I. Detailed introduction

Particle fluence φ (t, r) refers to the number of particles accumulated in the radiation field φ(T, r) with R point as the spherical center in T time. A physical quantity of radiation field, which represents the number of particles that reach a certain position r in the radiation field within a period of time t.

Draw a small spherical area around a point p of the radiation field. If the cross-sectional area of the sphere is da and the total number of particles incident on the sphere from all directions is dN, the quotient of dN and da is defined as the particle fluence at point P of the radiation field. DN/da

Definition: particle fluence φ (t, r) refers to the number of particles accumulated in the radiation field with φ(T, r) as the spherical center in t time. Mathematical expression: φ (t, r) = dn (t, r)/da. Where dN(T, r) is the cumulative number of particles entering the sphere with the radiation field r as the center within the time interval t, and the cross-sectional area is da. ..

Special case: for unidirectional radiation field, particle fluence can be defined as the cumulative number of particles passing through unit area perpendicular to the radiation incident direction. Unit: m-2, cm-2 is commonly used in practical work. Related physical quantities: particle fluence rate, energy fluence rate and energy fluence rate.

In the unidirectional parallel radiation field, the particle fluence is numerically equal to the number of particles passing through the unit area perpendicular to the particle incident direction. For non-parallel radiation field, it is defined as the quotient obtained by dividing the number of particles dN entering the sphere with this point as the center of the sphere by the cross-sectional area da of the sphere.