What is Radioactivity?

Md. Saifur Rahman

What is Radioactivity?

Radioactivity is the process of spontaneous disintegration of certain (unstable) atomic nuclei accompanied by the emission. Radiation is emitted by the unstable and exciting nuclei that can normally cause ionization in a matter through which they pass. These radiations can cause extensive. damage to the molecular structure of a substance either as a result of the direct transfer of energy to its atoms or molecules or as a result of the secondary electrons released by ionization. In biological tissue, the effect of ionizing radiation can be very serious. The ionizing radiation can cause harmful somatic and genetic effects on the human body.

Sources of Radiation

We like in an environment of low-level ionizing radiation. Ionizing radiation has been present on the earth since its creation and human beings are continuously being exposed to such radiation. The natural background radiation comes mainly from three sources viz -

♦ Cosmic radiation - here in the reaction 14N(n,p), 14C,14C is a β emitter having a half-life of ~ 5568 years.

♦ Radiation from naturally occurring radionuclides in the ground and building materials - Uranium, Thorium, Actinium, and Neptunium with their decay products, etc.

♦ Radioactivity in the body - 40k 14c and gaseous decay products of uranium and thorium i.e. radon and thoron.

After the discovery and use of artificial radiation, men are being exposed to both natural and artificial radiation. The amount of annual absorbed dose per capita is increasing day by day. It is for the contamination of the atmosphere, water (sea and river), and soil due to the nuclear fallout,

weapon test, and reactor accidents of developed countries. The use of nuclear energy and the application of its by-products i.e., ionizing radiation and radioactive substances, continue to increase around the world. A significant amount of radiation dose is received by the population from the

use of radioisotopes in industry, agriculture, and medicine, use of irradiator for food preservation, radiotherapy machines, and handling of radioisotopes in laboratories. The use of X-rays is another cause of the small amount of radiation.

Advantage

The uncontrolled application and misuse of ionizing radiation and radioactive materials are detrimental to the health and safety of the medical scientist's technician’s assistants, patients, and the public as well. Though radiation poses threats to our lives, it is on the other hand has been used to bring enormous benefits to our lives as well. Radioactivity and ionizing radiation find extensive use in industry to trace the flow of materials, in agriculture for genetic mutation and processing seeds. In food processing

for killing rotting bacteria’s in sterilizing medical equipment and in medicine for both diagnostic and therapeutic purposes. A more subtle advantage of radioisotopes is that they can be used on localized areas of organs by appropriate radiopharmaceuticals.

The Related Quantities

♦ Exposure Exposure is quantity expresses in the amount of ionizing caused in an X-radiation.

Exposures are commonly expressed in two ways.

♦ Acute Exposure

It is the exposure to a large dose of radiation within a relative's short time.

The radiation damages are much more severe in cases of acute exposure.

♦ Chronic Exposure

Chronic exposure is long-term, low-level overexposure. The total amount of radiation received may be the same as received in the acute exposure but the radiation damages are of much two severity.

Effects of Ionizing Radiation on Human Body

The effect of ionizing radiation on the human body is the result of damage to the individual cells. These effects may be conveniently divided into two classes namely somatic and genetic. These effects may arise from acute or chronic exposure. However, the effects of radiation on the biological matter depends on -

♦ the energy and the type of radiation

♦ the dose rate

♦ the volume irradiated, and

♦ the sensitivity of the tissue.

Somatic Effects

The somatic effects are from damage to the ordinary cells of the body and affect only the radio-exposed individual. The somatic effects depend on whether the irradiation is acute or chronic. These effects also depend on -

♦ the degree of oxidation and hence the temperature of the exposed part of the body

♦ the metabolic state and hence the diet

♦ the irradiated person’s sex; and

♦ the body color.

The somatic effects are-

♦ inhibition of mitosis

♦ chromosome aberration and breakage and

♦ death of a cell.

Genetic Effects

The genetic effects are due to the damage or mutation or alteration in the chromosome structure of sperm or ovum i.e. germ cells may be passed through generation to generation. Ionizing radiation acts directly on genetic materials. The effect is proportional to the dose and the dose rate.

Thus there is no threshold and a radio-exposed individual has a definite probability of producing a mutagenic effect. However, the natural background radiation is responsible for from 4 to 10% of all naturally occurring genetic mutations.

Biological Effects of Ionizing Radiation

In 1904, Madam Curie reported in her Ph. D thesis that a radium source she had placed on her husband’s arm for a few hours had produced a painful some that extended well below the skin and were slow to heal. The biological effects of ionizing radiation are of two general types somatic.

Somatic effects affect an individual directly (loss of hair, reddening of the skin, etc.). Genetic effects consist of mutations in the reproductive cells that affect later generations.

In order to evaluate the genetic effects of X-rays on the population, the concept of genetically significant dose (GSD) is useful. The GSD due to exposure depends on the dose to the individual’s ovaries or tests and the individual’s age. Somatic effects depend on the amount of radiation the part of the body irradiated and the age of the patient.

In general, the younger person, the more hazardous the radiation. In fact, the most dangerous period to receive radiation is before birth. At certain periods in the development of the fetus, radiation can produce deformities.

Immediate, Early or Short Term Effects

These effects are due to an acute radio - exposure and manifest within a few weeks of exposure. These are somatic effects and inevitable. The immediate effects manifest as Chromosome aberration, blood changes nausea, vomiting, and diarrhea loss of appetite, fatigue appellation, skin epilation, sterility, etc., and death.

Delayed Effects

These effects are due to acute or chronic radio exposure and generally manifest after a few years of exposure. These effects are various types of cancer, leukemia, contract, hereditary effects, etc.

Depending on the threshold dose and the probability of effects upon dose, the effects of radiation on the human body are classified into two types: stochastic effects and non-stochastic effects.

Stochastic effects: For the manifestation of certain biological effects no threshold dose can be defined.

These effects may occur at any dose, the probability for manifestation increases with absorbed dose.

Non-stochastic effects. The effects of ionizing radiation on the human body for which a threshold dose of occurrence can be defined are called nonstochastic effects.

Health Effects of Low-Level Radiation Exposure

Since there is no threshold dose for the induction of various types of cancer, leukemia, life-shortening, and hereditary effects, there exists a certain probability for the occurrence of the mentioned effects by low-level radiation exposure. The science of protecting workers and the public from unnecessary radiation is known as radiation protection. It involves the accurate measurement of radiation workers and the public and the design and use of methods to reduce this radiation. The radiation exposure to every individual should be kept as low as reasonably achievable; this can be achieved by -

♦ Keeping a maximum distance possible from the source

♦ Working with a source for the minimum time required

♦ Employing adequate shielding

♦ Shifting duties.

The patient's movement should be restricted in one place. Using syringe shields during dispensing and administration of radioactive injections can minimize exposures very efficiently.

The basic solution to the radiation protection problem in the medical field can be stated in one word - education. The medical user is often unconcerned by the hazards. X-rays are so common to them that they have a tendency not to worry about them just as we do not worry about having an automobile accident every time we get into a car.

There is probably no absolutely safe amount of radiation. The problem is to balance the benefits against the risks. When we go for a ride in a car or a place we realize in exchange for the benefits of the trip. Similarly, we should balance the ability of an X-ray to detect a medical problem against the slight risk from the radiation in research laboratories and the nuclear power station, so that the workers there receive no, in more than the permitted maximum level of radiation. Radioisotopes are handled by mechanical tongs operated by remote control equipment from behind thick walls made by lead, concrete, or other suitable material, which absorbs dangerous reactions.

The Dose Units Used in Radiotherapy

The amount of radiation dissipated in absorbed by a specific mass of a volume of material is referred to as a dose of radiation. In the very early days of radiation therapy, the unit used to measure the amount of radiation to the patient was the erythema dose the number of X-rays that caused reddening of the skin. From 1950 to 1975 "rad" was the official unit of absorbed dose. The "rad" is defined as 100 ergs/gm. That is a radiation bean that gives 100 ergs of energy to 1gm of tissue. It gives the tissue an absorbed dose of 1 rad. In 1975 the International Commission of Radiological units (ICRU) adopted the “gray” (GY) as the international (SI) unit of dose. 1GY = 1J/kg =100 rads. This unit was named after Harold Gray, the British medical physicist who discovered the oxygen effect.

Dose rate

The amount of radiation absorbed by a body per unit time is called the dose rate. The common unit of dose rate is GY/hour.

What is Radioactivity?