Radiation Risk

Because the energies of the particles emitted during radioactive processes are extremely high, nearly all such particles fall in the class of ionizing radiation.

Ionizing Radiation

The practical threshold for radiation risk is that of ionization of tissue. Since the ionization energy of a hydrogen atom is 13.6 eV, the level around 10 eV is an approximate threshold. Since the energies associated with nuclear radiation are many orders of magnitude above this threshold, in the MeV range, then all nuclear radiation is ionizing radiation. Likewise, x-rays are ionizing radiation, as is the upper end of the ultraviolet range.

All nuclear radiation must be considered to be ionizing radiation! 所有核辐射都必须被视为电离辐射！

In addition, the upper end of the electromagnetic spectrum is ionizing radiation. 此外，电磁波谱的高端是电离辐射

Activity of Radioactive Source

The curie (Ci) is the old standard unit for measuring the activity of a given radioactive sample. It is equivalent to the activity of 1 gram of radium. It is formally defined by:

1 curie = amount of material that will produce 3.7 x 1010 nuclear decays per second. 1居里等于产生每秒3.7×10¹⁰次核衰变的物质的量。 1 becquerel = amount of material which will produce 1 nuclear decay per second. 1 贝克勒尔等于每秒产生 1 个核衰变的材料的量。 1 curie = 3.7 x 1010 becquerels. 1 曐等于 3.7×10¹⁰ 贝克勒尔。 The bequerel is the more recent SI unit for radioactive source activity. 贝克勒尔是近年来用于放射性源活度的SI单位。

Intensity of Radiation

The roentgen (R) is a measure of radiation intensity of xrays or gamma rays. It is formally defined as the radiation intensity required to produce an ionization charge of 0.000258 coulombs per kilogram of air. It is one of the standard units for radiation dosimetry, but is not applicable to alpha, beta, or other particle emission and does not accurately predict the tissue effects of gamma rays of extremely high energies. The roentgen has mainly been used for calibration of xray machines.

Absorbed Dose of Radiation

The rad is a unit of absorbed radiation dose in terms of the energy actually deposited in the tissue. The rad is defined as an absorbed dose of 0.01 joules of energy per kilogram of tissue. The more recent SI unit is the gray, which is defined as 1 joule of deposited energy per kilogram of tissue. To assess the risk of radiation, the absorbed dose is multiplied by the relative biological effectiveness of the radiation to get the biological dose equivalent in rems or sieverts. 拉德是表示组织中实际沉积的辐射能量的吸收剂量单位。拉德定义为每千克组织沉积0.01焦耳能量的吸收剂量。更近期的SI单位是戈瑞，其定义为每千克组织沉积1焦耳能量的吸收剂量。为了评估辐射风险，吸收剂量需乘以辐射的相对生物效应性，以获得用雷姆或希沃特表示的生物等效剂量。

Biologically Effective Dose

The biologically effective dose in rems is the radiation dose in rads multiplied by a "quality factor" which is an assessment of the effectiveness of that particular type and energy of radiation. For alpha particles the relative biological effectiveness (rbe) may be as high as 20, so that one rad is equivalent to 20 rems. However, for x-rays and gamma rays, the rbe is taken as one so that the rad and rem are equivalent for those radiation sources. The sievert is equal to 100 rems. 用雷姆表示的生物有效剂量是辐射剂量（单位为拉德）乘以一个“品质因数”，该品质因数是对特定类型和能量的辐射效果的评估。对于α粒子，相对生物有效性（rbe）可能高达20，所以1拉德相当于20雷姆。然而，对于X射线和γ射线，rbe取为1，因此对于这些辐射源，拉德和雷姆是等价的。西弗特等于100雷姆。