David Davis will push ahead with plans to pull Britain out of the European civil nuclear regulator during Brexit talks in Brussels next week despite fears it could it could hit cancer treatments.
The Royal College of Radiologists (RCR) has issued a fresh warning that anything hitting the supply and transport of radioactive isotopes widely used in scans and other treatment could cause delays for patients.
But the Government said European Union treaties are "uniquely legally joined" with Euratom and insisted there is a "strong mutual interest" for close co-operation once the UK has left the bloc.
In the second round of negotiations with the EU's chief Brexit negotiator Michel Barnier, Mr Davis will call for minimised civil nuclear trade barriers after the divorce.
Papers setting out the Brexit Secretary's position say the UK is "keen to discuss this as quickly as possible" and wants a "smooth transition" with no interruptions in the safeguard arrangements.
The RCR said it remains concerned over the disruption of supply of medical materials once the UK is outside the nuclear common market, through higher costs, increased regulation or trade barriers.
Many of the medical materials used in treatment reach the UK via EU-based nuclear reactors, the college said.
Nicola Strickland, president of the RCR, said: "As a medical royal college, our primary goal is to ensure the safe and reliable delivery of medical services to patients who need scans and non-surgical cancer treatment.
"This is why we are calling for further clarity and dialogue on the future supply of radio isotopes.
"The Government has promised a statement on the matter. We hope that will be issued very soon and give the assurance that patients and doctors need."
Brexit minister Steve Baker said fears raised by medical experts over the impact of quitting Euratom are "not correct".
"We are certainly listening to those concerns but we believe those concerns are not correct," Mr Baker told BBC Radio 4's Today programme.
"Medical radio isotopes are not the kind of special fissile material - plutonium, uranium - covered by Euratom."
He added: "Our advice is that medical radio isotopes and their import into the United Kingdom is not covered by the safeguarding provisions."
The Government's position paper says consideration will be given to ownership of Euratom equipment and special fissile material.
Documents have also been released setting out how Mr Davis will approach legal proceedings in Europe in the talks and what will happen with protections for EU organisations in the UK.
Mr Davis will reaffirm the Government's position that the Court of Justice of the European Union should not be allowed to rule on UK cases that were not before the court on the day of Brexit.
Immunities for diplomats and privileges for EU bodies, such as the European Medicines Agency, should be extended for a short time after Britain quits to allow operations to be wound up, the papers say.
Mr Davis said: "While we're leaving the EU we are not leaving Europe, and we want to continue co-operating with our friends and neighbours on issues of mutual importance including nuclear safeguards.
"By ending the jurisdiction of the Court of Justice of the European Union, UK courts will be supreme once more. Our sensible approach to pending cases means there would be a smooth and orderly transition to when the court no longer has jurisdiction in the UK."
Tory MP Anna Soubry urged the Government to act in the national interest and try to stay in Euratom.
She told ministers not to "hide behind false red herrings like the ECJ, which is not a problem", and called for fresh legal advice on whether it would be possible to negotiate a way to stay in Euratom.
Ms Soubry told BBC Radio 4's World At One: "Spending all this time, energy and, I have to say, your listeners' hard-earned taxpayers' money on trying to reinvent something that works well, which nobody even vaguely sensible has a problem with us remaining in, is not great.
"And I would beg the Prime Minister, please, in this spirit, and in the reality of the General Election, but in the spirit of trying to build bridges and creating a sensible Brexit, could we all please put the national interest first?
#daviddavis does not seem serious. As main negotiator he should be. If serious re brexit he must present required paperwork by Monday.— jazzaoxon (@jazzaoxon) July 12, 2017
"And the national interest is to stay within Euratom."
Mr Davis suggested there could be some kind of association agreement regarding Euratom.
He told BBC News: "The first thing to understand is we are going to protect the safety of the British public. We will make sure the safeguards work properly.
"Whether we have an association agreement with the European Union or we have something independent under the International Atomic Energy Authority, we'll provide the sorts of safeguards that we have today at least.
"We're going to talk to the European Union about this as part of the negotiations because what we want is something quite close to what we currently have in terms of safeguards, in terms of agreements, in terms of oversight, in terms of the ability to transfer materials, all these sorts of things.
"Other countries have arrangements like that. The Japanese, the Americans, the Canadians all have independent arrangements.
"Some of them operate under the International Atomic Energy Authority, that's another way of doing it.
What we will do is come up with something which provides us with the safeguards we have now, the healthcare that we have now."