The general term for all types of subatomic particles which are of the smallest possible size allowed by Nature is “quanta.” “Quanta” is the plural; “quantum” is the singular. In its original meaning, a “quantum” is the tiniest particle of a substance that Nature allows.

Quantum is the Latin word for amount and, in modern understanding, means the smallest possible discrete unit of any physical property, such as energy or matter. Quantum came into the latter usage in 1900, when the physicist Max Planck used it in a presentation to the German Physical Society.

In physics, a quantum (plural quanta) is the minimum amount of any physical entity (physical property) involved in an interaction. This means that the magnitude of the physical property can take on only discrete values consisting of integer multiples of one quantum.

Photons exert no pressure. Momentum of photon is hvc . Rest mass of photon is zero. Energy of photon is hv.

(The radiation pressure of sunlight on Earth is very small: it is equivalent to that exerted by about a thousandth of a gram on an area of 1 square metre, or 10 μN/m2.) While it acts on all objects, its net effect is generally greater on smaller bodies, since they have a larger ratio of surface area to mass.

Calculate the intensity of solar radiation at the given distance from the Sun and use that to calculate the radiation pressure. From the pressure and area, calculate the force. I=Savg=3.8×1026W4π(9.0×1010m)2=3.7×103W/m2.

The solar radiation that reaches the Earth’s surface without being diffused is called direct beam solar radiation. The sum of the diffuse and direct solar radiation is called global solar radiation. Atmospheric conditions can reduce direct beam radiation by 10% on clear, dry days and by 100% during thick, cloudy days.

At high doses, radiation therapy kills cancer cells or slows their growth by damaging their DNA. Cancer cells whose DNA is damaged beyond repair stop dividing or die. When the damaged cells die, they are broken down and removed by the body. Radiation therapy does not kill cancer cells right away.

Typically, people have treatment sessions 5 times per week, Monday through Friday. This schedule usually continues for 3 to 9 weeks, depending on your personal treatment plan. This type of radiation therapy targets only the tumor. But it will affect some healthy tissue surrounding the tumor.

Almost all patients are able to drive while receiving radiotherapy treatment. However, with some types of cancer, driving may NOT be recommended due to fatigue or strong pain medication.