Mono-sheet heat-developable photosensitive material and method of forming image

1. A method of forming an image, which comprises: image-wise exposing a mono-sheet heat developable photosensitive material to laser diode light source having light intensity of not less than 1 mW/mm 2 at a wavelength of 350 nm to 430 nm, and heat-developing the exposed material at a temperature of from 110 to 150° C. by a heat-developing machine having an exposure section, a heat-development section and a cooling section, wherein a ratio of a zone length of the cooling section to a zone length of the heat-development section is not more than 3.5,

wherein the mono-sheet heat developable photosensitive material comprises a support having a layer thereon containing:

(a) a light-insensitive organic fatty acid silver salt including at least silver behenate having a specific surface area of not less than 10;

(b) a light-sensitive silver halide that is prepared in the absence of the light-insensitive organic fatty acid silver salt and has an average silver iodide content of from 70 to 100 mole %;

(c) a thermal developer;

(d) an organic polyhalogen compound that is represented by the following formula (H):

Q—(Y) n —C(Z 1 )(Z 2 )X  (H)

wherein Q represents an alkyl group, an aryl group or a heterocyclic group; Y represents a divalent connecting group; n represents 0 or 1; Z 1 and Z 2 each represents a halogen atom; and X represents a hydrogen atom or an electron withdrawing group;

(e) a phthalazine compound; and

(f) a binder,

and wherein the photosensitive material exhibits substantially no light-sensitivity after being subjected to heat-development.

2. The method as claimed in claim 1 , wherein the light-insensitive organic fatty acid silver salt including silver behenate a specific surface area of not less than 15.