Ken Mac is correct, melanin has an effect and you should also consider fatty people to be the heroes of your scenario. The physics forum would know, the radiation types are so variable. Originally there was the flash burn from the explosion and the fallout from the sky aftewards, i.e. in bomb tests near the Marshall islands.

Melanin can cause more surface burns compared to a person with light skin and good fat coverage.

Here's a study that states that black people complain of skin problems more often during radiation chemotherapy.

also this research:

Human and animal heterogeneity in terms of skin tissue distribution and impact on radiation dose distribution:

In humans, subcutaneous skin thickness and body fat vary as a function of age, sex and ethnicity. Fat tissue thickness can lead to wound variability, especially in the case of beta radiation, and the presence of MSCs in the adipose tissue could alter the response. Therefore, care must be used in selecting a model that minimizes these variables. In pig and mouse models, there can be different healing rates based on what part of the skin is irradiated. For example, in the pig, thicker dorsal skin heals differently than the thinner ventral skin. Mice also have similar skin location differences, in that radiation-induced damage can be very different in that of leg skin compared with that of ear skin. Proximity of the radiation exposure to bone can play a role in the extent of damage. Effect of skin melanization in view of possible differential radiation responses due to higher levels of melanin, as well as challenges involved in scoring erythema in pigmented skin: Concerning the use of a pig such as the Duroc, which is more heavily melanized, differential sensitivity to high-energy radiation may be observed due to the presence of melanin.

Marshall islands research.

Ken Mac is correct, melanin has an effect and you should also consider fatty people to be the heroes of your scenario.

Melanin can cause more surface burns compared to a person with light skin and good fat coverage.

Here's a study that states that black people complain of skin problems more often during radiation chemotherapy.

also this research:

Human and animal heterogeneity in terms of skin tissue distribution and impact on radiation dose distribution:

In humans, subcutaneous skin thickness and body fat vary as a function of age, sex and ethnicity. Fat tissue thickness can lead to wound variability, especially in the case of beta radiation, and the presence of MSCs in the adipose tissue could alter the response. Therefore, care must be used in selecting a model that minimizes these variables. In pig and mouse models, there can be different healing rates based on what part of the skin is irradiated. For example, in the pig, thicker dorsal skin heals differently than the thinner ventral skin. Mice also have similar skin location differences, in that radiation-induced damage can be very different in that of leg skin compared with that of ear skin. Proximity of the radiation exposure to bone can play a role in the extent of damage. Effect of skin melanization in view of possible differential radiation responses due to higher levels of melanin, as well as challenges involved in scoring erythema in pigmented skin: Concerning the use of a pig such as the Duroc, which is more heavily melanized, differential sensitivity to high-energy radiation may be observed due to the presence of melanin.

The physics forum would know, the radiation types are so variable. Older style atomic bombs had flash burn from the explosion and the fallout from the sky aftewards, i.e. in bomb tests near the Marshall islands.

Marshall islands research.