Appellant, John L. Sawyer, has noted an appeal from the Board of Veterans’ Appeals’ (BVA) denial of his claim for service connection for lung cancer. We find that the BVA erred in its decision in this case and, therefore, remand the case to the BVA for reconsideration pursuant to this opinion.
Appellant was in active service in the Armed Forces from March 26, 1951, to January 6, 1966. For approximately sixteen days, from May 15, 1953, to May 30, 1953, he was assigned temporary duty to attend Exercise Desert Rock Shot V-10, known as “Grable.” This was the tenth in a series of above-ground nuclear tests, known as “Operation UPSHOT-KNOTHOLE”, which took place in Nevada. Appellant was a member of an observer group called BCT Baker, which was situated an estimated five thousand yards from ground zero. Three seconds after the blast, he and his group were allowed to rise and observe the fireball. They were then ordered to walk through the “display area” which was located within five hundred yards of ground zero and observe the effects of the blast on objects placed there by the testers. This lasted for approximately 40 minutes after the blast.
On August 25, 1976, appellant was admitted to St. Francis Hospital in Wilmington, Delaware and was diagnosed as having a large tumor mass in his right lung. On September 2,1976, appellant underwent a right upper lobectomy. The pathology report revealed a diagnosis of anaplastic bronchogenic carcinoma (epidermoid type). On March 23, 1977, appellant filed a claim for disability benefits with the Veterans’ Administration (now the Department of Veterans Affairs) (VA) claiming service connection for his lung cancer. The Wilmington, Delaware, Veterans Administration Regional Office (Regional Office) denied appellant’s claim on the grounds that his lung cancer was not service-connected. On appeal to the BVA, the case was remanded to the Regional Office to gather more information on appellant’s medical records and his participation in the atomic bomb testing. On August 11, 1980, appellant’s claim was again denied by the Regional Office. The claim was rejected on the grounds that appellant’s exposure to radiation was brief, that he witnessed only one nuclear test, and that his dosage was small, estimated at 4.4 rem. According to the VA, 4.4 rem was “within the present national occupational radiation exposure standard which permit[s] 5.0 rem per calendar year.” R. at 250. The Board, in upholding the denial, also relied on the fact that appellant had smoked approximately a pack of cigarettes a day for some thirty-odd years. The BVA decision was issued on June 8, 1981.
The Veterans’ Dioxin and Radiation Exposure Compensation Standards Act, Pub.L. No. 98-542, 98 Stat. 2725 (pertinent provisions of which are codified at 38 U.S.C. § 354(a) (1988)), was enacted on October 24, 1984. That statute required the Secretary of Veterans Affairs to prescribe regulations for determining whether veterans were entitled to service connection for certain disabilities if they were exposed to dioxin in the Republic of Vietnam or to radiation from nuclear detonations while on active duty. The purpose of the statute was:
to ensure that Veterans’ Administration disability compensation is provided to veterans who were exposed during service in the Armed Forces in the Republic of Vietnam to a herbicide containing dioxin or to ionizing radiation in connection with atmospheric nuclear tests or in connection with the American occupation of Hiroshima or Nagasaki, Japan, for all disabilities arising after that service that are connected, based on sound scientific and medical evidence, to such service (and that Veterans’ Administration dependency and indemnity compensation is provided to survivors of those veterans for all deaths resulting from such disabilities).
Pub.L. No. 98-542, § 3, 98 Stat. 2725, 2727 (1984) (emphasis added).
Pursuant to Pub.L. No. 98-542 and 38 U.S.C. § 354(a) (1988), the VA promulgated 38 C.F.R. § 3.311b (1989) which identified a *133group of diseases as “radiogenic diseases” and set forth guidelines to be followed when determining whether to award disability to veterans who were exposed to radiation during service, and their survivors.
On June 10, 1986, appellant petitioned the Regional Office to reopen his claim based solely on the enactment of Pub.L. No. 98-542. Appellant offered no new and material evidence. The Regional Office, after reopening appellant’s claim, denied his claim, stating in the Statement of the Case, “he did not receive radiation dosages to warrant establishment of service connection for lung cancer based on criteria established by 38 C.P.R. § 3.311b.” R. at 823. However, on December 15, 1989, the BVA, in upholding the denial, ruled that “[t]he Board of Veterans’ Appeals decision of June 1981, denying service connection for lung cancer is final, and a new factual basis warranting the grant of service connection for lung cancer has not been presented.” John L. Sawyer, loc. no. 936226, at 7 (BVA Dec. 15, 1989). The BVA based its conclusion on 38 U.S.C. § 4004(b) (1988) and 38 U.S.C. § 3008 (1988); both govern the reopening of disallowed claims. Appellant filed a timely Notice of Appeal with the Court.
Appellant contends that 38 C.F.R. § 3.311b (1989) requires the Regional Office, and, subsequently, the BVA, in reviewing the Regional Office decision, to afford a de novo review to his claim. We agree.
The Court has jurisdiction to hear this appeal pursuant to 38 U.S.C. § 4052 (1988). In applying 38 C.F.R. § 3.311b (1989) to a veteran’s case, the spirit as well as the letter of Pub.L. No. 98-542 must be taken into account. That law was enacted to address a growing concern among veterans that many of their disabilities were caused by exposure to radiation and that there were no standards available to fairly and accurately adjudicate claims. See Veterans’ Dioxin and Radiation Exposure Compensation Standards Act, Pub.L. No. 98-542, §§ 2(1), (10), (11), (12), and 5(a), 98 Stat. 2725, 2725-2727 (1984). Realizing that many veterans were not being granted benefits because of a lack of uniformity in decisions by the VA on radiation cases, Congress passed 38 U.S.C. § 354(a) (1988), which states:
The [Secretary] shall include in the regulations pertaining to service-connection of disabilities (1) additional provisions in effect requiring that in each case where a veteran is seeking service-connection for any disability due consideration shall be given to the places, types, and circumstances of such veteran’s service as shown by such veteran’s service record, the official history of each organization in which such veteran served, such veteran’s medical records, and all pertinent medical and lay evidence, and (2) the provisions required by section 5 of the Veterans’ Dioxin and Radiation Exposure Compensation Standards Act.
(emphasis added). From the language of the statute, we hold that Congress intended the VA to examine a veteran’s entire record when determining whether benefits are to be awarded.
In circumstances involving a reopened claim that was previously denied, it is imperative that the veteran’s claim is examined thoroughly in light of the language of the new regulations. To implement 38 U.S.C. § 354(a) (1988), the VA promulgated 38 C.F.R. § 3.311b (1989), setting forth a list of requirements and steps the VA must follow in order to determine if a veteran’s disability, based on radiation exposure, is service-connected. Examination of the record suggests that some attempt was made to follow the proper steps under 38 C.F.R. § 3.311b (1989); however, it is not clear from the VA’s rating decision or the Statement of the Case that the Regional Office did conduct de novo review of appellant’s entire record. We find that, based on the record, the BVA did not conduct the required de novo review of appellant’s claim.
Legislative history of Pub.L. No. 98-542 shows that Congress not only had in mind those veterans who had not yet filed claims with the VA but those who had filed claims and were denied service connection. Dur*134ing debate over the legislation that became Pub.L. No. 98-542, the Chairman of the Senate Veterans Affairs Committee stated:
Of the 1,646 claims related to exposure through participation in the nuclear testing program, a total of only 30 have been granted; 14 of these were granted at the regional level and 16 were granted at the Board of Veterans Appeals. I want to stress that 945 — or 57 percent — of these nuclear-test related claims were for malignancies — solid tumors or cancer, as we nonmedical people would say — and for leukemias, and lymphomas. These are not frivolous claims. These are claims for benefits as a result of exposure to a hazard as to which medical science generally agrees that no level of exposure can be considered safe.
130 Cong.Rec. S6147 (daily ed. May 22, 1984).
We hold that Congress intended that those who had previously been denied claims could come forward and have their claims reevaluated under the new guidelines. Applying 38 U.S.C. § 4004(b) (1988) and 38 U.S.C. § 3008 (1988), in the manner in which appellee proposes, to claims such as appellant’s would render Pub.L. No. 98-542 a nullity. 38 U.S.C. § 4004(b) (1988) states that “except as provided in section 3008 of this title, when a claim is disallowed by the Board, the claim may not thereafter be reopened and allowed and a claim based upon the same factual basis may not be considered.” 38 U.S.C. § 3008 (1988) requires new and material evidence to be presented before a disallowed claim will be reopened. We conclude that, applying 38 U.S.C. §§ 4004(b) and 3008 (1988), as the BVA did in the present case, would not lead to the results Congress intended when it enacted Pub.L. No. 98-542. Therefore, the Court holds that 38 C.F.R. § 3.311b (1989) applies not just to claims that have never before been adjudicated, but to all claims involving disabilities possibly caused by exposure to radiation.
Appellee conceded in oral argument that appellant was entitled to a de novo review by the BVA and asserted that one was provided. However, the record does not offer any evidence to support ap-pellee’s claim. The Court agrees with ap-pellee that appellant is entitled to de novo review. We find it virtually impossible for the VA to render a decision under 38 C.F.R. § 3.311b (1989) without taking into consideration all of the evidence of record, new as well as old, when making a decision. The Regional Office must follow the guidelines listed in the Code of Federal Regulations. It has a duty to ensure that all of the relevant sections are fairly and impartially applied to each veteran’s claim in order to ensure that the veteran’s claim receives full and evenhanded consideration. The BVA, in reviewing the decisions of the Regional Office, must apply the appropriate regulations and, if the veteran is not entitled. to benefits under those regulations, must give reasons or bases explaining why. See Gilbert v. Derwinski, 1 Vet.App. 49 (1990).
In reviewing the Board’s decision of December 15,1989, the Court notes that, at pages six and seven of its decision, the Board appears to have applied an inappropriate standard, an absence of “probability”, in arriving at its determination. After a claim is forwarded for review by the Chief Benefits Director, the Chief Benefits Director must do one of three things: 1) determine that it “is at least as likely as not the veteran’s disease resulted from exposure to radiation in service,” 38 C.F.R. § 3.311b(c)(l)(i); 2) determine that “there is no reasonable possibility that the veteran’s disease resulted from radiation exposure in service,” 38 C.F.R. § 3.311b(c)(l)(ii); or 3) if the Chief Benefits Director requests an advisory medical opinion from the Chief Medical Director and, after considering that opinion, “is unable to conclude whether it is at least as likely as not, or that there is no reasonable possibility, the veteran’s disease resulted from radiation exposure in service, the Chief Benefits Director shall refer the matter to an outside consultant.” 38 C.F.R. § 3.311b(c)(2). Appellee, in his supplemental memorandum, asks the Court to treat an absence of “probability”, which the BVA uses in its decision as a *135standard identical to “no reasonable possibility.” The Court holds that the BVA, in reviewing the Regional Office denial of the claim, must use the same standard for its decision as that which governed the Regional Office’s determination — the standard set forth in 38 C.F.R. § 3.311b(c)(l) and (2). The Court further holds that an absence of “probability” is a higher standard than “no reasonable possibility”.
According to Black’s Law Dictionary 1201 (6th ed. 1990), “probability” means the “likelihood; appearance of reality or truth; reasonable ground of presumption; verisimilitude; consonance to reason.” Thus, an absence of “probability” would mean “[t]he [unlikelihood of a proposition or hypothesis being true, from its conformity to reason or experience, or from superior evidence or arguments adduced in its favor.” Id. at 1201. The definition further states that “there is more evidence [not] in favor of the existence of a given proposition than there is [for] it.” Id. Webster’s New World Dictionary 1118 (3d ed.1988) defines “reasonable” as “able to reason” or “just using or showing reason, or sound judgment; sensible.” Black’s Law Dictionary 1166 (6th ed.1990) defines “possible” as “capable of existing, happening, being, becoming or coming to pass; feasible, not contrary to the nature of things; neither necessitated nor precluded; free to happen or not; contrasted with impossible. [The] word denotes improbability, without excluding the idea of feasibility,” thereby differentiating the term from probability. Id. Examination of 38 C.F.R. § 3.102 (1989), shows that the VA recognizes a difference between the words “probability” and “possibility”:
By reasonable doubt is meant one which exists because of an approximate balance of positive and negative evidence which does not satisfactorily prove or disprove the claim. It is a substantial doubt and one within the range of probability as distinguished from pure speculation or remote possibility.
(emphasis added). Cf. I.N.S. v. Cardoza Fonseca, 480 U.S. 421, 107 S.Ct. 1207, 94 L.Ed.2d 434 (1987) (holding that the 8 U.S.C. § 1253(h) (1988) “clear probability standard of proof did not govern asylum applications under 8 U.S.C. § 1158(a) (1988) stated “that so long as an objective situation is established by the evidence, it need not be shown that the situation will probably result in persecution, but it is enough that persecution is a reasonable possibility”) (citing with approval, I.N.S. v. Stevic, 467 U.S. 407, 424-425, 104 S.Ct. 2489, 2498, 81 L.Ed.2d 321 (1984)); Garcia-Ramos v. I.N.S., 775 F.2d 1370 (9th Cir.1985); Castaneda-Hernandez v. I.N.S., 826 F.2d 1526 (6th Cir.1987); Evenson v. Osmose Wood Preserving Co. of America, 899 F.2d 701 (7th Cir.1990) (products liability case holding that a reasonable possibility was a lesser standard than a probability).
Appellant, in his supplemental memorandum, raises the question as to whether his claim falls within the terms specified in Chris L. Gott, 50 Fed.Reg. 45,703 (VA 1985) (Settlement Agreement), which resolved Gott v. Walters, 756 F.2d 902 (D.C.Cir.1985), vacated 791 F.2d 172 (D.C.Cir.1985). Based on our disposition of this appeal, it is unnecessary to address this issue.
Therefore, for the reasons stated herein, we remand the matter and direct the BVA and the VA to comply with the requirement of de novo review according to the guidelines in 38 C.F.R. § 3.311b (1989). We will retain jurisdiction and direct that, upon completion of the remand proceeding, whether the Secretary grants or denies appellant’s claim, he supplement the record on appeal to include the further action of the Board and the Department. The supplemental record shall be filed with the Court and a copy served upon the appellant.
It is so Ordered.