RMS - General definitions concerning health physics and radiation protection T-Z

General Definitions used in Health Physics & Radiation Protection

Radioactive Materials Branch

Tenth-value Layer (TVL)
The thickness of any given absorber that will reduce the intensity of a beam of radiation to one tenth of its initial value.

Thermoluminescent Dosimeter (TLD)
A device used to measure radiation by measuring the amount of visible light emitted from a crystal in the detector when exposed to radiation.

These Rules
Chapter 11 of the North Carolina Regulations for Protection Against Radiation.

Tight-fitting facepiece
A respiratory inlet covering that forms a complete seal with the face.

Toxic or hazardous constituent of the waste
The non-radioactive content of waste which, notwithstanding the radioactive content, would be classified as "hazardous waste" as defined in 15A NCAC 13A .0102(a).

Tritium (³H)
A radioactive isotope of hydrogen (one proton, two neutrons). Because it is chemically identical to natural hydrogen, tritium can easily be taken into the body by any ingestion path. It decays by beta emission. It has a radioactive half-life of about 12.5 years

Tritium neutron generator target source
A tritium source used within a neutron generator tube to produce neutrons for use in well logging applications.

Type A quantity
A quantity of radioactive material, the aggregate radioactivity of which does not exceed A₁ for special form radioactive material or A₂ for normal form radioactive material, where A₁ and A₂ are given in Rule .0113 of the North Carolina Regulations for Protection Against Radiation or may be determined by procedures described in Rule .0113 of the North Carolina Regulations for Protection Against Radiation. All quantities of radioactive material greater than a Type A quantity are Type B.

Type B quantity
A quantity of radioactive material that exceeds Type A quantities

Unrefined and unprocessed ore
Ore in its natural form prior to any processing, such as grinding, roasting, beneficiating, or refining.

Unrestricted area
An area, access to which is neither limited nor controlled by the licensee or registrant.

Uranium
The last of the naturally occurring elements in the periodic table, Uranium is radioactive. There are 14 known isotopes, with U-238 being the most abundant (99%).

User seal check (Fit check)
An action conducted by the respirator user to determine if the respirator is properly seated to the face. Examples include negative pressure check, positive pressure check, irritant smoke check, or isoamyl acetate check

Very high radiation area
An area, accessible to individuals, in which radiation levels could result in an individual receiving an absorbed dose in excess of 500 rads (5 grays) in one hour at one meter from a radiation source or from any surface that the radiation penetrates. At very high doses received at high dose rates, units of absorbed dose (e.g., rads and grays) are appropriate, rather than units of dose equivalent (e.g., rems and sieverts).

Waste
Means low-level radioactive waste as defined in G.S. 104E-5(9a) and includes licensed naturally occurring and accelerator produced radioactive material which is not subject to regulation by the U.S. Nuclear Regulatory Commission under the Atomic Energy Act of 1954, as amended, except as defined differently in Rule .1202 of this Chapter.

Waste, Class A
Is defined in Rule .1650 of the North Carolina Regulations for Protection Against Radiation.

Waste, Class B
Is defined in Rule .1650 of the North Carolina Regulations for Protection Against Radiation.

Waste, Class C
Is defined in Rule .1650 of the North Carolina Regulations for Protection Against Radiation.

Weighting factor ( w_T) for an organ or tissue (T)
The proportion of the risk of stochastic effects resulting from irradiation of that organ or tissue to the total risk of stochastic effects when the whole body is irradiated uniformly. For calculating the effective dose equivalent, the values of w_T are:

ORGAN DOSE WEIGHTING FACTORS
Organ or Tissue		w_T
Gonads		0.25
Breast		0.15
Red Bone Marrow		0.12
Lung		0.12
Thyroid		0.03
Bone Surfaces		0.03
Remainder		0.30^a
Whole Body		1.00^b
^a0.30 results from 0.06 for each of the 5 "remainder" organs (excluding the skin and the lens of the eye) that receive the highest doses
^b For the purpose of weighting the external whole body dose (for adding it to the internal dose), a single weighting factor, w_T = 1.0, has been specified. The use of other weighting factors for external exposure will be approved on a case-by-case basis until such time as specific guidance is issued.

Well Logging
The lowering and raising of measuring devices or tools which may contain sources of radiation into well-bores or cavities for the purpose of obtaining information about the well or adjacent formations.

Whole body
For purposes of external exposure, whole body means the head, trunk (including male gonads), arms above the elbow, or legs above the knee

Wireline
A cable containing one or more electrical conductors which is used to lower and raise logging tools in the well-bore

Wireline-service Operations
Any evaluation or mechanical service which is performed in the well-bore using devices on a wireline.

Worker
An individual engaged in work under a license or registration issued by the agency and controlled by a licensee or registrant, but does not include the licensee or registrant.

Working level (WL)
Any combination of short-lived radon daughters (for radon-222: polonium-218, lead-214, bismuth-214, and polonium-214; and for radon-220: polonium-216, lead-212, bismuth-212, and polonium-212) in one liter of air that will result in the ultimate emission of 1.3 x 10⁵ MeV of potential alpha particle energy.

Written directive
An order in writing for a specific patient, dated and signed by an authorized user prior to the administration of a radiopharmaceutical or radiation from a licensed source, except as specified in Sub-item (e) of this definition, containing the following information:

X-ray
Penetrating electromagnetic radiation (photon) having a wavelength that is much shorter than that of visible light. These rays are usually produced by excitation of the electron field around certain nuclei. In nuclear reactions, it is customary to refer to photons originating in the nucleus as gamma rays, and to those originating in the electron field of the atom as X-rays. These rays are sometimes called roentgen rays after their discoverer, W.K. Roentgen.

X-ray diffraction
The primary beam from the target of the x-ray tube passes through a collimator and strikes the sample, which diffracts it in a characteristic manner. This diffraction pattern in measured with a photographic film or a radiation counter. Primarily used in analytical work.

X-Ray fluorescence
When a sample is irradiated by X-rays at or above the K-shell binding energy, photoelectric absorption will induce characteristic X-ray emissions from the sample.

Year
The period of time beginning in January used to determine compliance with the provisions of Section .1600 of the North Carolina Regulations for Protection Against Radiation. The licensee or registrant may change the starting date of the year used to determine compliance by the licensee or registrant provided that the change is made at the beginning of the year and that no day is omitted or duplicated in consecutive years.

Zinc Sulfide Scintillator
One of the older inorganic scintillators, its main use is in the detection of alpha particle and heavy ion detection. This type of instrument played a key role in Rutherford's experiments, in which alpha particle interactions on a scintillation screen were visually observed through a low power microscope.

a) for the diagnostic administration of a radiopharmaceutical:
	(i) if greater than 30 microcuries of sodium iodide I-125 or I-131, the dosage to be administered in accordance with the diagnostic clinical procedures manual; or
	(ii) if not subject to Sub-item (a)(i) of this Item, the type of study to be performed in accordance with the diagnostic clinical procedures manual;
b) for the therapeutic administration of a radiopharmaceutical:
	(i) radiopharmaceutical;
	(ii) dosage; and
	(iii) route of administration;
c) for teletherapy or accelerator radiation therapy:
	(i) total dose;
	(ii) dose per fraction;
	(iii) treatment site; and
	(iv) overall treatment period;
d) for high-dose-rate remote afterloading brachytherapy:
	(i) radioisotope;
	(ii) treatment site; and
	(iii) total dose;
e) for all other brachytherapy:
	(i) prior to implantation:
		(A) radioisotope;
		(B) number of sources to be implanted; and
		(C) source strengths in millicuries; and
	(ii) after implantation but prior to completion of the procedure:
		(A) radioisotope;
		(B) treatment site; and
		(C) either:
			(I) total source strength and exposure time; or
			(II) total dose;
f) for gamma stereotactic radiosurgery:
	(i) target coordinates;
	(ii) collimator size;
	(iii) plug pattern; and
	(iv) total dose.