20 years ago I read a book about a physicist who was kidnapped (along
with his family) by a small group of terrorists and forced to help
construct a nuclear bomb. The twist early in the book is that the
people around the main family are not aware of the kidnapping because
they are led to believe that the family is going on holidays. While
the wife is constantly looking for ways to escape with her two
children, the husband begins to like his mission and start to
construct the bomb which used to explode at a major world congress. 
I do not know the name of the book, and I am trying to locate it so
that I can read it again. I need the book name and author and isbn if
possible. Also, if the book is in your possession, I am happy to
negotiate a purchase price to save some time so that I do not have to
go shopping for it. Please contact me at steve@visionlink.com.au
in Sydney, Australia. Thanks. BTW, here are some thoughts about which
I have some doubt, but I 'think' that the physicist was abducted frm
Germany. I 'think' the bomb was exploded in Geneva or Zurich. There
were two chilren, son and daughter. One of the terrorist's assistants
was badly hurts via radiation and died after badly handling the
plutonium. It might be a 1970s novel because there as little emphasis
on computers. The book was written prior to 1985. It was borrowed in
1985 from Mosman library, NSW, Australia. It might have been large
print hard cover. The story was not about the bomb, but about the
husband and wife and what happened to them, and how their charachters
changed as a result of the kidnapping.

The book is "Gadget" by Nicholas Freeling.

See this listing on Biblion:
Gadget. 
by Freeling, Nicolas. 
NY Coward McCann & Geoghegan 1977
"A terrorist group kidnap a scientist and his family to force him to
build them an atomic bomb"
http://www.biblion.com/search.php?searchby=Title&qsearch=gadget&submit.x=18&submit.y=12

Also see this listing on Alibris:
Gadget. 
by Freeling, Nicolas. 
NY Coward McCann & Geoghegan 1977
"Mystery Researcher in Germany is kidnapped for his nuclear
expertise."
http://www.alibris.com/search/detail.cfm?chunk=25&qwork=2512433&S=R&bid=8070788040&pqtynew=0&page=2&matches=38&qsort=r

Also see this description on the usenet group alt.war.nuclear by
e_erpelding (6/25/2000)
"Nicholas Freeling wrote a novel called "Gadget" in the
1970s. It was about a physicist kidnapped by sophisticated
terrorists in order to build them an Uranium gun-type bomb."
From:
http://groups.google.com/groups?selm=8j4avd%242he%241%40nnrp1.deja.com&output=gplain

Used copies of the book are widely available. Abebooks shows more than
100 copies:
http://dogbert.abebooks.com/abe/BookSearch?ph=2&an=freeling&tn=gadget

search terms: nuclear kidnapped

I hope this helps.

Wow. What a great service - thank you. I spent many hours using other
means to search for this answer.

kind regards

Steve Griffiths

Only one small thing - 
The ISDN: 0140048987
See: 
http://www.amazon.com/exec/obidos/ASIN/0140048987/ltc-political

Very appreciate this extra information - thankyou.

kind regards

Steve Griffiths