quality of life and years of life lost. Organs that are remote from
1584-858: The most noteworthy of the polymers. CR-39 is commonly used in the manufacturing of plastic eyeglass lenses . Ammonia was in short supply after the end of World War II; Columbia-Southern was expected to begin producing the chemical in late 1954. Around that same time, the company had a grant program, which gave money to many universities to test new agricultural chemicals on an array of crops under varied conditions. It has been claimed that Columbia-Southern lost over $ 845,000 due to unpaid invoices and seizure of property because of Fidel Castro 's government nationalization in Cuba. Chemical plant locations included Barberton , Ohio, Bartlett, California, Corpus Christi , Texas, Jersey City , New Jersey, Lake Charles , Louisiana, and New Martinsville , West Virginia in
1628-454: The occurrence of stochastic health effects is kept below unacceptable levels and that tissue reactions are avoided. It is difficult to compare the stochastic risk from localised exposures of different parts of the body (e.g. a chest x-ray compared to a CT scan of the head), or to compare exposures of the same body part but with different exposure patterns (e.g. a cardiac CT scan with a cardiac nuclear medicine scan). One way to avoid this problem
1672-423: The presence of ionising radiation . Energetic particles colliding with the polymer structure leave a trail of broken chemical bonds within the CR-39. When immersed in a concentrated alkali solution (typically sodium hydroxide ) hydroxide ions attack and break the polymer structure, etching away the bulk of the plastic at a nominally fixed rate. However, along the paths of damage left by charged particle interaction
1716-411: The radiation-sensitivity properties of CR-39 are also used for proton and neutron dosimetry and historically cosmic ray investigations. The ability of CR-39 to record the location of a radiation source, even at extremely low concentrations is exploited in autoradiography studies with alpha particles, and for (comparatively cheap) detection of alpha-emitters like uranium. Typically, a thin section of
1760-413: The required treatment absorbed dose and any collateral absorbed dose is monitored, and environmental, such as radon monitoring in buildings. There are several ways of measuring absorbed doses from ionizing radiation. People in occupational contact with radioactive substances, or who may be exposed to radiation, routinely carry personal dosimeters . These are specifically designed to record and indicate
1804-472: The same absorbed dose in Gy, alpha particles are 20 times as biologically potent as X or gamma rays. The measure of ‘dose equivalent’ is not organ averaged and now only used for "operational quantities". Equivalent dose is designed for estimation of stochastic risks from radiation exposures. Stochastic effect is defined for radiation dose assessment as the probability of cancer induction and genetic damage. As dose
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1848-407: The site of irradiation will only receive a small equivalent dose (mainly due to scattering) and therefore contribute little to the effective dose, even if the weighting factor for that organ is high. Effective dose is used to estimate stochastic risks for a ‘reference’ person, which is an average of the population. It is not suitable for estimating stochastic risk for individual medical exposures, and
1892-453: The surface or the bulk of the material. CR-39 is also resistant to most solvents and other chemicals, gamma radiation , aging, and to material fatigue . It can withstand the small hot sparks from welding , something glass cannot do. It can be used continuously in temperatures up to 100 °C and up to one hour at 130 °C. In the radiation detection application, CR-39 is used as a solid-state nuclear track detector (SSNTD) to detect
1936-510: Was a subsidiary of Pittsburgh Plate Glass Company . It produced heavy industrial chemicals for industry and agriculture, including: anhydrous ammonia , caustic soda , chlorine , titanium tetrachloride , and soda ash . During the Second World War , Columbia-Southern produced a line of 200 polymers . CR-39 (CR for "Columbia Resins" and 39 denoting it as the 39th polymer) had qualities suitable for plastic lenses, making it
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