[ RadSafe ] neutron sources for Cl-38 production

Bob Hearn rah at america.net
Fri Apr 1 13:38:28 CDT 2011

The list of isotopes I saw had Cl-38 as one of the highest activity
components, but no Na-24. If this is indeed due to neutron activation of
seawater, large quantities of Na-24 (higher neutron activation cross-section
and longer half-life) should be observed.

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Derek Putley
Sent: Friday, April 01, 2011 2:03 PM
To: radsafe at health.phys.iit.edu
Subject: Re: [ RadSafe ] neutron sources for Cl-38 production

Arvic / All
See below for a quote from one of your links:-
"Chlorine-38, which has a half-life of only 37 minutes, is created when
stable chlorine-37, which is about one-fourth of the chlorine in salt,
absorbs a neutron. Since seawater has been used to cool [the reactors],
there is now a large amount of salt * thousands of kilograms * in all
three reactors. 
Now, if a reactor is truly shut down, there is only one source of
neutrons * spontaneous fission of some heavy metals that are created
when the reactor is working that are present in the reactor fuel. 
The most important ones are two isotopes of plutonium and two of
But if accidental chain reactions are occurring, it means that the
efforts to completely shut down the reactor by mixing boron with the
seawater have not completely succeeded. Periodic criticalities, or even
a single accidental one, would mean that highly radioactive fission and
activation products are being (or have been) created at least in Unit 1
since it was shut down. It would also mean that one or more intense
bursts of neutrons, which cause heavy radiation damage to people, have
occurred and possibly could occur again, unless the mechanism is
understood and measures taken to prevent it. Measures would also need to
be taken to protect workers and to measure potential neutron and gamma
radiation exposure."
I've not done any sums to evaluate the magnitude of the effects, but I
do believe the 3rd paragraph in above quoted text has ignored neutron
production by means of (alpha, n) reactions. Some general background on
(alpha,n) sources can be found here:-
and an on-line calculator is available here:-
Message: 7
Date: Fri, 1 Apr 2011 15:07:34 +0100
From: "Arvic Harms" <Arvic.Harms at npl.co.uk>
Subject: Re: [ RadSafe ] Radioactive contamination  of the ocean
To: "The International Radiation Protection (Health Physics) Mailing
List"<radsafe at health.phys.iit.edu>
<A77B33D816BA6B4DB6BDA65A08DF8B990313E607 at exchsvr2.npl.ad.local>
Content-Type: text/plain;charset="us-ascii"

Dear all,

There are some reports on the presence of short-lived Cl-38, which
may indicate that nuclear chain reactions continue after shut-down:



Kind regards,

Arvic Harms

Dr Arvic Harms
Radioactivity Group
National Physical Laboratory

Best Regards

Derek Putley

Technical Area Lead (Criticality) 
Serco (Technical Services)
Thomson House, Risley, Warrington, Cheshire, WA3 6GA, UK

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