TECHNIQUE FOR DETERMINING THE KINETIC ENERGY OF A HADRON BEAM

Abstract

A technique for determining the kinetic energy of a hadron beam using elements of the particle time of flight method, where all amplitudes for the measured signals S.sup.A(k) and S.sup.B(k) are recorded simultaneously from two detectors (A) and (B) located at a precisely defined distance L from each other and connected to a processing unit enabling the analysis of images recorded by both detectors, placed along the line of the studied hadron beam, over a period of time corresponding at least to 100 times the theoretical value for the time of flight of a hadron beam particle between the detectors (A) and (B), with time resolution at least on the level of 0.5 ns.

Claims

1. Technique for determining the kinetic energy of a hadron beam using elements of the particle time of flight method, executed in a particle detector unit system equipped with a processing unit enabling the analysis of images recorded by the particle detectors and including an oscilloscope card with a minimum bandwidth of 200 MHz and a sampling frequency of at least 4 GS/s, characterised in that simultaneous, continuous recording of amplitude values for the S.sup.A and S.sup.B signals from the particle detector unit is started, with the first (A) and the second (B) detectors placed along the line of the studied hadron beam, with simultaneous parameters and specifications, located at a precisely determined mutual distance L and independently connected with the processing unit and comprising a previously calibrated system for execution of recording of the values of individual signal amplitudes S.sup.A and S.sup.B, which is executed with time resolution on the level of at least 0.5 ns, all amplitudes of the measured signals S.sup.A(k) and S.sup.B(k) from both detectors (A) and (B) are recorded simultaneously for a period of time corresponding to at least 100 times the theoretical time of flight of a single particle of the hadron beam between the detectors (A) and (B), the simultaneous records of amplitudes of the measured S.sup.A and S.sup.B signals from both particle detectors (A) and (B) are archived, and individual sampling points for both signals are recorded synchronously and indexed using the same variable specifying the recording step k, obtaining signal profiles S.sup.A(k) and S.sup.B(k), the amplitude value for signals S.sup.A(k) and S.sup.B(k) lower than the specified threshold value are considered to be zero and are eliminated, an analysis of the shape of individual signals S.sup.A(k) and S.sup.B(k) most frequently recorded for the protons of the measured beam is carried out and the shape pattern is determined for these signals, followed by the removal of signals deviating from this pattern, after the end of the recording period for amplitudes of signals S.sup.A(k) and S.sup.B(k) from both particle detectors (A) and (B), an analysis of the statistical correlation for the signal profiles for S.sup.A(k) and S.sup.B(k), left at both detectors by multiple particles, is carried out by shifting the recorded signal profile recorded from the particle detector (B) with its recording basis step k, compared to the constant signal profile from the particle detector (A), until the maximum overlap of signal profiles is achieved for S.sup.A(k) and S.sup.B(k), which is equivalent to achieving the minimum total difference between the amplitudes of signal profiles for S.sup.A(k) and S.sup.B(k), at the specified step k, corresponding to the time resolution used to record the signals, the number of steps k, determined during a measurement, from k=0 to k=N, is used to determine the multiplicity of steps k designated as .sup.D, by which the signal S.sup.B(k) is shifted compared to the signal S.sup.A(k), such that the following function reaches its minimum: $R\left({}^D\right)=\frac{1}{N-{}^D}\underset{k=0}{\overset{N-{}^D}{.Math.}}.Math.S^A\left(k\right)-S^B\left(k+{}^D\right).Math.$ where: .sup.D is a variable defining the shift between the compared signals and it assumes discreet values in the (0, N) range, the location of the global minimum of the R(.sup.D) function and the value .sup.D.sub.min, corresponding to the time of flight of hadrons between the detectors (A) and (B) expressed using the formula t=t*.sup.D.sub.min, where t is the length of a single sample interval (0.5 ns), are determined, the position of the global minimum of the continuous R(.sup.D) function is specified more precisely by fitting the polynomial around the previously determined minimum, using the least squares method for the distance (|R(.sup.D)(.sup.D)|), where designates the fitted polynomial, the average time of flight of the hadron beam is determined according to the relationship, t=t*.sub.min, where t is the length of a single sampling interval, while .sub.min designates the real number , for which the (.sup.D) polynomial fitted to the R(.sup.D) function reaches the minimum value, the kinetic energy value for the hadron beam is determined using the obtained time of flight t between the detectors A and (B) according to the known physical relationships for the given hadron beam, the determined value of kinetic energy of the hadron beam is corrected with the known energy loss occurring during the passage through the first detector (A), by subtracting the literature value of energy losses in the used detector (A), the procedure of kinetic energy determination for a hadron beam ends by presenting the determined energy value and with the removal of the (A) and (B) detectors from the motion path of the studied hadron beam.

2. A method according to claim 1, characterised in that scintillation detectors placed along the line of the studied hadron beam are used as particle detectors, such that the planes of the active part of the detectors are perpendicular to the direction of travel of the hadron beam.

3. A method according to claim 1, characterised in that the calibration measurement involves testing of the entire installation set up to execute the method of determination of kinetic energy of a hadron beam by carrying out individual measurements for detectors placed at a distance d=0 such that the active parts of both detectors are in contact and the system is considered as calibrated when the determined, average time of flight of the hadrons reaches 0.

4. A method according to claim 1, characterised in that the noise level is determined through algorithm calculations based on the statistical distribution of the sampled amplitudes and fitting the Gaussian function around the maximum count, followed by determination of the zero level for the average value of the distribution and of the noise as at least 3, where designates the standard deviation from the mean value of this distribution.

5. A method according to claim 1, characterised in that a reference profile is determined for individual signals, most frequently recorded for protons of the measured signal beam, and the pulse length and its integrated surface area are accepted as the conformity criterion, followed by the rejection (amplitude zeroing) of pulses deviating by at least 3 from the mean value for at least one parameter comprising the criterion.

Description

[0024] The method of determination of hadron beam kinetic energy is explained below using practical embodiments of the invention and the drawing, which shows, in

[0025] FIG. 1 presents the flow diagram of the algorithm of the method,

[0026] FIG. 2 presents example images of signals from both detectors acquired during a single measurement lasting wherein the top row shows signals from detectors (A) and (B) after the initial processing and saving in the buffers, while the bottom row shows signals from detectors (A) and (B) after the removal of signals from random particles from them on the basis of a shape analysis,

[0027] FIG. 3 shows the example values of the signal overlapping function R(.sup.D) [points], which depends on the signal shift step from detector (B), and the maximum signal overlapping occurs at the location of the R(.sup.D) function minimum,

[0028] FIG. 4 shows the results for a series of measurement of beam energy changed with a 10 MeV increment using a degrader, carried out at the experimental hall of the Bronowice Cyclotron Centre using the method according to the invention, and

[0029] FIG. 5 schematically presents the locations of the (A) and (B) detectors in the line of the Proteus-235 cyclotron beam at Bronowice Cyclotron Centre.

EXAMPLE 1

[0030] An example execution of the method of determination of hadron beam kinetic energy diffusion was carried out using a proton beam with the energy of 1.96 GeV and the current of approximately 1 pA, generated by the COSY cyclotron at Forschungszentrum Juliech.

[0031] The installation for execution of the method was assembled using two particle detectors And B. Both detectors used square scintillation plastic panels BICRON, 9090 mm and 5 mm thick as the active material. The light excited by the passing hadron beam particles was read on one side using four silicon photoamplifiers (3 mm, C-Series by Omicron). The photoamplifier unit installed on the side of the active material panel and the scintillating material itself were optically insulated against the ambient light as a standard.

[0032] The electric signal acquired from photoamplifiers was sent through concentric BNC cables to two channels of the oscilloscope card WaveSurfer 3024z installed in the central processing unit. The oscilloscope card channels were set to the single time interval of 5 ms recording, with a resolution of 0.5 ns per single bin (sampling interval). The signal from each detector was saved in a separate memory buffer. Each buffer was designed to store at least 1.010.sup.7 points. The signal profiles saved in the buffers and generated in the detectors by the passing particles of the measured hadron beam were analysed using an algorithm executing the method of determination of kinetic energy of the hadron beam.

[0033] The distance between the detectors was set as d=7.93 m. A calibration measurement involving individual measurements for detectors set at a distance of d=0, which means that the active parts of both detectors were in contact. The calibration measurement was carried out in order to verify that the records of signals from both detectors do not show any delays related to incorrect design of the system and is recorded synchronously in both channels as a consequence.

[0034] The execution of the method of determination of kinetic energy of a hadron beam was preceded by the placement of detectors along the line of the examined hadron beam at a distance d=7.93 m, followed by the emission of a proton beam with the energy of 1.96 GeV.

[0035] The execution of the method of determination of kinetic energy of a hadron beam began with starting the synchronised, simultaneous and continuous recording of the values of individual signal amplitudes S.sup.A and S.sup.B from both particle detectors (A) and (B). The individual (k-th) values of signal amplitudes S.sup.A(k) and S.sup.B(k) were sampled and recorded every 0.5 ns over a period of 5 ms. The recording of individual sampling points for both signals was carried out synchronously and indexed with the save variable determining the recording step k, as a result of signal recording throughout the entire measurement interval forming the profiles of signals S.sup.A(k) and S.sup.B(k). An initial analysis of the recorded signals was carried out and the zero level was determined for the signals, together with the noise level and the amplitudes of individual signal fragments with a value lower than the threshold limit were removed (zeroed). At the same time, the initial analysis determined the characteristic pulse profile and the profile most frequently corresponding to the signals generated by protons with the energy of the studied beam, and signals deviating from the determined signal reference profile for a single particle were zeroed (removed) from the recorded signals S.sup.A and S.sup.B. The pulse length and its integrated surface area were accepted as the conformity criteria. Pulses deviating by 3 from the mean value of at least one parameter comprising the criterion were rejected (the amplitudes were zeroed).

[0036] After the initial analysis, a statistical analysis was carried out for the correlation of S.sup.A and S.sup.B signal profiles left in the detectors by many particles. Each of the signal profiles comprised an array of N=1.010.sup.7 saved values of individual S.sup.A(k) and Sb(k).sup.B(k) amplitudes, numbered using a shared k index. The signal profile correlation analysis involved a shift of the recorded signal profile S.sup.B(k) by shifting the index using individual natural numbers .sup.D from the range [0, N), compared to the fixed signal profile S.sup.A(k), at the same time adding together the amplitude difference for the entire signal and obtaining a set of values R(.sup.D) such that:

[00002]$R\left({}^D\right)=\frac{1}{N-{}^D}\underset{k=0}{\overset{N-{}^D}{.Math.}}.Math.S^A\left(k\right)-S^B\left(k+{}^D\right).Math.$

[0037] Next, we select a .sup.D.sub.min value such that R(.sup.D.sub.min) assumes the lowest value of all R(.sup.D). The value of .sup.D.sub.min=57 was obtained.

[0038] This defined the global function minimum for the value .sup.D.sub.min, which is the best fit to the average time of flight of hadrons between the detectors, expressed with the formula t=t*.sup.D.sub.min, where t is the length of a single sample interval (0.5 ns). The value of t=28.50.5 ns was obtained.

[0039] The previously obtained value of time shift was made more precise by further specifying the location of the minimum (.sub.min) of the continuous function R() obtained by fitting a 5th order (()) polynomial to R(.sup.D.sub.min) using the least square method for length |R(.sup.D)(.sup.D)|.

[0040] Next, the average time of flight of particles was determined again, using the relationship t=t*.sub.min where t is the length of a single sampling interval, while .sub.min means a real number , for which the () polynomial fitted to the R() function, and thus the R() function reach the minimum value. The value of t=27.98+/0.07 ns was obtained.

[0041] The objective of the statistical analysis of signal profile correlation for S.sup.A and S.sup.B was to obtain the maximum overlap of the signal profiles S.sup.A and S.sup.B, which means that the minimum of the total sum of amplitude difference for the signal profiles S.sup.A(k) and S.sup.B(k) was reached over all sampling intervals k.

[0042] The obtained results provided the basis for determination of the kinetic energy value for the hadron beam, using the obtained time of flight t between the scintillation detectors A and B on the basis of known physical relationships for the given hadron beam.

[00003]$E_{kin}=m_0{c}^2\left(\frac{1}{\sqrt{1-{\left(\frac{v}{c}\right)}^2}}-1\right)$

where c is the speed of light, m.sub.0 the particle mass, and the particle velocity is

[00004]$v=\frac{L}{t},$

results from the knowledge of the time of flight t of this particle between two detectors A and B located at a specified distance L from each other.

[0043] The determined value of kinetic energy of the hadron beam was corrected with the known energy loss occurring during the passage through the detector A, by adding the literature value of energy losses in the used detector to the achieved value for energy.

[0044] The value of the kinetic energy of a hadron beam of 1.95+/0.1 GeV was obtained and the scintillation detectors A and B were removed from the motion path of the studied hadron beam.

EXAMPLE 2

[0045] The example method of determination of the kinetic energy of a hadron beam was executed using a proton beam generated by the Proteus-235 cyclotron at the Bronowice Cyclotron Centre. The output energy of the cyclotron beam was always 226 MeV and was reduced to the desired value using a specially prepared degrader set. The initial current of the beam was 1 nanoampere and was also reduced on a degrader. The tests were performed for energy in the 70-140 MeV range with a 10 MeV increment, while the beam current was reduced to several picoamperes.

[0046] The installation for execution of the method according to the invention was assembled using two particle detectors. Both detectors used square panels made of scintillating plastics BICRON as the active material, sized at 3030 mm and 5 mm thick. The light excited by the passing hadron beam particles was read on one side using one silicon photoamplifiers (3 mm, C-Series by Omicron). Both the panel made of active material and the photoamplifier installed on its side were optically insulated from ambient light as a standard, using material with known thickness. Example 2 involved the execution of the kinetic energy determination method for eight hadron beams, in the energy range of 70-140 MeV.

[0047] The distance between the detectors was set as d=2.66 m. A calibration measurement was carried out analogously to the description in Example 1. The method of kinetic energy determination for individual hadron beams started with emitting a proton beam with an energy of 70 MeV, for the first studied beam. The subsequent beams had their energy increased by 10 MeV, up to the eighth energy level of 140 MeV.

[0048] The method of determination of kinetic energy of the studied hadron beam involved synchronised, simultaneous and continuous recording of the values of individual signal amplitudes S.sup.A and S.sup.B from both particle detectors (A) and (B). The individual (k-th) values of signal amplitudes S.sup.A(k) and S.sup.B(k) were sampled and recorded every 0.5 ns over a period of 2 ms. The recording of individual sampling points for both signals was carried out synchronously and indexed with the save variable determining the recording step k, as a result of signal recording throughout the entire measurement interval forming the profiles of signals S.sup.A(k) and S.sup.B(k). An initial analysis of the recorded signals was carried out and the zero level was determined for the signals, together with the noise level and the amplitudes of individual signal fragments with a value lower than the threshold limit were removed (zeroed). At the same time, the initial analysis determined the characteristic pulse profile and the profile most frequently corresponding to the signals generated by protons with the energy of the studied beam, and signals deviating from the determined signal reference profile for a single particle were zeroed (removed) from the recorded signals S.sup.A and S.sup.B. The pulse length and its integrated surface area were accepted as the conformity criteria. Pulses deviating by 3 from the mean value of at least one parameter comprising the criterion were rejected (the amplitudes were zeroed). At the end of the initial analysis, a statistical analysis was carried out for the correlation of S.sup.A and S.sup.B signal profiles left in the detectors by many particles. Each of the signal profiles comprised an array of N=4.010.sup.6 saved values of individual S.sup.A(k) and Sb(k).sup.B(k) amplitudes, numbered using a shared k index. The signal profile correlation analysis involved a shift of the recorded signal profile S.sup.B(k) by shifting the index using individual natural numbers .sup.D from the range [0, N), compared to the fixed signal profile S.sup.A(k), at the same time adding together the amplitude difference for the entire signal and obtaining a set of values R(.sup.D) such that:

[00005]$R\left({}^D\right)=\frac{1}{N-{}^D}\underset{k=0}{\overset{N-{}^D}{.Math.}}.Math.S^A\left(k\right)-S^B\left(k+{}^D\right).Math.$

[0049] Next, the .sup.D.sub.min value was determined, such that R(.sup.D.sub.min) assumes the lowest value of all R(.sup.D). The .sup.D.sub.min values presented in Table 1 were obtained for individual beams:

TABLE-US-00001 TABLE 1 Hadron beam No. energy [MeV] .sup.D.sub.min value 1. 70 50 2. 80 48 3. 90 44 4. 100 42 5. 110 40 6. 120 39 7. 130 38 8. 140 37

[0050] This defined the global function minimum for the value .sup.D.sub.min, which is the best fit to the average time of flight of hadrons between the detectors, expressed with the formula t=t*.sup.D.sub.min where t is the length of a single sample interval (0.5 ns). The t values presented in Table 2 were obtained for individual beams:

TABLE-US-00002 TABLE 2 Hadron beam No. energy [MeV] t value 1. 70 25.0 +/ 0.5 2. 80 24.0 +/ 0.5 3. 90 22.0 +/ 0.5 4. 100 21.0 +/ 0.5 5. 110 20.0 +/ 0.5 6. 120 19.5 +/ 0.5 7. 130 19.0 +/ 0.5 8. 140 18.5 +/ 0.5

[0051] The previously obtained value of time shift was made more precise by further specifying the location of the minimum (.sub.min) of the continuous function R() obtained by fitting a 5th order (()) polynomial to R(.sup.D.sub.min) using the least square method for length |R(D)(.sup.D)|.

[0052] Next, the average time of flight of particles was determined again, using the relationship t=t*.sub.min, where t is the length of a single sampling interval, while .sub.min means a real number , for which the () polynomial fitted to the R() function, and thus the R() function reach the minimum value. The t values presented in Table 3 were obtained for individual beams:

TABLE-US-00003 TABLE 3 Hadron beam No. energy [MeV] t value 1. 70 24.89 +/ 0.08 2. 80 23.46 +/ 0.11 3. 90 22.12 +/ 0.09 4. 100 20.98 +/ 0.08 5. 110 20.15 +/ 0.07 6. 120 19.44 +/ 0.09 7. 130 18.82 +/ 0.06 8. 140 18.20 +/ 0.09

[0053] The obtained results were used as the basis for determination of the kinetic energy value for the hadron beam using the obtained time of flight t between the scintillating detectors A and B, according to the known physical relationships for the given hadron beam.

[0054] The value of kinetic energy of the hadron beam was corrected with the known energy loss occurring during the passage through the detector A, by adding the literature value of energy losses in the used detector to the achieved value for energy.

[0055] The results of energy determination for a series of measurements for the measured beams are presented in FIG. 5.

[0056] The kinetic energy determination procedures carried out for hadron beams in the examples according to the method according to the invention resulted in kinetic energy values for 9 hadron beams. The obtained results differed by <1% compared to the energy value determined using other, more complicated methods.

[0057] The use of the method of determination of hadron beam kinetic energy according to the invention enables the replacement or supplementation of difficult and complex methods previously used to determine the kinetic energy of hadron beams and surveillance expansion during the use of hadron beams to be achieved, which should contribute to the improved reliability of effects achieved in scientific, therapeutic and technical applications.