CN102799792B - Dead time correction method of reactor reactivity measured value - Google Patents

Abstract

The invention relates to a dead time correction method of a reactor reactivity measured value. The dead time correction method comprises the following steps of: estimating ns (0) to (tj, nj) by using a fitting iteration method; correcting a counting sequence (ti, ni) into (ti, n'i) by using a dead time initial assumed value tau(0); correcting the (ti, n'i) into (ti, n''i) by using ns(0); fitting by using ln(n''i) and ti according to a linear relation; calculating nali corresponding to the ti according to a fitting analysis formula, and correcting according to na2i= nali+ns; correcting the dead time values taui on each ti by na2i and ni, and obtaining an averaging value of the taui to obtain an iteration updated value tau(1); replacing tau(0) with tau(1) to carry out renewed fitting and iteration until tau convergence; and carrying out dead time correction on the previous nj by using the convergence tau value, and carrying out renewed fitting and iteration to obtain an updated value ns(1) until ns convergence. By adopting the method of the invention, a reasonable and effective counting dead time value can be acquired.

Description

A kind of dead-time control method of pile reactivity measured value

Technical field

The invention belongs to reactor detection system alignment technique field, be specifically related to a kind of dead-time control method of pile reactivity measured value.

Background technology

In reactor physics start-up course, neutron count rate level is lower, and under neutron detection system is usually operated at pulse mode, now measuring system exists the impact in dead time.Within certain a period of time (as 1s), the time shared by whole signal pulses of meter is leaked when dead time, (τ) referred to that measuring system is measured.Within the dead time, system no longer has response to the neutron entering detector, causes counting loss.Dead time effects can cause measurement result to depart from actual conditions, and dead time effects generally can cause reactivity measurement Lower result, especially when counting rate is relatively high.Therefore, necessary choose reasonable neutron count rate scope in physical start-up process, and dead time effects correction is carried out to measurement result, to reduce measuring error.Usually, when known measurement systems dead time τ, the meter numerical value of available following formula correction detector:

$n_r=\frac{n_m}{1-n_m\·\mathrm{\τ}}$

Wherein, n _mfor the counting rate measured, n _rfor revised counting rate.

According to revised count value, recalculate reactive value, reactivity measurement value more accurately can be obtained.Therefore, the dead time value of measuring system is one of key parameter being related to reactivity measurement result accuracy.In general, supply of material producer should provide the dead time value of neutron detection system, and producer can be obtained by certain methods measurement in the process of debugging detection system, such as double source method etc.

But, if detection system is not demarcated through the special dead time after installation is complete and before bringing into use, now determine that measuring system dead time value just becomes a problem again.At present, in such cases, three parameter fitness methods of band external source and dead time item can be used to determine the dead time value of detection system.But make the reactive size first needing in this way to determine exactly in measuring process, and before dead time value obtains accurately, be difficult to obtain reactive value accurately, this is an existing methodical weak point.

Summary of the invention

For the defect existed in prior art, the object of this invention is to provide the dead-time control method of pile reactivity measured value, adopt the method can obtain effectively simultaneously, reliable measuring system dead time value, and obtain accurate response value further.

For reaching above object, the technical solution used in the present invention is: a kind of dead-time control method of pile reactivity measured value, comprises the following steps:

The first step: determine the scope needing the counting rate n revised;

Second step: regulate reactor core to one positive period state, and allow counting rate increase to reach the first step the scope of counting rate select, record the counting sequence of overall process;

3rd step: select lower range of count rates (the such as n that dead time impact is less _j≤ 30000cps) corresponding to counting sequence (t _j, n _j), t _jrepresent time series, n _jrepresent and correspond to t _jthe counting rate of measurement, in this range of count rates, using the fitting iteration of external source correction to carry out, effective outside interruption is strong, reactivity is estimated, and obtains the significant response value n of detection system for outside interruption by formula (1) _sinitial value n _s ⁽⁰⁾,

n _s＝-ΛS/ρ (1)

In formula (1), Λ represents neutron generation time, is constant, and S, ρ represent that the effective outside interruption using the fitting iteration of external source correction to obtain is strong, reactive respectively;

4th step: select to need the counting sequence (t carrying out dead-time control _i, n _i), i > j, assuming that the initial assumed value of iteration of the dead time τ of system is τ ⁽⁰⁾, by formula (2) to counting sequence (t _i, n _i) carry out dead-time control, obtain the counting sequence (t after dead-time control _i, n ' _i),

${n^{\′}}_r=\frac{n_i}{1-n_i\·\mathrm{\τ}}---\left(2\right)$

In formula (2), n _ifor corresponding to time t _ithe counting rate of measurement, n ' _ifor the counting rate after dead-time control;

5th step: utilize the n determined in the 3rd step _scounting sequence (t after the dead-time control that value obtains the 4th step _i, n ' _i) carry out external source correction, obtain the revised counting sequence (t of external source _i, n " _i), wherein,

n″ _i＝n′ _i-n _s(3)；

6th step: to the revised counting rate n of external source " _iget natural logarithm, then press ln (n " _i)=A+B*t relation carries out linear fit to time variable t, obtains fitting parameter A and B;

7th step: fitting parameter A and B obtained according to the 6th step, obtains one group and corresponds to time series t _iparsing counting rate n ^a1 _i, push away surveymeter digit rate n by formula (4) is counter ^a2 _i,

n ^a2 _i＝n ^a1 _i+n _s(4)；

8th step: the surveymeter digit rate n obtained by the 7th step ^a2 _iand initial measured count rates n _i, revise each time point t by formula (5) _ion dead time value τ _i,

${\mathrm{\τ}}_i=\frac{n_i^{a2}-n_i}{n_i^{a2}\·n_i}$

Then to τ _iget arithmetic mean, obtain the iteration updated value of dead time value, count τ ⁽¹⁾;

9th step: with the iteration updated value τ of dead time τ ⁽¹⁾replace τ ⁽⁰⁾, repeat the 4th step to the 8th step, until dead time τ reaches default convergent requirement;

Tenth step: the value getting the dead time τ after holding back, by formula (2) to the counting rate n selected by the 3rd step _jscope carries out dead-time control, and repeats the 3rd step, uses revised counting sequence to re-start external source corrected Calculation, obtains new significant response value, counts n _s ⁽¹⁾;

11 step: if n _s ⁽¹⁾reach default convergent requirement, then stop calculating; If n _s ⁽¹⁾do not reach default convergent requirement, then replace τ with the value of the dead time τ after convergence ⁽⁰⁾, with n _s ⁽¹⁾replace n _s ⁽⁰⁾, repeat the 4th step to the tenth step, until significant response value n _sreach default convergent requirement.

Further, in the 3rd step, the fitting iteration of external source correction comprises the following steps:

(I) counting sequence (t will selected _j, n _j) as the raw data of matching iterative processing;

(II) S, ρ initial size S is supposed ⁽⁰⁾, ρ ⁽⁰⁾, by Λ S ⁽⁰⁾, ρ ⁽⁰⁾substitution formula (6) is to counting sequence (t _j, n _j) revise, obtain revised counting sequence (t _j, n ' _j),

${n^{\′}}_j=n_j+\frac{\mathrm{\ΛS}}{\mathrm{\ρ}}=c\·e^{\mathrm{\ω}{t}_j}---\left(6\right)$

In formula (6), c represents and reactive and initial count n ₀relevant constant, ω represents the solution of reactivity equation (8) corresponding to stable period;

(III) to revised counting n ' _jget natural logarithm, then press ln (n ' _j)=A '+B ' * t relation carries out linear fit to time variable t, obtains fitting parameter A ' and B ', and obtains according to formula (6):

A'＝lnc (7.1)

B'＝ω (7.2)

$c=n_0+\frac{\mathrm{\ΛS}}{\mathrm{\ρ}}---\left(7.3\right)$

In formula (7.3), n ₀the value of the counting rate n in initial t=0 moment in counting rate sequence handled by expression;

(IV) the parameter A ' obtained by matching and B ', obtains the iteration updated value of Λ S, ρ, counts Λ S by the inhour equation shown in formula (7.1)-(7.3) and formula (8) ⁽¹⁾, ρ ⁽¹⁾,

$\mathrm{\ρ}=\mathrm{\Λ\ω}+\underset{i=1}{\overset{M}{\mathrm{\Σ}}}\frac{{\mathrm{\β}}_i\mathrm{\ω}}{\mathrm{\ω}+{\mathrm{\λ}}_i}---\left(8\right)$

In formula (8), β _irepresent i-th group of effective delayed neutron fraction, λ _irepresent i-th group of delayed-neutron precursor disintegration constant, M is the total packet count of delayed-neutron precursor;

(V) with Λ S ⁽¹⁾, ρ ⁽¹⁾replace the Λ S in step (II) ⁽⁰⁾, ρ ⁽⁰⁾, repeat (II) ~ (IV) step, until the iteration updated value of Λ S, ρ reaches default convergent requirement, calculate n by the convergency value of Λ S, ρ _s.

Further again, in the fitting iteration of external source correction, adopt method process same group of counting sequence (t of repeatedly slippage iteration _j, n _j): to counting sequence (t _j, n _j) the individual point of common N ' in, data volume handled by each matching iteration selects the individual point of M ', and iteration gets n first _k~ n _{k+M '-1}, second time iteration gets n _k+1~ n _{k+M '}, iteration gets n for the third time _k+2~ n _{k+M '+1}..., 1≤k≤N '-M '+1, continues iteration, until reach the slippage iterations of specifying, finally gets the arithmetic mean of the convergency value that repeatedly slippage iteration obtains respectively as strong, the reactive value of final effective outside interruption.

Further, select the counting sequence of the measurement that many groups are different, get the dead time value of arithmetic mean as final neutron detection system of the dead time value that multi-group data process obtains.

Further, in method, the counting sequence (t that same group of the method process of repeatedly slippage iteration is to be revised can be adopted _i, n _i): to counting sequence (t _i, n _i) common N number of point in, data volume handled by each matching iteration selects M point, and iteration gets n first _k~ n _k+M-1, second time iteration gets n _k+1~ n _k+M, iteration gets n for the third time _k+2~ n _k+M+1..., 1≤k≤N-M+1, continues iteration, until reach the slippage iterations of specifying, finally gets the dead time value of arithmetic mean as final neutron detection system of the dead time value that repeatedly slippage iteration obtains.

The present invention adopts fitting iteration can obtain the size of dead time value and Λ S and ρ restrained very soon.Experiment proves, the fitting iteration that the present invention proposes has higher validity to dead time process.

Accompanying drawing explanation

Fig. 1 is the calculation flow chart of the dead-time control method of pile reactivity measured value provided by the present invention;

Fig. 2 is the comparison diagram of counting rate before adopting method of the present invention to carry out the counting rate after the dead time and revise, and its center line a represents the counting rate before correction, and line b represents revised counting rate.

Embodiment

Below in conjunction with the drawings and specific embodiments, the invention will be further described.

For the validity that the fitting iteration of checking this patent proposition processed for the dead time, using in China Experiment Fast Reactor physical start-up process is definite kernel examining system source range dead time and one group of data gathering, analyzes the dead time of source range IA and IB passage.For solving the result of calculation fluctuation problem that counting fluctuation causes, repeatedly slippage alternative manner process is adopted to count.

Here use the algorithm flow shown in Fig. 1, concrete steps are as follows:

The first step: for China Experiment Fast Reactor Nuclear measurement system source range, the scope of the counting rate n revised is needed to be roughly IA passage 10000-60000cps, IB passage 4000-26000cps (this scope is the IB channel counts corresponding with time series selected by IA passage);

Second step: regulate reactor core to one positive period state, and allow the counting rate of each passage increase to reach the first step the scope of counting rate selected, record the counting sequence of each passage overall process;

3rd step: for each passage, selects the lower counting sequence (t that dead time impact is less respectively _j, n _j) (such as IA passage, get n _j≤ 30000cps, IB passage gets the counting respective value of same time sequence), in this range of count rates, use the fitting iteration of external source correction to estimate effective outside interruption strong, reactive, obtain the significant response value n of detection system for outside interruption by formula (1) _sinitial value n _s ⁽⁰⁾, Λ value is neutron generation time (the Λ value of each passage is identical) here

n _s＝-ΛS/ρ (1)

4th step: select to need the counting sequence (t carrying out dead-time control _i, n _i) (in such as the present embodiment, IA channel counts rate≤60000cps, IB channel counts rate≤26000cps), i > j, assuming that the initial assumed value of iteration of the dead time τ of system is τ ⁽⁰⁾, by formula (2) to counting sequence (t _i, n _i) carry out dead-time control, obtain the counting sequence (t after dead-time control _i, n ' _i),

${n^{\′}}_r=\frac{n_i}{1-n_i\·\mathrm{\τ}}---\left(2\right)$

5th step: utilize the n determined in the 3rd step _s(n _sinitial value n is got before not upgrading _s ⁽⁰⁾) counting sequence (t after dead-time control that the 4th step is obtained _i, n ' _i) carry out external source correction, obtain the revised counting sequence (t of external source _i, n " _i), wherein,

n″ _i＝n′ _i-n _s(3)；

6th step: to the revised counting rate n of external source " _iget natural logarithm, then press ln (n " _i)=A+B*t relation carries out linear fit to time variable t, obtains fitting parameter A and B;

7th step: fitting parameter A and B obtained according to the 6th step, obtains one group and corresponds to time series t _iparsing counting rate n ^a1 _i, push away surveymeter digit rate n by formula (4) is counter ^a2 _i,

n ^a2 _i＝n ^a1 _i+n _s(4)；

8th step: the surveymeter digit rate n obtained by the 7th step ^a2 _iand initial measured count rates n _i, revise each time point t by formula (5) _ion dead time value τ _i,

${\mathrm{\τ}}_i=\frac{n_i^{a2}-n_i}{n_i^{a2}\·n_i}---\left(5\right)$

Then to τ _iget arithmetic mean, obtain the iteration updated value of dead time value, count τ ⁽¹⁾;

9th step: with the iteration updated value τ in dead time ⁽¹⁾replace τ ⁽⁰⁾, repeat the 4th step to the 8th step, until the value of dead time τ reaches default convergent requirement;

Tenth step: the value getting the dead time τ after holding back, by formula (2) to the counting rate n selected by the 3rd step _jscope carries out dead-time control, and repeats the 3rd step, uses revised counting sequence to re-start external source corrected Calculation, obtains new significant response value, counts n _s ⁽¹⁾;

11 step: if n _s ⁽¹⁾reach default convergent requirement, then stop calculating; If n _s ⁽¹⁾do not reach default convergent requirement, then replace τ with the value of the dead time τ after convergence ⁽⁰⁾, with n _s ⁽¹⁾replace n _s ⁽⁰⁾, repeat the 4th step to the tenth step, until significant response value n _sreach default convergent requirement.

Wherein, in the 3rd step, the fitting iteration of external source correction comprises the following steps:

(I) counting sequence (t will selected _j, n _j) as the raw data of matching iterative processing;

(II) S, ρ initial size S is supposed ⁽⁰⁾, ρ ⁽⁰⁾, by Λ S ⁽⁰⁾, ρ ⁽⁰⁾substitution formula (6) is to counting sequence (t _j, n _j) revise, obtain revised counting sequence (t _j, n ' _j),

${n^{\′}}_j=n_j+\frac{\mathrm{\ΛS}}{\mathrm{\ρ}}=c\·e^{\mathrm{\ω}{t}_j}---\left(6\right)$

(III) to revised counting n ' _jget natural logarithm, then press ln (n ' _j)=A '+B ' * t relation carries out linear fit to time variable t, obtains fitting parameter A ' and B ', and obtains according to formula (6):

A'＝lnc (7.1)

B'＝ω (7.2)

$c=n_0+\frac{\mathrm{\ΛS}}{\mathrm{\ρ}}---\left(7.3\right)$

In formula (7.3), n ₀the value of the counting rate n in initial t=0 moment in counting rate sequence handled by expression;

(IV) the parameter A ' obtained by matching and B ' value, obtain the iteration updated value of Λ S, ρ, count Λ S by the inhour equation shown in formula (7.1)-(7.3) and formula (8) ⁽¹⁾, ρ ⁽¹⁾,

$\mathrm{\ρ}=\mathrm{\Λ\ω}+\underset{i=1}{\overset{M}{\mathrm{\Σ}}}\frac{{\mathrm{\β}}_i\mathrm{\ω}}{\mathrm{\ω}+{\mathrm{\λ}}_i}---\left(8\right)$

In formula (8), M value generally gets 6 groups, accordingly, and β _i, λ _ifor constant, immobilize in method.

(V) with Λ S ⁽¹⁾, ρ ⁽¹⁾replace the Λ S in step (II) ⁽⁰⁾, ρ ⁽⁰⁾repeat (II) ~ (IV) step, until the iteration updated value of Λ S, ρ reaches default convergent requirement, calculate n by the convergency value of Λ S, ρ _s.

In the present embodiment, the dead time of three parameter fitting method process to source range IA and IB passage of the outer source item of existing band and dead time item is adopted to analyze.The China Experiment Fast Reactor Nuclear measurement system intermediate quantity number of passes that the method is measured according to homogeneous comes the predefined cycle that this is measured or reactive size according to (middle range neutron count rate level is low, and dead time impact is less).

The contrast of above-mentioned two kinds of method gained dead time values is in table 1.Before and after the range IA passage dead-time control of source, Fig. 2 is shown in counting rate contrast.

Table 1 measured data dead time result contrasts

As can be seen from Table 1, adopt the dead time value of the source range IA that obtains of the inventive method and IB passage all to have good consistance with three parameter fitting methods, this shows that fitting iteration that the present invention proposes is effective for the process in dead time.Deviation between two kinds of method results is less than 5%.

Above-described embodiment just illustrates of the present invention, and the present invention also can implement with other ad hoc fashion or other particular form, and does not depart from main idea of the present invention or essential characteristic.Therefore, description embodiment from the viewpoint of any all should be considered as illustrative but not determinate.Scope of the present invention should be illustrated by the claim of adding, any also should be within the scope of the present invention with the intention of claim and the change of scope equivalence.

Claims (5)

1. a dead-time control method for pile reactivity measured value, comprises the following steps:

The first step: determine the scope needing the counting rate n revised;

Second step: regulate reactor core to one positive period state, and allow counting rate increase to reach the first step the scope of counting rate select, record the counting sequence of overall process;

3rd step: select counting sequence (t _j, n _j), t _jrepresent time series, n _jrepresent and correspond to t _jthe counting rate of measurement, in this range of count rates, using the fitting iteration of external source correction to carry out, effective outside interruption is strong, reactivity is estimated, and obtains the significant response value n of detection system for outside interruption by formula (1) _sinitial value n _s ⁽⁰⁾,

n _s＝-ΛS/ρ (1)

In formula (1), Λ represents neutron generation time, is constant, and S, ρ represent that the effective outside interruption using the fitting iteration of external source correction to obtain is strong, reactive respectively;

4th step: select to need the counting sequence (t carrying out dead-time control _i, n _i), i > j, assuming that the initial assumed value of iteration of the dead time τ of system is τ ⁽⁰⁾, by formula (2) to counting sequence (t _i, n _i) carry out dead-time control, obtain the counting sequence (t after dead-time control _i, n ' _i),

${n^{\′}}_i=\frac{n_i}{1-n_i\·\mathrm{\τ}}---\left(2\right)$

In formula (2), n _ifor corresponding to time t _ithe counting rate of measurement, n ' _ifor the counting rate after dead-time control;

5th step: utilize the n determined in the 3rd step _scounting sequence (t after the dead-time control that value obtains the 4th step _i, n ' _i) carry out external source correction, obtain the revised counting sequence (t of external source _i, n " _i), wherein,

n″ _i＝n′ _i-n _s(3)；

6th step: to the revised counting rate n of external source " _iget natural logarithm, then press ln (n " _i)=A+B*t relation carries out linear fit to time variable t, obtains fitting parameter A and B;

7th step: fitting parameter A and B obtained according to the 6th step, obtains one group and corresponds to time series t _iparsing counting rate n ^a1 _i, push away surveymeter digit rate n by formula (4) is counter ^a2 _i,

n ^a2 _i＝n ^a1 _i+n _s(4)；

8th step: the surveymeter digit rate n obtained by the 7th step ^a2 _iand initial measured count rates n _i, revise each time point t by formula (5) _ion dead time value τ _i,

${\mathrm{\τ}}_i=\frac{n_i^{a2}-n_i}{n_i^{a2}\·n_i}---\left(5\right)$

Then to τ _iget arithmetic mean, obtain the iteration updated value of dead time value, count τ ⁽¹⁾;

9th step: with the iteration updated value τ of dead time τ ⁽¹⁾replace τ ⁽⁰⁾, repeat the 4th step to the 8th step, until dead time τ reaches default convergent requirement;

Tenth step: get the dead time τ value after holding back, by formula (2) to the counting rate n selected by the 3rd step _jscope carries out dead-time control, and repeats the 3rd step, uses revised counting sequence to re-start external source corrected Calculation, obtains new significant response value, counts n _s ⁽¹⁾;

11 step: if n _s ⁽¹⁾reach default convergent requirement, then stop calculating; If n _s ⁽¹⁾do not reach default convergent requirement, then replace τ with the dead time τ value after convergence ⁽⁰⁾, with n _s ⁽¹⁾replace n _s ⁽⁰⁾, repeat the 4th step to the tenth step, until significant response value n _sreach default convergent requirement.

2. the dead-time control method of a kind of pile reactivity measured value according to claim 1, is characterized in that, in the 3rd step, the fitting iteration of external source correction comprises the following steps:

(I) counting sequence (t will selected _j, n _j) as the raw data of matching iterative processing;

(II) S, ρ initial size S is supposed ⁽⁰⁾, ρ ⁽⁰⁾, by Λ S ⁽⁰⁾, ρ ⁽⁰⁾substitution formula (6) is to counting sequence (t _j, n _j) revise, obtain revised counting sequence (t _j, n ' _j),

$n_j^{\′}=n_j+\frac{\mathrm{\ΛS}}{\mathrm{\ρ}}=c\·e^{{\mathrm{\ωt}}_j}---\left(6\right)$

In formula (6), c represents and reactive and initial count n ₀relevant constant, ω represents the solution of reactivity equation (8) corresponding to stable period;

(III) to revised counting n ' _jget natural logarithm, then press ln (n ' _j)=A '+B ' * t relation carries out linear fit to time variable t, obtains fitting parameter A ' and B ', and obtains according to formula (6):

A'＝lnc (7.1)

B'＝ω (7.2)

$c=n_0+\frac{\mathrm{\ΛS}}{\mathrm{\ρ}}---\left(7.3\right)$

In formula (7.3), n ₀the value of the counting rate n in initial t=0 moment in counting rate sequence handled by expression;

(IV) the parameter A ' obtained by matching and B ', obtains the iteration updated value of Λ S, ρ, counts Λ S by the inhour equation shown in formula (7.1)-(7.3) and formula (8) ⁽¹⁾, ρ ⁽¹⁾,

$\mathrm{\ρ}=\mathrm{\Λ\ω}+\underset{i=1}{\overset{M}{\mathrm{\Σ}}}\frac{{\mathrm{\β}}_i\mathrm{\ω}}{\mathrm{\ω}+{\mathrm{\λ}}_i}---\left(8\right)$

In formula (8), β _irepresent i-th group of effective delayed neutron fraction, λ _irepresent i-th group of delayed-neutron precursor disintegration constant, M is the total packet count of delayed-neutron precursor;

(V) with Λ S ⁽¹⁾, ρ ⁽¹⁾replace the Λ S in step (II) ⁽⁰⁾, ρ ⁽⁰⁾, repeat (II) ~ (IV) step, until the iteration updated value of Λ S, ρ reaches default convergent requirement, calculate n by the convergency value of Λ S, ρ _s.

3. the dead-time control method of a kind of pile reactivity measured value according to claim 2, is characterized in that, in the fitting iteration of external source correction, adopts method process same group of counting sequence (t of repeatedly slippage iteration _j, n _j): to counting sequence (t _j, n _j) the individual point of common N ' in, data volume handled by each matching iteration selects the individual point of M ', and iteration gets n first _k~ n _{k+M '-1}, second time iteration gets n _k+1~ n _{k+M '}, iteration gets n for the third time _k+2~ n _{k+M '+1}..., 1≤k≤N '-M '+1, continues iteration, until reach the slippage iterations of specifying, finally gets the arithmetic mean of the convergency value that repeatedly slippage iteration obtains respectively as strong, the reactive value of final effective outside interruption.

4. the dead-time control method of a kind of pile reactivity measured value according to claim 1, it is characterized in that, in 4th step, select the counting sequence to be revised that many groups are different, get the dead time value of arithmetic mean as final neutron detection system of the dead time value that multi-group data process obtains.

5. the dead-time control method of a kind of pile reactivity measured value according to claim 1, is characterized in that, adopts the counting sequence (t that same group of the method process of repeatedly slippage iteration is to be revised in method _i, n _i): to counting sequence (t _i, n _i) common N number of point in, data volume handled by each matching iteration selects M point, and iteration gets n first _k~ n _k+M-1, second time iteration gets n _k+1~ n _k+M, iteration gets n for the third time _k+2~ n _k+M+1..., 1≤k≤N-M+1, continues iteration, until reach the slippage iterations of specifying, finally gets the dead time value of arithmetic mean as final neutron detection system of the dead time value that repeatedly slippage iteration obtains.