Question

Explain why most persons receive a dose ofionising radiation every day (i) 12 marks] 2 marks] 12 marks] 2 iarks (ii) it is important to distinguish between dose and dose rate diy sonme ypes or onising radiation ae mitn 2 mnriea Some organs within the body are more susceptible to radiation damage than others. (iv)

Answer 1

Answer (i) Radiation sources

People are exposed to natural radiation sources as well as human-made sources on a daily basis. Natural radiation comes from many sources including more than 60 naturally-occurring radioactive materials found in soil, water and air. Radon, a naturally-occurring gas, emanates from rock and soil and is the main source of natural radiation. Every day, people inhale and ingest radionuclides from air, food and water.

People are also exposed to natural radiation from cosmic rays, particularly at high altitude. On average, 80% of the annual dose of background radiation that a person receives is due to naturally occurring terrestrial and cosmic radiation sources. Background radiation levels vary geographically due to geological differences. Exposure in certain areas can be more than 200 times higher than the global average.

Human exposure to radiation also comes from human-made sources ranging from nuclear power generation to medical uses of radiation for diagnosis or treatment. Today, the most common human-made sources of ionizing radiation are medical devices, including X-ray machines.

Answer (iii) If the radiation dose is low and/or it is delivered over a long period of time (low dose rate), the risk is substantially lower because there is a greater likelihood of repairing the damage. There is still a risk of long-term effects such as cancer, however, that may appear years or even decades later. Effects of this type will not always occur, but their likelihood is proportional to the radiation dose. This risk is higher for children and adolescents, as they are significantly more sensitive to radiation exposure than adults.

Epidemiological studies on populations exposed to radiation, such as atomic bomb survivors or radiotherapy patients, showed a significant increase in cancer risk at doses above 100 mSv. More recently, some epidemiological studies in individuals exposed to medical exposures during childhood (paediatric CT) suggested that cancer risk may increase even at lower doses (between 50-100 mSv).

Prenatal exposure to ionizing radiation may induce brain damage in foetuses following an acute dose exceeding 100 mSv between weeks 8-15 of pregnancy and 200 mSv between weeks 16-25 of pregnancy. Before week 8 or after week 25 of pregnancy human studies have not shown radiation risk to fetal brain development. Epidemiological studies indicate that the cancer risk after fetal exposure to radiation is similar to the risk after exposure in early childhood.

Answer (iv) Deterministic effects are dose-related, acute health effects caused by exposure to high levels of radiation that cause large numbers of cells to die or lose their ability to replicate. Organs containing these cells then fail to function correctly. Such effects include nausea (radiation syndrome), reddening of the skin, cataracts, sterility and bone marrow failure. Each effect becomes apparent only above a threshold level and the severity of the effect depends on the level of exposure above its threshold. Below the threshold, the body can cope with the level of cell death by repair and replacement, when no explicit damage is seen.

Extreme doses of radiation to the whole body (around 10 sieverts and above), received in a short period, cause so much damage to internal organs and tissues of the body that vital systems cease to function and death may result within days or weeks. Very high doses (between about 1 sievert and 10 sieverts), received in a short period, kill large numbers of cells, which can impair the function of vital organs and systems. Acute health effects, such as nausea, vomiting, skin and deep tissue burns, and impairment of the body’s ability to fight infection may result within hours, days or weeks.

Answer (ii)
A dose of medical radiation is not like a dose of medicine. When it comes to radiation dose, there are different types of and units of measurement. Radiation dose is a complicated topic.

Radiation dose is not like medicine. A dose of radiation is not the same as a dose of medication.

Radiation dose has many forms and includes absorbed dose, equivalent dose and effective dose.

There are several quantities in which dose is measured (e.g., mGy, mSv). There are other dose quantities that have not been discussed