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46-485: 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 a variety of monitoring, bio-assay or radiation imaging techniques, whilst external dosimetry

92-448: 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

138-401: 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

184-576: A fuller description of each. In the United Kingdom the HSE has issued a user guidance note on selecting the correct radiation measurement instrument for the application concerned [2] Archived 2020-03-15 at the Wayback Machine . This covers all ionising radiation instrument technologies, and is a useful comparative guide. Dosimeters are devices worn by the user which measure the radiation dose that

230-484: A good practice guide through its Ionising Radiation Metrology Forum concerning the provision of such equipment and the methodology of calculating the alarm levels to be used. Portable instruments are hand-held or transportable. The hand-held instrument is generally used as a survey meter to check an object or person in detail, or assess an area where no installed instrumentation exists. They can also be used for personnel exit monitoring or personnel contamination checks in

276-540: 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 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

322-630: 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

368-530: 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

414-526: 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 is unexpected, such as in the contained aftermath of the Three Mile Island , Chernobyl or Fukushima radiological release incidents. The public dose take-up

460-423: 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 is to simply average out a localised dose over the whole body. The problem of this approach

506-411: 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,

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552-402: 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 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

598-681: 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 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

644-434: 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 is averaged over the whole organ; equivalent dose is rarely suitable for evaluation of acute radiation effects or tumour dose in radiotherapy. In

690-555: 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, 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

736-465: 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 the same absorbed dose in Gy, alpha particles are 20 times as biologically potent as X or gamma rays. The measure of ‘dose equivalent’

782-512: 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 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

828-424: 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

874-562: Is usually calculated and calibrated as dose to water. National standards laboratories such as 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

920-587: The British Institute of Radiology ) established a committee on X-ray injuries, thus initiating the discipline of radiation protection. According to Paul Frame: "The term Health Physics is believed to have originated in the Metallurgical Laboratory at the University of Chicago in 1942, but the exact origin is unknown. The term was possibly coined by Robert Stone or Arthur Compton , since Stone

966-515: 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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1012-496: The absorbed dose deposited by a radiation beam into a medium as it varies with depth along the axis of the beam. The dose values are divided by the maximum dose, referred to as d max , yielding a plot in terms of percentage of the maximum dose. Dose measurements are generally made in water or "water equivalent" plastic with an ionization chamber , since water is very similar to human tissue with regard to radiation scattering and absorption. Percent depth dose (PDD), which reflects

1058-405: The equivalent dose was defined to give an approximate measure of the biological effect of radiation. It is calculated by multiplying the absorbed dose by a weighting factor W R , which is different for each type of radiation (see table at Relative biological effectiveness#Standardization ). This weighting factor is also called the Q (quality factor), or RBE ( relative biological effectiveness of

1104-483: 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 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

1150-649: The Plutonium Project to define that field in which physical methods are used to determine the existence of hazards to the health of personnel.' A variation was given by Raymond Finkle, a Health Division employee during this time frame. 'The coinage at first merely denoted the physics section of the Health Division... the name also served security: ' radiation protection ' might arouse unwelcome interest; 'health physics' conveyed nothing.'" The following table shows radiation quantities in SI and non-SI units. Although

1196-613: The UK it is the Ionising Radiation Regulations 1999. The measuring instruments for radiation protection are both "installed" (in a fixed position) and portable (hand-held or transportable). Installed instruments are fixed in positions which are known to be important in assessing the general radiation hazard in an area. Examples are installed "area" radiation monitors, Gamma interlock monitors, personnel exit monitors, and airborne contamination monitors. The area monitor will measure

1242-572: The United States Nuclear Regulatory Commission permits the use of the units curie , rad, and rem alongside SI units, the European Union European units of measurement directives required that their use for "public health ... purposes" be phased out by 31 December 1985. Percentage depth dose curve In radiotherapy , a percentage depth dose curve (PDD) (sometimes percent depth dose curve) relates

1288-502: The United States Nuclear Regulatory Commission permits the use of the units curie , rad, and rem alongside SI units, the European Union European units of measurement directives required that their use for "public health ... purposes" be phased out by 31 December 1985. Health physics There are many sub-specialties in the field of health physics, including The subfield of operational health physics, also called applied health physics in older sources, focuses on field work and

1334-443: The ambient radiation, usually X-Ray, Gamma or neutrons; these are radiations which can have significant radiation levels over a range in excess of tens of metres from their source, and thereby cover a wide area. Interlock monitors are used in applications to prevent inadvertent exposure of workers to an excess dose by preventing personnel access to an area when a high radiation level is present. Airborne contamination monitors measure

1380-415: 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 a certain biological effect varies between different types of radiation, such as photons , neutrons or alpha particles . This

1426-476: 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

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1472-399: 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

1518-415: 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 the occurrence of stochastic health effects is kept below unacceptable levels and that tissue reactions are avoided. It

1564-616: The concentration of radioactive particles in the atmosphere to guard against radioactive particles being deposited in the lungs of personnel. Personnel exit monitors are used to monitor workers who are exiting a "contamination controlled" or potentially contaminated area. These can be in the form of hand monitors, clothing frisk probes, or whole body monitors. These monitor the surface of the workers body and clothing to check if any radioactive contamination has been deposited. These generally measure alpha or beta or gamma, or combinations of these. The UK National Physical Laboratory has published

1610-410: 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

1656-458: 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

1702-530: The field. These generally measure alpha, beta or gamma, or combinations of these. Transportable instruments are generally instruments that would have been permanently installed, but are temporarily placed in an area to provide continuous monitoring where it is likely there will be a hazard. Such instruments are often installed on trolleys to allow easy deployment, and are associated with temporary operational situations. A number of commonly used detection instruments are listed below. The links should be followed for

1748-419: 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

1794-443: 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

1840-426: The laboratory, where it 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

1886-507: The practical application of health physics knowledge to real-world situations, rather than basic research. The field of Health Physics is related to the field of medical physics and they are similar to each other in that practitioners rely on much of the same fundamental science (i.e., radiation physics, biology, etc.) in both fields. Health physicists, however, focus on the evaluation and protection of human health from radiation, whereas medical health physicists and medical physicists support

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1932-563: The radiation). For comparison, the average 'background' dose of natural radiation received by a person per day, based on 2000 UNSCEAR estimate, makes BRET 6.6 μSv (660 μrem). However local exposures vary, with the yearly average in the US being around 3.6 mSv (360 mrem), and in a small area in India as high as 30 mSv (3 rem). The lethal full-body dose of radiation for a human is around 4–5 Sv (400–500 rem). In 1898, The Röntgen Society (Currently

1978-476: 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 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

2024-408: The use of radiation and other physics-based technologies by medical practitioners for the diagnosis and treatment of disease. Practical ionising radiation measurement is essential for health physics. It enables the evaluation of protection measures, and the assessment of the radiation dose likely, or actually received by individuals. The provision of such instruments is normally controlled by law. In

2070-578: The user is receiving. Common types of wearable dosimeters for ionizing radiation include: The fundamental units do not take into account the amount of damage done to matter (especially living tissue) by ionizing radiation. This is more closely related to the amount of energy deposited rather than the charge. This is called the absorbed dose . Equal doses of different types or energies of radiation cause different amounts of damage to living tissue. For example, 1 Gy of alpha radiation causes about 20 times as much damage as 1 Gy of X-rays . Therefore,

2116-539: Was the head of the Health Division and Arthur Compton was the head of the Metallurgical Laboratory. The first task of the Health Physics Section was to design shielding for reactor CP-1 that Enrico Fermi was constructing, so the original HPs were mostly physicists trying to solve health-related problems. The explanation given by Robert Stone was that '...the term Health Physics has been used on

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