Photothermographic material and image forming method

1. A photothermographic material comprising, on at least one side of a support, an image forming layer comprising at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent, and a binder, wherein 50% or more of the total projected area of the photosensitive silver halide is occupied by tabular grains having an aspect ratio of 2 or more, and the grains have at least one epitaxial junction portion having a multifold structure.

2. The photothermographic material according to claim 1 , wherein the multifold structure is at least a twofold structure comprising a core part and a shell part.

3. The photothermographic material according to claim 2 , wherein the core part has a silver chloride content of 40 mol % or higher and the shell part has a silver chloride content of 30 mol % or lower.

4. The photothermographic material according to claim 3 , wherein the core part comprises silver chloride and the shell part comprises silver bromide.

5. The photothermographic material according to claim 1 , wherein the multifold structure comprises at least a threefold structure comprising a core part, an intermediate part, and a shell part.

6. The photothermographic material according to claim 5 , wherein at least one of the core part or the intermediate part has a silver iodide content of 4 mol % or higher.

7. The photothermographic material according to claim 6 , wherein a silver iodide content of the intermediate part is 10 mol % or higher.

8. The photothermographic material according to claim 5 , wherein the core part comprises silver chloride or silver bromide, the intermediate part comprises silver iodide, and the shell part comprises silver bromide.

9. The photothermographic material according to claim 8 , wherein the core part comprises silver chloride.

10. The photothermographic material according to claim 1 , wherein an average silver iodide content of the tabular grains is 40 mol % or higher.

11. The photothermographic material according to claim 10 , wherein the average silver iodide content of the tabular grains is 80 mol % or higher.

12. The photothermographic material according to claim 11 , wherein the average silver iodide content of the tabular grains is 90 mol % or higher.

13. The photothermographic material according to claim 1 , wherein a mean equivalent spherical diameter of the silver halide is from 0.3 μm to 5.0 μm.

14. The photothermographic material according to claim 1 , wherein a mean aspect ratio of the silver halide is 5 or more.

15. The photothermographic material according to claim 10 , further comprising a silver iodide complex-forming agent.

16. The photothermographic material according to claim 1 , having the image forming layer on both sides of the support.

17. An image forming method using a photothermographic material comprising, on both sides of a support, an image forming layer comprising at least a photosensitive silver halide, a non-photosensitive organic silver salt, a reducing agent, and a binder, wherein 50% or more of a total projected area of the photosensitive silver halide is occupied by tabular grains having an aspect ratio of 2 or more, and the grains have at least one epitaxial junction portion having a multifold structure, wherein the method comprises:

(a) providing an assembly for forming an image by placing the photothermographic material between a pair of fluorescent intensifying screens;

(b) putting an analyte between the assembly and an X-ray source;

(c) irradiating the analyte with X-rays having an energy level in a range of from 25 kVp to 125 kVp;

(d) taking the photothermographic material out of the assembly; and

(e) heating the removed photothermographic material in a temperature range of from 90° C. to 180° C.