Study Of Nuclear Analysis Method For The Measurement Of Protein Content And Depth Distribution In Grain Seeds

Protein is an extremely complex nitrogenous organic compound, which is the substance basis of living phenomenon. Any living activities are closely related to protein. The supply state of protein is directly related to human health and intelligence.So it is the important sign of the degree to measure the level of economy and civilization development for the country. Supplying more protein and increasing the quality of protein, that is one of main task of food program in our country.At present,the obtain of animal protein is mostly based on the consumption of plant protein. So how to increase the output of plant protein is the crux of the matter. Through the breeding of the grain varieties with high protein content and high protein quality to increase the protein harvest per unit area, that is one of the most perspective method.Along with continuous population growth in our country and the increasement of people living standard, on the one hand,it requires to consume more grain.On the other hand,the area under cultivation and water resources are gradually decreased year by year. The tendency must not take a turn for the worse. For this reason,the successful breeding of grain varieties with high protein content and high protein quality have particular importance. Through increasing nutritive value to increase its use value, its significance is the same as that of output increasement.Plant breeding programmes for increasing protein content and improving protein quality are confronted with the need for protein screening.The first step will always be protein determination in seeds.So it's important to establish a easy and reliable screening method for protein.In large-scale breeding programm, a large number of samples are collected.In order to separate usable cross combination or variants, the number of samples need to analynize is tens of thousands.Moreover,in the early time, the seed amount is limited. Only a few of grain seeds may be separated for analysis.At the same time, due to the extreme variability of protein content in grain seeds, the measurement of protein content in seeds and screening method have corresponding requirements: 1)quick, low price to satisfy the requirement of analysis for tens of thousands of the sample; 2) analysis may carry out for a little amount of sample, that is to say, can be realized for a few of grain; 3) genotype can be distinguished, thus, the seeds with high protein content caused by non-genetic factor may be removed at the early phase of breeding.So the work load can be decreased,and the effectiveness for seed selection may increase. In numerous measuring methods of grain protein content,the method based on ¹⁴N(d, p) ¹⁵N nuclear reaction has its characterizations which can satisfy the requirements for grain breeding. There is 1.2M cyclotron in Institute of nuclear science and technology of Sichuan University. The equipment condition is ready for establishing the nuclear reaction analysis method for the determination of protein content in grain. So by using the(d, p) nuclear reaction induced by 13.6MeV duteron in grain,we began the research work for the measrement of protein content and depth distribution in grain seeds.And the analysis method was established to fit the requirements of breeding research work.Grain seeds are composed of four major elements:carbon,oxygen,hydrogen and nitrogen.Nitrogen is mainly existed in protein and the content of nitrogen in various kinds of protein is nearly the same. So the nitrogen concentration is closely related to the protein content of seeds. As the carbon content in the major organic matters of seed(protein,cellulose, starch,sugar etc) is about the same, carbon may serve as an indicator for dry organic matter. So the ratio of ¹⁴N/¹²C may indicate the content of protein in seeds.When the grain sample was impacted by deuteron beam,(d,p)reactions with carbon,oxygen and nitrogen were induced. Due to ¹⁴N(d, p) ¹⁵N nuclear reaction has much higher Q value, the proton energy produced is much higher, Thus, there is a range of proton energy without the contribution of protons from ¹²C(d, p) ¹³C,¹⁶O(d, p) ¹⁷O. By distinguishing the protons from ¹⁴N(d, p) ¹⁵N reaction, it may evaluate the content of nitrogen element in the sample. Due to the energy loss of charged particles(incident deuteron and proton produced by reaction) in sample material, the proton energy produced by ¹⁴N(d, p)¹⁵N reaction in different depth is different.The proton energy recoded and distance depart from sample surface are correlative. Thus, by using energy spectrum of proton may obtain nitrogen distribution with depth in the sample.Through the analysis of the element composition in grain and physical characterization of nuclear reaction produced by 13.6MeV with those elements, the optimum measurement conditions for grain sample with homogeneous distribution of protein content are explained on the basis of nuclear reaction analysis principle.The relevant factors influencing the depth distribution measurement in seeds are analyzed and calculated.C_sI(TI) crystal is used as detector. Analyzing system with multiple-angle, multiple-channel detectors has been set up. Through the measurement on the ratio of nitrogen and carbon, the protein content in grain sample with homogeneous protein distribution has been determined quickly. By adopting standard method for the measurement of protein content in grain-K method, the correctness of the method is verified. At the same time the change relations between the nitrogen, carbon ratio and protein content has been calibrated.By using characterizations of differential cross-section of ¹²C(d, p), ¹⁶O(d, p) reactions, the synchronous monitor system has been set up for the change of water content in samples. By using the analyzing system established,the measurement of ratio of nitrogen and carbon elements has been carried out for wheat, rice and rape.In our multiple-angle, multiple-channel detector system, the detector at every angle has single function and easily calibrated.At the same angle,annularly multiple-channel detectors are set up, that may further increase analyzing speed for sample.During the analysis process,the data treatment is simple, so it is easy to realize automatic for analyzing. Under the irradiation of 350nA deuteron beam current, the analysis for one grain sample may be finished within 5 seconds, that satisfy the requirement of analyzing speed for grain protein breeding programm.By using semiconductor detector,the energy spectrum analyzing system has been set up.The depth distribution of nitrogen element in grain seeds has been measured.By using a-sources,energy calibration has been carried out on semiconductive detector. By irradiating thin nitrogenous target with 13.6MeV deuterons,the proton energy range which is suitable for the measurement of depth distribution has been determined. The experiment calibration was carried out for the correlation between proton energy(channels) and nitrogen depth. By using thick standard samples with homogeneous depth distribution of nitrogen element, the influence of the variation of differential cross-section for ¹⁴N(d, p)¹⁵N reaction with energy was eliminated, and nitrogen element distribution with depth in seed sample was obtained. By using the energy spectrum analyzing system established,the nitrogen depth distribution in wheat seed has been measured.The effective depth of analysis is about 300μm, and the depth resolution is about 25μm.It is enough to distinguish the different parts of wheat seed.So it can be used for the investigation of the correlations between the depth distribution of protein and the genotypic characters for grains.