According to GFI, the book is promoted via spambots on Twitter. Every time a user tweets something about the disaster - and likely when the word "radiation" is used - spambots step up and offer the book to the user:
The link takes the user to radiationhealth(dot)com where the book is further promoted. The site is still up and the domain has apparently been registered today.
To buy the eBook one must to part with $19.95. According to the link at the bottom of the payment page, the payment will end up in the hands of Lean Secret. What is Lean Secret? "That site has been around since January, but currently has no content other than a landing page and uses the same Whois privacy service as the site promoting 'Radiation health' eBooks," says Christopher Boyd.
All in all, it doesn't seem very legitimate. The fact that they are "advertise" the book via spambots only makes me more sure that this is an offer every user should refuse.