Mass estimation method and x-ray inspection apparatus

An X-ray inspection apparatus comprising:

• a transport unit that transports a sample that is the same type as an inspection object and that has known mass N times;
• an X-ray source that irradiates the sample transported by the transport unit with X-rays;
• an X-ray detector that detects the X-rays transmitted through the sample for each transmission region of the sample;
• an X-ray transmission image data generation unit that generates, for each transportation, X-ray transmission image data corresponding to a transmission amount of the X-rays for each transmission region of the sample based on detection information of the X-ray detector;
• a histogram generation unit that generates a histogram of pixel values of pixels that are included in N pieces of the X-ray transmission image data of the sample generated by the X-ray transmission image data generation unit and that correspond to the respective transmission regions;
• a histogram matrix generation unit that generates a histogram matrix consisting of N row vectors corresponding to N histograms of the sample generated by the histogram generation unit;
• a weight vector calculation unit that uses a product of the histogram matrix and a weight vector consisting of a weight coefficient for each pixel value of the N pieces of X-ray transmission image data as a relative mass estimation value vector consisting of N relative mass estimation values of the sample, to calculate the weight vector that minimizes a variance of the N relative mass estimation values;
• and
• a mass estimation unit that estimates mass of one or more inspection objects transported by the transport unit, by using the weight vector calculated by the weight vector calculation unit.