Managing Space Radiation Risk in the New Era of Space Exploration (2008) / Chapter Skim
Currently Skimming:
3 Radiation Effects
3 Radiation Effects
Pages 49-61
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 49... ...
The number of cells required for proper tissue and organ function is determined by the ability of cells to divide and maintain their structure. The function of tissues and organs is determined by the ability of constituent cells to keep sending and receiving the required signaling molecules.
|
From page 50... ...
These different radiation time courses are referred to as "early" and "late," to describe how the body responds to different dose rates. Cellular repair mechanisms are not always fully successful.
|
From page 51... ...
Also important in understanding radiation sensitivity studies are several physical and biological variables: dose size, dose mode (internal or external) , dose rate, fractionation (division of the total dose into small doses administered at intervals)
|
From page 52... ...
As an example, Figure 3-3 shows the calculated probability of radiation exposure leading to death as a function of radiation dose and medical treatment. The acute response curves in the figure show that thresholds are generally quite sharp, so that any uncertainty in the dose (or in conversion of the dose into a biological common scale)
|
From page 53... ...
. The use of a linear extrapolation without a threshold, as is customary in the interpretation of the atomic bomb survivor data on which epidemiological dose response is based, means that, at any given dose, there is a definite probability of incurring a fatal cancer, even if the mean (or any other point estimate)
|
From page 54... ...
(1995) estimated the radiation risk uncertainty ratio to be 4-15×.
|
From page 55... ...
Recent radiation biology research has demonstrated that there are still fundamental responses of cells and tissues to radiation that are not clearly understood and that might affect risk assessments. Rather than uniformly decreasing the uncertainties associated with risk estimates, some discoveries may reduce the uncertainties and may even reveal that the risks are currently overestimated; conversely, some new discoveries may reveal increased risks, or increased uncertainty about risks thought to be well understood at present.
|
From page 56... ...
The model generally used for establishing radiation limits is based on the detailed epidemiological and medical observations of atomic bomb survivors, supplemented, where appropriate, with data from occupational radiation, medical, and accidental radiation exposures. Dose-response curves from atomic bomb survivor data, mainly survivors exposed to relatively high doses of instantaneously delivered gamma rays, are used in conjunction with other information to extrapolate the probability of health effects to lower doses, delivered over long periods of time, to peacetime populations other than Japanese survivors, and to other kinds of radiation.
|
From page 57... ...
Acute radiation effects generally have a threshold, corresponding to relatively high radiation dose, as may be seen in Table 3-1. Note that Table 3-1 refers to absorbed doses and not to dose equivalent, showing the lack of information required to convert such acute-effect data from low-LET x-rays and gamma rays to charged particles.
|
From page 58... ...
In addition, hematopoietic stem cells are among the most radiosensitive cells in the body, and acute radiation effects include a marked depression of lymphocytes at doses near 100 cSv within the first 6 hours following radia tion exposure. Effects of radiation exposure at much lower doses have been observed, suggesting a possibility for radiogenic immune dysfunction in astronauts during the time frame of their spaceflight.
|
From page 59... ...
Dose-rate effects track the incident radiation rate, typically a gamma background level, and refer to a continuum effect rather than to ionization associated with a single heavy particle. Displacement damage can inject a severe degradation in the gain of a semiconductor that anneals out in the period as early as 1 microsecond and extending out to several months after the irradiation with, approximately, an exponential time constant (Messenger and Ash, 1986)
|
From page 60... ...
is implemented through flight rules to ensure that astronauts do not approach these limits and to reduce the risk of exposing the astronauts to acute radiation effects. Among these flight rules will be a requirement to return to the most heavily shielded shelter if the radiation flux exceeds a predetermined dose-rate threshold.
|
From page 61... ...
2005. Managing Lunar and Mars Mission Radiation Risks.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.