What Does Radiation Do to Living Cells?
Human radiation effects refer to various effects produced by people after they are exposed to ionizing radiation. Objects appearing according to effects can be divided into somatic effects and genetic effects; according to the occurrence of effects, they can be divided into non-stochastic effects and stochastic effects The time of the effect can be divided into short-term effect and long-term effect.
- Random effects If the irradiated cells are not killed but are still alive but changed, the effect will be very different from the deterministic effect. There are two types of effects with random effects. One is caused by damage to somatic cells. If the clone of a damaged somatic cell undergoes proliferation, if it is not eliminated by the body's defense mechanism, after a considerable incubation period, it may develop into a malignant state of uncontrolled cell proliferation, known as cancer. Radiation carcinogenesis is the most important late effect caused by radiation. Different tissues and organs have different sensitivities to radiation carcinogenesis. Radiation sensitivity is also related to factors such as age and gender. The other is caused by the gonads being damaged by irradiation. Germ cells have the ability to pass genetic information to offspring. When the damage (mutation and chromosomal aberration) occurs, it may be passed as incorrect genetic information, and the offspring of the exposed person will have various types of genetic diseases of varying severity, such as premature death and severe mental retardation , Light as skin spots.
Characteristics of random effects of human radiation effects
- The random effect is characterized in that its probability of occurrence increases with increasing dose, but its severity is independent of the size of the dose. Figure (a) illustrates this characteristic of the randomness effect. Taking cancer as an example, the severity of the induced cancer is not caused by the small and large doses, and its severity is only affected by the type and location of the cancer. The occurrence of cancer and genetic effects may originate from a single cell that is damaged. The process is random in nature, and the name of random effects is derived from this. Random effects may not have a threshold dose, but so far no scientific conclusions can be made. For the purpose of radiation protection, it is generally assumed that there is no threshold dose, which means that no matter how small the dose is, a certain dose is always associated with a certain risk of random effects. In this way, it is impossible to completely prevent the random effect from happening, but to reduce the dose to limit the probability of its occurrence. It is also assumed in radiation protection that there is a linear relationship between the dose and the incidence of random effects in the entire range of dose equivalents and dose equivalent rates involved in daily radiation protection. In order to quantitatively represent the danger of random effects, the concept of probability coefficient is adopted, which refers to the probability of random effects induced by unit dose equivalent irradiation. The random effect probability coefficient is composed of three kinds of effects: lethal cancer, non-lethal cancer and severe genetic effect. The specific values are shown in Table 3.
- Table 3 Nominal value of probability coefficient of randomness effect
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- The probability coefficient of lethal cancer is mainly based on the results of a systematic and long-term epidemiological survey of more than 100,000 survivors after the atomic bombing of Hiroshima and Nagasaki in 1945. Surveys have shown that the incidence of certain cancers in survivors is indeed higher than in the control group, and the probability of radiation causing cancer can be estimated. But this is the result of instantaneous exposure to large doses, and people are more concerned about the carcinogenic effects of radiation at very small doses and dose rates involved in radiation protection. The carcinogenic effect in the latter condition is lighter than that in the former condition. Therefore, the results obtained from the data of Hiroshima and Nagasaki need to be divided by an appropriate reduction factor to be applicable to the case of small doses and small dose rates. At present, ICRP recommends that this reduction factor be 2 based on the results of radiobiological studies and with reference to data from Hiroshima and Nagasaki. This is how the relevant data in Table 3 are derived.
- Recently, the ICRP discussed the influence of genetic factors on the risk of radiation carcinogenesis, and proposed that for cancer-susceptible families with dominant inheritance of mutations in strongly suppressed tumor suppressor genes, the probability of radiation carcinogenesis may increase by 5 to 100 times, with some associated with Disorders of DNA repair defects also increase the risk of cancer after irradiation. Since the incidence of familial cancer in the population is only 1% or less, it does not affect the population's cancer risk estimates.
- The genetic effects of radiation have always been of great concern, but to date there is no definitive evidence that human offspring has suffered genetic damage due to natural or artificial radiation, even in large-scale surveys of the offspring of survivors in Hiroshima and Nagasaki. No statistically significant increase in genetic damage was found. However, a large number of experimental studies using animals and plants have shown that there is a genetic effect of radiation. Therefore, from the standpoint of radiation protection, it is necessary to assume that this effect also exists in humans. The data on genetic effects in Table 3 are mainly derived from the results of studies on experimental animals (mainly mice).
Effects of human radiation effects on genetic diseases
- When considering the impact of radiation on genetic diseases, ICRP considers it necessary to consider multifactorial diseases (such as hypertension, coronary heart disease, congenital malformations, etc.) and their mutation-related and environmental factors. The concept of mutation share was used to explore the effect of radiation on the increase in mutation rate. The basic conclusion is that the generation of low-level radiation will not have a significant effect on the incidence of multifactorial disease .
- The degree of danger of radiation-induced random effects of different types and energies is not exactly the same. In terms of radiation protection, several common radiation types are divided as follows: is the same level as X-rays and electrons. If it is assumed to be 1, the neutron is 5 to 20, and the specific value depends on its energy; The number of particles is 20. In Table 3, since the probability coefficient is expressed as the probability of a unit dose equivalent, the influence of the type and energy of radiation on the induced random effect has actually been considered.