Setup and testing of the BBNCC neutron well counter.
Date: 2025-07-28
Institutions: Joint Research Centre
Subjects: fundamental particle, nuclear energy, nuclear research, nuclear safety, nuclear technology, prototype

Setup and testing of the BBNCC 
Neutron Well Counter 

Pedersen, B., Varasano, G. 

2025 

ISSN 1831-9424 

 EUR 40329 

  
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Contact information  
Name: Bent Pedersen 
Address: JRC, Via E. Fermi 2749, I-21027 Ispra (VA), Italy 
Email: bent.pedersen@ec.europa.eu 
Tel.: +39 0332 789802 

EU Science Hub 
https://joint-research-centre.ec.europa.eu 

JRC140186 

EUR 40329 

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ISBN 978-92-68-27768-3   ISSN 1831-9424   doi:10.2760/4642029  

KJ-01-25-299-EN-N 

Luxembourg: Publications Office of the European Union, 2025  

© European Atomic Energy Community, 2025  

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How to cite this report: Pedersen, B. and Varasano, G., Setup and testing of the BBNCC Neutron Well Counter, Publications Office of the 
European Union, Luxembourg, 2025, https://data.europa.eu/doi/10.2760/4642029, JRC140186. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Setup and Testing of the BBNCC Neutron Well Counter 

Contents 
Abstract ................................................................................................................................................... 3 

Acknowledgements ................................................................................................................................. 3 

1. 

Introduction ..................................................................................................................................... 4 

1.1. Comparison of BF3 to the standard 3He neutron detector ........................................................ 4 

2.  Detector design ............................................................................................................................... 6 

3. 

Front-end electronics ...................................................................................................................... 7 

3.1. Description of pre-amp and amplifier/shaper ............................................................................. 7 

3.2. Pre-amplifier circuit ..................................................................................................................... 8 

4.  Application to safeguards assay .................................................................................................. 10 

4.1. The Point Model in neutron correlation counting ...................................................................... 10 

5. 

Instrument assay parameters ...................................................................................................... 12 

5.1. High voltage setting of the gas proportional counters ............................................................. 12 

5.2. Measurement of the die-away time .......................................................................................... 13 

5.3. Pre-delay and Gate settings ...................................................................................................... 14 

5.4. Neutron background under standard conditions ....................................................................... 16 

5.5. Dead-time effect in the counting chains .................................................................................. 16 

5.6. Dead-time correction in coincidence counting .......................................................................... 18 

5.7. Detection efficiency determined from R1 and R2 for a 252Cf source ......................................... 20 

5.8. Dead-time correction in multiplicity counting ........................................................................... 20 

5.9. Sensitivity to high gamma fields............................................................................................... 22 

5.10. Limitations of use due to high dead-time and die-away time .............................................. 22 

5.11. Summary of instrument parameters for safeguards assay .................................................. 23 

6.  Conclusions ................................................................................................................................... 24 

References ............................................................................................................................................ 25 

List of figures ........................................................................................................................................ 26 

List of tables ......................................................................................................................................... 26 

Annexes ................................................................................................................................................. 27 

Annex 1.  Example of neutron background measured over long time ............................................ 27 

Annex 2.  Measured and dead-time corrected count rates of certified 252Cf sources .................... 35 

Annex 3.  Effect of  pile-up on neutron count rates for background and a small 252Cf source .... 36 

2 

 
 
 
 
Abstract 

A new prototype well counter for nuclear safeguards using non-standard neutron detection mechanism 
has been designed, constructed, and taken into operation at JRC.  The instrument, named Boron Based 
Neutron Correlation Counter or BBNCC, employs 24 BF3 gas proportional counters to achieve a neutron 
detection  efficiency  of  26%.    This  report  describes  details  of  the  detector  design  and  includes  the 
results of the initial characterisation of the detector in terms of safeguards assay parameters, e.g. die-
away  time,  detection  efficiency  and  dead-time,  as  an  instrument  intended  for  verification  of  bulk  Pu 
samples.    Besides  the  use  of  neutron  detectors  different  from  the  standard  3He  gas  counters,  the 
BBNCC  also  became  the  testbed  for  the  newly  in-house  developed  front-end  electronics  for  gas 
proportional counters.  The tests carried out thus also represent the first in-situ application of the new 
detector  electronics.    For  this  reason,  some  details  of  the  performance  testing,  e.g.  stability  and 
electronic noise level, of the detection system is also reported.   

At this point the BBNCC, although a prototype instrument, is fully prepared for inspection use and can 
thus  be  considered  a  valid  alternative  to  the  standard  counters  currently  operated  by  Euratom 
Safeguards of DG ENER.  

Acknowledgements 
The  authors  wish  to  thank  Dr.  Marita  Mosconi  from  DG  ENER  (Euratom  Safeguards)  for  the  MCNP 
calculations of the BBNCC design, and Dr. Tatjana Bogucarska (JRC)  for assisting with the laboratory 
measurements. 
Many thanks are due to the colleagues from the LABEL laboratory of JRC for lending and installing the 
gamma dose meter. 

Authors: 

Bent Pedersen, Giovanni Varasano 

3 

 
 
 
 
 
 
 
 
1.  Introduction 

The  Boron  Based  Neutron  Correlation  Counter  (BBNCC)  is  a  prototype  well  counter  for  nuclear 
safeguards verification measurements.  The BBNCC was conceived at JRC around 2014 as part of the 
JRC research programme in “alternatives to 3He” in response to the emerging shortage of 3He gas for 
neutron detectors.  

The  BBNCC  was  designed  to  have  the  same  sample  cavity  dimensions  as  the  standard  High  Level 
Neutron Coincidence Counter (HLNCC-II) [1] which for decades had been the workhorse in Euratom and 
IAEA  safeguards  inspections  of  bulk  Pu  samples.    Having  the  same  sample  cavity  dimensions,  the 
target application area was the same as for the HLNCC-II.  However the intention was to incorporate 
improved  assay  parameters  with  respect  to  the  HLNCC-II  in  order  to  improve  the  verification 
performance.    In  particular,  the  HLNCC-II  has  been  applied  in  so-called  neutron  coincidence 
measurements, but not in neutron multiplicity measurements.  The main reason for this, although not 
the  only  reason,  was  the  relatively  low  neutron  detection  efficiency  of  17%  being  insufficient  for  a 
stable  measurement  of  the  neutron  triples  rate  (proportional  to  the  detection  efficiency  in  the  3rd 
power)  in  routine  safeguards  verification  measurements.    The  BBNCC,  besides  being  a  3He-free 
detector,  intended  to  overcome  this  limitation  by  implementing  more  detectors  to  achieve  a 
substantially higher efficiency (measured at 26.65%).  The design of the BBNCC was presented to the 
safeguards  community  in  2015  [2]  following  extensive  Monte  Carlo  calculations  [3].    Shortly 
afterwards,  the  BBNCC  was  built  and  operated  in the  JRC laboratory.    Since  then  JRC  had  concluded 
work on a new front-end electronics circuit for gas proportional counters that would be free from the 
usual issues of double-pulsing and other electric noise often seen in commercial electronics, and which 
should  become  the  standard  electronics  for  use  in  JRC  future  neutron  detector  heads.    The  BBNCC 
prototype, configured with six parallel counting chains, was a suitable full-scale testbed for taking the 
new homemade electronics into operation. 

The  present  report  describes  the  performance  of  the  BBNCC,  the  newly  implemented  front-end 
electronics, as well as safeguards assay parameters of this passive neutron counter. 

1.1. Comparison of BF3 to the standard 3He neutron detector 
Standard neutron detectors for nuclear safeguards, employ 3He in form of a gas proportional counter.  
The  standard  format  is  a  one-inch  (25.4mm)  tube  diameter  at  4  bar  pressure.    At  this  pressure  the 
tube is still sensitive only to thermal neutrons, and as an absorber can be considered almost “black”.  
Higher  pressures  can  be  applied  to  detect  also  epi-thermal  neutrons,  and  additional  quench  gas  can 
make  the  charge  collection  time  shorter.    Adding  heavier  poly-atomic  gas  however  increases  the 
sensitivity to gamma rays.  The only real disadvantage of the  3He tube is the high price, and in recent 
years the limited availability. 
In  contrast,  BF3  gas  is  inexpensive  when  compared  to  3He.    The  counter  tube  design  is  practically 
identical to that of  3He.  Even the process of enriching natural boron to a level above 95% in the  10B 
isotope is inexpensive and technically straightforward. 
Also  regarding  nuclear  properties  related  to  neutron  detection,  BF3  is  a  valid  alternative  to  3He  gas.  
Both isotopes produce charged particles from the neutron capture reaction 

10B(n, )7Li 
10B(n, )7Li 
3He(n, p)3T 

Q = 2.31 MeV    
Q = 2.792 MeV   
Q = 0.764 MeV 

(7Li* in 1st excited state, 93%) 
(7Li in ground state, 7%) 

The large Q value for these reactions is released as kinetic energy of the charged fragments.  

4 

 
 
 
 
 
 
 
 
 
 
 
The  (n,  )  and  (n, p)  reactions,  respectively, both  follow  the  1/v  behaviour,  and  have  very  high  cross 
sections at thermal energy.  The thermal neutron (0.0253 eV) reaction cross sections for  10B and  3He 
are  

10B(n, )7Li 
3He(n, p)3T 

3844 b 
5316 b 

The pressure in BF3 detectors is normally limited to little more than one bar compared to four bar for 
3He  gas.  To  achieve  similar  macroscopic  cross  section  for  the  two  standard  configurations,  the 
diameter of BF3 tubes is often doubled (to two inches) to yield a four times larger gas volume, so that 
“pressure  volume / unit length” amounts to roughly the same for the two neutron absorbers.  
The  charged  ions  from the  neutron  reaction  event  lose  their  kinetic  energy  through  ionization  of  the 
counter gas.  The free electrons accelerate towards the anode in the electrical field between the anode 
wire (at high voltage potential) and the tube wall (at ground potential), with subsequent collection of 
electron charge on the anode wire as a means to register the neutron capture event.  
Except for the so-called wall effect, the kinetic energy of the reactions is deposited in the gas through 
ionization.   The higher Q value for the  10B neutron  reaction and the lower ionization energy for  10BF3 
compared to  3He gas suggest that even more electron charge can be  collected at the anode for this 
compound.  This is however also influenced by other factors including BF3 (in contrast to He) being a 
poly-atomic compound, gas pressure, high-voltage potential, and anode wire diameter in the gas tube, 
and others.  A potentially larger charge collection, however, should in principle allow for an even better 
pulse height separation of neutron detection events and gamma-rays interactions and electrical noise.  
The  heavier  BF3  compound  however  may  be  more  susceptible  to  gamma-ray  interactions  and  thus 
“gamma pile-up” effects in the detector electronics.  This was a subject of testing as reported below. 

The BBNCC, being a safeguards instrument of the category “alternatives to  3He” i.e. a passive neutron 
detector  head  based  on  a  neutron  detection  mechanism  other  than  the  (n,  p)  reaction  in  3He, 
incorporates  most  of  the  standard  features  known  from  3He  based  systems.    Features  that  other 
“alternatives” often lack to different degree, including: 

- 

The detection mechanism is based on an exothermic nuclear reaction (n, ) producing charged 
particles in the gas.  This allows for electric charge collection, and subsequent easy conversion 
to an electrical signal representing a discrete neutron detection event. 

-  A  gas  proportional  counter  based  on  a  nuclear  reaction  depositing  a  substantial  amount  of 
energy in the gas (and where the energy deposition is proportional to the signal pulse height), 
allows for a simple pulse height discrimination between the neutron detection event, and other 
reactions depositing energy in the gas. 

-  As 10B is a neutron absorber with a high thermal cross section, the detectors are fitted with the 
standard  neutron  moderator  surrounding  the  gas  proportional  counters  exactly  as  for  3He 
based counters.  This causes slowing down times and thermal neutron life-times similar to 3He 
systems thus requiring the usual  settings in neutron counting electronics of parameters such 
as pre-delay and Gate width, and indeed similar neutron detection efficiencies. 
The  “updating  dead-time”  phenomenon  in  gas  proportional  counters  is  well  understood  and 
corrected for in the same fashion for the two types of neutron absorbers, 10B and 3He. 

- 

-  Gas-based detectors with charge collection have a uniform neutron detection efficiency along 

the length of the detector. Their lengths can even be very large. 

-  Gas-based detectors are known for their long durability. 

5 

 
 
 
 
 
 
 
 
 
 
 
These  similarities  between  3He  and  10B  when  used  in  gas  proportional  counters  have  the  advantage 
that  the  safeguards  inspector  can  readily  apply  the  same  analysers,  the  well-tested  analysis 
algorithms, and software packages routinely used in neutron safeguards measurements today.  This is 
an important bonus that many other “alternatives” often lack.  

BF3 is a corrosive gas which may result in a shorter lifetime of the detector assembly compared to 3He 
detector based systems.  In addition, the toxicity of BF3 gas has been suggested to be a safety concern 
for use in nuclear facilities.  To counteract such concerns, the BBNCC counter tubes have been limited 
to 0.95 bar pressure, amounting to roughly 50 grams of BF3 gas distributed in 24 2-inch tubes.  In the 
event  of a gas leakage, this means that the BF3 gas would  be released only slowly, and out-of-tube 
pressure in the instrument would not increase.  The BBNCC design incorporates an additional airtight 
barrier confined to the volume of the moderator tube channels together with the internal junction box 
volume.    This  is  achieved  by  applying  O-ring  seals  on  all  seams  and  joints  towards  the  external.    A 
chemical  agent  to  neutralise  the  fluoride  gas in  case  of  leakage  is  placed inside  the  junction  box  to 
guard  against  a  possible  release  of  the  toxic  BF3  gas  to  the  environment  (more  information  in  [2]).  
Similar safety measures are adopted in the shipping industry  for transportation of bulk quantities of 
fluoride gas.  

2.  Detector design 
The  BBNCC  was  designed  with  the  help  of  Monte  Carlo  calculations  [3].    A  report  on  this  work  was 
presented in the Manchester ESARDA annual symposium in Manchester in 2015 [2].  The calculations 
included various configurations of gas tubes of both 25.4 mm and 50.8 mm diameters, various number 
of  tubes,  as  well  as  optimisation  of  their  position  in  the  moderator.    The  tubes  were  placed  in 
concentric rings in a HDPE moderator surrounding the central sample cavity with the ring radii and the 
moderator dimensions as variables.  The calculations also included design of the top and bottom plug 
of the cavity.   The tube pressure was kept at 0.95 bar  (99% enriched in  10B) mainly to maintain the 
good linearity in signal pulse height as function of energy deposition in the gas, although a 20% higher 
pressure  in  this  regard  would  have  been  acceptable.    Also  the  internal  cavity  diameter  was  kept 
constant.    The  optimisation  criteria  included  the  neutron  detection  efficiency  and  die-away  time  in  a 
single figure-of-merit parameter, but also compactness of the moderator was taken into account.  The 
calculations  assumed  a  thick  stainless-steel  containment  around  the  spontaneous  fissile  source  to 
mimic a plutonium storage container, yielding  optimal tube ring radii slightly smaller than for a bare 
source.  The final design incorporated 24 tubes of 50.8 mm in a two-ring configuration.  Figure 1 below 
is from the design study [2].  

The dimensions of the central sample cavity were selected to be similar to that of the HLNCC-II device, 
known to be sufficient to accommodate most industrial bulk Pu containers.  With the top and bottom 
plugs fully inserted, the cavity height is approx. 430 mm and usable diameter is 166 mm.   
The  top  and  bottom  plugs  are  made  of  solid  graphite  of  density  of  1.67  g/cm3.  The  Monte  Carlo 
calculations showed that this material performed better as a fast neutron reflector than combinations 
of  polyethylene  and  aluminium  [2].    A  1  mm  cadmium  liner  completely  covers  the  moderator  block 
internal and external surfaces, as well as the top and bottom plug surfaces facing the sample cavity. 

6 

 
 
 
 
 
 
Figure 1.  Final dimensions of the BBNCC counter as optimised by Monte Carlo simulations 

Source: JRC analysis. 

For  the  routing  of  high  voltage  (HV)  to  the  anode  wires,  the  24  BF3  gas  proportional  counters  are 
grouped in six parallel chains of four detectors each.  Each group includes two detectors from the inner 
and two from the outer ring, producing same counting rates in  all  groups for a centred homogenous 
sample.    The  HV  rail  to  each  chain  has  the  usual  R-C  low-pass  filter  (R  of  1.5  M  and  C  of  10  nF) 
followed  by  a  current  limiting  resistor  (R  of  24  M).    This  relatively  large  resistor  was  selected  to 
eliminate spurious discharges in the detector tubes.  Finally a large HV decoupling capacitor connects 
to the input of the pre-amplifier.  

3.  Front-end electronics 
JRC has worked in recent years on the development of new front-end electronics for gas proportional 
counters for neutron detection.  The scope has been to develop circuitries that would be inexpensive in 
large  quantity  productions,  and  that  could  substitute  the  electronics  currently  used  in  many  aging 
neutron  well  counters.    As  a  first  step,  a  new  amplifier/shaper  had  been  designed  which  would 
accommodate a commercial Cremat pre-amplifier [4].  This amplifier circuit, together with the Cremat 
CR-110 pre-amplifier (see  www.cremat.com), was tested  extensively in different experimental  setups 
and in the JRC Drum Monitor, a large passive neutron counter with 28 parallel electronics chains and a 
total  of  148  3He  detector  tubes.    In  a  second  step  a  new  pre-amplifier  [5],  pin-compatible  with  the 
Cremat  CR-110,  was  developed  at  JRC.    This  combination  of  the  in-house  built  pre-amplifier  and 
amplifier  was  first  installed  in  the  BBNCC.    In  this  manner,  the  BBNCC  became  the  testbed  for 
configuration  and  performance  testing  of  these  new  circuits.    After  the  test  phase,  the  neutron 
experiments presented in this report were performed with this electronics configuration.  

3.1. Description of pre-amp and amplifier/shaper 
The schematic principle of the standard amplifier circuit is shown in Figure 2 which however does not 
show  the  discriminator  and  digital  pulse  processing  circuit.    These  details,  including  the  complete 
circuitry  layout  with  component  values  and  PCB  design,  are  given  in  Ref.  4.    The  amplifier  circuit  is 

7 

8.4 cm18 cm12 cm1 mm Cd2.54 mm75.1 cm16.71 cm1 mm Cd40.05 cm24 cm 
 
 
 
 
 
 
 
basically  composed  of  the  separate  pre-amplifier  board  (in  Figure  2  the  Cremat  CR-110 is  depicted) 
followed by a pole/zero network, followed by the main amplifier and shaper.  

Figure 2.  Schematic of the JRC amplifier for charge collection proportional counters 

Source: JRC analysis. 

The  main  amplifier  includes  a  standard  digital  discriminator  circuit  producing  a  digital  TTL  pulse  for 
each neutron detection event.  In the BBNCC, a digital signal mixer and de-randomizer was not applied 
to the six parallel chains.  The reason is that JRC uses signal analysers capable of processing the six 
parallel lines separately.  When a single signal output from the BBNCC is desired, e.g. to suit a single-
input analyser, the digital outputs from the amplifier circuits can simply be daisy-chained. 
A  pole/zero  network  was  implemented  at  the  output  of  the  CREMAT  pre-amplifier  [4].    The  design 
allowed  for  three  different  shaping  times  to  be  implemented:  500  ns,  (default),  750  ns  and  1  µs.  
These  different values  can  be  achieved  by  applying  solder  jumpers  to  select the  different  capacitors 
available on the printed circuit board.  With reference to Figure 2, the expected signal waveform of the 
analogue amplifier pulse has these characteristics: 

Pre-amplifier DC gain:   
P/Z net DC gain:  
Integrator DC gain: 

k Q / CF 
- R2 / (R0+R1) 
- R3 / R4, 

3.2. Pre-amplifier circuit 
The in-house developed pre-amplifier is best described as a differential cascode charge sensitive pre-
amp  (n-Channel  Low  noise  JFETs  Input  Stage)  implemented  in  a  four-layer  printed  circuit  board.  
Details  are  given  in  ref  5.    The  benefits  of  this  choice  include  a  high  gain,  good  noise  immunity 
(cancellation),  and  small  footprint  (fewer  components).    One  drawback  is  the  need  for  a  dual  power 
supply rather than a single supply voltage.  [To facilitate this, a 5V to ± 9V very-low-noise DC converter 
was designed and manufactured although not used in the BBNCC.  This DC converter however makes it 
easy to introduce the JRC amplifier into existing systems that apply the standard 5V supply]. 
The  classical  direct  cascode  amplifier  is  constructed  from  two  JFET  (Junction  FET)  transistors  where 
one  operates  as  a  common  source  (CS)  and  the  other  as  a  common  gate  (CG).    Of  the  FET’s  Gate, 
Source and Drain terminals, the Source of the top  JFET is held at a constant voltage eliminating the 
reverse transmission of the variation of the Drain output voltage which  (across the capacitance from 
Gate  to  Drain)  would  be  transmitted  to  the  bottom  FET.    This  fact  reduces,  or  quite  eliminates,  the 
Miller  effect  and  contributes  to  a  much  higher  bandwidth  with  respect  to  a  CS  amplifier.    The 
decoupling of the output from the input contributes to a faster response and makes the stage largely 
immune to fluctuations.  The fluctuations of the output baseline are further held quite constant by the 
usage of the “differential configuration”. 
The JRC pre-amplifier circuit is shown in Figure 3, as an adaptation of the circuit suggested in ref. 6. 

8 

 
 
 
 
 
 
 
Figure 3.  The JRC differential cascode charge sensitive pre-amplifier 

Source: JRC analysis. 

In our design, the cascode configuration is mirrored.  A one-sided cascode circuit would also work but 
the voltage  waveform  at the output  would have an important DC component.   Using this differential 
(mirrored)  stage,  the  potential  difference  from  one  input  to  the  other  (fixed  at  ground)  is  amplified.  
The voltages at the output lines (Drain terminals) change like a seesaw (when one decreases, the other 
increases  and  vice  versa).    The  open-loop  operational  amplifier  simply  receives  the  signal  difference 
and returns it to the input via an Rf Cf network (this feedback network is not shown in Figure 3).  The 
total gain equals 1/Cf, and the ideal integrator is reduced to an approximate integrator by the discharge 
resistor which also defines the long discharge time of the amplifier.  This fall-time is in our case set to 
140 us in order to remain similar to that of the (previously used) CR-110 pre-amplifier.  The indicated 
Rz  and  Cz  in  the  differential  stage  are  chosen  to  create  a  pole-zero  compensation  on  the  used 
operational amplifier, making it less prone to create instabilities (instabilities are reduced by the basic 
workings of the feedback compensated networks). 

Figure 4.  BBNCC front-end electronics 

(a)  BBNCC  open  junction  box  with  six  parallel 
amplifier circuits mounted 

(b)  View  of  amplifier  (horizontal)  and  pre-amplifier 
(vertical) boards, and external supply voltage filters 

Source: JRC analysis. 

9 

 
 
 
 
 
 
 
The  electronics  configuration  shown  was  first  tested  in  the  BBNCC.    One  concern  in  the  new 
implementation  was  the  possible  feedback  from  fluctuations  on  the  positive  and  negative  voltage 
supply rails to (neighbouring) pre-amplifier inputs.  To avoid this, a substantial LC filter was applied on 
each of the voltage rails for each chain.  This is visible in Figure 4b.  The blue capacitors (C) of 4.7 mF 
are inserted from voltage rail to ground, and the inductor (L) of 150 H on the rail line, working as a 
simple LC filter mainly against high frequency noise.  In addition, each amplifier board has two small 
EMI  (Electro  Magnetic  Interference)  T-type  (L-C-L)  surface  mount  filters  in  series  with  a  tantalum 
capacitor  (Ct)  on  each  rail  to  restrain  electromagnetic  interference  signals.    Also  for  the  on-board 
filters, the capacitors are connected to ground, and the two inductors (L) are connected in series (L-C-
L-Ct-L-C-L).    In  this  fashion,  significant  measures  were  taken  to  attenuate  possible  external 
electromagnetic noise on the principle of maximum impedance mismatching.  

4.  Application to safeguards assay  
The BBNCC well counter is  intended  for  Pu  mass determination of  sealed  samples by detection (and 
counting)  of  neutrons  emitted  from  the  same  fission  event,  the  so-called  correlated  neutrons.    This 
type of measurements is often referred to as neutron coincidence counting, or multiplicity counting.  
For  the  nuclear  inspector,  the  method  provides  a  very  high  degree  of  confidence  in  the  Pu  mass 
determination.    The  reason  is  that  multiple  quantities  related  to  the  spontaneous  fission  rate  of  the 
sample  are  measured  directly,  and  from  which  the  Pu  mass  is  calculated  together  with  other 
interlinked sample parameters.  This determination of multiple parameters that uniquely relate to the 
Pu  sample  in  a  single  measurement,  provides  the  high  confidence in  the  Pu mass verification  result.  
This important fact makes neutron multiplicity  counting, the workhorse among methods  for Pu mass 
verification despite it being an NDA method with a typically limited accuracy. 
In neutron multiplicity counting, the Pu mass can even be calculated directly without the need for prior 
calibration measurements with known samples, simply by utilizing exclusively the measured quantities, 
some nuclear data, and some pre-determined instrument parameters.  

4.1. The Point Model in neutron correlation counting 
The  BBNCC  design,  as  for  all  passive  neutron  well  counters,  is  tailored  to  satisfy  the  so-called  Point 
Model.    The  Point  Model  operates  with  single-value  parameters  such  as  for  example  the  neutron 
detection probability.  In order to achieve the same detection probability of all neutrons emitted from 
the  sample  volume,  the  detectors  are  arranged  in  an  approximate  4  geometry  surrounding  the 
sample cavity.  In the BBNCC this is implemented as a cylindrical detector/moderator with  large fast-
neutron reflectors on top and bottom. 
Another  important  Point  Model  parameter  is  the  average  thermal  neutron  lifetime  of  the 
detector/moderator  assembly,  also  known  as  the  die-away  time.    Covering  the  cavity  walls  with  a  1 
mm cadmium liner helps to  achieve the same value independent of where in the sample volume the 
neutron is emitted and making the value (relatively) independent of the neutron source spectrum.  
In neutron counting for safeguards purposes, JRC applies the Point Model as developed at JRC several 
years ago by W. Hage [7, 8 ,9, 10].  In this comprehensive work, signals representing neutron detection 
events are counted in either signal triggered or periodically triggered observation intervals, resulting in 
frequency distributions of the number of intervals containing 1, 2, 3, … , 255 signals.  The key element 
in  the  analysis  of  these  measured  distributions  is  to  form  the  normalised  factorial  moments 
representing signal multiplets of 1st, 2nd and 3rd order, and from where the rates of single (R1) events, 
and  correlated  double  (R2)  and  triple  (R3)  events  are  derived.    In  this  context  “correlated”  refers  to 
neutrons originating from the same fission event.  
The most powerful feature of the Point Model is that these three measured rates, in simple equations, 
can  be  expressed in terms  of  sample  quantities  and  instrument  parameters, all  of  which  include  the 

10 

 
 
 
 
spontaneous fission rate in the first power (eqs. 1-3).  In practice, this feature allows for a very good 
determination  of  the  spontaneous  fission  rate  which  in  turn  yields  the  mass  of  spontaneous  fissile 
isotopes (mass of 240Pu-effective) of the sample. 
The equations 1 to 3 relates the measured rates of singles and the correlated doubles and triples (left-
hand side) to the physical quantities (right-hand side) [8].  

𝑅1 = 𝐹𝑠𝑠(1)𝜀𝑀(1 + 𝛼)  

𝑅2 = 𝐹𝑠𝑠(2)𝜀2𝑀2 [1 + (𝑀 − 1)(1 + 𝛼)

𝑠(1)𝐼(2)
(𝐼(1)−1)𝑠(2)

] 

𝑅3 = 𝐹𝑠𝑠(3)𝜀3𝑀3 [1 + 2(𝑀 − 1)

𝑠(2)𝐼(2)
(𝐼(1)−1)𝑠(3)

+(𝑀 − 1)(1 + 𝛼)

𝑠(1)
(𝐼(1) − 1)𝑠(3)

{𝐼(3) + 2(𝑀 − 1)

2
𝐼(2)
(𝐼(1) − 1)

}] 

where:   

the alpha ratio is given as 

𝛼 =

𝑆𝛼
𝐹𝑠𝑠(1)

(1) 

(2) 

(3) 

𝑀 =

the multiplication factor is  

(1−𝑝)
(1−𝑝𝐼(1))
Fs   is spontaneous fission rate of the sample, 
(1), (2), (3)   are the 1st, 2nd and 3rd order normalised factorial moments 
     of the P distribution for having  neutrons emitted in a fission event, 
    is the neutron detection probability, 
p    is the fast neutron fission probability, 
S  is the (α, n) reaction rate of the sample, 
indices s and I represent spontaneous and induced fission, respectively. 

From these three equations, three unknowns among the right-hand side quantities can be determined 
rigidly.  This includes the spontaneous fission rate (yielding the mass of  240Pu- effective) together with 
two parameters among M, α and . 
In  routine  safeguards  applications,  sometimes  the  mass  is  determined  indirectly  using  calibration 
curves of R2 against mass of  240Pu-eff.  This is possible when calibration curves have been produced 
using standards which are representative of the unknown samples in terms of mass range, container 
type, sample shape, density, and chemical composition. 

In  principle  a  fourth  equation  could  easily  be  added  to  the  Point  Model.    However  in  practice,  the 
measured  R4  is  associated  with  large  uncertainty  partly  because  of  the  detection  probability  () 
appearing  in  the  fourth  power,  and  the  (4)  for  spontaneous  and  induced  fission  for  Pu  isotopes 
including only the tail end of the P distributions. 

The  Point  Model  is  applied  to  assay  of  Pu  in  a  variety  of  forms  and  scenarios  for  verification 
measurements in  Pu processing facilities.  In practical  applications, deviations from the  requirements 
of  the  Point  Model  e.g.  the  validity  of  the  single  parameter  values  of  M,  α  and   can  sometimes  be 
identified.  An example if this is the case of Pu assay in large waste containers where the sheer spatial 
distribution of the spontaneous fission source, and a non-uniform waste matrix, makes maintaining a 
single value of  difficult.  Despite such deviations in the requirements, it is noteworthy how accurate 
neutron correlation counting actually is in determining Fs (proportional to the mass).  Admittedly, the 

11 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
other  parameters  are  often  less  well  determined  as  per  the  non-linear  way  they  appear  in  the 
equations (1 – 3).  

5.  Instrument assay parameters 
The BBNCC instrument parameters used in coincidence and multiplicity counting applications have been 
determined  experimentally  and  are  shown  in  this  chapter.    For  this  characterisation,  the  BBNCC  had 
been  configured  with  the  in-house  built  electronics  described  in  the  previous  chapter.    A  series  of 
laboratory  measurements  as  described  below  is  normally  required  whenever  a  new  passive  neutron 
well counter for safeguards inspections is taken into operation.  

5.1. High voltage setting of the gas proportional counters 
During the installation and testing of the electronics, each amplifier gain had been adjusted to yield a 
3.5 V full-energy analogue pulse height for thermal neutron detections @ 1800 V high voltage (HV) on 
the anode wires.  The discriminator threshold was set to 0.6 V. 
Figure 5 shows the number of total counts in a given measurement time as function of HV setting for 
all chains, also known as the high voltage plateau curve.  

Figure 5.  BBNCC high voltage plateau curve 

Source: JRC analysis. 

The plot shows a near-constant plateau over at least 250 V (1750 - 2000 V) confirming that indeed 
the  six  amplifier  chains  behave  similarly.    Based  on  Figure  5,  a  common  HV  value  of  1800  V  was 
selected for the six amplifier chains.  The reason for selecting a value on the lower end of the plateau, 
rather than e.g. at the middle of the plateau, is that in increasing gamma-ray fields (e.g. for larger Pu 
sample)  the  plateau  narrows  from  the  high  end.  In  other  words,  at  higher  gains  (higher  HV  values) 
multiple gamma rays will eventually deposit sufficient energy to overcome the discriminator threshold 

12 

 
 
 
 
 
 
as expected for a proportional counter.  This is the main reason for the departure from the plateau at 
higher HV settings, in Figure 5 at around 2100 V. 

5.2. Measurement of the die-away time 
The  die-away  time  of thermal  neutrons in  the  detector-moderator  assembly, or  the  average  thermal 
neutron  lifetime,  is  as  key  parameter  in  neutron  correlation  counting.    When  the  thermal  neutron 
detectors are embedded in a polyethylene moderator, with a Cd liner on all surfaces, some parameters 
that influence the value of the die-away time are the thickness, density, and absorption properties of 
the  moderator  block.    Also  the  number  of  thermal  neutron  absorbers  (including  detectors),  their 
macroscopic  absorption  cross  section,  and  their  position  in  the  moderator  impacts  the  resulting  die-
away time.  
Despite the many design parameters influencing the die-away time, a single exponential decay curve 
of  the  die-away  is  quite  easily  achieved.    This  is  desirable  because  the  algorithms  for  mass 
determination,  including  the  analytical  dead-time  correction,  are  much  simpler  when  a  single 
exponential die-away can be assumed.  But most importantly, in cases where this is not achieved, the 
die-away time (as the detection probability) tends to become sensitive to the spectrum of the incoming 
fast neutrons.  In addition, only if the detectors can be considered purely thermal neutron absorbers, 
will (approximately) all fast neutrons follow the same die-away curve, and have same average thermal 
neutron lifetime (die-away time).  In reactor physics, this is known as the fundamental mode decay, i.e. 
the longest decay mode represented by the smallest eigenvalue in the solution to the neutron diffusion 
equation. 
There are many methods for measuring the die-away time.  All of them concern measurement with a 
neutron source where multiple  fast  neutrons are injected simultaneously into the detector/moderator 
assembly,  and  a  signal  analyser  where  neutron  detections  are  counted  in  time  gates  following  a 
(trigger) detection event at time zero.  A spontaneous fission source (e.g. 240Pu, 244Cm or 252Cf) emitting 
bursts  of  prompt  fission  neutrons  can  conveniently  be  used,  together  with  e.g.  the  standard  Shift 
Register analyser.   
Figure  6  is  the  result  of  a  long measurement  using a  small  252Cf source in  the  centre  of  the  BBNCC 
cavity and recording the time histogram of neutron detection events with a multi-channel scaler (MCS).  
The MCS is configured to record events in time channels (bins) following a trigger event (at time zero).  
A trigger event initiates a scan of the time channels, and subsequent events increment the counter of 
the corresponding channel.  When the scan is completed, the MCS waits for the next trigger to initiate 
the next scan.  There is zero dead-time between channels so that the duration of a scan equals (set 
number of channels) x (set channel dwell-time).  In the measurement of Figure 6, the MCS was set to 
4k channels, a dwell-time of 260 ns.  More than a million scans were accumulated. 
In  the  first  few  microseconds  after  the  trigger  the  measured  curve  is  increasing  rather  than 
decreasing (Figure 6).  This is mainly due to dead-time effects immediately after the neutron 
detection event at time zero, and to a lesser extend due to ongoing slowing down (or higher 
decay modes) of neutrons born in the same fission event as the neutron detected at time zero.  
Also,  in  Figure  6  is  shown  the  result  of  a  least-squares  fit  of  the  bin  values  to  a  single  decaying 
exponential curve (plus a constant level), excluding the first few microseconds.   

13 

 
 
 
 
 
 
 
 
 
 
Figure 6.  MCS histogram with 252Cf source of neutron detection events and exponential fit 

In the fit, the die-away time (i.e. the reciprocal of the exponential decay constant) is determined to be 

Source: JRC analysis. 

1
𝜆⁄ = 83.47  ± 0.084 𝜇𝑠 

where  is the decay constant of the exponential decay fit. 

5.3. Pre-delay and Gate settings 
The standard Shift Register employs signal triggered multiplicity counting using a prompt (R+A) and a 
delayed  (A)  Gate.    A  fixed-time  pre-delay  is  introduced  between  the  trigger  and  the  opening  of  the 
prompt  Gate.    The  pre-delay  serves  to  eliminate  the  dead-time  effect  from  the  trigger  signal  in  the 
prompt  Gate.    The  pre-delay  should  be  set  large  enough  to  overcome  this  dead-time  effect  so  that 
when measuring a random source (e.g. an AmLi source) the prompt and the delayed gates experience 
same dead-time effects thus counting equally.  
Just as the pre-day should be set large enough to avoid trigger dead-time in the prompt Gate, it should 
be no larger in order to maximise the fraction of correlated neutrons collected in the prompt Gate (see 
e.g. Figure 6).  
The optimal pre-day is easily determined by observing the pair counts in the prompt and the delayed 
Gate for variable pre-delay settings when measuring a random (i.e. uncorrelated) neutron source.  The 
optimal  pre-delay  is  chosen  as  the  smallest  value  yielding  the  same  counts,  within  statistical 
uncertainty, in the prompt (R+A) Gate and the delayed (A) Gate.  

14 

 
 
 
 
 
 
For this purpose an AmLi neutron source was centred in the BBNCC cavity.  The measurement time at 
each pre-delay setting was 600 s. The Gate width was set short, at 20 s, to maximise any dead-time 
effect from the trigger signal in the prompt gate.   
The  difference  between  the  two  gates  (R  =  [R+A]  –  [A])  should  (statistically)  be  zero  except  for  the 
missing  counts  in  the  (R+A)  Gate  caused  by  the  trigger  dead-time.    In  other  words  the  difference 
remains negative until the pre-delay is set sufficiently large.  Figure 7 shows R/(R) as function of pre-
delay, where one standard deviation of the uncertainty on R is calculated as (𝑅) = √[𝑅 + 𝐴]2 + [𝐴]2 
The lowest pre-delay value on the plateau of (statistically) zero is optimal.  In Figure 7 arguably a pre-
delay of 3.5 s appears to be sufficient.  However, from this point onwards a conservative value of 4.5 
s is selected.  

Figure 7.  Shift Register measurements of R = ([R+A] – [A]) in units of standard deviations as function of pre-
delay for an AmLi random neutron source 

Source: JRC analysis. 

The  selection  of  the  optimal  Gate  width  was  done  in  a  similar  fashion.  When  measuring  a  small  Cf 
source, the Gate width that yields the smallest relative uncertainty of the measured doubles ((R)/R as 
above) for a given measurement time, can be considered the optimal Gate width.  It is well-known that 
for  a  weak  source  (causing  a  small  dead-time  effect)  this  value  is  approx.  1.257    die-away  time.  
Based  on  the  measured  die-away  time  in  Figure  6,  the  Gate  width  for  multiplicity  counting  in  the 
BBNCC is conveniently selected to 100 µs.  

15 

 
 
 
 
 
5.4. Neutron background under standard conditions 
Part of the efforts of testing for electronic noise in the counter involves observing the stability of the 
neutron  background  in  repeated  measurements.    The  neutron  background  consists  mainly  of  single 
neutron events originating from the atmosphere, the ground and building materials such as concrete.  
A  small  part  of  the  background  however  comes  in  form  of  high  multiplicity  bursts  produced  mainly 
from  high  energy  atmospheric  particles  interacting  with  materials  of  or  around  the  counter.    These 
relatively rare high multiplicity bursts do produces Double and Triple background events in the counter.   
Annex  1  shows  an  example  of  recorded  background  counting  rates  in  the  BBNCC.    This  background 
measurement includes a total of 999 repetitions, each of 100 s measurement time, which successfully 
passed  the  QC  test.    The QC test,  performed  on  the  measured  rates  of  Singles,  Doubles  and  Triples, 
consisted of forming the mean value of all repetitions and discarding individual repetitions with a value 
outside  four  standard  deviations  (4)  of  the  mean.    In  Annex  1,  repetitions  passing  the  QC  test  are 
labelled “Pass”, whereas failed repetitions are labelled “Fail”.  In this example a total of 49 repetitions, 
or 4.7%, failed the QC test. 
The repetitions labelled “Fail” are not necessarily  produced by electrical  noise but may well originate 
from  neutron  bursts  in  this  particular  case.    The  fact  that  in  this  measurement  the  “Fail”  repetitions 
have  only  slightly  higher  Doubles  or  Triples  rates  without  a  measurable  increase  in  Singles  rate, 
indicates that this is caused by rare neutron bursts of high multiplicity which are typical for high energy 
atmospheric particle interactions.  
Measurements such as Annex 1, and many similar measurements, confirm that the BBNCC counter has 
indeed a very low, or possibly absent, level of electrical noise in the front-end electronics.  
Notice  that,  even  though  it  is  possible  to  eliminate  the  effect  of  atmospheric  neutron  bursts  in 
background  measurements  by  reducing  the  outlier  criterion  to  e.g.  2  instead  of  4,  in  sample 
measurements with (much) higher Doubles and Triples rates the background bursts will be masked and 
not eliminated by the QC test.  For this reason the background subtraction is better done by including 
the “natural” bursts also in the background measurement.  The QC test should normally remove  only 
“unnatural” electrical noise events.  

5.5. Dead-time effect in the counting chains  
The six parallel counting chains of the BBNCC have the same counting rates for a centred homogenous 
neutron source, at least to the extend the detector gas pressure and the amplifier characteristics are 
the same for all chains.  
Figure  8  is  an  MCS  histogram  of  neutron  detections  in  the  six  chains  following  a  detection  event  at 
time zero for a random neutron source such as AmLi.  The curve shape should be flat except for the 
signals  lost  to  the  dead-time  of  the  trigger  event.    At  times  up  to  the  flat  level,  the  curve  has  an 
“elongated  S”  shape  due  to  the  variable  analogue  pulse  width  at  the  discriminator  level.    The  slight 
differences in the curve shapes of Figure 8 are attributed to differences in electronics components of 
the circuits. In general, the behaviour is strictly as expected in a system of gas proportional counters 
displaying updating dead-time.  
The gain of each amplifier was set to yield the same full-energy pulse height.  Figure 8 shows that the 
mean dead-time due to the processing time of the analogue pulse is approx. 2.5 µs.  This rather large 
value is consistent with the full-energy analogue pulse width at the discriminator level.  The reason is 
that from the outset, the amplifier  shaping time was set  rather large  in order to  avoid  any  potential 
double-pulsing  (one  detection  event  causing  two  digital  output  pulses  due  to  imperfections  in  the 
analogue pulse shape) in the large-diameter detectors.  

16 

 
 
 
 
 
 
 
Figure 8.  Dead-time effect in each counting chain recorded with an AmLi neutron source conditioned with a 
neutron detection event at time zero 

Source: JRC analysis. 

Notice  also  in  Figure  8 the  absence  of  an  “overshoot”  where the  curves  recover  to the  flat  level.    In 
systems prone to double-pulsing, often caused by a too short amplifier shaping time, an overshoot is 
sometimes  seen.    Electronic  double-pulsing  is  particularly  disturbing  in  neutron  correlation  counting 
where signal multiplets from fission events are sought after. 

In Figure 9 the number of counting chains has been increased one by one up to finally all six chains.  
Each chain is added at the digital output stage of the previous chain (daisy-chained).  As expected the 
dead-time effect (the portion of missing pulses up to about 2.5 s) reduces with increasing number of 
parallel chains: i.e. with two parallel chains the missing portion is roughly 1/2 of that of a single chain, 
with three chains the missing portion is 1/3, with six chains it is roughly 1/6.  In other words, when one 
chain is “busy” processing a detection event, the other chains remain available to detect other neutrons 
(satisfying one condition of the theoretical “updating dead-time”).  

17 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 9.  Reduction of overall dead-time effect by adding more parallel chains as recorded with an AmLi 
neutron source 

Source: JRC analysis. 

5.6. Dead-time correction in coincidence counting 
A standard method for quantifying the effect of dead-time in a passive neutron counter involves the 
measurement of at least two 252Cf sources of different source strength.  The method takes advantage 
of  the  fact  that  for  gas  proportional  counters  for  neutron  detection,  a  good,  although  empirical 
formula,  for  correcting  the  singles  and  doubles  count  rates  (coincidence  counting)  for  dead-time 
effects is through the exponential correction using the singles (R1) in the following manner 

𝑅20 = 𝑅2𝑒𝑥𝑝(𝑎𝑅1 + 𝑏𝑅1
𝑅10 = 𝑅1𝑒𝑥𝑝 (1

(𝑎𝑅1 + 𝑏𝑅1

2) 

2)) 

4

(4) 

(5) 

where:   

and 

R1 and R2 are the measured rates, and R10 and R20 are the rates corrected for 
dead-time effect, 
a and b are the dead-time coefficients with the units s and s2, respectively 

For  the  measurement  of  any  given  252Cf  source,  the  ratio  R2/R1  (according  to  the  equations  1-3)  is 
independent  of  the  fission  rate  and  thus  should  be  constant  for  all  252Cf  sources  (measured  at  the 
exact same location) independent of source strength.  This would be true except for the ever-increasing 
dead-time effect with increasing count rates.  
Inserting  the  exponential  corrections  given  above  in  the  R2/R1  ratio,  the  following  equation  for  the 
determination of the dead-time correction factors a and b is achieved.   

18 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
𝑅2
𝑅1

=

𝑅20
𝑅10

 𝑒𝑥𝑝 (−

3

4

(𝑎𝑅1 + 𝑏𝑅1

2)) 

A useful quantity A is calculated from each of the measured data points. A is given as: 

𝐴 = −

4

3

ln (

𝑅2
⁄
𝑅1
𝑅20
⁄
𝑅10

)   

(6) 

(7) 

In order to determine the dead-time parameters (a, b), a series of six  252Cf sources of different source 
strength were measured in the centre of the otherwise empty BBNCC cavity.  The parameters a and b 
are determined by a least-squares fit of the measured points to a 2nd order polynomial: 

2 
𝐴 =  𝑎𝑅1 + 𝑏𝑅1

(8) 

In Figure 10 the parameter A is plotted against the count rate R1 for the 252Cf sources.   

Figure 10.  Plot of A against R1 of six 252Cf sources for the determination of the dead-time coefficients a, b by 
least-squares fitting to a 2nd order polynomial 

The fitted exponential curve in Figure 10 gives the following dead-time parameters: 

Source: JRC analysis. 

a = (1.96407 ± 0.03975)  10-6 s 
b = (0.80029 ± 0.10171)  10-12 s2 

Some  examples  of  the  performance  of  this  dead-time  correction  are  shown  for  four  different  252Cf 
sources in Annex 3.  

19 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5.7. Detection efficiency determined from R1 and R2 for a 252Cf source 
The  ratio  of  R2/R1  is  often  used  to  determine  a  value  for  the  detection  efficiency  as  this  ratio  is 
independent  of  the  fission  rate.    Similarly  the  detection  efficiency  can be  determined  from  the  fit  in 
Figure  10.    Clearly  the  value  of  A  at  R1=0  as in  eq. 8  above  does  not  affect  the  shape  of  the  fitted 
curve in Figure 10, i.e. the fitted parameters a and b.  
The  condition  (R1,  A0)  =  (0,0)  at  the  origin  implies  that  for  a  small  source  with  strictly  no  dead-time 
effect, the following is valid 

𝑅2
𝑅1

=  

𝑅20
𝑅10

=  𝜀 ∙

𝑠(2)
𝑠(1)

∙

1

𝑓

(9) 

in agreement with the Point Model equations 1 and 2 when inserting M = 1 and  = 0.  
In  other  words,  the  dead-time  corrected  R1  and  R2  values  for  any  252Cf  source  yields  the  same  R2/R1 
ratio.  The efficiency  value for a dead-time free  252Cf source can also be determined from the fitted 
curve  A(R1)  by leaving  A0 (the intercept)  a  free  parameter,  and  adjusting  the   values  until  A0  =  0  is 
achieved in the fit.  For the BBNCC this yields the value  = 0.2585.  

5.8. Dead-time correction in multiplicity counting 
Multiplicity counting of large Pu samples require a method for dead-time correction of the measured 
Singles (R1), Doubles (R2) and Triples rates (R3) before inserting in the Point Model equations (eqs. 1, 2 
and 3).  At JRC, the dead-time correction method applied over the last two decades is detailed in ref. 
10.  This includes an analytical method for a paralyzing, or updating, dead-time detection system.  The 
basis of the method is that a neutron detection event requires a fixed time, , for charge collection on 
the anode wire and analogue signal processing in the amplifier.  If another detection event takes place 
before    has  elapsed,  the  dead-time  period  is  extended  by  the  time    (hence  “updating”).    During  a 
dead-time  period,  the  given  electronic  chain  is  unable  to  register  additional  detection  events  (hence 
“paralysing”),  although  the  other  chains  can  (as  evidenced  in  Figure  9).    This model is  a  rather  good 
description of gas proportional counters in parallel counting chains.  Ref. 10 lists the detailed formulas 
necessary for implementing this method in software, starting from the normalised factorial moments 
of the measured prompt and delayed frequency distributions in signal triggered observation intervals 
(Shift Register principle), and yielding the dead-time corrected Singles, Doubles and Triples.  
The dead-time effect of the BBNCC is shown in Figures 9 and 11.  Figure 11 is a repeat of the summed 
output  of all  six counting chains.  The total  dead-time effect can be  observed as the missing counts 
after a detection event at time zero i.e. the missing area under the fictive horizontal red line fitted to 
the constant flat level (Figure 11).  By equalizing the area of the rectangle (zero to blue dotted line) x 
(zero  to  red  dotted  line)  to  the  area  of  missing  counts,  an  equivalent  value  for  the  dead-time    is 
obtained on the time axis.   
In this case the value  = 460.8 ns is obtained. 

20 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 11.  Dead-time effect in the BBNCC counter following a signal at time zero as recorded with an AmLi 
neutron source 

Source: JRC analysis. 

Experience with other  well counters have shown that this way  of determining the  parameter, even 
without further fine-tuning, provides good values for the dead-time corrected R1, R2 and R3.  This is the 
case if non-updating (or non-paralysing) effects do not contribute/influence significantly the total count 
losses.  Such potential (non-updating) effects could be digital signal losses, amplifier uncompensated 
pole-zero, and double pulsing in faulty electronics.  

At  the  time  of  the  testing  of  the  dead-time  correction  with  the  BBNCC  large  Pu  samples  were  not 
available.    For  this  reason  some  intermediate  size  252Cf  sources  were  measured,  and  the  multiplicity 
dead-time  correction  method  of  [10]  applied  using  the  dead-time  of    =  460.8  ns  as  determined  in 
Figure 11. 
Four numerical examples are shown in Annex 2 of sources ranging from 4 thousand to 220 thousand 
counts per second.  For comparison also the dead-time correction using the dead-time parameters a, b 
as derived from Figure 10 were applied to correct the values of R1 and R2, (as in standard coincidence 
counting) and shown in Annex 2.  
In general the data of Annex 2 show good dead-time correction with accuracy of less than 2% for R1 
and R2 using either multiplicity dead-time correction or the standard coincidence dead-time correction.  
For the Triples rate, R3, however already at singles rates of 100k counts per second a deviation of the 
expected value of 10% is observed.  Such a deviation would in Pu measurements lead to a deviation in 
mass assay of typically 5-6%.  However the correction on R3 using the dead-time model of Ref. 10 

21 

 
 
 
 
performs an astonishing correction of the measured R3 of the uncorrected rate of -13k s-1 to the 
dead-time corrected rate of +21k s-1.   
It  should  be  further  noted  that  the    value,  as  applied  here  for  the  BBNCC,  is  unusually  large  for  a 
neutron well counter.  The reason is partly due to the use of 2-inch gas counters, but first of all due to 
the  long  shaping  time  selected  in  the  amplifiers  in  the  present  setup.    The  long  shaping  time  was 
implemented as a conservative choice mainly to make sure the requirement of a pure updating dead-
time system was fulfilled.  

5.9. Sensitivity to high gamma fields 
Besides neutrons from fission events and (, n) reactions, also a substantial number of -rays emerge 
from a Pu samples.  The quantity and emerging spectrum of -rays depends on many factors such as 
the size of the sample, the isotope composition, the 241Am content, presence of fission products etc. 
A  single  -ray  can  deposit  energy  in  the  detector  gas  through  e.g.  Compton  scattering.    This  energy 
deposition however is small, and not comparable to the deposition from a neutron absorption event in 
10B.  In very strong   fields however, pile-up  of  -ray interactions with the gas may produce a signal 
exceeding the amplifier threshold level, causing a false neutron detection event.  The degree to which 
this happens depends on the gas pressure, gas composition as well as amplifier characteristics such as 
input dynamic range.  
To quantify the sensitivity of the BBNCC to  pile-up, experiments were carried out with a strong 137Cs  
source  at  various  distances  from  the  centre  of  the  BBNCC  cavity,  while  keeping  a  calibrated   
dosimeter  at the  centre.   It  is  noted  that  with  the    source  in  the  centre  position  (highest  dose), the 
distance to the inner row of BF3 tubes is approx. 12 cm.  
For  each  -dose  measurement,  the  neutron  counting  rates  of  the  BBNCC  were  recorded  both  for 
background  and  for  a  small  252Cf  source.    The  dosimeter  was  a  Double  Geiger  MERCURY  GMP  WR 
detector  with  a  Saturn 
I  5700  RTM  Acquisition  &  Control  unit  (from  Else  Nuclear  Srl, 
www.elsenuclear.com).  
As  pile-up essentially appears as an additional (independent) source of signals, the effect is expected 
to be mostly visible at low neutron counting rates.  Also, as  pile-up essentially is random in nature (as 
are spontaneous fission events), the determination of neutron doubles and triples by means of forming 
the difference between the contents of prompt and delayed gates, is expected to render doubles and 
triples less sensitive to  pile-up than singles.  
The recorded data are listed in Annex 3.  In neutron background, the singles rate is increased by more 
than 3 at as little as 17.4 µSv/h of added -dose.  This increase grows to a factor 3.4 on the singles 
rate at 16.2 mSv/h.  Both doubles and triples background rates however are unaffected  even at 16.2 
mSv/h at the given measurement uncertainty.  
For the small  252Cf neutron source yielding a singles rate of 2910 s-1, only the highest -dose of 16.6 
mSv/h has an influence on the singles rate (of less than 3 permille).  For the doubles rate, only at the 
highest -dose of 16.6 mSv/h an influence beyond 3 could be observed. For the triples rate no effect 
was observed.  
In summary, the measurements with the strong  source show the BBNCC to be quite immune to the 
effect of  pile-up.  Clearly the use of 0.95 bar BF3 detectors does not pose a problem in this regard.  It 
should be noted that 16 mSv/h is indeed a high -dose which would not normally be encountered from 
Pu samples of even a few kilograms, except if fission products remain in the sample.  

5.10. Limitations of use due to high dead-time and die-away time 
Two specific design features make the BBNCC less desirable for assay of large, i.e. high count rate, Pu 
samples. They are: 

22 

 
 
 
 
a)  The BBNCC has a relatively high die-away time due to the use detector tubes of low-pressure 
and of 2-inch diameter imbedded in the polyethylene moderator block.  The moderator block is 
made relatively wide in order to accommodate the many detector tubes in two rings with an 
optimal  pitch  minimising  the  shadowing  effect  of  neighbouring  tubes  which  would  lead  to  a 
reduced overall neutron detection efficiency.  The large moderator block (and the low-pressure 
tubes) inevitably produces a long die-away time of the thermal neutron population.  The long 
die-away  time  in  turn  necessitates  a  long  Gate  width  (of  100  µs)  in  order  to  collect  the 
correlated neutron multiplets.  

b)  The  amplifiers  were  configured  with  a  relatively  large  shaping  time  (four  times  that  of  the 
AMPTEK A-111) for the purpose of eliminating the risk of double pulsing that is so detrimental 
to the multiplicity counting technique.  The BBNCC in fact displays a low level of electrical noise 
as  can  be  observed  for  example  in  background  measurements  (see  Annex  1).    The  long 
amplifier  shaping  time  however  means  that  the  analogue  waveform  remains  above  the  TTL 
trigger level for longer, which in turn results in a relatively long dead-time of each processing 
chain (see Figures 9 and 11).  

Both the  need for a relatively  long Gate width, and the long dead-time of the counter, have adverse 
effect on the accurate determination of R1, R2 and R3 for samples producing high counting rates.  
These  well-known  effects  however  were  considered  acceptable  as  the  BBNCC  already  from  the 
conceptual stage was designed for use with the JRC source inventory of relatively low Pu mass.  
However,  the  low-noise  operation  of  the  BBNCC  that  ensued  gave  confidence  that  the  implemented 
long  shaping  time  was  indeed  overly  conservative.    The  front-end  electronics  used  in  the  BBNCC 
represented  the  2nd  generation  built  at  JRC.    Currently  a  3rd  generation  is  in  elaboration,  which  will 
implement a significantly shorter shaping time with significant benefits expected at higher count rates.  

5.11. Summary of instrument parameters for safeguards assay 
The parameters discussed in this report to be applied in standard safeguards assay are summarized in 
Table 1.  

Table 1.  Table 1. Summary of assay parameters determined for the BBNCC 

Gate width 
Pre-delay 
High voltage 
Die-away time 
Dead-time parameters, 

a 
b 

Multiplicity dead-time 
Detection efficiency 
Typical background rates, 
singles 
doubles 
triples 

100 µs 
4.5 µs 
1800 V 
83.47 ± 0.08 µs 

(1.96407 ± 0.03975)  10-6 s 
(0.80029 ± 0.10171)  10-12 s2 
461 ns 
0.2585 

2.828 ± 0.006  s-1 
0.050 ± 0.001  s-1 
0.006 ± 0.000  s-1 

Source: JRC analysis. 

23 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
6.  Conclusions 
The Boron Based Neutron Correlation Counter (BBNCC) as a prototype “helium-free” neutron multiplicity 
counter for safeguards verifications of bulk plutonium samples was designed, built and tested at JRC.  
The  BBNCC  well  counter  incorporates  24  proportional  detectors  containing  boron  trifluoride  gas 
enriched in 10B.  
The tests described in this report concludes the testing phase of the counter.  The assay parameters 
such as die-away time, dead-time parameters and neutron detection efficiency were determined.  The 
efficiency above 25% for prompt fission neutrons makes the counter suitable for neutron multiplicity 
measurements in nuclear safeguards.  The layout of the 2-inch detector tubes and the large moderator 
block  (necessary  to  achieve  the  high  detection  efficiency)  has  the  negative  effect  of  producing  a 
relatively  high  die-away  time.    The  high  die-away  time  makes  the  counter  less  suitable  for 
measurement of large bulk Pu samples.  
The  laboratory  tests  with  the  BBNCC  also  represented  the  first  field  tests  of  the  JRC  2nd  generation 
front-end  electronics  for  gas  proportional  counters.    The  six  unit  of  the  electronics  appeared  both 
stable, of low noise as evidenced in long background measurements (see Annex 1), and free from false 
double  pulsing  events  so  often  observed  in  in  similar  electronics  and  which  can  be  devastating  in 
multiplicity  counting.    It  should  be  noted  that  to  apply  the  present  electronics  to  3He  proportional 
counters or in  high-rate applications, the shaping time  of the analogue pulse produced by the  circuit 
should  be  reduced  for  the  purpose  of  reducing  the  time  above  the  trigger  level  and  with  that  the 
overall dead-time of the electronic chain.  This modification will be implemented in the 3rd generation 
of this circuit which is currently under development.  

24 

 
 
 
 
References 

[1]  M. S. Krick and H. O. Menlove, “The High-Level Neutron Coincidence Counter (HLNCC): Users’ 

Manual, LA-7779-M,” 1978. 

[2]  B. Pedersen, J.-M. Crochemore, M. Mosconi, V. Mayorov, H. Tagziria, A. Ocherashvili, E. Roesgen and 
P. Schwalbach, “A prototype BF3 based neutron multiplicity counter for nuclear safeguards,” in 37th 
ESARDA Symposium on Safeguards and Nuclear Non-Proliferation, Manchester, 2015.  

[3]  J. F. Briesmeister (Ed), “MCNP—A General Monte Carlo N-Particle Transport Code, Version 4C; LA-

13709-M,” Los Alamos National Laboratory, 2000. 

[4]  G. Varasano, T. Bogucarska, B. Pedersen, " Calibration of Charge Amplifier and Discriminator Circuits 
used in the JRC Drum Monitor, Slab counter and BBNCC devices", JRC Technical Reports, JRC114077, 
2019. 

[5]  G. Varasano, B. Pedersen, "Novel front-end electronics for the Boron Based Neutron Correlation 

Counter (BBNCC)” JRC Technical Reports, JRC124954, 2021. 

[6]  G. Zeng, C. Hu, S. Woi, Y. J., L. Q., G. L. and G. Tan, “Research and development of a high-

performance differential-hybrid charge sensitive amplifier,” Applied Radiation and Isotopes, vol. 120, 
pp. 95-100, 201. 

[7]  W. Hage and D.M. Cifarelli, Correlation analysis with neutron count distributions in randomly and 

signal triggered time intervals for assay of special fissile materials, Nuclear Science and Engineering 
89 (1985) 159 - 176. 

[8]  W. Hage and D.M. Cifarelli, On the factorial moments of the neutron multiplicity distribution of 
fission cascades, Nuclear Instruments and Methods in Physics Research A236 (1985) 165 - 177. 

[9]  D.M. Cifarelli and W. Hage, Models for a three-parameter analysis of neutron signal correlation 

measurements for fissile material assay, Nuclear Instruments and Methods in Physics Research A251 
(1986) 550 - 563. 

[10]  W. Hage and D.M. Cifarelli, Correlation Analysis with Neutron Count Distribution for a Paralyzing 
Dead-Time Counter for the Assay of Spontaneous Fissioning Material, Nuclear Science and 
Engineering 112 (1992) 136 – 158. 

25 

 
 
 
 
 
 
 
 
 
 
 
 
 
List of figures 

Figure 1.  Final dimensions of the BBNCC counter as optimised by Monte Carlo simulations ................. 7 
Figure 2.  Schematic of the JRC amplifier for charge collection proportional counters ........................... 8 
Figure 3.  The JRC differential cascode charge sensitive pre-amplifier .................................................... 9 
Figure 4.  BBNCC front-end electronics ...................................................................................................... 9 
Figure 5.  BBNCC high voltage plateau curve ........................................................................................... 12 
Figure 6.  MCS histogram with 252Cf source of neutron detection events and exponential fit ............... 14 
Figure 7.  Shift Register measurements of R = ([R+A] – [A]) in units of standard deviations as function 
of pre-delay for an AmLi random neutron source ..................................................................................... 15 
Figure 8.  Dead-time effect in each counting chain recorded with an AmLi neutron source conditioned 
with a neutron detection event at time zero ............................................................................................. 17 
Figure 9.  Reduction of overall dead-time effect by adding more parallel chains as recorded with an 
AmLi neutron source ................................................................................................................................... 18 
Figure 10.  Plot of A against R1 of six 252Cf sources for the determination of the dead-time 
coefficients a, b by least-squares fitting to a 2nd order polynomial ......................................................... 19 
Figure 11.  Dead-time effect in the BBNCC counter following a signal at time zero as recorded with an 
AmLi neutron source ................................................................................................................................... 21 

List of tables 

Table 1.  Table 1. Summary of assay parameters determined for the BBNCC ....................................... 23 
Table 2.  Comparison of expected to un-corrected and dead-time corrected signal multiplets ............. 35 
Table 3.   Measurements with a strong 137Cs source at variable distance to dosimeter placed at centre 
of BBNCC cavity .......................................................................................................................................... 36 

26 

 
 
 
 
 
 
 
 
 
Annexes 

Annex 1.  Example of neutron background measured over long time 
The list below shows the sequence of repetitions of a long background measurement with the BBNCC, 
including cycle number, the observed counts per second of Singles, Doubles and Triples, and the result 
of the outlier test.  
Measurement time per repetition: 100 s.  
Analyser settings:  pre-delay 4.5 µs, Gate 100 µs. 

Cycle  Singles 

Doubles 

Triples 

QC 
Tests 

1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 
39 
40 
41 
42 
43 
44 
45 
46 
47 
48 
49 
50 
51 
52 
53 

2.79 
3.09 
3.01 
2.64 
2.84 
3.07 
2.80 
2.80 
3.24 
3.17 
2.91 
2.95 
3.07 
2.91 
2.96 
2.81 
2.50 
2.81 
3.08 
3.05 
2.81 
2.92 
3.09 
3.40 
2.76 
2.95 
3.22 
2.83 
2.80 
2.82 
2.33 
2.99 
2.86 
3.02 
2.93 
3.03 
2.65 
2.86 
2.84 
2.97 
2.80 
2.66 
3.18 
2.86 
2.83 
2.76 
2.87 
2.88 
2.72 
2.83 
2.79 
3.07 
2.86 

0.03 
0.10 
0.09 
0.04 
0.05 
0.08 
0.05 
0.03 
0.09 
0.05 
0.02 
0.09 
0.04 
0.05 
0.11 
0.02 
0.05 
0.04 
0.03 
0.13 
0.05 
0.05 
0.03 
0.08 
0.03 
0.13 
0.11 
0.07 
0.06 
0.16 
0.01 
0.05 
0.03 
0.03 
0.07 
0.01 
0.08 
0.04 
0.10 
0.02 
0.02 
0.06 
0.06 
0.13 
0.09 
0.03 
0.04 
0.01 
0.05 
0.07 
0.05 
0.06 
0.02 

0.00  Pass 
0.02  Pass 
0.03  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.02  Pass 
0.02  Pass 
0.01  Pass 
0.01  Pass 
0.08  Fail 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.02  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 

27 

54 
55 
56 
57 
58 
59 
60 
61 
62 
63 
64 
65 
66 
67 
68 
69 
70 
71 
72 
73 
74 
75 
76 
77 
78 
79 
80 
81 
82 
83 
84 
85 
86 
87 
88 
89 
90 
91 
92 
93 
94 
95 
96 
97 
98 
99 
100 
101 
102 
103 
104 
105 
106 
107 
108 

2.78 
2.69 
3.03 
3.05 
2.58 
2.72 
2.86 
3.02 
2.92 
2.52 
2.58 
2.63 
2.92 
2.80 
3.05 
2.74 
2.64 
2.50 
2.85 
2.89 
2.67 
2.91 
2.80 
2.78 
2.62 
3.02 
3.10 
2.92 
2.94 
2.58 
3.14 
2.73 
2.81 
2.65 
2.58 
2.93 
2.80 
2.89 
3.05 
2.99 
3.13 
3.13 
2.61 
2.99 
2.91 
2.37 
2.91 
2.91 
3.00 
2.95 
2.66 
2.77 
2.77 
2.50 
2.78 

0.08 
0.01 
0.07 
0.02 
0.00 
0.03 
0.06 
0.08 
0.02 
0.04 
0.00 
0.02 
0.05 
0.05 
0.06 
0.03 
0.05 
0.07 
0.06 
0.08 
0.01 
0.11 
0.02 
0.05 
0.05 
0.02 
0.08 
0.06 
0.03 
0.09 
0.07 
0.02 
0.06 
0.01 
0.01 
0.05 
0.08 
0.04 
0.04 
0.09 
0.02 
0.09 
0.02 
0.08 
0.14 
0.03 
0.05 
0.13 
0.03 
0.10 
0.04 
0.01 
0.02 
0.05 
0.04 

0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.05  Fail 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 

 
 
 
 
 
109 
110 
111 
112 
113 
114 
115 
116 
117 
118 
119 
120 
121 
122 
123 
124 
125 
126 
127 
128 
129 
130 
131 
132 
133 
134 
135 
136 
137 
138 
139 
140 
141 
142 
143 
144 
145 
146 
147 
148 
149 
150 
151 
152 
153 
154 
155 
156 
157 
158 
159 
160 
161 
162 
163 
164 
165 
166 
167 
168 
169 
170 
171 
172 
173 
174 
175 
176 
177 
178 
179 

3.01 
2.92 
2.53 
2.82 
2.73 
2.97 
2.73 
2.73 
3.23 
2.89 
2.77 
2.87 
2.61 
2.99 
2.80 
3.01 
2.95 
2.69 
2.56 
2.82 
2.58 
2.88 
2.96 
3.04 
2.78 
2.73 
3.13 
2.91 
2.99 
3.16 
3.19 
2.86 
2.71 
2.82 
2.80 
3.04 
2.90 
2.79 
2.90 
2.76 
2.69 
3.02 
2.78 
2.89 
2.75 
2.84 
2.75 
2.78 
2.82 
2.57 
2.82 
2.51 
2.57 
2.88 
2.57 
2.78 
2.81 
2.95 
2.79 
2.98 
2.97 
2.76 
2.73 
2.83 
2.78 
2.68 
2.92 
2.71 
2.88 
2.91 
2.82 

0.21 
0.03 
0.05 
0.14 
0.02 
0.15 
0.06 
0.06 
0.17 
0.09 
0.05 
0.06 
0.03 
0.08 
0.00 
0.07 
0.10 
0.03 
0.00 
0.01 
0.04 
0.08 
0.01 
0.09 
0.02 
0.09 
0.05 
0.05 
0.03 
0.07 
0.46 
0.06 
0.01 
0.01 
0.07 
0.07 
0.00 
0.02 
0.01 
0.03 
0.05 
0.09 
0.01 
0.01 
0.04 
0.04 
0.01 
0.03 
0.05 
0.06 
0.07 
0.01 
0.03 
0.06 
0.02 
0.11 
0.08 
0.05 
0.06 
0.04 
0.03 
0.04 
0.03 
0.08 
0.02 
0.01 
0.03 
0.04 
0.07 
0.04 
0.03 

0.07  Fail 
0.00  Pass 
0.00  Pass 
0.05  Fail 
0.00  Pass 
0.06  Fail 
0.01  Pass 
0.01  Pass 
0.06  Fail 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.70  Fail 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 

28 

180 
181 
182 
183 
184 
185 
186 
187 
188 
189 
190 
191 
192 
193 
194 
195 
196 
197 
198 
199 
200 
201 
202 
203 
204 
205 
206 
207 
208 
209 
210 
211 
212 
213 
214 
215 
216 
217 
218 
219 
220 
221 
222 
223 
224 
225 
226 
227 
228 
229 
230 
231 
232 
233 
234 
235 
236 
237 
238 
239 
240 
241 
242 
243 
244 
245 
246 
247 
248 
249 
250 

2.95 
2.82 
2.75 
2.81 
2.89 
3.03 
2.85 
2.65 
3.13 
3.03 
2.58 
2.97 
2.69 
3.14 
2.69 
2.86 
2.88 
2.89 
2.49 
3.03 
2.59 
2.96 
2.76 
2.71 
3.23 
2.82 
2.71 
2.75 
2.91 
2.96 
2.62 
2.82 
3.15 
3.02 
2.64 
2.64 
2.69 
2.88 
2.91 
2.75 
2.64 
2.91 
2.66 
2.99 
2.43 
2.94 
3.11 
2.97 
2.82 
2.91 
2.55 
2.80 
2.94 
2.85 
2.77 
2.75 
2.77 
2.91 
2.88 
3.08 
2.55 
2.72 
3.15 
2.81 
2.55 
2.87 
3.01 
2.87 
2.99 
2.95 
2.83 

0.00 
0.09 
0.04 
0.05 
0.06 
0.12 
0.03 
0.02 
0.05 
0.01 
0.04 
0.03 
0.04 
0.10 
0.00 
0.06 
0.03 
0.04 
0.08 
0.12 
0.02 
0.07 
0.01 
0.07 
0.15 
0.04 
0.05 
0.09 
0.03 
0.03 
0.05 
0.02 
0.24 
0.03 
0.04 
0.11 
0.06 
0.06 
0.04 
0.01 
0.00 
0.05 
0.01 
0.07 
0.00 
0.04 
0.05 
0.03 
0.06 
0.02 
0.07 
0.03 
0.06 
0.08 
0.02 
0.21 
0.07 
0.04 
0.05 
0.12 
0.11 
0.01 
0.06 
0.00 
0.05 
0.08 
0.04 
0.15 
0.03 
0.12 
0.07 

0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.21  Fail 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.15  Fail 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.03  Pass 
0.07  Fail 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.07  Fail 
0.00  Pass 
0.02  Pass 
0.03  Pass 

 
 
251 
252 
253 
254 
255 
256 
257 
258 
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260 
261 
262 
263 
264 
265 
266 
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268 
269 
270 
271 
272 
273 
274 
275 
276 
277 
278 
279 
280 
281 
282 
283 
284 
285 
286 
287 
288 
289 
290 
291 
292 
293 
294 
295 
296 
297 
298 
299 
300 
301 
302 
303 
304 
305 
306 
307 
308 
309 
310 
311 
312 
313 
314 
315 
316 
317 
318 
319 
320 
321 

2.75 
2.99 
3.06 
2.92 
2.56 
2.97 
2.50 
3.02 
2.74 
2.86 
2.71 
2.85 
2.79 
2.62 
2.71 
3.08 
2.76 
2.70 
2.87 
2.86 
2.43 
2.90 
2.79 
2.66 
2.90 
3.08 
2.69 
2.89 
2.83 
2.57 
2.96 
3.15 
3.14 
2.99 
2.99 
2.33 
2.81 
3.20 
2.71 
2.88 
2.69 
2.77 
2.50 
2.77 
2.90 
2.82 
2.56 
2.93 
3.13 
2.67 
2.88 
2.93 
2.64 
2.91 
2.58 
2.88 
2.78 
2.97 
2.67 
3.08 
2.68 
2.92 
2.95 
2.81 
2.83 
2.83 
2.99 
3.17 
2.96 
3.00 
2.66 

0.04 
0.06 
0.03 
0.04 
0.00 
0.05 
0.03 
0.09 
0.03 
0.11 
0.03 
0.05 
0.07 
0.04 
0.07 
0.06 
0.07 
0.04 
0.07 
0.05 
0.00 
0.06 
0.06 
0.03 
0.05 
0.09 
0.04 
0.06 
0.06 
0.03 
0.05 
0.05 
0.07 
0.01 
0.10 
0.01 
0.07 
0.14 
0.04 
0.11 
0.03 
0.05 
0.02 
0.10 
0.06 
0.03 
0.07 
0.05 
0.12 
0.02 
0.13 
0.06 
0.05 
0.03 
0.10 
0.06 
0.04 
0.08 
0.07 
0.01 
0.07 
0.06 
0.09 
0.07 
0.11 
0.04 
0.00 
0.11 
0.27 
0.02 
0.07 

0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.02  Pass 
0.01  Pass 
0.03  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.10  Fail 
0.00  Pass 
0.03  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 
0.02  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.02  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.20  Fail 
0.00  Pass 
0.01  Pass 

29 

322 
323 
324 
325 
326 
327 
328 
329 
330 
331 
332 
333 
334 
335 
336 
337 
338 
339 
340 
341 
342 
343 
344 
345 
346 
347 
348 
349 
350 
351 
352 
353 
354 
355 
356 
357 
358 
359 
360 
361 
362 
363 
364 
365 
366 
367 
368 
369 
370 
371 
372 
373 
374 
375 
376 
377 
378 
379 
380 
381 
382 
383 
384 
385 
386 
387 
388 
389 
390 
391 
392 

2.59 
2.89 
2.57 
2.62 
2.68 
2.59 
2.69 
2.71 
2.61 
2.78 
2.78 
2.68 
2.90 
2.68 
2.91 
2.86 
2.73 
2.72 
2.79 
2.84 
2.84 
2.73 
2.64 
2.74 
2.97 
3.01 
2.83 
2.42 
2.81 
2.82 
2.75 
3.05 
3.07 
2.79 
3.05 
2.82 
2.69 
2.80 
3.19 
3.07 
2.94 
2.78 
2.90 
3.00 
3.10 
2.99 
2.93 
2.95 
2.66 
2.81 
2.83 
2.77 
2.69 
2.98 
2.93 
3.16 
2.78 
2.76 
2.58 
2.94 
2.69 
3.02 
2.76 
2.95 
3.55 
3.12 
3.03 
2.83 
2.56 
3.08 
2.79 

0.03 
0.06 
0.04 
0.03 
0.02 
0.03 
0.06 
0.06 
0.02 
0.04 
0.04 
0.03 
0.07 
0.02 
0.07 
0.02 
0.06 
0.07 
0.02 
0.05 
0.17 
0.05 
0.04 
0.03 
0.04 
0.16 
0.00 
0.08 
0.06 
0.07 
0.03 
0.07 
0.04 
0.06 
0.04 
0.02 
0.04 
0.11 
0.07 
0.03 
0.02 
0.06 
0.02 
0.07 
0.03 
0.03 
0.07 
0.10 
0.05 
0.07 
0.05 
0.03 
0.02 
0.05 
0.02 
0.03 
0.22 
0.04 
0.06 
0.04 
0.07 
0.10 
0.09 
0.09 
0.06 
0.01 
0.07 
0.05 
0.04 
0.14 
0.19 

0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.11  Fail 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.05  Fail 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.11  Fail 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.10  Fail 
0.10  Fail 

 
 
393 
394 
395 
396 
397 
398 
399 
400 
401 
402 
403 
404 
405 
406 
407 
408 
409 
410 
411 
412 
413 
414 
415 
416 
417 
418 
419 
420 
421 
422 
423 
424 
425 
426 
427 
428 
429 
430 
431 
432 
433 
434 
435 
436 
437 
438 
439 
440 
441 
442 
443 
444 
445 
446 
447 
448 
449 
450 
451 
452 
453 
454 
455 
456 
457 
458 
459 
460 
461 
462 
463 

3.36 
2.73 
2.57 
2.71 
2.83 
2.69 
2.83 
2.95 
2.54 
2.94 
2.69 
3.17 
2.94 
2.84 
2.67 
2.94 
2.84 
2.91 
2.71 
2.61 
2.69 
2.99 
2.69 
2.81 
2.92 
2.62 
2.89 
2.79 
2.85 
2.98 
2.87 
2.64 
2.87 
2.77 
2.73 
2.83 
2.69 
2.76 
2.60 
3.27 
2.79 
2.82 
2.44 
2.93 
2.86 
2.65 
2.67 
3.00 
2.78 
2.53 
2.57 
2.43 
2.88 
2.99 
2.72 
2.54 
2.77 
2.71 
2.94 
2.78 
2.75 
2.72 
2.46 
2.78 
2.74 
2.68 
2.79 
2.82 
2.86 
2.80 
2.85 

0.08 
0.06 
0.02 
-0.01 
0.05 
0.02 
0.02 
0.05 
0.03 
0.08 
0.04 
0.06 
0.07 
0.06 
0.06 
0.03 
0.07 
0.04 
0.05 
0.07 
0.07 
0.05 
0.02 
0.06 
0.12 
0.01 
0.04 
0.05 
0.09 
0.04 
0.08 
0.04 
0.07 
0.02 
0.00 
0.05 
0.01 
0.04 
0.02 
0.06 
0.02 
0.04 
0.03 
0.02 
0.03 
0.00 
0.04 
0.12 
0.15 
0.05 
0.03 
0.03 
0.10 
0.02 
0.03 
0.05 
0.04 
0.12 
0.10 
0.07 
0.03 
0.06 
-0.01 
0.02 
0.03 
0.01 
0.07 
0.03 
0.07 
0.07 
0.04 

0.04  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.02  Pass 
0.01  Pass 
0.02  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.05  Fail 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.11  Fail 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.03  Pass 
0.02  Pass 
0.00  Pass 

30 

464 
465 
466 
467 
468 
469 
470 
471 
472 
473 
474 
475 
476 
477 
478 
479 
480 
481 
482 
483 
484 
485 
486 
487 
488 
489 
490 
491 
492 
493 
494 
495 
496 
497 
498 
499 
500 
501 
502 
503 
504 
505 
506 
507 
508 
509 
510 
511 
512 
513 
514 
515 
516 
517 
518 
519 
520 
521 
522 
523 
524 
525 
526 
527 
528 
529 
530 
531 
532 
533 
534 

2.69 
3.14 
3.13 
2.93 
2.82 
3.01 
2.73 
2.63 
2.75 
2.91 
2.89 
2.84 
2.89 
2.60 
2.85 
3.07 
2.78 
2.56 
2.77 
3.05 
2.72 
3.08 
2.94 
3.06 
2.73 
2.98 
2.74 
2.84 
2.79 
2.70 
2.73 
2.82 
2.89 
3.05 
2.58 
2.79 
2.84 
2.54 
2.63 
2.81 
2.66 
2.61 
3.21 
2.48 
3.05 
2.55 
2.89 
3.00 
2.50 
2.99 
2.88 
2.71 
2.54 
2.70 
2.69 
2.89 
2.86 
2.87 
2.96 
2.83 
2.84 
2.63 
2.77 
2.86 
3.09 
2.88 
3.05 
2.78 
2.64 
2.70 
3.07 

0.01 
0.06 
0.09 
0.02 
0.06 
0.07 
0.04 
0.02 
0.01 
0.06 
0.05 
0.01 
0.03 
0.04 
0.03 
0.07 
0.08 
0.05 
0.11 
0.06 
0.03 
0.01 
0.01 
0.03 
0.02 
0.03 
0.08 
0.09 
0.26 
0.01 
0.06 
0.05 
0.07 
0.03 
0.08 
0.03 
0.04 
0.05 
0.03 
0.01 
0.05 
0.04 
2.54 
0.02 
0.12 
0.05 
0.13 
0.04 
0.10 
0.06 
0.13 
0.08 
0.01 
0.08 
0.09 
0.02 
0.01 
0.04 
0.04 
0.02 
0.09 
0.02 
0.18 
0.02 
0.07 
0.00 
0.09 
0.03 
0.07 
0.14 
0.07 

0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.02  Pass 
0.01  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.26  Fail 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
13.75  Fail 
0.00  Pass 
0.03  Pass 
0.01  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.03  Pass 
0.01  Pass 
0.00  Pass 
0.04  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.07  Fail 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.01  Pass 

 
 
535 
536 
537 
538 
539 
540 
541 
542 
543 
544 
545 
546 
547 
548 
549 
550 
551 
552 
553 
554 
555 
556 
557 
558 
559 
560 
561 
562 
563 
564 
565 
566 
567 
568 
569 
570 
571 
572 
573 
574 
575 
576 
577 
578 
579 
580 
581 
582 
583 
584 
585 
586 
587 
588 
589 
590 
591 
592 
593 
594 
595 
596 
597 
598 
599 
600 
601 
602 
603 
604 
605 

3.08 
2.92 
2.68 
2.80 
2.99 
2.86 
2.92 
2.84 
2.96 
2.94 
2.74 
2.80 
2.74 
2.83 
3.13 
2.76 
2.91 
3.01 
2.60 
2.98 
2.58 
2.87 
2.78 
2.93 
2.83 
3.28 
2.87 
2.85 
2.84 
2.89 
2.67 
2.96 
2.98 
2.80 
2.46 
2.69 
2.40 
2.72 
2.73 
2.46 
2.76 
2.72 
2.88 
2.91 
2.74 
2.74 
3.09 
2.87 
3.15 
2.89 
2.69 
2.56 
2.95 
2.83 
2.84 
2.96 
2.77 
2.83 
2.38 
2.82 
2.66 
2.74 
2.71 
3.05 
2.51 
2.85 
2.83 
2.86 
2.78 
2.75 
3.00 

0.03 
0.03 
0.02 
0.10 
0.06 
0.03 
0.06 
0.20 
0.07 
0.12 
0.02 
0.03 
0.02 
0.18 
0.07 
0.10 
0.05 
0.21 
0.00 
0.08 
0.01 
0.02 
0.06 
0.03 
0.06 
0.10 
0.05 
0.03 
0.04 
0.03 
0.09 
0.12 
0.03 
0.02 
0.04 
0.04 
0.09 
0.08 
0.03 
0.03 
0.07 
0.09 
0.00 
0.05 
0.01 
0.02 
0.07 
0.02 
0.11 
0.05 
0.02 
0.07 
0.01 
0.03 
0.02 
0.13 
0.02 
0.02 
0.02 
0.02 
0.04 
0.13 
0.05 
0.02 
0.04 
0.09 
0.00 
0.06 
0.02 
0.03 
0.12 

0.00  Pass 
0.01  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.10  Fail 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.10  Fail 
0.02  Pass 
0.03  Pass 
0.01  Pass 
0.17  Fail 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.03  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.05  Fail 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.05  Fail 

31 

606 
607 
608 
609 
610 
611 
612 
613 
614 
615 
616 
617 
618 
619 
620 
621 
622 
623 
624 
625 
626 
627 
628 
629 
630 
631 
632 
633 
634 
635 
636 
637 
638 
639 
640 
641 
642 
643 
644 
645 
646 
647 
648 
649 
650 
651 
652 
653 
654 
655 
656 
657 
658 
659 
660 
661 
662 
663 
664 
665 
666 
667 
668 
669 
670 
671 
672 
673 
674 
675 
676 

3.15 
3.02 
2.62 
2.89 
2.94 
3.02 
2.67 
2.83 
2.79 
2.93 
2.71 
2.78 
2.57 
2.98 
3.04 
2.59 
2.78 
2.95 
2.56 
2.57 
2.57 
2.45 
3.04 
2.57 
2.62 
2.63 
2.94 
2.62 
2.69 
2.97 
2.85 
2.59 
2.88 
2.87 
2.76 
2.91 
3.06 
2.93 
2.66 
2.58 
3.03 
3.22 
2.65 
2.54 
2.70 
2.77 
2.77 
2.89 
2.58 
2.80 
2.50 
2.73 
2.75 
2.82 
2.73 
2.70 
2.69 
2.87 
2.62 
2.76 
2.67 
2.49 
2.81 
2.72 
3.24 
2.83 
2.81 
2.66 
2.87 
2.86 
2.68 

0.05 
0.13 
0.01 
0.09 
0.15 
0.04 
0.00 
0.07 
0.05 
0.05 
0.04 
0.15 
0.02 
0.09 
0.07 
0.02 
0.03 
0.09 
0.06 
0.01 
0.04 
0.01 
0.04 
0.03 
0.06 
0.00 
0.13 
0.06 
0.06 
0.04 
0.01 
0.02 
0.03 
0.08 
0.02 
0.05 
0.03 
0.03 
0.05 
0.15 
0.07 
0.05 
0.08 
0.02 
0.12 
0.07 
0.03 
0.09 
0.03 
0.01 
0.04 
0.05 
0.09 
0.00 
0.02 
0.02 
0.08 
0.15 
0.14 
0.07 
0.04 
0.01 
0.08 
0.03 
0.07 
0.05 
0.02 
0.03 
0.08 
0.05 
0.07 

0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.10  Fail 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.10  Fail 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.03  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.02  Pass 
0.07  Fail 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 

 
 
677 
678 
679 
680 
681 
682 
683 
684 
685 
686 
687 
688 
689 
690 
691 
692 
693 
694 
695 
696 
697 
698 
699 
700 
701 
702 
703 
704 
705 
706 
707 
708 
709 
710 
711 
712 
713 
714 
715 
716 
717 
718 
719 
720 
721 
722 
723 
724 
725 
726 
727 
728 
729 
730 
731 
732 
733 
734 
735 
736 
737 
738 
739 
740 
741 
742 
743 
744 
745 
746 
747 

3.02 
3.04 
2.85 
3.08 
2.97 
2.79 
2.88 
2.97 
2.85 
3.16 
2.65 
2.82 
2.53 
2.36 
2.70 
2.87 
2.94 
3.17 
2.88 
2.98 
2.47 
2.91 
2.69 
2.59 
2.22 
2.62 
2.71 
3.07 
2.69 
2.98 
2.71 
2.76 
2.87 
2.54 
2.90 
2.77 
2.93 
2.98 
3.08 
2.97 
2.83 
2.81 
2.61 
3.05 
2.65 
2.81 
2.65 
2.71 
2.84 
3.05 
2.87 
2.78 
2.68 
3.04 
2.87 
2.82 
3.09 
2.69 
2.57 
2.82 
2.92 
2.74 
2.87 
2.85 
2.78 
3.12 
2.90 
2.76 
2.91 
2.66 
2.84 

0.06 
0.06 
0.04 
0.04 
0.07 
0.04 
0.06 
0.03 
0.10 
0.03 
0.04 
0.03 
0.07 
0.09 
0.01 
0.09 
0.01 
0.03 
0.12 
0.02 
0.03 
0.04 
0.05 
0.04 
0.04 
0.02 
0.06 
0.03 
0.06 
0.03 
0.04 
0.03 
0.03 
0.08 
0.02 
0.05 
0.05 
0.03 
0.07 
0.11 
0.03 
0.04 
0.16 
0.09 
0.06 
0.01 
0.02 
0.02 
0.06 
0.05 
0.02 
0.05 
0.03 
0.10 
0.06 
0.02 
0.08 
0.03 
0.06 
0.04 
0.04 
0.02 
0.10 
0.01 
0.08 
0.07 
0.07 
0.06 
0.11 
0.05 
0.04 

0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.11  Fail 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.04  Pass 
0.01  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.02  Pass 
0.01  Pass 
0.00  Pass 

32 

748 
749 
750 
751 
752 
753 
754 
755 
756 
757 
758 
759 
760 
761 
762 
763 
764 
765 
766 
767 
768 
769 
770 
771 
772 
773 
774 
775 
776 
777 
778 
779 
780 
781 
782 
783 
784 
785 
786 
787 
788 
789 
790 
791 
792 
793 
794 
795 
796 
797 
798 
799 
800 
801 
802 
803 
804 
805 
806 
807 
808 
809 
810 
811 
812 
813 
814 
815 
816 
817 
818 

2.80 
2.75 
2.83 
2.97 
2.78 
3.03 
2.85 
2.92 
3.13 
2.97 
2.74 
2.86 
2.98 
2.73 
2.52 
2.84 
2.75 
2.85 
3.09 
2.69 
3.02 
2.60 
2.66 
3.04 
2.85 
2.96 
2.64 
2.91 
2.93 
2.54 
3.02 
3.01 
2.84 
2.95 
3.04 
2.98 
2.97 
2.68 
2.65 
3.06 
2.84 
2.73 
2.81 
2.95 
2.74 
2.76 
3.24 
3.16 
2.70 
2.84 
2.90 
3.17 
2.54 
3.18 
2.61 
2.47 
2.68 
3.23 
3.12 
2.72 
2.67 
2.98 
2.85 
3.01 
2.84 
2.82 
2.96 
2.81 
2.92 
2.79 
3.16 

0.04 
0.02 
0.05 
0.32 
0.06 
0.08 
0.00 
0.03 
0.04 
0.09 
0.02 
0.05 
0.04 
0.03 
0.04 
0.13 
0.13 
0.06 
0.05 
0.04 
0.03 
0.00 
0.02 
0.10 
0.05 
0.04 
0.07 
0.07 
0.08 
0.04 
0.09 
0.01 
0.08 
0.06 
0.08 
0.16 
0.05 
0.05 
0.05 
0.03 
0.01 
0.03 
0.06 
0.25 
0.02 
0.10 
0.09 
0.18 
0.08 
0.02 
0.05 
0.08 
0.06 
0.02 
0.03 
0.04 
0.04 
0.17 
0.04 
0.03 
0.04 
0.08 
0.03 
0.08 
0.04 
0.03 
0.05 
0.05 
0.02 
0.09 
0.04 

0.00  Pass 
0.00  Pass 
0.00  Pass 
0.31  Fail 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.07  Fail 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.01  Pass 
0.06  Fail 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.27  Fail 
0.00  Pass 
0.02  Pass 
0.02  Pass 
0.11  Fail 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.05  Fail 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 

 
 
819 
820 
821 
822 
823 
824 
825 
826 
827 
828 
829 
830 
831 
832 
833 
834 
835 
836 
837 
838 
839 
840 
841 
842 
843 
844 
845 
846 
847 
848 
849 
850 
851 
852 
853 
854 
855 
856 
857 
858 
859 
860 
861 
862 
863 
864 
865 
866 
867 
868 
869 
870 
871 
872 
873 
874 
875 
876 
877 
878 
879 
880 
881 
882 
883 
884 
885 
886 
887 
888 
889 

2.72 
3.06 
2.82 
3.06 
2.71 
2.72 
2.77 
2.87 
2.81 
2.79 
2.90 
2.62 
2.89 
2.43 
2.59 
2.93 
2.70 
2.81 
2.56 
2.90 
2.97 
2.63 
2.91 
2.61 
3.20 
3.06 
3.01 
2.65 
2.53 
2.76 
2.66 
3.08 
2.93 
2.63 
2.80 
2.78 
3.00 
2.68 
2.65 
3.08 
2.56 
2.81 
2.85 
2.89 
2.93 
2.81 
3.21 
2.55 
3.03 
2.67 
2.65 
2.99 
2.89 
2.49 
2.56 
2.80 
2.64 
2.62 
2.75 
2.82 
2.61 
3.05 
2.84 
3.00 
3.18 
2.99 
2.85 
3.09 
3.04 
3.26 
2.94 

0.01 
0.06 
0.04 
0.05 
0.04 
0.08 
0.07 
0.05 
0.02 
0.03 
0.08 
0.03 
0.05 
0.06 
0.04 
0.03 
0.02 
0.03 
0.02 
0.13 
0.06 
0.01 
0.07 
0.06 
0.11 
0.15 
0.63 
0.15 
0.03 
0.09 
0.07 
0.11 
0.01 
0.04 
0.05 
0.03 
0.04 
0.05 
0.04 
0.01 
0.03 
0.09 
0.05 
0.13 
0.02 
0.05 
0.06 
0.07 
0.02 
0.03 
0.03 
0.03 
0.12 
0.07 
0.05 
0.01 
0.09 
0.01 
0.06 
0.03 
0.04 
0.04 
0.14 
0.06 
0.09 
0.04 
0.01 
0.07 
0.04 
0.06 
0.13 

0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.01  Pass 
0.00  Pass 
0.04  Pass 
0.01  Pass 
0.03  Pass 
0.05  Fail 
1.65  Fail 
0.05  Fail 
0.00  Pass 
0.02  Pass 
0.01  Pass 
0.03  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.05  Fail 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.11  Fail 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 

33 

890 
891 
892 
893 
894 
895 
896 
897 
898 
899 
900 
901 
902 
903 
904 
905 
906 
907 
908 
909 
910 
911 
912 
913 
914 
915 
916 
917 
918 
919 
920 
921 
922 
923 
924 
925 
926 
927 
928 
929 
930 
931 
932 
933 
934 
935 
936 
937 
938 
939 
940 
941 
942 
943 
944 
945 
946 
947 
948 
949 
950 
951 
952 
953 
954 
955 
956 
957 
958 
959 
960 

2.76 
2.80 
2.73 
3.10 
2.80 
2.66 
2.72 
2.86 
2.83 
2.45 
2.87 
2.62 
2.97 
2.77 
2.81 
3.00 
2.79 
3.06 
2.86 
2.89 
2.82 
2.77 
2.98 
2.83 
2.82 
2.65 
2.83 
3.16 
2.86 
3.13 
2.55 
2.83 
2.67 
3.01 
2.62 
2.54 
2.90 
3.01 
2.74 
2.63 
3.06 
2.66 
2.95 
2.92 
2.97 
2.75 
2.80 
2.94 
2.74 
2.52 
2.96 
3.04 
2.90 
2.92 
2.90 
2.92 
2.66 
2.79 
2.92 
3.01 
2.83 
2.70 
2.85 
2.97 
2.81 
2.93 
2.72 
2.75 
2.99 
3.25 
2.93 

0.03 
0.04 
0.02 
0.03 
0.04 
0.04 
0.02 
0.04 
0.04 
0.02 
0.05 
0.05 
0.03 
0.04 
0.07 
0.04 
0.07 
0.05 
0.03 
0.02 
0.07 
0.05 
0.09 
0.13 
0.01 
0.02 
0.06 
0.13 
0.05 
0.03 
0.05 
0.09 
0.07 
0.11 
0.07 
0.07 
0.14 
0.05 
0.06 
0.02 
0.06 
0.12 
0.24 
0.06 
0.04 
0.04 
0.03 
0.13 
0.03 
0.03 
0.05 
0.03 
0.05 
0.13 
0.09 
0.13 
0.07 
0.09 
0.04 
0.06 
0.16 
0.03 
0.04 
0.07 
0.01 
0.07 
0.02 
0.08 
0.08 
0.07 
0.03 

0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.02  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.02  Pass 
0.00  Pass 
0.04  Pass 
0.02  Pass 
0.01  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.04  Pass 
0.17  Fail 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.05  Fail 
0.01  Pass 
0.08  Fail 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.05  Fail 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.04  Pass 
0.01  Pass 
0.01  Pass 
0.00  Pass 

 
 
1032 
1033 
1034 
1035 
1036 
1037 
1038 
1039 
1040 
1041 
1042 
1043 
1044 
1045 
1046 
1047 
1048 

2.95 
2.78 
2.93 
2.95 
2.80 
2.74 
3.09 
2.62 
2.84 
2.76 
2.75 
2.80 
2.76 
3.03 
2.97 
3.00 
2.92 

0.12 
0.12 
0.10 
0.09 
0.02 
0.06 
0.11 
0.07 
0.01 
0.02 
0.06 
0.02 
0.01 
0.11 
0.02 
0.07 
0.07 

0.02  Pass 
0.04  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.01  Pass 
0.04  Pass 
0.00  Pass 
0.00  Pass 
0.00  Pass 
0.01  Pass 
0.00  Pass 
0.00  Pass 
0.09  Fail 
0.00  Pass 
0.01  Pass 
0.00  Pass 

The mean rates produced by the 999 “Pass” 
repetitions are calculated to: 

Singles:  
Doubles: 
Triples:   

2.828 ± 0.006  s-1 
0.050 ± 0.001  s-1 
0.006 ± 0.000  s-1 

961 
962 
963 
964 
965 
966 
967 
968 
969 
970 
971 
972 
973 
974 
975 
976 
977 
978 
979 
980 
981 
982 
983 
984 
985 
986 
987 
988 
989 
990 
991 
992 
993 
994 
995 
996 
997 
998 
999 
1000 
1001 
1002 
1003 
1004 
1005 
1006 
1007 
1008 
1009 
1010 
1011 
1012 
1013 
1014 
1015 
1016 
1017 
1018 
1019 
1020 
1021 
1022 
1023 
1024 
1025 
1026 
1027 
1028 
1029 
1030 
1031 

3.23 
2.85 
2.90 
2.96 
2.75 
2.67 
3.03 
2.51 
2.75 
3.04 
2.78 
3.22 
2.88 
3.01 
2.38 
3.17 
3.21 
3.06 
2.90 
2.95 
2.87 
2.87 
3.21 
2.90 
2.88 
2.64 
2.60 
3.07 
2.36 
2.34 
2.63 
2.95 
2.67 
2.91 
2.85 
2.65 
2.50 
2.78 
2.81 
2.80 
2.90 
2.76 
3.05 
2.73 
2.85 
2.97 
2.80 
2.72 
3.31 
3.02 
2.49 
2.82 
2.73 
2.76 
2.63 
2.79 
2.78 
2.82 
2.89 
3.17 
2.98 
2.78 
2.59 
2.80 
2.90 
3.28 
2.76 
2.79 
2.89 
2.72 
2.84 

0.05 
0.04 
0.10 
0.05 
0.01 
0.03 
0.06 
0.01 
0.03 
0.04 
0.05 
0.11 
0.07 
0.05 
0.03 
0.04 
0.11 
0.07 
0.14 
0.09 
0.00 
0.07 
0.05 
0.09 
0.05 
0.02 
0.09 
0.08 
0.03 
0.01 
0.06 
0.07 
0.07 
0.03 
0.05 
0.10 
0.01 
0.04 
0.03 
0.04 
0.04 
0.05 
0.03 
0.05 
0.01 
0.03 
0.06 
0.03 
0.07 
0.12 
0.11 
0.02 
0.05 
0.03 
0.05 
0.05 
0.10 
0.04 
0.03 
0.03 
0.07 
0.07 
0.03 
0.06 
0.05 
0.11 
0.05 
0.07 
0.03 
0.05 
0.11 

0.00  Pass 
0.00  Pass 
0.01  Pass 
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0.05  Fail 

34 

 
 
 
 
 
 
Annex 2.  Measured and dead-time corrected count rates of certified 252Cf 
sources 

Table 2.  Comparison of expected to un-corrected and dead-time corrected signal multiplets 

Source A 

Source B 

Source C 

Source D 

1)expected rates, decay corrected, and efficiency accounted for 

R1,  (s-1) 
R2,  (s-1) 
R3,  (s-1) 

4038.58 
1660.27 
  379.00 

98245.48 
40365.73 
  9209.28 

2)raw measured rates, corrected for Gate fraction 

R1,  (s-1) 
R2,  (s-1) 
R3,  (s-1) 

3955.98 
1614.75 
  353.49 

2)dead-time corrected rates, multiplicity 

R1,  (s-1) 
R2,  (s-1) 
R3,  (s-1) 
deviation from 
expected (%), 
R1   
R2   
R3   

3972.21 
1633.29 
  374.61 

-1.64 
-1.63 
-1.16 

2)dead-time corrected rates, coincidence 

92348.63 
32908.74 
      10.17 

96773.34 
39637.91 
  8300.02 

 -1.50 
 -1.80 
-9.74 

128205.17 
  52697.56 
  12029.73 

118087.06 
  40705.16 
    -767.35 

125388.30 
  51877.56 
  13201.95 

226518.80 
  93063.29 
  21239.01 

199154.32 
  59644.10 
  -13731.35 

220983.99 
  92124.07 
  21108.21 

-2.20 
-1.56 
 9.74 

-2.44 
-1.01 
-0.62 

R1,  (s-1) 
R2,  (s-1) 
deviation from 
expected (%), 
R1   
R2   

Source: JRC analysis. 

3963.68 
1627.37 

96797.58 
39723.49 

125486.09 
  51906.59 

221362.94 
  91039.16 

-1.85 
-1.98 

-1.47 
-1.59 

-2.12 
-1.50 

-2.28 
-2.18 

1) 

2) 

3) 

The expected rates are calculated from the decay corrected fission rate, taking into account both 252Cf and 
250Cf isotopes, but excluding estimates of contributions from delayed neutrons, induced fission, and (, n) 
reactions.  The detection efficiency used is assumed as   = 0.2585. 

The measured and dead-time corrected rates are corrected for background, and for Gate fraction (by the factor 
f on R2, and f2 on R3).  

Standard deviations on the rates are not quoted here. However, the largest rel. uncertainty on the measured 
data (on triple rates) was less than 1%.  

35 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Annex 3.  Effect of  pile-up on neutron count rates for background and a small 252Cf source 

Table 3.   Measurements with a strong 137Cs source at variable distance to dosimeter placed at centre of BBNCC cavity 

Measurement 
configuration  
Background 
 source,    absent 
 source,  156 cm 
 source,  120 cm 
 source,    60 cm 
 source,    20 cm 
 source,      0 cm 
252Cf source 
 source,    absent 
 source,  156 cm 
 source,  120 cm 
 source,    60 cm 
 source,    20 cm 
 source,      0 cm 

Source: JRC analysis. 

Dose (Sv/h)1) 2) 
   rate             1  

R1, singles  (s-1) 
     rate             1  

R2, doubles  (s-1) 
     rate            1  

R3, triples  (s-1) 
     rate            1  

meas. time 
x 100 (s) 

0.123 
17.406  
34.542 
171.24 
1645.0 
16182. 

0.689 
17.738 
33.396 
176.60 
1174.2 
16582. 

0.016 
0.229 
0.102 
0.255 
8.906 
16.97 

0.023 
0.149 
0.033 
0.544 
14.06 
63.02 

3.983 
4.301 
4.543 
4.690 
8.559 
13.632 

2910.126 
2907.951 
2910.667 
2908.641 
2907.795 
2918.404 

0.043 
0.064 
0.051 
0.052 
0.075 
0.085 

0.260 
1.763 
1.417 
1.960 
1.670 
1.783 

0.071 
0.064 
0.080 
0.075 
0.053 
0.056 

768.242 
768.282 
767.324 
766.817 
766.191 
770.111 

0.006 
0.011 
0.009 
0.010 
0.008 
0.007 

0.251 
1.668 
1.386 
1.973 
1.785 
1.529 

0.010 
0.007 
0.013 
0.008 
0.005 
0.006 

108.797 
108.048 
109.680 
106.548 
108.943 
109.148 

0.002 
0.003 
0.006 
0.003 
0.002 
0.003 

0.196 
1.455 
1.455 
1.247 
0.995 
1.262 

36 
16 
15 
18 
18 
18 
755 
over night 
18 
18 
18 
18 
18 

1) 
2) 

The gamma dose rate for each position is the mean and standard deviation of 3 repetitions of 10-minute integration time. 
The uncertainty quoted on the dose measurement does not include the uncertainty in the source position. 

36 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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