Endoscope

1. An endoscope comprising:

an insertion portion including an image pickup section and an illumination section in a distal end portion thereof; and

a light guide inserted through an inside of the insertion portion, the light guide including a plurality of fibers made of a glass not containing lead, the plurality of fibers guiding illuminating light from a light source apparatus connected to a proximal end portion side to the illumination section, the light guide having a numerical aperture (NA) of 0.46 to 0.90,

wherein a core glass of the fibers has a refractive index nd of 1.56 to 1.74, and has a composition of (A) 20 to 55 wt % SiO 2 , (B1) exceeding 2.0 wt % to equal to or less than 4.0 wt % B 2 O 3 , (B2) neither P 2 O 5 nor GeO 2 contained, (C) 25 to 72 wt % (BaO+SrO+La 2 O 3 +Lu 2 O 3 +Ta 2 O 5 +Gd 2 O 3 +WO 3 ), (D) 0 to 30 wt % ZnO, (E) no Al 2 O 3 contained, (F) no ZrO 2 contained, (G) neither PbO nor As 2 O 3 contained, (H) 0 to 15 wt % (Na 2 O+K 2 O), (I) 0 to 0.050 wt % Sb 2 O 3 and (J) 0.26 to 1.63 wt % (Na 2 SO 4 +K 2 SO 4 ).

2. The endoscope according to claim 1 , wherein an integrated light amount of light of 380 to 750 nm after an X-ray resistance test in which recovery processing of guiding light of 64 lumen/mm 2 for 600 minutes is performed after irradiation with an X-ray of 2.5 Gy is no less than 67% of an integrated light amount before the X-ray resistance test, and a blue color light amount ratio, indicated by a ratio of integrated light amount of light of 380 to 470 nm to integrated light amount of light of 470 to 580 nm, after the X-ray resistance test is no less than 60% of a blue color light amount ratio before the X-ray resistance test.

3. The endoscope according to claim 2 , wherein at least one of an inner portion and an outer portion of the light guide includes a flexible X-ray blocking member that blocks an X-ray.

4. The endoscope according to claim 3 , wherein the X-ray blocking member covers a length of the insertion portion, the length being no less than 70% relative to a length of the insertion portion subjected to X-ray irradiation.

5. The endoscope according to claim 3 , wherein the X-ray blocking member is made of a metal, a metal oxide or an alloy of W, Ta or Bi.

6. The endoscope according to claim 2 , wherein each of the plurality of fibers includes an X-ray blocking coating layer that blocks an X-ray at a surface thereof.

7. The endoscope according to claim 6 , wherein the X-ray blocking coating layer is made of a metal, a metal oxide or an alloy of W, Ta or Bi.

8. The endoscope according to claim 7 , wherein the X-ray blocking coating layer has a thickness of no less than 0.5 μm and no more than 3 μm.

9. The endoscope according to claim 2 , wherein the integrated light amount of light of 380 to 750 nm in the light guide after the X-ray resistance test is no less than 110% of an integrated light amount in a light guide in an endoscope not including the X-ray blocking member after the X-ray resistance test.

10. The endoscope according to claim 2 , wherein X-ray blocking particles that block an X-ray are provided in a gap between the plurality of fibers.

11. The endoscope according to claim 10 , wherein the X-ray blocking particles are made of a metal, a metal oxide or an alloy of W, Ta or Bi.

12. The endoscope according to claim 11 , wherein an occupancy of the X-ray blocking particles in a tube housing the plurality of fibers is no less than 0.5% and no more than 5%.

13. The endoscope according to claim 1 , wherein the image pickup section picks up a color image.

14. The endoscope according to claim 1 , wherein the core glass of the fiber has a composition of (C1) 39 to 46 wt % (BaO+SrO+La 2 O 3 +Lu 2 O 3 +Ta 2 O 5 +Gd 2 O 3 +WO 3 ), (D1) 4 to 16 wt % ZnO, (H1) 4 to 10 wt % (Na 2 O+K 2 O), (I1) 0.001 to 0.010 wt % Sb 2 O 3 and (J1) 0.32 to 0.78 wt % (Na 2 SO 4 +K 2 SO 4 ).