Question

11. (a) If you are consuming a meat that is contaminated with 2 radioisotopes, 210 Po and 210 Pb
in same amount, which one would pose greater risk to your health and why? (b) One of the major consequences of Chernobyl nuclear accident was reported to be the higher frequency of thyroid cancer in neighbouring population. Explain how and why this might have occurred. (c) Explain why the bone marrows or reproductive tissues are more sensitive to ionizing radiation than muscles or nerves. (d) Typically, to indicate the safe doses of ionizing radiation exposure, the unit Sv (sievert) is used instead of Bq (becquerel). Explain why.

Answer 1

(a) The alpha-radioactive polonium 210 (Po-210) is one of the most powerful. Polonium-210 (210Po, Po-210, historically radium F) is an isotope of polonium. It undergoes alpha decay to stable 206Pb. It is also extremely toxic to humans as a result of its intense radioactivity. So Po is more harmful than Pb

(b) Radiation is a well-known risk factor for thyroid cancer especially for papillary carcinoma. Radiation-induced carcinogenesis especially affects vulnerable organs such as the thyroid gland. Long half-lives of some radioactive isotopes still continue their harmful effects on sensitive organs. High levels of radioactive iodine were released in the environment from the Chernobyl reactor after the accident, and accumulated in pastures which were eaten by cows. The milk was later consumed by children who already had an iodine deficient diet, therefore causing more of the radioactive iodine to be accumulated. Radioactive iodine has a short half-life, 8.02 days, if the contaminated milk would have been avoided or stopped, it is likely that most of the rise in radiation-induced thyroid cancer wouldn’t have happened.

(c) Living cells can be classified according to their rate of reproduction, which also indicates
their relative sensitivity to radiation. This means that different cell systems have different sensitivities.
Lymphocytes (white blood cells) and cells that produce blood are constantly regenerating, and are,
therefore, the most sensitive. Reproductive and gastrointestinal cells are not regenerating as quickly and
are less sensitive. The nerve and muscle cells are the slowest to regenerate and are the least sensitive
cells. The sensitivity of the various organs of the human body correlates with the relative sensitivity of the cells
from which they are composed. For example, since the blood-forming cells were one of the most
sensitive cells due to their rapid regeneration rate, the blood-forming organs are one of the most sensitive
organs to radiation. Muscle and nerve cells were relatively insensitive to radiation, and therefore, so are
the muscles and the brain.

(d)Units for dose equivalent are the roentgen equivalent man (rem) and sievert (Sv). The becquerel is the SI derived unit of radioactivity It should be remembered that Sv is not a physical dose unit that can be measured with dosimeters. The radiation dose is measured in Gray – and if a reliable RBE-value exists the equivalent dose in Sv
can be observed. If the radiation in question consists of x-rays, g-rays, b-particles or a mixture of them (this is the
case in most situations with radioactive isotopes) the RBE-value would be close to 1.0 Different organs and types of tissue have different sensitivities with regard to what is termed the late effects of radiation. Late effects are biological
responses that are only observed after a substantial amount of time has passed, often years. Induction of cancer is a late effect. In order to compare the risk for late effects of different types of radiation, the so-called effective dose is used. If one part of the body (e.g.,the lungs) receives a radiation dose, it represents a risk for a particularly damaging effect (e.g., lung cancer). If the same dose is given to another organ it represents a different risk factor. So to indicate the safe doses of ionizing radiation exposure, the unit Sv (sievert) is used instead of Bq (becquerel).

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