The CONSORT REACTOR - Analytical Services Group

Transcription

1 The CONSORT REACTOR - Analytical Services Group Nasser Baghini to provide a national neutron activation analysis service

2 The Delayed Neutron Counting (DNC) System consists of: A suitable neutron source The Consort Reactor, thermal neutron flux =1x10 12 ncm - 2 s -1 Neutron irradiation control unit Programmable Logic Control (PLC) Unit + Sample Loader Set irradiation time, provides the necessary signals to the sample loader to load, blow in and blow out samples Fast sample transport from neutron source to the neutron detector, transit time < 10 seconds Distance between reactor core and the neutron detector ~ 50 m, sample speed ~ 20 ms - 1, transit time ~ 3 seconds Neutron detector An assembly of 18 BF3 proportional counters

3 PLC Unit Interface Computer Neutron Counter Sample capsules L O A D E R Reactor hall DNC laboratory EAS ~50 m Vacuum generator Sample diverter Vacuum diverter REACTOR CORE BF 3 detectors Polyethylene beads Cadmium liner Paraffin wax Sample dump The Automated Delayed Neutron Counting System

4 Inside CONSORT- Neutron source Irradiation Tube used for DNC Control Absorber Fuel Assembly Water

5 Sample Loader To the Reactor core To the DNC laboratory

6 Programmable Logic Control Unit Auto mode, communicates with DNC computer via an interface unit

7 DNC Interface Unit From DNC Computer From Reactor PLC Interface unit providing communications between the Reactor PLC and the DNC Computer

8 Vacuum diverter changes direction of the vacuum from neutron detector rig to the sample dump

9 Sample dump

10 Sample diverter changes the direction of sample passage from the reactor to the dump

11 From the reactor to neutron detector From the neutron detector to the dump

12

13 Primary concrete shieldslowing down fast neutrons Primary Cd shield- cutting off thermal neutrons Polyethylene tube Vacuum line

14 Wooden box in which the neutron detector rig is housed

15 Perspex box Concentric rings Polythene base

16 Centronic BF3 Proportional Counter- > 90% Enriched 10 B, 140 cms Hg pressure Operating voltage 3000 v

17 Inner ring of BF3 counters

18 Outer ring of BF3 counters

19 Combined inner and outer rings of BF3 counters

20 Polythene tube attached to the passing through the detector Centre of the detectorstopping pin

21 Stopping pin

22 Polythene beads delayed neutron moderator

23 Secondary cadmium shield

24 Detector secured to the wooden box

25 Top view Pre-amplifier cable

26 Pre-amplifier connections

27 Wooden box filled with wax blocks secondary neutron moderator

28

29 2 Dual Spec Amplifiers Dual Sum & Invert Amplifier Neutron Counter 4 Bias Supply Units

30 4 Single Channel Analysers

31 Preamplifier 1 Energy Preamp Power In Preamplifier 2 Energy Preamp Power In BIAS SUPPLY BIAS SUPPLY DUAL SPEC AMP AMP 1 In Uni Out Preamp Power DUAL SPEC AMP AMP 2 In Uni Out Preamp Power SINGLE CHANNEL ANALYSER 1 Input SCA Out SINGLE CHANNEL ANALYSER 2 Input SCA Out DUAL SUM AND INVERT AMP A Input A1 Input A2 Input A3 (at the back) Output A QUAD COUNTER TIMER Preamplifier 3 Energy Preamp Power In BIAS SUPPLY DUAL SPEC AMP AMP 3 In Uni Out Preamp Power SINGLE CHANNEL ANALYSER 3 Input SCA Out Input A4 (at the back) AMP B Input B1 Preamplifier 4 Energy Preamp Power In BIAS SUPPLY DUAL SPEC AMP AMP 4 In Uni Out Preamp Power Bi Out SINGLE CHANNEL ANALYSER 4 Input SCA Out Input B2 Output B Counter Inputs DUAL SPEC AMP AMP 5 In Preamp Power Uni Out Setting up the DNC BF3 detectors assembly

32 Background Neutron Counts Frequency of Neutron Counts Neutron Counts Per Minute

33 Efficiency Depends on sample volume For 1 ml solid or powder materials- 25% For 30 ml liquid samples 30%

34 What is the DNC facilities used for? Total Uranium Delayed Neutron Groups half-lives lives Can be used to determine Pu-239 with better detection limit than U-235U U-235 depletion or enrichment

35 Total Uranium Examples: Natural and uranium contaminated soil and water, fossilized bones, milk, grass, crops, fruits and vegetables, human urine For solid materials: g For liquid samples: ml Better detection limit if samples are concentrated e.g. by ashing 1 litre of milk a detection limit of 0.3 ug/litre (6 mbq/litre) of total natural uranium can be obtained. 100 ug natural uranium standard

36 Delayed Neutron Groups Half-lives Delayed Neutrons Experiment Semi-log graph of Neutron Count Rate versus Time Neutron Count Rate Time /Seconds

37 Group1- Half-life of Br-87 Group Neutron Count Rate (cps) y = e x R 2 = The group 1 half-life = Ln(2)/ = 55.8 s Time (seconds)

38 Outer container Inner container for liquids Inner container for solid samples

39 Analytical Services Group Imperial College Reactor Centre Imperial College at Silwood Park Delayed Neutron Count Run 25th November 2004 Customer: Our Ref.: EE49 Tirr: 60sTdk: 15sTct: 60s Standards every 4th irradiation Blank Neutron Count Time Gamma Count In Reactor Time Out Reactor Time Start Count Time EE49B :03: :00:52 15:01:51 15:02:06 EE49B :05: :03:21 15:04:20 15:04:35 EE49B :08: :05:49 15:06:48 15:07:04 EE49B :10: :08:18 15:09:17 15:09:32 EE49B :13: :10:46 15:11:45 15:12:01 Mean Blank Count: 20.2 (13.28%) Sample Neutron Count Time Gamma Count In Reactor Time Out Reactor Time Start Count Time EE49U :15: :13:36 15:14:35 15:14:50 EE :18: :16:04 15:17:03 15:17:19 EE :28: :25:59 15:26:58 15:27:14 EE49U :30: :28:28 15:29:27 15:29:43 EE :33: :30:58 15:31:57 15:32:12 EE :35: :33:26 15:34:25 15:34:41 EE49U :45: :43:21 15:44:20 15:44:35 EE49Q :22: :20:30 16:21:29 16:21:44 Mean Standard Count: (1.33%)

40 Analysis for Uranium by DNC Mean Blank Count Uncer. Dtl Dtl Dtl Dtl ASG No. (cpm) (%) (cpm) (ug Unat) (Bq Unat) (ug 235U) EE49B % ASG No. Mass of Standard Unat Uncer. Unat (ug) (cpm) (%) (cpm/ug) EE49U % Sample Sample Spl-Bkd 235U Uncer. 2σ Unat Uncer. 2σ ASG No. Customer No. mass (g) (cpm) (cpm/g) (mg/kg) (mgkg) (mg/kg) (mg/kg) EE EE EE EE EE EE49Q1 IAEA Soil Copy no. Name Date Prepared by N.M. Baghini Checked by P. Curtis