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Filtered neutron beam studies (biological effects)

Objective

FILTERED NEUTRON BEAM STUDIES (BIOLOGICAL EFFECTS)
BACKGROUND: THE IMPORTANCE OF NEUTRONS IN RADIOLOGICAL PROTECTION IS INCREASING BECAUSE OF THE GROWING USE OF NEUTRONS IN MEDICINE, IN ACTIVATION ANALYSIS, IN BIOLOGICAL RESEARCH AND BECAUSE OF NEUTRONS PRODUCED DURING THE PRODUCTION OF OTHER HIGH ENERGY PARTICLES. MORE IMPORTANTLY, HOWEVER, IS THE LIKELY INCREASE IN NEUTRONS RESULTING FROM THE PRODUCTION OF ELECTRICITY BY NUCLEAR POWER. NEUTRON EMISSIONS FROM IRRADIATED NUCLEAR FUEL DEPEND CRITICALLY ON THE IRRADIATION HISTORY AND CURRENT AND FUTURE PRACTICES (I.E., HIGHER BURN-UP, USE OF FAST REACTOR FUELS, LONGER COOLING TIMES PRIOR TO REPROCESSING) LEAD TO HIGHER RATIOS OF NEUTRON TO GAMMA RAY EMISSIONS. HENCE, THERE IS AN INCREASING IMPORTANCE OF NEUTRONS COMPARED WITH GAMMA RADIATION IN RADIATION PROTECTION. IN ADDITION, IT HAS BEEN SHOWN (HARVEY AND BEYNON, 1972) THAT A SIGNIFICANT PROPORTION OF THE NEUTRON DOSE IN THE WORKING ENVIRONMENTS AROUND NUCLEAR REACTORS AND OTHER NEUTRON-PRODUCING ESTABLISHMENTS IS DUE TO NEUTRONS WHITH ENERGIES BELOW 30-100 KEV, REFERRED TO AS THE INTERMEDIATE ENERGY REGION).
THE PROBLEM OF THE PRODUCTION OF INTENSE SOURCES OF MONO-ENERGETIC NEUTRONS IN THE INTERMEDIATE-ENERGY RANGE WAS ADDRESSED IN TWO PREVIOUS CEC CONTRACTS (135-74-BIO-UK AND 188-76-BIO-UK). THE OUTCOME OF THESE STUDIES IS CONTAINED IN A CEC PUBLICATION (EUR 6107 EN BY A.J. MILL AND J.R. HARVEY). THE MOST PROMISING METHOD FOR PRODUCING INTENSE BEAMS OF INTERMEDIATE-ENERGY NEUTRONS IS BY USING NEUTRON FILTERS INSTALLED IN THE BEAM TUBE OF A HIGH-FLUX REACTOR. ADDITIONALLY, A RECENT INTERNATIONAL MEETING HELD LAST YEAR AT BERKELEY NUCLEAR LABORATORIES DISCUSSED THE APPLICATIONS OF SUCH FILTERED BEAMS. THIS MEETING WAS SPONSORED BY CENDOS, A CEC DOSIMETRY ORGANISATION.
The relative biological effectiveness of 24 keV neutrons in a range of biological systems has been shown to be high and comparable to the effectiveness of high linear energy transfer (LET) alpha particles. However this response is well predicted by the LET distribution of 24 keV neutrons and is in broad agreement with the currently used values of the quality factor for intermediate energy neutrons.
PROJECT (1) BIOLOGICAL EFFECTS OF INTERMEDIATE-ENERGY NEUTRONS
THE FILTERED BEAM, CURRENTLY BEING DEVELOPED AT AERE-HARWELL, WILL BE USED TO INVESTIGATE THE BIOLOGICAL EFFECTS OF 25-KEV NEUTRONS. IN THE FIRST INSTANCE, EXPERIMENTS INVOLVING THE SURVIVAL OF A MAMMALIAN CELL LINE WILL BE USED TO INVESTIGATE THE RELATIVE BIOLOGICAL EFFECTIVENESS FOR CELL KILLING. THE DOSE-RATE TO A SMALL TISSUE SAMPLE IS EXPECTED TO BE 0.3 GY H TO THE POWER OF MINUS 1 AND HENCE IT WILL ALSO BE IMPORTANT TO ESTABLISH DOSE-RESPONSE CURVES UNDER THESE CONDITIONS OF DOSE-RATE BUT USING CONVENTIONAL RADIATION SOURCES. IN ADDITION, IT WILL BE IMPORTANT TO USE SMALL VOLUMES OF CELL SUSPENSIONS FOR THESE EXPERIMENTS IN ORDER TO MINIMISE THERMALISATION OF THE INCIDENT NEUTRON BEAM. IT WILL ALSO BE IMPORTANT TO ESTABLISH THE EFFECT OF THE LONG IRRADIATION TIMES NEEDED ON THE VIABILITY AND OXYGEN CONCENTRATION OF THE CELL SUSPENSION. HOWEVER, IT HAS BEEN SHOWN TO BE POSSIBLE TO OBTAIN MEANINGFUL RESULTS USING THIS CELL LINE FROM PREVIOUS WORK (MILL ET AL., 1976 A,B), WITH DOSE-RATES AS LOW AS 0.1 GY H TO THE POWER OF MINUS 1 IN A BEAM OF NEGATIVE PI-MESONS.
FURTHER STUDIES ARE ALSO PLANNED USING HUMAN LYMPHOCYTES. THE INCIDENCE OF CHROMOSOME ABERRATIONS ON THESE CELLS WILL BE USED AS A BIOLOGICAL END-POINT. THIS SYSTEM IS, OF COURSE, PARTICULARLY RELEVANT FOR RADIATION PROTECTION SINCE SUCH A METHOD IS USED FOR BIOLOGICAL DOSIMETRY. IT IS ALSO EXPECTED THAT OTHER RELEVANT HUMAN SYSTEMS WILL BE USED FOR THESE INVESTIGATIONS (E.G., CHROMOSOME ABERRATIONS IN HUMAN HAIR CULTURES AND CHROMOSOME BANDING CHANGES - THESE ARE TECHNIQUES BEING DEVELOPED IN OUR LABORATORY).
OTHER INVESTIGATIONS TO BE CONSIDERED WILL INCLUDE DOSE-RATE EFFECTS AND FRACTIONATION. HOWEVER, THE LOW DOSE-RATE AVAILABLE AT 25-KEV MAY PRECLUDE THE USEFULNESS OF THESE STUDIES.
DETAILED DESCRIPTION OF THE RESEARCH WORK PROPOSED: OTHER RADIOBIOLOGICAL RESEARCH GROUPS (INCLUDING MRC RADIOBIOLOGY GROUP, HARWELL; AERE-HARWELL AND CRC NORMAL TISSUE RESEARCH GROUP AT THE CHURCHILL HOSPITAL) ARE ALSO PLANNING RADIOBIOLOGICAL INVESTIGATIONS USING 25-KEV NEUTRONS. THE RADIOBIOLOGY RESEARCH PROGRAMME WILL BE A COORDINATED AND COLLABORATIVE EFFORT BETWEEN THESE GROUPS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

CENTRAL ELECTRICITY GENERATING BOARD
Address
Berkeley Nuclear Laboratories
Berkeley
United Kingdom