RADIATION SAFETY

Introduction • Man and all other forms of life inhabiting on earth have evolved in an

environment enveloped in nuclear radiation. Thus mankind and radiation are old acquaintances and have learned to live together without danger to life or deleterious effects.

• Now a days all public attention and apprehension appear to be focused on nuclear power, which in the last four decades has only contributed a small increment of man-made radiation to natural radiation environment.

• Incidents and accidents which involve exposure to ionizing radiation have become matters of great public concern. It leads fears of cancer epidemics occurring among the general public as a result of exposures to even very low levels of radiation.

• The aim of this presentation is to remove such fear and provide certain basic idea about radiation and safety

• This report briefly describes the meaning of different terms such as ionizing radiation, radioactivity, half-life, radiation dose, different units of radiation dose, external and internal radiation exposure etc.

• This report high light the methods used to control external and internal exposures and also the biological effects of radiation

DISCOVERY OF NUCLEAR RADIATION

• Roentgen discovered X-rays in 1895 and Henri Becquerel discovered nuclear radiations in 1896.

• Henri Becquerel identified three types of radiations namely alpha (), beta () and gamma ()

• Alpha particles possess 2 units of positive charge and 4 units of mass. Alpha particles are nothing but helium nuclei, i.e. helium atoms minus their two orbiting electrons. For example U-238 (an isotope of uranium with atomic mass of 238) tend to disintegrate spontaneously by ejecting an alpha particle and transforms itself to Th-234, an isotope of thorium.

• Beta particles were identified as electrons and they carry 1 unit of negative charge. In beta decay, a neutron in the nucleus is converted to a proton and an electron and an anti-neutrino are ejected. Electrons emitted during beta-decay have a continuous distribution of energy ranging from zero to a maximum energy which is characteristic of a particular nucleus. The most probable electron energy is approximately one-third of the maximum energy. The neutrino is unimportant in radiation protection because of its extremely weak interaction with matter. For example tritium (3H) decays to helium (3He) by emitting an electron (e-) and an anti-neutrino (V-).

• Gamma radiations are electromagnetic radiations like sunlight or radio waves, but of much shorter wavelengths.

• Each gamma ray may be thought of as a packet of energy. These packets behave much as particles do and are given the special name photons.

• Gamma rays have no mass or charge. In many cases, after emission of an alpha particle or a beta particle, the nucleus is in excited state and it may re-arrange itself. In this process it may release energy in the form of a gamma-ray.

• X-rays are identical to gamma rays except for their origin. The former originate from outside the nucleus, the latter from within.

• The energy of radiation is expressed in a unit called electron volt (eV). 1ev=1.6 x 10-19 joules.

• Alpha and beta particles have energized of several million electron volts (MeV).

• Gamma ray energies range from several kilo electron volts (k eV) up to many MeV.

Radioactivity and Radiation

• Radioactivity and Radiation : An unstable nuclide transforms spontaneously into the nuclide of

another element, and in doing so, emits radiation. This property is called radioactivity, the transformation is termed decay, and the nuclide is said to be a radio-nuclide.

• for example, Carbon-14 is an unstable nuclide, which decays to nitrogen-14, a stable nuclide.

• Activity and half-life: The quantity of radio-nuclide is described by its activity which is the rate

at which spontaneous decay occurs in it. The activity is expressed in a unit called Becquerel (Bq) named after the scientist who discovered nuclear radiation.

• The time taken for the activity of a radionuclide to loose half its value by decay is called the half-life.

• For example the half-life of carbon-14 is 5730 years and for Pu-239 is 24,131 years

Ionizing and non-ionizing radiation

Ionizing radiation : when radiation interacts with matter produces a positive and

negative ion and hence the name ionizing radiation. * Radiations such as alpha, beta, gamma and x-ray come

under ionizing type of radiationNon-ionizing radiation: When radiation interacts with matter do not have such

ability to produce ions and hence the name non-ionizing radiation.

* Heat, light and UV radiation come under non-ionizing type of radiation.

RADIATION UNIT

• The charges created by ionization can serve as good index of the radiation exposure received by the object, the energy expended in producing those charges is used as a measure of radiation dose or exposure.

• Exposure is a quantity expressing the amount of ionization caused in air by X or gamma radiation.

• The standard unit of radiation-absorbed dose is Gray (usually abbreviated as Gy) that corresponds to an average energy deposition of one Joule per kilogram of the object.

• 1Gy=1000 mGy• 1Gy=100rad (radiation absorbed dose) • Sievert is a new unit.• 1 Sv = 100 rem (roentgen equivalent man)

Irradiation, External Radiation, Contamination

• Irradiation: Irradiation is a general term used to describe

exposure to radiation originating from any source.• External Radiation: External radiation indicates the exposure is due to

X or gamma radiation originating from an external source. The implication here is that there is no direct contact between the radiation source and the recipient of the exposure.

• Contamination: Contamination results when radioactive material is

deposited externally on the skin or internally.

Control of internal radiation exposure• Internal exposure is due to presence of radioactive material present in the body.

Internal radiation exposure occur through (1) inhalation through air (2) ingestion through food and water and (3) absorption through wound.

• To prevent the internal radiation exposure, air borne radioactivity is continually measured to know the levels of air activity in the laboratory.

• To prevent the radioactivity entering the body through food due to the contamination of hands the workers monitor their hands for any contamination in the hand monitor.

• To avoid any direct entry of radioactive material through wound the workers are not allowed to carryout the radioactive work if they have any open wound.

• Generally workers will be wearing gloves and laboratory coat to prevent the contamination of hands and personal clothing.

Control of external radiation exposure

• External radiation exposure can be controlled by three ways (1) Reducing the time of work (2) Increasing the distance between the radioactive source and the

person and (3) Providing a shielding material between the radioactive source

and the person. • Alpha radiation even a thin sheet of paper will stop alpha radiation

as these are comparatively heavy particle. • Beta radiation can be stopped by Perspex or by using low atomic

number material like aluminum. • Gamma radiation is highly penetrating and hence it requires high

atomic number material such as lead for shielding to reduce the radiation level.

chromosomal aberration technique

• chromosomal aberration technique:• This technique can be used when the exposure is of

the order of 100 mSv and above. • To carryout this assay about 0.5 ml blood sample is

collected from the exposed individual and the sample is cultured to get metaphase chromosomes.

• These metaphase chromosomes are screened under microscope for scoring di-centric chromosomes.

• From the frequency of di-centric chromosomes the radiation dose is estimated.

Permissible Radiation Dose

• The maximum permissible whole body effective dose limit is 100 mrem (1 mSv) in a year.

• The average dose over a defined period of 5 years does not exceed 100 mrem (1 mSv) per year.

• For Occupational exposure, the maximum permissible level of exposures is 2 rem (20 mSv) for whole body in a year, averaged over 5 years ( 100 mSv in 5 years), with the provision that the effective dose should not exceed 30 m Sv (AERB recommendation) in any single year.

• For lens of eye 15 rem (150 mSv) in a year• For skin 50 rem (500 mSv) in a year

Effects of radiation• Effects of doses received by homogeneous irradiation of the

whole body • From 0 to 250 m Gy: no biological or medical effect, immediate

or long-term, has been observed in children or adults. This is the domain of low doses.

• From 250 to 1000 m Gy: some nausea may appear along with a slight decrease in the number of white blood cells.

• From 1000 to 2500 mGy: vomiting, change in the blood count, but satisfactory recovery or complete cure assured.

• From 2500 to 5000 mGy: consequences on health become serious; hospitalization is mandatory; a dose of 5,000 mSv received all at once is lethal for one out of two people.

• More than 5000 mGy: death is almost certain.

Conclusion • Conclusion:• Good and bad are seen in all forms of radiation. For example we

have been exposed to radiation from the sun. We are looking upon sunlight as some thing good and useful. We cannot live without sun. Yet sunlight has it dangers too. We take precautions against sunburn and sunstroke. Similarly we have been living with nuclear radiation for long time. These radiations can be measured easily to levels far below those of interest to health. Radiation dose to the public from Nuclear power plants is trivial. Risks from radiations are well understood compared with many other hazards. Thus it may be concluded that we respect radiation and do not have fear of radiation.